Holography Pres

HOLOGRAPHIC DATA STORAGE

Nityanand Sharma 3rd SemCELOS ,CUSAT

HOLOGRAPHIC DATA STORAGE • Optical disc technology still in research stage. • Storage capacity up to 3.9 terabytes. • Data transfer rate of 1 gigabit/sec. • 6000 times the capacity of a CD-ROM. • 830 times the capacity of a DVD. • 160 times the capacity of a Blu-ray discs

Basics of holography • Holography was invented in 1947 by Hungarian physicist Dennis Gabor . • Holography means complete recording • The first holograms were made of normal (non-coherent) light. • The theories found real application only after the discovery of the laser.

Basics of holography • Holography is a method of recording information from a three dimensional object. • Light wave interference pattern is recorded • Recorded pattern is called hologram. • Hologram can produce a 3-dimensional image when illuminated properly.

Recording of hologram A laser beam is split into two- a reference beam and an object beam 

Reference beam aimed directly onto photo sensitive plate 



Object beam is aimed at object.

The object reflects some of the light on the holographic film-plate. 

The superposition of these two beams produces an interference pattern on the film. This is the hologram 

Recording of hologram .

Interference Patterns

Information Beam (A)

Two crests coincideConstructive interference

Crest of A concides with trough of B-Destructive intererence

Referance beam (B)

Reconstruction of hologram

Reconstruction of hologram • Illuminate the hologram by a beam called reconstruction beam from original direction of the reference beam. • 3-D virtual image of the object appears where the original image was. • Reconstructed wave front is sent to a CMOS sensor to produce original image.

Reconstruction of hologram • The hologram is sensitive to the exact recreation of the reference beam. A change in angle, position, or wavelength of the beam will lead to a failure to reconstruct the image. • The sensitivity increases with thickness of the holographic material.

Multiplexing • Multiple object images can be stored in a single piece of holographic material. • Multiplexing can be accomplished by changing either the angle or wavelength of the reference beam or by changing position of the holographic material relative to the beams

HOLOGRAPHIC DATA STORAGE • Electronic data of 1s and 0s converted to a page containing light and dark areas by Spatial Light Modulator (SLM) • Signal/information beam passes through the SLM. • Reference beam and signal beam meet to form the holographic data. • Data stored on photopolymer disc as hologram.

HOLOGRAPHIC DATA STORAGE Two types •

Two axis Holographic Data Storage

•

Collinear Holographic Data Storage

Two axis Holography

Basic components • • • • • • •

Blue-green argon laser Beam splitters to spilt the laser beam Mirrors to direct the laser beams Spatial light modulator ( LCD panel) Lenses to focus the laser beams Lithium-niobate crystal or photopolymer Charge Coupled Device (CCD) camera

Lasers • Lasers generate coherent light. • The laser beam is split into two separate beams: a reference beam, and an information beam • Signal/information beam passes through the SLM. • Reference beam and signal beam meet to form the holographic data.

Spatial Light Modulator • SLM imposes some form of spatially-varying modulation on a beam of light. • The SLM is a planar array of thousand of pixels. • Each pixel is an independent optical switch that can be set to either block or pass light. • SLM translates electronic data of 1’s and 0’s into an optical ‘checker board’ pattern of light and dark pixels.

Spatial Light Modulator

Spatial Light Modulator • Randomly-arranged LCs pass light normally (“off” state) • Liquid crystals arranged to block light (“on” state)

Spatial Light Modulator

checker board pattern

Spatial Light Modulator • Signal/information beam passes through the SLM. • Portions of light are blocked by opaque areas and portions pass through the translucent areas. • Modern LCD display technology allows high-resolution rapidly changeable SLMs. Arrays of MEMS micro mirrors can also be used.

Storage medium Requirements • linear response to light • Stability of the recorded pattern • low noise Materials • Low-shrinkage photopolymers are used in Write once, read many (WORM) materials. • Lithium-niobate (LiNbO3 ) doped with Fe, can be erased and rewritten via exposure to blue light.

Reading System

Readout • Data are read using an array of detector pixels such as CCD camera or CMOS sensing array. • Interpret the opaque and translucent areas as 0’s and 1’s of the binary code

Two axis Holography- Disadvantages • Reference beam and object beam are sent at two different axes. • Highly complex optical system. • Contained no servo data. • Incompatibility with current technology.

Collinear holography • Developed by Optware • Information and reference beams travel in the same axis and strike recording medium at same angle. • Requires only less complex optical system. • Two lasers are used • Green (data recording & reading) • Red (servo mechanism).

Collinear holography

The HVD : Writing system System uses beams of two different wavelengths. • 532 nm Green solid laser for data recording and reading • 650 nm Red semiconductor laser to control tracking and focus servo control. Adjust the focal point of the objective lens onto the recording media correctly and to locate the address of the holograms.

The HVD : Writing system

Structure of HVD 1.Green laser 2.Red laser 3. Hologram (data) 4. Polycarbon layer 5. Photo polymeric layer 6. Distance layers 7. Dichroic layer 8. Aluminum reflective layer 9. Transparent base P. PIT

Structure of HVD • Green laser (532 nm) for data recording and reading. • Red laser (650 nm) for addressing and servo mechanism. • Dichroic mirror layer reflects green laser and passes red laser. Prevents the interference between green laser and servo data pits.

Structure of HVD •

Polycarbon layer provides the disc depth necessary for laser focus .It also gives the disc enough strength to remain flat. • Interference pattern is recorded on the photopolymer layer (Data containing layer) •

Aluminum reflective layer reflect red light

Collinear holography vs Two axis holography.

•

CMOS

Information Beam Reference Beam Reconstruction Beam

Obj. Lens 2 Media

Reflective Layer with Servo and Address information Obj. Lens 1 Disc Obj. Lens SLM

( Conventional Holography

CMOS SLM

Collinear Holography

Holographic Recording Patterns

“Stop and Go” Conventional Holography

“On the Fly” Collinear Holography

Comparison with other Technologies Page Data

1 Bit Data

~1μm

Volumetric Recording Layer

Substrate

Data are recorded on to the surface as bit by bit in CD/DVD System

Surface Recording Layer

Conventional Optical Disc

Page data are recorded into the volumetric recording layer in Holographic recording

HVD

Optical Disc Technology 0.7 GB

9 GB

30~50 GB

. .

Holographic versatile disc developed by Optware

HVD-Applications

Video-On-Demand

Multimedia

Portable Computing

Consumer Audio/Video

Imagine ...



A disc with 4000 Hours of Video

 The entire Encyclopedia Britannica stored in a Dime...  A device that can store information 1000 times more densely and fetch it 100 times more quickly than any Magnetic or Optical Disk….

Holographic Technology will bring this, and Much More... At Our Fingertips…

Questions ?

References •

Ashley. J.et.al, (2000): Holographic Data Storage. IBM Journal of Research and Development.Vol 44(3) 341-367. http://www.research.ibm.com/journal/rd/443/ashley.html

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Hideyoshi Horimal and Xiaodi Tan(2005): Advanced Collinear Holography . OPTICAL REVIEW Vol. 12, No. 2 (2005) 90–92

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Huang, T.G. (2005): Holographic Memory. http://www.technologyreview.com

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Mellor, C. (2006): Chasing the Mirage? Some Holographic Storage Facts of Life. http://www.techworld.com.

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Optware Corporation; www.optware.com

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InPhase Technologies. ; http://www.inphase-tech.com/

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www.howstuffwork.com

Thank You