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Blu-ray disc
seminar 2004
BLU‐RAY DISC SEMINAR REPORT 2004 DONE BY
CIMI JOSE 01‐616
Electronics & Communication Department
Government Engineering College Thrissur Department of ECE
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ACKNOWLEDGMENT
I would like to thank everyone who helped to see this seminar to completion. In particular, I would like to thank my seminar coordinator Mrs. Muneera.C.R for her moral support and guidance to complete my seminar on time. Also I would like to thank Mr. C. D. Anil Kumar for his invaluable help and support.
I would like to take this opportunity to thank Prof. Indiradevi, Head of the Department, Electronics & Communication Engineering for her support and encouragement. I express my gratitude to all my friends and classmates for their support and help in this seminar. Last, but not the least I wish to express my gratitude to God almighty for his abundant blessings without which this seminar would not have been successful.
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ABSTRACT Optical disks share a major part among the secondary storage devices.Blu‐ray Disc is a next‐generation optical disc format. The technology utilizes a blue laser diode operating at a wavelength of 405 nm to read and write data. Because it uses a blue laser it can store enormous more amounts of data on it than was ever possible. Data is stored on Blu‐Ray disks in the form of tiny ridges on the surface of an opaque 1.1‐millimetre‐thick substrate. This lies beneath a transparent 0.1mm protective layer. With the help of Blu‐ray recording devices it is possible to record up to 2.5 hours of very high quality audio and video on a single BD. Blu‐ray also promises some added security, making ways for copyright protections. Blu‐ray discs can have a unique ID written on them to have copyright protection inside the recorded streams. Blu‐ray disc takes the DVD technology one step further, just by using a laser with a nice color.
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TABLE OF CONTENTS ABSTRACT ……………………………………………………………2 1. HISTORY OF BLU‐RAY DISC……………………………………5 2. GLOSSARY OF TERMS………………………………………...…7 3. OPTICAL DATA STORAGE FOR DIGITAL VIDEO……..…12 4. DIFFERENT FORMATS OF BD………………………………....26 5. TWO VERSIONS OF RECORDING……………………….…...27 6. BLU‐RAY DISC STRUCTURE……………………………….…..29 7. SPECIFICATIONS………………………………………….……..31 8. BASIC BLU‐RAY CHARACTERISTICS………………….…....32 9. BLU‐RAY FOUNDERS………………………..……………….….33 10. COMPARISONS………………………………….……….……...34 11. BD AND HD‐DVD…………………………….………................35 12. ADVANTAGES..............................................................…............37 13. APPLICATIONS………………………………………………….39 14. REQUIREMENTS……………………………………….……..…43 15. CHALLENGES………………........................................................43 16. FUTURE DEVELOPMENTS…………………………………….44 17. CONCLUSION………………………..………….……………….45 Department of ECE
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18. REFERENCES……………………………………………………..46
1.History of Blu‐ray Disc
1.1 First Generation When the CD was introduced in the early 80s, it meant an enormous leap from traditional media. Not only did it offer a significant improvement in audio quality, its primary application, but its 650 MB storage capacity also meant a giant leap in data storage and retrieval. For the first time, there was a universal standard for pre‐recorded, recordable and rewritable media, offering the best quality and features consumers could wish for themselves, at very low costs.
1.2 Second Generation Although the CD was a very useful medium for the recording and distribution of audio and some modest data‐applications, demand for a new medium offering higher storage capacities rose in the 90s. These demands lead to the evolution of the DVD specification and a five to ten fold increase in capacity. This enabled high quality, standard definition video distribution and recording. Furthermore, the increased capacity accommodated more demanding data applications. At the same time, the DVD spec used the same form factor as the CD, allowing for seamless migration to the next generation format and offering full backwards compatibility.
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1.3 Third Generation Now High Definition video is demanding a new solution. History proved that a significant five to ten time increase in storage capacity and the ability to play previous generation formats are key elements for a new format to succeed. This new format has arrived with the advent of Blu‐ray Disc, the only format that offers a considerable increase in storage capacity with its 25 to 50 GB data capacity. This allows for the next big application of optical media: the distribution and recording of High Definition video in the highest possible quality. In fact, no other proposed format can offer the data capacity of Blu‐ray Disc, and no other format will allow for the same high video quality and interactive features to create the ultimate user experience. As with DVD, the Blu‐ ray Disc format is based on the same, bare disc physical form factor, allowing for compatibility with CD and DVD. The Blu‐ray Disc specification was officially announced in February 2002. Blu‐ray Disc recorders were first launched in Japan in 2003. •
1982 ‐First working CD player developed by Philips. Philips and Sony
developed CD standard – 12cm disk, 74 minutes on a single spiral •
1983 ‐First CD players sold
•
1985 ‐CD‐ROM introduced – not popular at first. More powerful PCs lead
to demand for multimedia, image processing and larger applications. Growth in sales brings prices down.
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•
1990’s ‐ CD‐R and CD‐RW introduced – big success.
•
1996 ‐DVD introduced
•
1999 ‐DVD becomes mainstream
•
2003 ‐BD introduced
2. Glossary of Terms
2.1 HDTV (High Definition Video) This high resolution 16:9 ratio, progressive scan format can now be recorded to standard miniDV cassettes Consumer high definition cameras are becoming available but this is currently an expensive, niche market. It is also possible to capture video using inexpensive webcams. These normally connect to a computer via USB. While they are much cheaper than DV cameras, webcams offer lower quality and less flexibility for editing purposes, as they do not capture video in DV format. Digital video is available on many portable devices from digital stills cameras to mobile phones. This is contributing to the emergence of digital video as a standard technology used and shared by people on a daily basis.
2.2 MPEG MPEG, the Moving Picture Experts Group, overseen by the International Standards Organization (ISO), develops standards for
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digital video and digital audio compression. MPEG‐1 with a default resolution of 352x240 was designed specifically for Video‐CD and CD‐imedia and is often used in CD‐ROMs. MPEG‐1 audio layer‐3 (MP3) compression evolved from early MPEG work. MPEG1 is an established, medium quality format (similar to VHS) supported by all players and platforms. Although not the best quality it will work well on older specification machines. MPEG‐2 compression (as used for DVD movies and digital television set‐top boxes) is an excellent format for distributing video, as it offers high quality and smaller file sizes than DV. Due to the way it compresses video MPEG‐2‐encoded footage is more problematic to edit than DV footage. Despite this, MPEG2 is becoming more common as a capture format. MPEG 2 uses variable bit rates allowing frames to be encoded with more or less data depending on their contents. Most editing software now supports MPEG2 editing. Editing and encoding MPEG2 requires more processing power than DV and should be done on well specified machines. It is not suitable for internet delivery. MPEG‐4 is a set of video and audio standards intended to deliver quality video over limited bandwidths that also support a range of other media types such as text, still image and animation. MPEG‐4 offers high‐ quality, scaleable streaming over a range of bandwidths, including those provided by mobile networks. The standards also include components and
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elements that allow the viewer to interact with the picture on the screen or to manipulate individual elements in real time. The MPEG4 format is a container for various versions called layers. There are different implementations, some of which are proprietary and not compliant with the ISO MPEG4 standard. It was initially thought that MPEG4 would become the default format for video over the internet. With support from Apple, Real Networks and others this may still be the case. However, problems over licensing costs and the lack of digital rights management in the standard made many content providers slow to embrace it. These issues are being tackled but it also faces competition from proprietary formats such as Windows Media. MPEG4 is beginning to be supported in other areas such as mobile video (3G), mobile television, set‐top boxes and video on demand (VoD).
2.3 Gigabyte (GB) A gigabyte equals about 1,000 megabytes (MB). A Blu‐ray Disc capable of recording 50 GB therefore stores about 50,000 megabytes
2.4 Layer
In Blu‐ray Disc, data is recorded on a single side of the disc. However, a disc can store two data layers, both at the same side. The read‐ out or recording laser of the Blu‐ray Disc device will first read from or record to one layer, and then re‐focuses on the second layer. All this is done
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automatically without any user interference. A double layer Blu‐ray Disc can store up to 50 GB of data.
2.5 SDTV
Standard Definition Television. Generic term used for
conventional television sets, based on the NTSC or PAL standards. SD television consists of 480 to 570 visible lines.
2.6 Numerical Aperture and Resolution The numerical aperture of a microscope objective is a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance. Image‐forming light waves pass through the specimen and enter the objective in an inverted cone as illustrated in Figure 1. A longitudinal slice of this cones of light shows the angular aperture, a value that is determined by the focal length of the objective.
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The angle μ is one‐half the angular aperture (A) and is related to the numerical aperture through the following equation: Numerical Aperture (NA) = n (sin μ) Where n is the refractive index of the imaging medium between the front lens of the objective and the specimen cover glass, a value that ranges from 1.00 for air to 1.51 for specialized immersion oils. Many authors substitute the variable μ for μ in the numerical aperture equation. From this equation it is obvious that when the imaging medium is air (with a refractive index, n = 1.0), then the numerical aperture is dependent only upon the angle μ whose maximum value is 90°. The sin of the angle μ, therefore, has a maximum value of 1.0 (sin90° = 1), which is the theoretical maximum numerical aperture of a lens operating with air as the imaging medium (using ʺdryʺ microscope objectives).
2.7 THE BLUE LASER The laser used with the Blu‐ray disc has a wavelength of 405nm.Though the red and the green lasers were discovered much earlier, it was only in 1996 that the blue laser was discovered. Actually, the wavelength 405nm would correspond to the blue‐violet part of the visible light, in the spectrum. This achievement is attributed to the efforts of Shuji Nakamura of Nichia Corporation, Japan. The device utilizes a GaN diode as its laser source. The operating current is kept between 60mA and 70mA for optimum performance.
