Annauniversity Optical Communication Question Paper

B.E./B.TECH.DEGREE EXAMINATION NOV/DEC 2005 VII -SEMESTER OPTICAL COMMUNICATION TIME :3 hrs MAX MARKS :100 PART -A (10 X 2 = 20 MARKS) 1. A point sorce of ligth is 12 cm below the surface of a large body of water (n = 1.33). What is the radius of the largest circle on the water surface through which the light can emerge? 2. Consider a parabolic index waveguide with n1 =1.75 ,n2 = 1.677 and core radius 25 micro meter. Calculate the numerical aperture at the axis and at a point 20 micro meter from the axis 3. Write the expression for the effective number of modes guided by a curved multimode fiber of radius 'a' 4. Define normalized propagation constant. 5. Draw the three key transistion process involved in laser action 6. Write the concept of indirect bandgap semiconductor materials 7. Define responsivity of photodiode. 8. Define quantum efficiency of a photodetector 9. List the sysyem requirements neede in analyzing a point -to- point link 10. Write the concept of solition PART - B (5 X 16 =80) 11(i) Diacuss the signal distortion in single mode fibers (ii) Discuss pulse broadening in graded index fibers with necessary equations 12(a) (i) Briefly explain the evolution of fiber optic system (ii) Compare the configuration of different types of fibers . OR (b)(i) Derive modal equation (ii) Discuss the modes in step- index fibers 13(a) Draw the structures of edge-emitting LED and surface emitting LED and explain the operation OR (b) (i)Discuss the LASER diode principle , modes and threshold conditions 14(a) Draw the schematics of pin photodiode and APD and explain. OR (b) Explain the fundamental receiver operation in optical communication

15(a) Explain various types of fiber splicing techniques and fiber connectors OR (b) (i) Explain the operational principles of WDM (ii) Explain the rise-time budget.

B.E./B.TECH.DEGREE EXAMINATION APRIL/MAY 2005 VII -SEMESTER OPTICAL COMMUNICATION TIME :3 hrs MAX MARKS :100 PART -A (10 X 2 = 20 MARKS) 1. Define numerical aperture of a step index fiber 2. Define mode-field diameter 3. Give expression for the effective number of modes guided by a curved multimode fiber 4. What are the causes of absorption? 5. What is meant by hetero junction? 6. What is meant by indirect band gap semi conductor material? 7. Define responsivity 8. A given APD has a quantum efficiency of 65 % at a wavelength of 90 nm . If 0.5 micro watt of optical power produces a multiplied photocurrent of 10 micro Ampere , find the multiplication M 9. What is meant by solitron? 10 What is meant by modal noise? PART-B (5 X 16 = 80) 11(I) Discuss the propagation modes in single -mode fiber (ii) Discuss the structure of graded index fiber 12(a) (i) What is meant by material dispersion? (ii) Derive an expression for material dispersion

(iii) Derive the expression for wave guide dispersion OR (b) Discuss the pulse broadening in graded index fibers 13(a) Draw the structure of edge emitting and surface emitting LEDs and explain OR (b) Discuss the laser diode structures and radiation patterns 14(a) An InGaAs 1300 nm : I D = negligible. The bandwidth is 20 OR (b) Discuss the error

pin photodiode has the following parameters at a wavelength of 4 nA, ? = 0.9, RL = 1000 ohms and the surface leakage current is incident optical power is 300 nw (- 35 dBm), and the receiver MHz . Find the various noise terms of the receiver performance of digital receiver by defining the probability of

15 (a) (i) Discuss the operational principles of WDM (ii) Describe the key features of WDM OR (b) Explain the rise-time budget of a fiber –optic point – to – point link

B.E./B.TECH.DEGREE EXAMINATION MAY/JUNE 2006 VII -SEMESTER OPTICAL COMMUNICATION TIME :3 hrs MAX MARKS :100 PART -A (10 X 2 = 20 MARKS) 1. Commonly available single mode fibers have beat lengths in the range 10 cm < Lp <2 m . What range of refractive index diffrences does this correspond to? (for wavelength = 1300 nm) 2. Define mode field diameter 3. Find the coupling loss for two fibers having core refractive index profiles alpha E = 2.0 and alpha R = 1.5 . 4. What causes mode coupling? 5. Give example for direct and indirect semiconductor materials 6. Calculate the ratio of stimulated emission rate to the spontaneous emission rate for a lamp operating at a temperature of 100 K . Assume average operating wavelength is 0.5 micro meter 7. Define long wavelength cutoff of a photodiode 8 What is meant by quantum limit? 9. Write the basic concept of solition generation 10 Write the concept of link power budget

PART B (5 X 16 = 80) 11(i) What is meant by 'material dispersion'? Derive its expression (ii) Discuss the pulse broadening in graded index fiberss 12(a) (i) List the advantages of optical fiber comminication (ii) Draw the elements of an optical fiber transmission link and explain OR (b) (i) Discuss the mode theory of circular waveguide 13(a)(i) What is meant by heterojunction ? Give example. (ii) Derive the internal quantum efficiency of an LED OR (b) (i) Explain optical feedback and laser oscillation. (ii) Derive the threshold condition for lasing 14 (a) Discuss the principle of operation of APD wiht neat circuit diagram. Also discuss the requirements of photo detector. OR (b) Discuss the fundamentals of receiver operations with neat block diagram 15 (a) Draw the point-to -point fiber optic link and discuss the system considerations OR (b) Discuss the principle ,requirement and applications of WDM

BE./B.Tech. DEGREE EXAMINATION, MAY/JUNE 2007. Seventh Semester Electronics and Communication Engineering EC 433 — OPTICAL COMMUNICATION Time: Three hours Maximum: 100 marks PART A — (10 x 2 = 20 marks) Answer ALL questions. 1. What is the fundamental parameter of a single mode fiber? 2. A step index fiber has a normalized frequency V = 26.6 at 1300 nm wavelength. If the core radius is 25 pm, find the numerical aperture. 3. Mention the two causes of intra-modal dispersion. 4. Define fiber loss. 5. Compare LED and LASER. 6. What is meant by population inversion? 7. A photodiode is constructed of GaAs, which has band gap energy of 1.43 eV at 300 K. What is meant by long wavelength cutoff? 8. What are the benefits of a trans-impedance amplifier? 9. List the key requirements needed in analyzing a link.

10. Define Modal Noise. PART B — (5 x 16 = 80 marks) 11. (a) What are fiber modes? Explain mode theory for optical fibers in detail. Or (b) Compare Single mode fibers and Graded index fibers. Explain the requirements for fiber materials. 12. (a) Discuss various kinds of losses that an optical signal might suffer while propagating through fiber, Which is most important one? What is the effect of these losses on light power and pulse shape? Or (b) What is mode coupling? Discuss pulse broadening in Gl fibers. 13. (a) With neat diagram explain the construction and working of high radiance surface emitting LED. Or (b) Discuss about modulation of Laser diodes. Why thermoelectric cooler are used in Laser diodes? 14. (a) What is known as quantum limit? A digital fiber optic link operating at 850 nm requires a maximum BER of 10*9. Find the minimum incidental optical power Po to achieve this BER at a data rate of 10 Mb/s for a simple binary level signaling scheme. (ry: 1), [1/r : B/2]. Or (b) Discuss in detail digital receiver performance calculation and sensitivity calculation in detail. 15. (a) What are the system consideration in point to point links? Explain in detail. Or (b) Discuss in detail Fiber splicing and connectors. Explain the operation principles of WDM.

B.E / B.Tech. DEGREE EXAMINATION,NOV/DEC 2007 OPTICAL COMMUNCATION VII SEMESTER Time : 3 Hrs Max Marks : 100 PART A (10 X 2 = 20 )

1. Give the relationship between rays and modes 2. A silica fiber as a core refractive index of 1.5 and a cladding refractive index of 1.47 . Determine the acceptance angle in air for the fibr 3. What do you mean by polorization mode dispersion?

4. Distinguish dispersion shifted and dispersion flattened fibers 5. What do you mean by heterojunction ? Mention its advantages 6. List different types of mechanical misalignments that can occur between two joined fibers 7. What are the desired features of photodetector? 8. Define quntum limit 9. What are the advantages of WDM? 10 Distinguish fundamental and higher order solitions.

PART - B ( 5 X 16 = 80) 11 (a) (i) Explain with neat diagram the elements of an optical fiber transmission link. (ii) A multimode index difference refractive index number of guided OR

step index fiber with a core diameter of 80 µm and a relative of 1.5 % is operating at a wavelength of 0.85 µm .If the core is 1.48 ,estimate the normalized frequency for the fiber and the modes

(b) (i) Discuss the evolution of fiber optic communication system (ii) Sketch and explain the electric field disturbution of the lower order guided modes in symmetrical slab waveguide (iii) Draw the structures of step index and graded index fibers with their typical dimensions 12(a) (i) When the mean optical power launched into an 8 Km length of fiber is 120 µW , the mean optical power at the fiber output is 3µW.Determine (1) Overall signal attenuation in dB/Km and (2) The overall signal attenuation for a 10 Km optical link using the same fiber with splices at 1 Km intervals ,each giving an attenuation of 1 dB (ii) Explain with suitable diagrams the different mechanism that contribute to attenuation in optical fibers OR (b) (i) Discuss in detail intramodel dispersion with relevant expressions and diagrams (ii) Write a brief note on design optimization of single mode fibers 13 (a) (i) Draw and explain the LED structures based double Hetero structure configuration (ii) Discuss the principle of operation of laser diodes .What are the effects of temperature on the performance of a laser diode?

OR (b) (i) Explain the different lensing schemes available to improve the power coupling efficiency. (ii) Explain the fiber splicing techniques with necessary diagrams 14 (a) (i) A silicon p-i-n photodiode incorporated into an optical receiver has a quantum efficiency of 60 % at a wavelength of 0.9µm.The dark current is 3 nA and load resitence is 4 K ohms.The incident opical power is 200 nw and the receiver bandwidth is 5 MHz .Determine (1)Mean square quantum noise current, (2)Mean square dark current and (3)Mean square thermal noise current at a temperature of 20 degree c (ii) Draw and explain the operation of APD OR (b) (i) Discuss the different noise sources and disturbances in the optical pulse detection mechanism (ii) Derive an expression for the bit error rate of an optical digital receiver 15 (a) Explain the significance of link power budget and rise time budget with one illustration for each OR (b) (i) Explain the principle of operation of Erbium doped fiber amplifier (ii) Give a brief account of the principles of SONET