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For writing into the disc, the power of the laser used is about 6mW. For reading from the disc, much lesser power is required, only about 0.7mW.The GaN source can give a power of about 65mW. So, it is an ideal choice for the laser source to be used with the Blu‐ray disc. Due to the much lower wavelength involved, the amorphous mark size (bit size) is small, leading to higher storage capacity on disc of the same size, about five to six times the capacity of a DVD.
3. Optical Data Storage for Digital Video 3.1 Introduction Optical data storage is commercially successful in the form of Compact Discs (CDs) for audio and software distribution and Digital Versatile Discs (DVDs) for video distribution. CDs and DVDs look very similar because the fundamental optical technology for both devices is the same. This similarity is also true for the next generation of optical data storage, which may be used for digital home theater recording and HDTV distribution. However, CDs, DVDs and next generation products are different in terms of specific optical components in the drive, in how data are managed and in details of the disk structure used to store the information. These differences allow a larger volume of data to be recorded on each successive generation. Larger data volumes translate into higher quality video and longer playing time.
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3.2 Parameters for HD Video Storage with Optical Disks
¾ Optical Parameters ¾ Disk Structure Parameters ¾ Data Management Parameters Optical parameters include laser wavelength, objective lens numerical aperture, protective layer thickness and free working distance. Data management parameters include data rate, video format, HDTV play time and bit‐rate scheme. Disk structure parameters are user data capacity, minimum channel bit length and track‐to‐track spacing.
3.2.1 Optical Parameters
Fig 1
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Digital information is stored on optical disks in
the form of arrangements of data marks in spiral tracks. The process for exposing data marks on a recordable optical disk is shown in Fig. 1, where an input stream of digital information is converted with an encoder and modulator into a drive signal for a laser source. The laser source emits an intense light beam that is directed and focused onto the surface by the objective lens. As the surface moves under the scanning spot, energy from the intense scan spot is absorbed, and a small, localized region heats up. The surface, under the influence of heat beyond a critical writing threshold, changes its reflective properties. Modulation of the intense light beam is synchronous with the drive signal, so a circular track of data marks is formed as the surface rotates. The scan spot is moved slightly as the surface rotates to allow another track to be written on new media during the next revolution. Data marks on prerecorded disks are fabricated by first making a master disk with the appropriate data‐mark pattern. Masters for prerecorded CDs and DVDs are often exposed in a similar manner to exposing data marks on recordable optical disks, except that the light‐sensitive layer is designed to produce pits in the master that serve as data marks in the replicas. Inexpensive replicas of the master are made with Injection‐molding equipment.
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Fig 2 Readout of data marks on the disk is illustrated in Fig.2, where the laser is used at a constant output power level that does not heat the data surface beyond its thermal writing threshold. The laser beam is directed through a beam splitter into the objective lens, where the beam is focused onto the surface. As the data marks to be read pass under the scan spot, the reflected light is modulated. Modulated light is collected by illumination optics and directed by the beam splitter to servo and data optics, which converge the light onto detectors. The detectors change light modulation into current modulation that is amplified and decoded to produce the output data stream. A fundamental limitation to the number of
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data marks per unit area is due to the size of the focused laser beam that illuminates the surface. Small laser spots are required to record and read out small data marks. More data marks per unit area translate into higher capacity disks, so evolution of optical data storage is toward smaller spot sizes.
Fig 3 Figure 3 shows a detailed picture of the laser irradiance approaching the surface, where irradiance is defined as the laser power per unit area. Ideally, maximum irradiance is located at the recording material, along with the smallest spot size s. As the distance increases away from the ideal focus, the spot size increases and the peak irradiance decreases. A defocus distance δz of only a few micrometers dramatically reduces peak
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irradiance and increases spot size. An approximate formula used to estimate the ideal spot size at best focus is s = λ/(sin θ), where θ is the marginal ray angle of the illumination optics, as shown in Fig. 1. Spot size s is the full width of the irradiance distribution at the 1/e2 (13.5%) irradiance level relative to the peak. The value of sin q is often called the numerical aperture or NA of the optical
system.
Fig 4 Instead of focusing directly on the recording surface, optical disks focus through a protective layer, as shown in Fig.4 for a simple CD‐ROM. The protective layer prevents dust and other contamination from directly obstructing the laser spot at the data marks. Instead, the out‐of‐ focus contamination only partially obscures the laser focus cone, and data can
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usually be recovered reliably. If the protective layer is scratched or damaged, it can be cleaned or buffed. As the protective layer gets thinner, the error rate increases to an unacceptable threshold due to obscuration of the laser beam. This sensitivity decreases as NA increases, due to the smaller defocus range associated with these systems. In addition, the free working distance separates the objective lens from the spinning disk. This separation protects the disk against accidental contact between the objective lens and the disk. In order to maximize disk capacity, the optical system uses high NA and short wavelength. For maximum contamination protection, the protective layer should be as thick as possible. However, the combination of thick protective layer and high NA is not easily accomplished. High NA systems are sensitive to changes in substrate thickness and disk tilt. Manufacturing variations create thickness no uniformities, which are usually a small percentage of the total disk thickness. Motor instabilities induce tilt as the disk spins. Energy from the central portion of the spot is redistributed to concentric rings, which degrade the quality of the read out signal. This Degrades the read out signal. Tilt causes coma, which is another form of aberration effect, is called spherical aberration.
Sensitivity of the spot to degradation from
thickness variations and disk tilt is plotted in Fig. 5 as a function of total protective layer thickness for two values of NA. In order to limit these effects,
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the substrate is made as thin as possible without sacrificing contamination protection.
Fig 5 The most conservative technology is the Video CD. Its thick protective layer, relatively low NA and long laser wavelength produce a stable system that is not very sensitive to environmental factors like dust and scratches. The ideal spot size is about 0.78/0.5 = 1.6 micrometers. Although the cover layer is thick at 1.2 mm, the sensitivity to thickness variations and disk tilt is low because of the low NA. DVD technology uses a shorter wavelength laser, higher NA optics and a thinner protective layer. The
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combination of short wavelength and higher NA produce a spot size of about 1.1 micrometers. The protective layer had to be made thinner, because the sensitivity to thickness variations and disk tilt is too high otherwise. DVDs are slightly more sensitive to dust and scratches than CDs. The net effect is not great, because higher NA reduces the focal depth and DVDs have a more robust error management strategy. The Advanced Optical Disk and Blu‐Ray systems both use a new blue laser source that emits 0.405 micrometer light. The Advanced Optical Disk system uses the same protective layer thickness as a DVD, and it uses the same NA objective lens. Due to the short wavelength, the spot size for the Advanced Optical Disk is about 0.62 micrometers. Sensitivity to dust and scratches is about the same as a DVD, as well as the sensitivity to thickness variations and disk tilt. The Blu‐Ray system uses both higher NA and thinner cover layer. The spot size is 0.405/0.85 = 0.48 micrometers, which is the smallest spot size of all the technologies. However, because of the high NA, the protective layer had to be made thin to limit sensitivity to thickness variations and disk tilt. Therefore, Blu‐Ray disks are sensitive to dust and scratches. The free working distance is nearly is same for all technologies except Blu‐Ray. Blu‐Ray systems utilize more complicated lens systems due to the high NA, so working distance had to be reduced. The integrity of this reduced working distance is not clear at this time.
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3.2.2 Disk Structure Parameters The spot size created from the NA and wavelength parameters is the most important factor to determine the track‐to‐track spacing and the minimum channel bit length along the track. Several channel bits are encoded into each data mark. The number of channel bits per data mark depends on the modulation scheme. The relatively large spot produces relatively large data marks and correspondingly wide tracks and large channel‐bit lengths. Progressively smaller spot sizes enable smaller track spacing and shorter channel bit lengths.
Fig 6
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To the user, all generations of optical disks look very similar. They all are round disks that are approximately 120 mm in diameter, have a central mounting hole and are approximately 1.2 mm thick. Through many years of experience with CDs, this format has proven effective and mechanically reliable. However, the manner in which data layers are arranged on the disk depends on the technology used. For example, the CD uses a simple 1.2 mm thick substrate, as shown in Fig. 6A. Data are recorded on only one side of the disk, through the clear 1.2 mm substrate, which also serves as the protective layer. DVDs, Warner HD‐DVDs and Advanced Optical Disks use the format shown in Fig. 6B, where two 0.6 mm substrates are bonded together and the data are recorded on the bond side of each substrate. DVDs also allow more two layers per side (A, B in Fig. 6B), where the layers are separated by a thin adhesive spacer. The two layers are fabricated before bonding at the same time as the individual 0.6 mm substrates. Like the CD, data are recorded and read through the clear substrates. It is likely that the Warner HDDVD and Advanced Optical Disk will also take advantage of this multiple‐layer concept. A potential implementation of the Blu‐Ray disk is shown in Fig. 6C, where the protective layers on each side are very thin at 0.1 mm. In this case, data are recorded on the substrate, which does not serve as the protective layer. Instead, a protective layer resin is spun on and hardened or a thin protective sheet is bonded on each side of the substrate. Because of the thin protective layer, the Blu‐Ray disk must also be used with a cartridge.
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The only optical disk technology that plans to
use a Cartridge is the Blu‐Ray system. The Blu‐Ray cartridge is necessary for contamination Protection, but the working distance of around 0.1 mm and protective layer thickness of 0.1 mm are large compared to the contact recording The technology for making disks is very similar to existing DVD technology. Higher‐resolution mastering machines and finer control over the injection molding process should produce the required changes without substantially retooling the industry. The Blu‐Ray system requires the most changes of the three, including a blue laser, detector, and advanced objective lens. Blu‐Ray also requires new disk and cartridge manufacturing technology, which may be difficult to implement in a short time frame.
3.2.3 Data Management Parameters
The logical organization of data on the disk
and how those data are used are considerations for data management. Data management considerations have important implications in the application of optical disk technology to storage for HDTV. For example, simply using a more advanced error correction scheme on DVDs allows a 30% higher disk capacity compared to CDs. Data rate, video format, bit‐rate scheme and HDTV play time are all data management issues.
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There is a basic difference in data management between CDs and DVDs. Since CDs were designed for audio, data are managed in a manner similar to data management for magnetic tape. Long, contiguous files are used that are not easily subdivided and written in a random access pattern. Efficient data retrieval is accomplished when these long files are read out in a contiguous fashion. To be sure, CDs are much more efficient that magnetic tape for pseudorandom access, but the management philosophy is the same. On the other hand, DVDs are more like magnetic hard disks, where the file structure is designed to be used in random‐access architecture. That is, efficient recovery of variable length files is achieved. In addition, the Original error correction strategy for CDs was designed for error concealment when listening to audio, where DVDs utilize true error correction. Later generations of optical disks also follow the DVD model. The random‐access nature of DVDs allows very efficient methods for data compression. For example, MPEG‐2 with variable bit rate allows data to be read out from the disk as they are required, rather than supplying data at a constant rate. Slowly moving scenes, like love scenes or conversations, require much less information per frame than a fast‐moving car chase or explosion. In these fast‐moving scenes, the maximum amount of information per scene is limited only by the maximum data rate of the player. For HDTV, acceptable picture quality is obtained by using MPEG‐2 with a maximum data rate of about 13‐25 Mbps for most scenes. During a slow
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scene, not as many files are accessed, and much less storage area on the disk is used. This architecture leaves room on the disk for the data associated with faster‐moving scenes.
Fixed‐rate schemes, like magnetic tape, supply data at a
constant rate, no matter what the requirements of the scene. During fast‐moving scenes, the data stream from the tape supplies an adequate data rate. The tape speed and data
rate for these devices are set by the upper limit of the scene requirements. Since the tape does not slow down during slower scenes, the data stream is ‘padded’ at these times with useless information that takes up valuable storage area on the tape. Overall, the random‐access architecture of optical disks is a much more efficient way to use the available storage area. That is, optical disks do not require as many gigabytes of user data capacity for an equivalent length and quality HDTV presentation. It is not practical to store HDTV on CDs and DVDs with MPEG‐2. For CDs, special multiple‐beam readout or high velocity disk dives could produce the data rate, which is an advantage of the fixed‐bit‐rate scheme. However, the play time would be only a few minutes, at best. DVDs are not capable of the 13 Mbps random data rate to support MPEG‐2. The Advanced Optical Disk exhibits acceptable data rate and reasonable user data capacity for up to two hours of HDTV per side compressed with variable bit‐ rate MPEG‐2. Blu‐ray has slightly higher capacity and data rate. The two‐hour play time for HDTV with Blu‐Ray in Table I is really a specification for real‐ time recording, which is not easily compressed into an efficient variable‐rate
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scheme. Blu‐Ray should easily provide two hours or longer of prerecorded HDTV per side compressed with MPEG‐2. MPEG‐2 is a technique for compressing video data and replaying the data associated with certain rules that are defined in the MPEG‐2 specifications. The action of the optical disk system is not to compress data or interpret the video information rules. Instead, the optical disk system only stores and retrieves data on command from the video operating system. Therefore, as video operating systems and associated compression technology become more advanced, no fundamental changes are required to the optical disk system. MPEG‐4 technology is an advanced video compression scheme that utilizes advanced pre‐filtering and post‐filtering, in addition to a rule‐based algorithm. Estimated improvement in compression is a around a factor of three beyond MPEG‐2.
4. Different Formats of Blu‐ray Disc BD‐ROM: a read only format developed for prerecorded content
BD‐R : a write once format developed for PC storage BD‐RW : a rewritable format developed for PC storage BD‐RE : a rewritable format developed for HDTV recording
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5. Two Versions of Recording 5.1 One Time Recording
Making permanent changes to a disc. If we use
BD‐R the material on the disc itself is changed forever. There is no way to get the material back into its old state. The recording material is crystalline in nature. As scan spot falls on the surface it changes to amorphous. We cannot change it back to crystal state.
5.2 Record Many Times
If we use a BD‐RW the material on the disc
itself changes, but can be changed back again .We can do this as long as the material doesn’t get worn out. By heating up the crystals, they change form. Now when we quickly cool them, they stay in that form itself. That is the material is changed from crystal state to amorphous state.
Now, if we want to erase the BD‐RW, we have
to make sure that we lose all the data. So we want to get rid of that amorphous state. By heating up the material again, but this time taking more time and less heat, the material gradually wants to take its old form again, and thus the information is erased. This state is called the crystalline state.
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cooling it, give the crystal another state (Amorphous state) which thus contains the data and by very quite slowly heating it and cooling it, we can give the crystals their old form back (crystalline state) which contains no more data. It’s a constant change of phases. And so it is called as phase change recording.
Data is stored in the form of grooves, on an optical disc. Next to the grooves, there are lands. Lands are the borders between the grooves. Grooves and lands have a sinus form. This is called a wobbled groove. In the groove, pits are formed to store data.
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6. Blu‐ray Disc Structure
The structure of the BD is as shown. The 0.1mm transparent cover layer is made of a spin‐coated UV resin. It is formed by sandwiching a transparent layer between a protective coating and a bonding layer. This layer offers excellent birefringence. Beneath, there is a layer of Antis layer acts as a heat sink, dissipating the excess heat during the write process. A spacer layer made of ZnS‐SiO2 comes next. Then, the recording layer made of AgInSbTeGe comes. Grooves are formed on this layer for recording.A reflective layer of Ag alloy falls beneath and finally a plastic substrate comes. The key features of the technology are introduced as follows
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Highly flat and smooth cover layer:
At the high speed recording rate involved, the linear velocity of the disc reaches 20m/s or more and as a result accurate focus control becomes difficult. Various experiments showed that flatness and smoothness of the transparent cover layer have a marked influence on the focus control capability. This end is achieved by using the spin coating method for obtaining the transparent cover layer. Thus stable record ability at high speed recording is secured. ¾
Phase change film for high speed recording: The phase change film should have high
recrystallisation speed to enable direct recording at the high linear velocities involved. A recording layer made of AgInSbTeGe meets this purpose.
¾
Super advanced rapid cooling structure:
The excess heat from the LASER irradiation causes distortion of the recorded mark edge. So, to diffuse the remaining excess heat, a transparent di‐electric film of high thermal conductivity, for example, AlN is used.
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7. Specifications:
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8. Basic Blu‐ray Disc Characteristics 8.1 Large Recording Capacity
The Blu‐ray disc enables the recording, rewriting and playback of HD video unto 27 GB of data on a single sided single layer. It is enough to put 2.5 hours of HDTV recording on it. It also can record over 13 hours of standard TV broadcasting using the VHS/ standard definition picture quality.
8.2 High Speed It has a data transfer rate of 36 Mbps. Because of this high speed transfer rates it can also record the data in very little time. In a perfect environment it would take about 2.5 hours to fill the entire BD with 27 GB of data. More than enough transfer capacity for real time recording and playback.
8.3 Resistant to Scratches and Fingerprints
The protective layer is hard enough to prevent
accidental abrasions and allows fingerprints to be removed by wiping the disc with a tissue.
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9. Blu‐ray Founders
The
following
companies
have
jointly
established the basic specifications Blu‐ray disc video recording format
1. Hitachi , Ltd 2. LG Electronics Inc. 3. Matsushita Electric Industrial Co. Ltd. 4. Mitsubishi Electric Corporation 5. Pioneer Corporation 6. Royal Philips Electronics 7. Samsung Electronics Co. Ltd. 8. Sharp Corporation 9. Sony Corporation 10. Thomson
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10. Comparisons
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11. Blu‐ray Disc and HD‐DVD: The HD‐DVD format, originally called AOD or Advanced Optical Disc, is based on much of todayʹs DVD principles and as a result, suffers from many of its limitations. The format does not provide as big of a technological step as Blu‐ray Disc. For example, its pre‐recorded capacities are only 15 GB for a single layer disc, or 30 GB for a double layer disc. Blu‐ray Disc provides 67% more capacity per layer at 25 GB for a single layer and 50GB for a double layer disc. Although the HD‐DVD format claims it keeps initial investments for disc replicates and media manufacturers as low as possible, they still need to make substantial investments in modifying their production equipment to create HD‐DVDs. But whatʹs more important is that HD‐DVD can be seen as just a transition technology, with a capacity not sufficient for the long term. It might not offer enough space to hold a High Definition feature along with bonus material in HD quality and additional material that can be revealed upon authorization via a network. When two discs are needed, this will degrade the so‐called cost benefit substantially. It is even possible that the HD‐DVD specification will be followed up by a renewed version of the technology within a few years, requiring media manufacturers to upgrade their existing production lines again, and consumers to replace their existing playback/recording equipment. On the
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other hand, the Blu‐ray Disc format was designed to be a viable technology for a period of at least 10 to 15 years.
Also on the application layer, the HD‐DVD
format incorporates many compromises. As the capacity is not likely to be sufficient to encode a full‐length feature plus additional bonus materials using the MPEG‐2 format, different and stronger encoding formats need to be used. Although Blu‐ray Disc offers these advanced codecs as well, the disc has such high capacity that publishers can still use the MPEG‐2 encoding format at bit rates up to 54 Mbit/sec. As MPEG‐2 is the de‐facto standard used in almost any industry involved in digital video (DVD, HDTV, digital broadcast), many authoring solutions are available. Chances are high that a full line MPEG‐2 encoding suite is already available, which can be used with no or minor adaptations to encode High Definition content for Blu‐ray Disc. But perhaps the most important factor for the success of Blu‐ray Disc is its overwhelming industry‐wide support. Almost all consumer electronics companies in the world (combined market share of about 90%) and the worldʹs two largest computer companies support the Blu‐ray Disc format. This ensures a large selection of Blu‐ray Disc players, recorders, PC drives, Blu‐ray Disc equipped PCs and blank media will become available. A competing format will not have the manufacturing power to penetrate the market in a level even approaching that of Blu‐ray Disc
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12. Advantages The main advantages of the Blu‐ray disc are
¾ More storage capacity on a disc of the same size. The data storage capacity on a Blu‐ray disc is 27GB on a single layer and 54GBon dual layer, which is about five to six times the capacity of a DVD. It would mean about 2.5 hours of HDTV video and about 13 hours of SDTV video.
¾ High data transfer rate. The basic data transfer rate in Blu‐ray disc is about 36Mbps which is about three times that of a DVD and thirty times that of a CD.
¾ Available in different versions like ROM, R and RE The BD is available in different versions like the ROM (write once), R (read only), RE (rewritable).
¾ Backward compatible. The BD drives are designed to be backward compatible, i.e. CDs and DVDs work equally well with the BD drives.
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¾ Strong content protection. The features of the content protection system are •
Format Developed with Input from Motion Picture Studios
•
Strong Copy Protection by
•
Renewability with Renewal Key Block and Device Key
•
Enhanced Encryption Algorithm: AES 128 bit
•
Physical Hook Against Bit by Bit Encrypted Content Copy
•
Title‐based Expandable Content Control File
•
Production Process Control Works Against Professional Piracy
•
Public Key Based Authentication in PC Environment
¾ Compatible with analog and digital transmission. The BD fares well with analog as well as digital transmission. It offers the only means to the recording and reproducing of digital HDTV video. Format for encoding analog signals also, called SESF (Self Encoded Stream Format) is also incorporated into the BD.
¾ Higher disc life. In the case of ordinary discs, the disc life is less fir the rewritable versions, as re‐writing is done repeatedly to one area of the disc most probably, the inner perimeter. This limits the disc life. But, the BDFS(Blu‐ray Disc File Structure is designed so as to avoid this problem, by using a system that uses free disc spaces with equal frequency
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13. Applications ¾
High Definition Television Recording
¾
High Definition Video Distribution
¾
High Definition Camcorder Archiving
¾
Mass Data Storage
¾
Digital Asset Management and Professional Storage
The Blu‐ray Disc format was designed to offer the best performance and features for a wide variety of applications. High Definition video distribution is one of the key features of Blu‐ray Disc, but the formatʹs versatile design and top‐of‐the‐line specifications mean that it is suitable for a full range of other purposes as well.
13.1 High Definition Television Recording High Definition broadcasting is vastly expanding in the US and Asia. Consumers are increasingly making the switch to HDTV sets to enjoy the best possible television experience. The Blu‐ray Disc format offers consumers the ability to record their High Definition television broadcasts in their original quality for the first time, preserving the pure picture and audio level as offered by the broadcaster. As such it will become the next level in home entertainment, offering an unsurpassed user experience. And since the
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Blu‐ray Disc format incorporates the strongest copy protection algorithms of any format or proposal to date, the format allows for recording of digital broadcasts while meeting the content protection demands of the broadcast industry.
13.2 High Definition Video Distribution
Due to its enormous data capacity of 25 to 50
GB per (single sided) disc, the Blu‐ray Disc format can store High Definition video in the highest possible quality. Because of the huge capacity of the disc, there is no need to compromise on picture quality. Depending on the encoding method, there is room for more than seven hours of the highest HD quality video. There is even room for additional content such as special features and other bonus material to accompany the High Definition movie. Furthermore, the Blu‐ray Disc movie format greatly expands on traditional DVD capabilities, by incorporating many new interactive features allowing content providers to offer an even more incredible experience to consumers. An Internet‐connection may even be used to unlock additional material that is stored on the disc, as there is enough room on the disc to include premium material as well.
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13.3 High Definition Camcorder Archiving
As the market penetration of High Definition
TV sets continues to grow, so does the demand of consumers to create their own HD recordings. With the advent of the first HD camcorders, consumers can now for the first time record their own home movies in a quality level unlike any before. As these camcorders are tape‐based, consumers cannot benefit from the convenience and direct access features they are used to from the DVD players and recorders. Now, the Blu‐ray Disc format, with its unprecedented storage capacity, allows for the HD video recorded with an HD camcorder to be seamlessly transferred to a Blu‐ray Disc. When the HD content is stored on a Blu‐ray Disc, it can be randomly accessed in a way comparable to DVD. Furthermore, the Blu‐ray Disc can be edited, enhanced with interactive menus for an even increased user experience and the disc can be safely stored for many years, without the risk of tape wear.
13.4 Mass Data Storage
In its day, CD‐R/RW meant a huge increase in
storage capacity compared to traditional storage media with its 650 MB. Then DVD surpassed this amount by offering 4.7 to 8.5 GB of storage, an impressive 5 to 10 times increase. Now consumers demand an even bigger storage capacity. The growing number of broadband connections allowing
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consumers to download vast amounts of data, as well as the ever increasing audio, video and photo capabilities of personal computers has lead to yet another level in data storage requirements. In addition, commercial storage requirements are growing exponentially due to the proliferation of e‐mail and the migration to paperless processes. The Blu‐ray Disc format again offers 5 to 10 times as much capacity as traditional DVD resulting in 25 to 50 GB of data to be stored on a single rewritable or recordable disc. As Blu‐ray Disc uses the same form factor as CD and DVD, this allows for Blu‐ray Disc drives that can still read and write to CD and DVD media as well.
13.5 Digital Asset Management and Professional Storage
Due to its high capacity, low cost per GB and
extremely versatile ways of transferring data from one device to another (because of Blu‐ray Discʹs extremely wide adoption across the industry), the format is optimized for Digital Asset Management and other professional applications that require vast amounts of storage space. Think of medical archives that may contain numerous diagnostic scans in the highest resolution, or catalogs of audiovisual assets that need to be instantly retrieved in a random access manner, without the need to ʺrestoreʺ data from a storage carrier. One Blu‐ray Disc may replace many backup tapes, CDs, DVDs or other less common or proprietary storage media. And contrary to network solutions, the discs can be physically stored in a different location for backup and safekeeping
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14. Requirements 1) Blue laser 2) Detector 3) Advanced objective lens 4) New disk and cartridge manufacturing technologies
15. Challenges: ¾ High cost The technology is not that popular and hence, the price of the BD recorders and players available in the market is very high.
¾ HD‐DVD The HD‐DVD (High Definition DVD) based on the Advanced Optical System championed by Toshiba and NEC is the primary rival to BD in the market. Though its data storage density is lower, it has lower manufacturing costs also, which may prove challenging to the Blu‐ray disc.
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16. Future Developments: Efforts are progressing on many fronts to make the Blu‐ray discs, players and recorders cheaper. On 15 April 2004 for instance, Sony and Toppan Printing announced the successful development of a Blu‐ ray Disc that is 51% (by mass) composed of paper, which could reduce production costs and improve its environmental friendliness.The cost would come down as BD becomes more and more popular. TDK has been researching the hard coat technology that will provide protection against fingerprints and scratches. Colloidable silica dispersed UV‐curable resin is being used for the researches and results are encouraging.
Figure shows the cross section of the disc being developed.
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17. Conclusion: The BD represents a major advancement in capacity as well as data transfer rate. It would be an ideal choice for the secondary storage purposes.The semiconductor storage for secondary memory is large, consumes more power and is more expensive. HDTV video recording and reproducing would essentially require the large storage capacity and data transfer rates, as offered by the Blu‐ray disc. The Blu‐ray disc has a wide variety of applications and is the ultimate storage device that would lead to digital convergence, ultimately leading to the convergence of the PC and CE technologies. In the opinion of many researchers (including those at the BDF group themselves), BD possibly represents the last of the plastic‐ based, visible laser optical disc systems. Shorter violet and ultraviolet wavelengths are absorbed strongly by the plastic used in disc manufacturing, and itʹs difficult to cheaply manufacture a much higher‐quality lens. The light absorbed by the disk would not make it back out to be read by the drive. In addition, most plastics decay when exposed to ultraviolet light, changing color and becoming brittle. An ultraviolet system would destroy plastic media used with it. Future technologies would likely involve glass platters (which donʹt absorb long‐wave ultraviolet nearly as much as plastic), ultraviolet readout lasers, and/or multilayer fluorescent media. An emergence of the magneto‐optical system for secondary storage is also a big possibility
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18. References 1. Digital Digest Magazine Published by Digital Tech Consulting L.L.C, September 2003, “Blu‐Ray Format Positioning As Next Generation DVD.”
2. Optical Recording: A Technical Overview, Addison‐ Wesley, Reading, Massachusetts,pp321‐323(1990)
3. Optical Disc Systems Dec 2002,”The Blue Disc Recording Technology” 4. Spectrum, Magazine Published by IEEE, June 2003, “The Great Gallium Nitride Gamble”
5. www.bluray.com 6. www.google.com 7. www.opticaldisc_system.com
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BLU‐RAY DISC SEMINAR REPORT 2004 DONE BY
CIMI JOSE 01‐616
Electronics & Communication Department
Government Engineering College Thrissur Department of ECE
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ACKNOWLEDGMENT
I would like to thank everyone who helped to see this seminar to completion. In particular, I would like to thank my seminar coordinator Mrs. Muneera.C.R for her moral support and guidance to complete my seminar on time. Also I would like to thank Mr. C. D. Anil Kumar for his invaluable help and support.
I would like to take this opportunity to thank Prof. Indiradevi, Head of the Department, Electronics & Communication Engineering for her support and encouragement. I express my gratitude to all my friends and classmates for their support and help in this seminar. Last, but not the least I wish to express my gratitude to God almighty for his abundant blessings without which this seminar would not have been successful.
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ABSTRACT Optical disks share a major part among the secondary storage devices.Blu‐ray Disc is a next‐generation optical disc format. The technology utilizes a blue laser diode operating at a wavelength of 405 nm to read and write data. Because it uses a blue laser it can store enormous more amounts of data on it than was ever possible. Data is stored on Blu‐Ray disks in the form of tiny ridges on the surface of an opaque 1.1‐millimetre‐thick substrate. This lies beneath a transparent 0.1mm protective layer. With the help of Blu‐ray recording devices it is possible to record up to 2.5 hours of very high quality audio and video on a single BD. Blu‐ray also promises some added security, making ways for copyright protections. Blu‐ray discs can have a unique ID written on them to have copyright protection inside the recorded streams. Blu‐ray disc takes the DVD technology one step further, just by using a laser with a nice color.
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TABLE OF CONTENTS ABSTRACT ……………………………………………………………2 1. HISTORY OF BLU‐RAY DISC……………………………………5 2. GLOSSARY OF TERMS………………………………………...…7 3. OPTICAL DATA STORAGE FOR DIGITAL VIDEO……..…12 4. DIFFERENT FORMATS OF BD………………………………....26 5. TWO VERSIONS OF RECORDING……………………….…...27 6. BLU‐RAY DISC STRUCTURE……………………………….…..29 7. SPECIFICATIONS………………………………………….……..31 8. BASIC BLU‐RAY CHARACTERISTICS………………….…....32 9. BLU‐RAY FOUNDERS………………………..……………….….33 10. COMPARISONS………………………………….……….……...34 11. BD AND HD‐DVD…………………………….………................35 12. ADVANTAGES..............................................................…............37 13. APPLICATIONS………………………………………………….39 14. REQUIREMENTS……………………………………….……..…43 15. CHALLENGES………………........................................................43 16. FUTURE DEVELOPMENTS…………………………………….44 17. CONCLUSION………………………..………….……………….45 Department of ECE
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18. REFERENCES……………………………………………………..46
1.History of Blu‐ray Disc
1.1 First Generation When the CD was introduced in the early 80s, it meant an enormous leap from traditional media. Not only did it offer a significant improvement in audio quality, its primary application, but its 650 MB storage capacity also meant a giant leap in data storage and retrieval. For the first time, there was a universal standard for pre‐recorded, recordable and rewritable media, offering the best quality and features consumers could wish for themselves, at very low costs.
1.2 Second Generation Although the CD was a very useful medium for the recording and distribution of audio and some modest data‐applications, demand for a new medium offering higher storage capacities rose in the 90s. These demands lead to the evolution of the DVD specification and a five to ten fold increase in capacity. This enabled high quality, standard definition video distribution and recording. Furthermore, the increased capacity accommodated more demanding data applications. At the same time, the DVD spec used the same form factor as the CD, allowing for seamless migration to the next generation format and offering full backwards compatibility.
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1.3 Third Generation Now High Definition video is demanding a new solution. History proved that a significant five to ten time increase in storage capacity and the ability to play previous generation formats are key elements for a new format to succeed. This new format has arrived with the advent of Blu‐ray Disc, the only format that offers a considerable increase in storage capacity with its 25 to 50 GB data capacity. This allows for the next big application of optical media: the distribution and recording of High Definition video in the highest possible quality. In fact, no other proposed format can offer the data capacity of Blu‐ray Disc, and no other format will allow for the same high video quality and interactive features to create the ultimate user experience. As with DVD, the Blu‐ ray Disc format is based on the same, bare disc physical form factor, allowing for compatibility with CD and DVD. The Blu‐ray Disc specification was officially announced in February 2002. Blu‐ray Disc recorders were first launched in Japan in 2003. •
1982 ‐First working CD player developed by Philips. Philips and Sony
developed CD standard – 12cm disk, 74 minutes on a single spiral •
1983 ‐First CD players sold
•
1985 ‐CD‐ROM introduced – not popular at first. More powerful PCs lead
to demand for multimedia, image processing and larger applications. Growth in sales brings prices down.
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•
1990’s ‐ CD‐R and CD‐RW introduced – big success.
•
1996 ‐DVD introduced
•
1999 ‐DVD becomes mainstream
•
2003 ‐BD introduced
2. Glossary of Terms
2.1 HDTV (High Definition Video) This high resolution 16:9 ratio, progressive scan format can now be recorded to standard miniDV cassettes Consumer high definition cameras are becoming available but this is currently an expensive, niche market. It is also possible to capture video using inexpensive webcams. These normally connect to a computer via USB. While they are much cheaper than DV cameras, webcams offer lower quality and less flexibility for editing purposes, as they do not capture video in DV format. Digital video is available on many portable devices from digital stills cameras to mobile phones. This is contributing to the emergence of digital video as a standard technology used and shared by people on a daily basis.
2.2 MPEG MPEG, the Moving Picture Experts Group, overseen by the International Standards Organization (ISO), develops standards for
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digital video and digital audio compression. MPEG‐1 with a default resolution of 352x240 was designed specifically for Video‐CD and CD‐imedia and is often used in CD‐ROMs. MPEG‐1 audio layer‐3 (MP3) compression evolved from early MPEG work. MPEG1 is an established, medium quality format (similar to VHS) supported by all players and platforms. Although not the best quality it will work well on older specification machines. MPEG‐2 compression (as used for DVD movies and digital television set‐top boxes) is an excellent format for distributing video, as it offers high quality and smaller file sizes than DV. Due to the way it compresses video MPEG‐2‐encoded footage is more problematic to edit than DV footage. Despite this, MPEG2 is becoming more common as a capture format. MPEG 2 uses variable bit rates allowing frames to be encoded with more or less data depending on their contents. Most editing software now supports MPEG2 editing. Editing and encoding MPEG2 requires more processing power than DV and should be done on well specified machines. It is not suitable for internet delivery. MPEG‐4 is a set of video and audio standards intended to deliver quality video over limited bandwidths that also support a range of other media types such as text, still image and animation. MPEG‐4 offers high‐ quality, scaleable streaming over a range of bandwidths, including those provided by mobile networks. The standards also include components and
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elements that allow the viewer to interact with the picture on the screen or to manipulate individual elements in real time. The MPEG4 format is a container for various versions called layers. There are different implementations, some of which are proprietary and not compliant with the ISO MPEG4 standard. It was initially thought that MPEG4 would become the default format for video over the internet. With support from Apple, Real Networks and others this may still be the case. However, problems over licensing costs and the lack of digital rights management in the standard made many content providers slow to embrace it. These issues are being tackled but it also faces competition from proprietary formats such as Windows Media. MPEG4 is beginning to be supported in other areas such as mobile video (3G), mobile television, set‐top boxes and video on demand (VoD).
2.3 Gigabyte (GB) A gigabyte equals about 1,000 megabytes (MB). A Blu‐ray Disc capable of recording 50 GB therefore stores about 50,000 megabytes
2.4 Layer
In Blu‐ray Disc, data is recorded on a single side of the disc. However, a disc can store two data layers, both at the same side. The read‐ out or recording laser of the Blu‐ray Disc device will first read from or record to one layer, and then re‐focuses on the second layer. All this is done
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automatically without any user interference. A double layer Blu‐ray Disc can store up to 50 GB of data.
2.5 SDTV
Standard Definition Television. Generic term used for
conventional television sets, based on the NTSC or PAL standards. SD television consists of 480 to 570 visible lines.
2.6 Numerical Aperture and Resolution The numerical aperture of a microscope objective is a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance. Image‐forming light waves pass through the specimen and enter the objective in an inverted cone as illustrated in Figure 1. A longitudinal slice of this cones of light shows the angular aperture, a value that is determined by the focal length of the objective.
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The angle μ is one‐half the angular aperture (A) and is related to the numerical aperture through the following equation: Numerical Aperture (NA) = n (sin μ) Where n is the refractive index of the imaging medium between the front lens of the objective and the specimen cover glass, a value that ranges from 1.00 for air to 1.51 for specialized immersion oils. Many authors substitute the variable μ for μ in the numerical aperture equation. From this equation it is obvious that when the imaging medium is air (with a refractive index, n = 1.0), then the numerical aperture is dependent only upon the angle μ whose maximum value is 90°. The sin of the angle μ, therefore, has a maximum value of 1.0 (sin90° = 1), which is the theoretical maximum numerical aperture of a lens operating with air as the imaging medium (using ʺdryʺ microscope objectives).
2.7 THE BLUE LASER The laser used with the Blu‐ray disc has a wavelength of 405nm.Though the red and the green lasers were discovered much earlier, it was only in 1996 that the blue laser was discovered. Actually, the wavelength 405nm would correspond to the blue‐violet part of the visible light, in the spectrum. This achievement is attributed to the efforts of Shuji Nakamura of Nichia Corporation, Japan. The device utilizes a GaN diode as its laser source. The operating current is kept between 60mA and 70mA for optimum performance.
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For writing into the disc, the power of the laser used is about 6mW. For reading from the disc, much lesser power is required, only about 0.7mW.The GaN source can give a power of about 65mW. So, it is an ideal choice for the laser source to be used with the Blu‐ray disc. Due to the much lower wavelength involved, the amorphous mark size (bit size) is small, leading to higher storage capacity on disc of the same size, about five to six times the capacity of a DVD.
3. Optical Data Storage for Digital Video 3.1 Introduction Optical data storage is commercially successful in the form of Compact Discs (CDs) for audio and software distribution and Digital Versatile Discs (DVDs) for video distribution. CDs and DVDs look very similar because the fundamental optical technology for both devices is the same. This similarity is also true for the next generation of optical data storage, which may be used for digital home theater recording and HDTV distribution. However, CDs, DVDs and next generation products are different in terms of specific optical components in the drive, in how data are managed and in details of the disk structure used to store the information. These differences allow a larger volume of data to be recorded on each successive generation. Larger data volumes translate into higher quality video and longer playing time.
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3.2 Parameters for HD Video Storage with Optical Disks
¾ Optical Parameters ¾ Disk Structure Parameters ¾ Data Management Parameters Optical parameters include laser wavelength, objective lens numerical aperture, protective layer thickness and free working distance. Data management parameters include data rate, video format, HDTV play time and bit‐rate scheme. Disk structure parameters are user data capacity, minimum channel bit length and track‐to‐track spacing.
3.2.1 Optical Parameters
Fig 1
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Digital information is stored on optical disks in
the form of arrangements of data marks in spiral tracks. The process for exposing data marks on a recordable optical disk is shown in Fig. 1, where an input stream of digital information is converted with an encoder and modulator into a drive signal for a laser source. The laser source emits an intense light beam that is directed and focused onto the surface by the objective lens. As the surface moves under the scanning spot, energy from the intense scan spot is absorbed, and a small, localized region heats up. The surface, under the influence of heat beyond a critical writing threshold, changes its reflective properties. Modulation of the intense light beam is synchronous with the drive signal, so a circular track of data marks is formed as the surface rotates. The scan spot is moved slightly as the surface rotates to allow another track to be written on new media during the next revolution. Data marks on prerecorded disks are fabricated by first making a master disk with the appropriate data‐mark pattern. Masters for prerecorded CDs and DVDs are often exposed in a similar manner to exposing data marks on recordable optical disks, except that the light‐sensitive layer is designed to produce pits in the master that serve as data marks in the replicas. Inexpensive replicas of the master are made with Injection‐molding equipment.
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Fig 2 Readout of data marks on the disk is illustrated in Fig.2, where the laser is used at a constant output power level that does not heat the data surface beyond its thermal writing threshold. The laser beam is directed through a beam splitter into the objective lens, where the beam is focused onto the surface. As the data marks to be read pass under the scan spot, the reflected light is modulated. Modulated light is collected by illumination optics and directed by the beam splitter to servo and data optics, which converge the light onto detectors. The detectors change light modulation into current modulation that is amplified and decoded to produce the output data stream. A fundamental limitation to the number of
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data marks per unit area is due to the size of the focused laser beam that illuminates the surface. Small laser spots are required to record and read out small data marks. More data marks per unit area translate into higher capacity disks, so evolution of optical data storage is toward smaller spot sizes.
Fig 3 Figure 3 shows a detailed picture of the laser irradiance approaching the surface, where irradiance is defined as the laser power per unit area. Ideally, maximum irradiance is located at the recording material, along with the smallest spot size s. As the distance increases away from the ideal focus, the spot size increases and the peak irradiance decreases. A defocus distance δz of only a few micrometers dramatically reduces peak
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irradiance and increases spot size. An approximate formula used to estimate the ideal spot size at best focus is s = λ/(sin θ), where θ is the marginal ray angle of the illumination optics, as shown in Fig. 1. Spot size s is the full width of the irradiance distribution at the 1/e2 (13.5%) irradiance level relative to the peak. The value of sin q is often called the numerical aperture or NA of the optical
system.
Fig 4 Instead of focusing directly on the recording surface, optical disks focus through a protective layer, as shown in Fig.4 for a simple CD‐ROM. The protective layer prevents dust and other contamination from directly obstructing the laser spot at the data marks. Instead, the out‐of‐ focus contamination only partially obscures the laser focus cone, and data can
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usually be recovered reliably. If the protective layer is scratched or damaged, it can be cleaned or buffed. As the protective layer gets thinner, the error rate increases to an unacceptable threshold due to obscuration of the laser beam. This sensitivity decreases as NA increases, due to the smaller defocus range associated with these systems. In addition, the free working distance separates the objective lens from the spinning disk. This separation protects the disk against accidental contact between the objective lens and the disk. In order to maximize disk capacity, the optical system uses high NA and short wavelength. For maximum contamination protection, the protective layer should be as thick as possible. However, the combination of thick protective layer and high NA is not easily accomplished. High NA systems are sensitive to changes in substrate thickness and disk tilt. Manufacturing variations create thickness no uniformities, which are usually a small percentage of the total disk thickness. Motor instabilities induce tilt as the disk spins. Energy from the central portion of the spot is redistributed to concentric rings, which degrade the quality of the read out signal. This Degrades the read out signal. Tilt causes coma, which is another form of aberration effect, is called spherical aberration.
Sensitivity of the spot to degradation from
thickness variations and disk tilt is plotted in Fig. 5 as a function of total protective layer thickness for two values of NA. In order to limit these effects,
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the substrate is made as thin as possible without sacrificing contamination protection.
Fig 5 The most conservative technology is the Video CD. Its thick protective layer, relatively low NA and long laser wavelength produce a stable system that is not very sensitive to environmental factors like dust and scratches. The ideal spot size is about 0.78/0.5 = 1.6 micrometers. Although the cover layer is thick at 1.2 mm, the sensitivity to thickness variations and disk tilt is low because of the low NA. DVD technology uses a shorter wavelength laser, higher NA optics and a thinner protective layer. The
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combination of short wavelength and higher NA produce a spot size of about 1.1 micrometers. The protective layer had to be made thinner, because the sensitivity to thickness variations and disk tilt is too high otherwise. DVDs are slightly more sensitive to dust and scratches than CDs. The net effect is not great, because higher NA reduces the focal depth and DVDs have a more robust error management strategy. The Advanced Optical Disk and Blu‐Ray systems both use a new blue laser source that emits 0.405 micrometer light. The Advanced Optical Disk system uses the same protective layer thickness as a DVD, and it uses the same NA objective lens. Due to the short wavelength, the spot size for the Advanced Optical Disk is about 0.62 micrometers. Sensitivity to dust and scratches is about the same as a DVD, as well as the sensitivity to thickness variations and disk tilt. The Blu‐Ray system uses both higher NA and thinner cover layer. The spot size is 0.405/0.85 = 0.48 micrometers, which is the smallest spot size of all the technologies. However, because of the high NA, the protective layer had to be made thin to limit sensitivity to thickness variations and disk tilt. Therefore, Blu‐Ray disks are sensitive to dust and scratches. The free working distance is nearly is same for all technologies except Blu‐Ray. Blu‐Ray systems utilize more complicated lens systems due to the high NA, so working distance had to be reduced. The integrity of this reduced working distance is not clear at this time.
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3.2.2 Disk Structure Parameters The spot size created from the NA and wavelength parameters is the most important factor to determine the track‐to‐track spacing and the minimum channel bit length along the track. Several channel bits are encoded into each data mark. The number of channel bits per data mark depends on the modulation scheme. The relatively large spot produces relatively large data marks and correspondingly wide tracks and large channel‐bit lengths. Progressively smaller spot sizes enable smaller track spacing and shorter channel bit lengths.
Fig 6
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To the user, all generations of optical disks look very similar. They all are round disks that are approximately 120 mm in diameter, have a central mounting hole and are approximately 1.2 mm thick. Through many years of experience with CDs, this format has proven effective and mechanically reliable. However, the manner in which data layers are arranged on the disk depends on the technology used. For example, the CD uses a simple 1.2 mm thick substrate, as shown in Fig. 6A. Data are recorded on only one side of the disk, through the clear 1.2 mm substrate, which also serves as the protective layer. DVDs, Warner HD‐DVDs and Advanced Optical Disks use the format shown in Fig. 6B, where two 0.6 mm substrates are bonded together and the data are recorded on the bond side of each substrate. DVDs also allow more two layers per side (A, B in Fig. 6B), where the layers are separated by a thin adhesive spacer. The two layers are fabricated before bonding at the same time as the individual 0.6 mm substrates. Like the CD, data are recorded and read through the clear substrates. It is likely that the Warner HDDVD and Advanced Optical Disk will also take advantage of this multiple‐layer concept. A potential implementation of the Blu‐Ray disk is shown in Fig. 6C, where the protective layers on each side are very thin at 0.1 mm. In this case, data are recorded on the substrate, which does not serve as the protective layer. Instead, a protective layer resin is spun on and hardened or a thin protective sheet is bonded on each side of the substrate. Because of the thin protective layer, the Blu‐Ray disk must also be used with a cartridge.
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The only optical disk technology that plans to
use a Cartridge is the Blu‐Ray system. The Blu‐Ray cartridge is necessary for contamination Protection, but the working distance of around 0.1 mm and protective layer thickness of 0.1 mm are large compared to the contact recording The technology for making disks is very similar to existing DVD technology. Higher‐resolution mastering machines and finer control over the injection molding process should produce the required changes without substantially retooling the industry. The Blu‐Ray system requires the most changes of the three, including a blue laser, detector, and advanced objective lens. Blu‐Ray also requires new disk and cartridge manufacturing technology, which may be difficult to implement in a short time frame.
3.2.3 Data Management Parameters
The logical organization of data on the disk
and how those data are used are considerations for data management. Data management considerations have important implications in the application of optical disk technology to storage for HDTV. For example, simply using a more advanced error correction scheme on DVDs allows a 30% higher disk capacity compared to CDs. Data rate, video format, bit‐rate scheme and HDTV play time are all data management issues.
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There is a basic difference in data management between CDs and DVDs. Since CDs were designed for audio, data are managed in a manner similar to data management for magnetic tape. Long, contiguous files are used that are not easily subdivided and written in a random access pattern. Efficient data retrieval is accomplished when these long files are read out in a contiguous fashion. To be sure, CDs are much more efficient that magnetic tape for pseudorandom access, but the management philosophy is the same. On the other hand, DVDs are more like magnetic hard disks, where the file structure is designed to be used in random‐access architecture. That is, efficient recovery of variable length files is achieved. In addition, the Original error correction strategy for CDs was designed for error concealment when listening to audio, where DVDs utilize true error correction. Later generations of optical disks also follow the DVD model. The random‐access nature of DVDs allows very efficient methods for data compression. For example, MPEG‐2 with variable bit rate allows data to be read out from the disk as they are required, rather than supplying data at a constant rate. Slowly moving scenes, like love scenes or conversations, require much less information per frame than a fast‐moving car chase or explosion. In these fast‐moving scenes, the maximum amount of information per scene is limited only by the maximum data rate of the player. For HDTV, acceptable picture quality is obtained by using MPEG‐2 with a maximum data rate of about 13‐25 Mbps for most scenes. During a slow
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scene, not as many files are accessed, and much less storage area on the disk is used. This architecture leaves room on the disk for the data associated with faster‐moving scenes.
Fixed‐rate schemes, like magnetic tape, supply data at a
constant rate, no matter what the requirements of the scene. During fast‐moving scenes, the data stream from the tape supplies an adequate data rate. The tape speed and data
rate for these devices are set by the upper limit of the scene requirements. Since the tape does not slow down during slower scenes, the data stream is ‘padded’ at these times with useless information that takes up valuable storage area on the tape. Overall, the random‐access architecture of optical disks is a much more efficient way to use the available storage area. That is, optical disks do not require as many gigabytes of user data capacity for an equivalent length and quality HDTV presentation. It is not practical to store HDTV on CDs and DVDs with MPEG‐2. For CDs, special multiple‐beam readout or high velocity disk dives could produce the data rate, which is an advantage of the fixed‐bit‐rate scheme. However, the play time would be only a few minutes, at best. DVDs are not capable of the 13 Mbps random data rate to support MPEG‐2. The Advanced Optical Disk exhibits acceptable data rate and reasonable user data capacity for up to two hours of HDTV per side compressed with variable bit‐ rate MPEG‐2. Blu‐ray has slightly higher capacity and data rate. The two‐hour play time for HDTV with Blu‐Ray in Table I is really a specification for real‐ time recording, which is not easily compressed into an efficient variable‐rate
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scheme. Blu‐Ray should easily provide two hours or longer of prerecorded HDTV per side compressed with MPEG‐2. MPEG‐2 is a technique for compressing video data and replaying the data associated with certain rules that are defined in the MPEG‐2 specifications. The action of the optical disk system is not to compress data or interpret the video information rules. Instead, the optical disk system only stores and retrieves data on command from the video operating system. Therefore, as video operating systems and associated compression technology become more advanced, no fundamental changes are required to the optical disk system. MPEG‐4 technology is an advanced video compression scheme that utilizes advanced pre‐filtering and post‐filtering, in addition to a rule‐based algorithm. Estimated improvement in compression is a around a factor of three beyond MPEG‐2.
4. Different Formats of Blu‐ray Disc BD‐ROM: a read only format developed for prerecorded content
BD‐R : a write once format developed for PC storage BD‐RW : a rewritable format developed for PC storage BD‐RE : a rewritable format developed for HDTV recording
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5. Two Versions of Recording 5.1 One Time Recording
Making permanent changes to a disc. If we use
BD‐R the material on the disc itself is changed forever. There is no way to get the material back into its old state. The recording material is crystalline in nature. As scan spot falls on the surface it changes to amorphous. We cannot change it back to crystal state.
5.2 Record Many Times
If we use a BD‐RW the material on the disc
itself changes, but can be changed back again .We can do this as long as the material doesn’t get worn out. By heating up the crystals, they change form. Now when we quickly cool them, they stay in that form itself. That is the material is changed from crystal state to amorphous state.
Now, if we want to erase the BD‐RW, we have
to make sure that we lose all the data. So we want to get rid of that amorphous state. By heating up the material again, but this time taking more time and less heat, the material gradually wants to take its old form again, and thus the information is erased. This state is called the crystalline state.
Department of ECE
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Blu-ray disc
seminar 2004 So, by very quickly heating it and very quickly
cooling it, give the crystal another state (Amorphous state) which thus contains the data and by very quite slowly heating it and cooling it, we can give the crystals their old form back (crystalline state) which contains no more data. It’s a constant change of phases. And so it is called as phase change recording.
Data is stored in the form of grooves, on an optical disc. Next to the grooves, there are lands. Lands are the borders between the grooves. Grooves and lands have a sinus form. This is called a wobbled groove. In the groove, pits are formed to store data.
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6. Blu‐ray Disc Structure
The structure of the BD is as shown. The 0.1mm transparent cover layer is made of a spin‐coated UV resin. It is formed by sandwiching a transparent layer between a protective coating and a bonding layer. This layer offers excellent birefringence. Beneath, there is a layer of Antis layer acts as a heat sink, dissipating the excess heat during the write process. A spacer layer made of ZnS‐SiO2 comes next. Then, the recording layer made of AgInSbTeGe comes. Grooves are formed on this layer for recording.A reflective layer of Ag alloy falls beneath and finally a plastic substrate comes. The key features of the technology are introduced as follows
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seminar 2004
Highly flat and smooth cover layer:
At the high speed recording rate involved, the linear velocity of the disc reaches 20m/s or more and as a result accurate focus control becomes difficult. Various experiments showed that flatness and smoothness of the transparent cover layer have a marked influence on the focus control capability. This end is achieved by using the spin coating method for obtaining the transparent cover layer. Thus stable record ability at high speed recording is secured. ¾
Phase change film for high speed recording: The phase change film should have high
recrystallisation speed to enable direct recording at the high linear velocities involved. A recording layer made of AgInSbTeGe meets this purpose.
¾
Super advanced rapid cooling structure:
The excess heat from the LASER irradiation causes distortion of the recorded mark edge. So, to diffuse the remaining excess heat, a transparent di‐electric film of high thermal conductivity, for example, AlN is used.
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7. Specifications:
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8. Basic Blu‐ray Disc Characteristics 8.1 Large Recording Capacity
The Blu‐ray disc enables the recording, rewriting and playback of HD video unto 27 GB of data on a single sided single layer. It is enough to put 2.5 hours of HDTV recording on it. It also can record over 13 hours of standard TV broadcasting using the VHS/ standard definition picture quality.
8.2 High Speed It has a data transfer rate of 36 Mbps. Because of this high speed transfer rates it can also record the data in very little time. In a perfect environment it would take about 2.5 hours to fill the entire BD with 27 GB of data. More than enough transfer capacity for real time recording and playback.
8.3 Resistant to Scratches and Fingerprints
The protective layer is hard enough to prevent
accidental abrasions and allows fingerprints to be removed by wiping the disc with a tissue.
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9. Blu‐ray Founders
The
following
companies
have
jointly
established the basic specifications Blu‐ray disc video recording format
1. Hitachi , Ltd 2. LG Electronics Inc. 3. Matsushita Electric Industrial Co. Ltd. 4. Mitsubishi Electric Corporation 5. Pioneer Corporation 6. Royal Philips Electronics 7. Samsung Electronics Co. Ltd. 8. Sharp Corporation 9. Sony Corporation 10. Thomson
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10. Comparisons
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11. Blu‐ray Disc and HD‐DVD: The HD‐DVD format, originally called AOD or Advanced Optical Disc, is based on much of todayʹs DVD principles and as a result, suffers from many of its limitations. The format does not provide as big of a technological step as Blu‐ray Disc. For example, its pre‐recorded capacities are only 15 GB for a single layer disc, or 30 GB for a double layer disc. Blu‐ray Disc provides 67% more capacity per layer at 25 GB for a single layer and 50GB for a double layer disc. Although the HD‐DVD format claims it keeps initial investments for disc replicates and media manufacturers as low as possible, they still need to make substantial investments in modifying their production equipment to create HD‐DVDs. But whatʹs more important is that HD‐DVD can be seen as just a transition technology, with a capacity not sufficient for the long term. It might not offer enough space to hold a High Definition feature along with bonus material in HD quality and additional material that can be revealed upon authorization via a network. When two discs are needed, this will degrade the so‐called cost benefit substantially. It is even possible that the HD‐DVD specification will be followed up by a renewed version of the technology within a few years, requiring media manufacturers to upgrade their existing production lines again, and consumers to replace their existing playback/recording equipment. On the
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other hand, the Blu‐ray Disc format was designed to be a viable technology for a period of at least 10 to 15 years.
Also on the application layer, the HD‐DVD
format incorporates many compromises. As the capacity is not likely to be sufficient to encode a full‐length feature plus additional bonus materials using the MPEG‐2 format, different and stronger encoding formats need to be used. Although Blu‐ray Disc offers these advanced codecs as well, the disc has such high capacity that publishers can still use the MPEG‐2 encoding format at bit rates up to 54 Mbit/sec. As MPEG‐2 is the de‐facto standard used in almost any industry involved in digital video (DVD, HDTV, digital broadcast), many authoring solutions are available. Chances are high that a full line MPEG‐2 encoding suite is already available, which can be used with no or minor adaptations to encode High Definition content for Blu‐ray Disc. But perhaps the most important factor for the success of Blu‐ray Disc is its overwhelming industry‐wide support. Almost all consumer electronics companies in the world (combined market share of about 90%) and the worldʹs two largest computer companies support the Blu‐ray Disc format. This ensures a large selection of Blu‐ray Disc players, recorders, PC drives, Blu‐ray Disc equipped PCs and blank media will become available. A competing format will not have the manufacturing power to penetrate the market in a level even approaching that of Blu‐ray Disc
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12. Advantages The main advantages of the Blu‐ray disc are
¾ More storage capacity on a disc of the same size. The data storage capacity on a Blu‐ray disc is 27GB on a single layer and 54GBon dual layer, which is about five to six times the capacity of a DVD. It would mean about 2.5 hours of HDTV video and about 13 hours of SDTV video.
¾ High data transfer rate. The basic data transfer rate in Blu‐ray disc is about 36Mbps which is about three times that of a DVD and thirty times that of a CD.
¾ Available in different versions like ROM, R and RE The BD is available in different versions like the ROM (write once), R (read only), RE (rewritable).
¾ Backward compatible. The BD drives are designed to be backward compatible, i.e. CDs and DVDs work equally well with the BD drives.
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¾ Strong content protection. The features of the content protection system are •
Format Developed with Input from Motion Picture Studios
•
Strong Copy Protection by
•
Renewability with Renewal Key Block and Device Key
•
Enhanced Encryption Algorithm: AES 128 bit
•
Physical Hook Against Bit by Bit Encrypted Content Copy
•
Title‐based Expandable Content Control File
•
Production Process Control Works Against Professional Piracy
•
Public Key Based Authentication in PC Environment
¾ Compatible with analog and digital transmission. The BD fares well with analog as well as digital transmission. It offers the only means to the recording and reproducing of digital HDTV video. Format for encoding analog signals also, called SESF (Self Encoded Stream Format) is also incorporated into the BD.
¾ Higher disc life. In the case of ordinary discs, the disc life is less fir the rewritable versions, as re‐writing is done repeatedly to one area of the disc most probably, the inner perimeter. This limits the disc life. But, the BDFS(Blu‐ray Disc File Structure is designed so as to avoid this problem, by using a system that uses free disc spaces with equal frequency
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13. Applications ¾
High Definition Television Recording
¾
High Definition Video Distribution
¾
High Definition Camcorder Archiving
¾
Mass Data Storage
¾
Digital Asset Management and Professional Storage
The Blu‐ray Disc format was designed to offer the best performance and features for a wide variety of applications. High Definition video distribution is one of the key features of Blu‐ray Disc, but the formatʹs versatile design and top‐of‐the‐line specifications mean that it is suitable for a full range of other purposes as well.
13.1 High Definition Television Recording High Definition broadcasting is vastly expanding in the US and Asia. Consumers are increasingly making the switch to HDTV sets to enjoy the best possible television experience. The Blu‐ray Disc format offers consumers the ability to record their High Definition television broadcasts in their original quality for the first time, preserving the pure picture and audio level as offered by the broadcaster. As such it will become the next level in home entertainment, offering an unsurpassed user experience. And since the
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Blu‐ray Disc format incorporates the strongest copy protection algorithms of any format or proposal to date, the format allows for recording of digital broadcasts while meeting the content protection demands of the broadcast industry.
13.2 High Definition Video Distribution
Due to its enormous data capacity of 25 to 50
GB per (single sided) disc, the Blu‐ray Disc format can store High Definition video in the highest possible quality. Because of the huge capacity of the disc, there is no need to compromise on picture quality. Depending on the encoding method, there is room for more than seven hours of the highest HD quality video. There is even room for additional content such as special features and other bonus material to accompany the High Definition movie. Furthermore, the Blu‐ray Disc movie format greatly expands on traditional DVD capabilities, by incorporating many new interactive features allowing content providers to offer an even more incredible experience to consumers. An Internet‐connection may even be used to unlock additional material that is stored on the disc, as there is enough room on the disc to include premium material as well.
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13.3 High Definition Camcorder Archiving
As the market penetration of High Definition
TV sets continues to grow, so does the demand of consumers to create their own HD recordings. With the advent of the first HD camcorders, consumers can now for the first time record their own home movies in a quality level unlike any before. As these camcorders are tape‐based, consumers cannot benefit from the convenience and direct access features they are used to from the DVD players and recorders. Now, the Blu‐ray Disc format, with its unprecedented storage capacity, allows for the HD video recorded with an HD camcorder to be seamlessly transferred to a Blu‐ray Disc. When the HD content is stored on a Blu‐ray Disc, it can be randomly accessed in a way comparable to DVD. Furthermore, the Blu‐ray Disc can be edited, enhanced with interactive menus for an even increased user experience and the disc can be safely stored for many years, without the risk of tape wear.
13.4 Mass Data Storage
In its day, CD‐R/RW meant a huge increase in
storage capacity compared to traditional storage media with its 650 MB. Then DVD surpassed this amount by offering 4.7 to 8.5 GB of storage, an impressive 5 to 10 times increase. Now consumers demand an even bigger storage capacity. The growing number of broadband connections allowing
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consumers to download vast amounts of data, as well as the ever increasing audio, video and photo capabilities of personal computers has lead to yet another level in data storage requirements. In addition, commercial storage requirements are growing exponentially due to the proliferation of e‐mail and the migration to paperless processes. The Blu‐ray Disc format again offers 5 to 10 times as much capacity as traditional DVD resulting in 25 to 50 GB of data to be stored on a single rewritable or recordable disc. As Blu‐ray Disc uses the same form factor as CD and DVD, this allows for Blu‐ray Disc drives that can still read and write to CD and DVD media as well.
13.5 Digital Asset Management and Professional Storage
Due to its high capacity, low cost per GB and
extremely versatile ways of transferring data from one device to another (because of Blu‐ray Discʹs extremely wide adoption across the industry), the format is optimized for Digital Asset Management and other professional applications that require vast amounts of storage space. Think of medical archives that may contain numerous diagnostic scans in the highest resolution, or catalogs of audiovisual assets that need to be instantly retrieved in a random access manner, without the need to ʺrestoreʺ data from a storage carrier. One Blu‐ray Disc may replace many backup tapes, CDs, DVDs or other less common or proprietary storage media. And contrary to network solutions, the discs can be physically stored in a different location for backup and safekeeping
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14. Requirements 1) Blue laser 2) Detector 3) Advanced objective lens 4) New disk and cartridge manufacturing technologies
15. Challenges: ¾ High cost The technology is not that popular and hence, the price of the BD recorders and players available in the market is very high.
¾ HD‐DVD The HD‐DVD (High Definition DVD) based on the Advanced Optical System championed by Toshiba and NEC is the primary rival to BD in the market. Though its data storage density is lower, it has lower manufacturing costs also, which may prove challenging to the Blu‐ray disc.
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16. Future Developments: Efforts are progressing on many fronts to make the Blu‐ray discs, players and recorders cheaper. On 15 April 2004 for instance, Sony and Toppan Printing announced the successful development of a Blu‐ ray Disc that is 51% (by mass) composed of paper, which could reduce production costs and improve its environmental friendliness.The cost would come down as BD becomes more and more popular. TDK has been researching the hard coat technology that will provide protection against fingerprints and scratches. Colloidable silica dispersed UV‐curable resin is being used for the researches and results are encouraging.
Figure shows the cross section of the disc being developed.
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17. Conclusion: The BD represents a major advancement in capacity as well as data transfer rate. It would be an ideal choice for the secondary storage purposes.The semiconductor storage for secondary memory is large, consumes more power and is more expensive. HDTV video recording and reproducing would essentially require the large storage capacity and data transfer rates, as offered by the Blu‐ray disc. The Blu‐ray disc has a wide variety of applications and is the ultimate storage device that would lead to digital convergence, ultimately leading to the convergence of the PC and CE technologies. In the opinion of many researchers (including those at the BDF group themselves), BD possibly represents the last of the plastic‐ based, visible laser optical disc systems. Shorter violet and ultraviolet wavelengths are absorbed strongly by the plastic used in disc manufacturing, and itʹs difficult to cheaply manufacture a much higher‐quality lens. The light absorbed by the disk would not make it back out to be read by the drive. In addition, most plastics decay when exposed to ultraviolet light, changing color and becoming brittle. An ultraviolet system would destroy plastic media used with it. Future technologies would likely involve glass platters (which donʹt absorb long‐wave ultraviolet nearly as much as plastic), ultraviolet readout lasers, and/or multilayer fluorescent media. An emergence of the magneto‐optical system for secondary storage is also a big possibility
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18. References 1. Digital Digest Magazine Published by Digital Tech Consulting L.L.C, September 2003, “Blu‐Ray Format Positioning As Next Generation DVD.”
2. Optical Recording: A Technical Overview, Addison‐ Wesley, Reading, Massachusetts,pp321‐323(1990)
3. Optical Disc Systems Dec 2002,”The Blue Disc Recording Technology” 4. Spectrum, Magazine Published by IEEE, June 2003, “The Great Gallium Nitride Gamble”
5. www.bluray.com 6. www.google.com 7. www.opticaldisc_system.com
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