Optical Fiber Communication - Jan 2012

Electronics & Communication (Semester 7)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) Enlise the advantage of optical fibers,compared to the usage of a copper cables in the communication.(6 marks) 1 (b) With relevent diagrams,explain the different types of optical fibers,considering the number of the modes and material composition of the core. (8 marks) 1 (c) Light traveling in air strikes a glass plate at an angel ?₁33°,where &theta₁ is measured between the incoming ray and glass surface. If the refracted and reflacted beams make an angel of 90° with each other,what is the refractive index of the glass?What is the critical angle?(6 marks) 2 (a) Explain the mechanisms which cause absorption in the optical fibers.mention the measured which can reduce this type of single degradation .(6 marks) 2 (b) Prove that,delay differnce between the axial ray and extreme meridional ray is $$ \delta T_s\cong \frac{Ln_1\Delta}{c} $$(8 marks) 2 (c) A 6km optical link consists of multicode step-index fiber,with a core RI of 1.5 and relative index differnce of 1%. Estimate,<br.delay difference="" between="" slowest="" and="" fastest="" modes="" at="" the="" fiber="" output<br="">rms pulse broadening due to intermodal dispersion on the link
Maximum bit rate that may be obtained without substational errors on the link assuming only intermodal disapersion</br.delay>(6 marks) 3 (a) Draw and expalin the cross -sectional view of a typical GaAlAs double heterostructure LED,along with the energy band diagrams and variation in RI profile.(10 marks) 3 (b) What is quntum efficiency?How are the 'responsivity' and 'quantum efficiency' realted?(4 marks) 3 (c) A given silicomn avalanche photodiode has a quantum efficiency of 65% at a wavelength of 900_nm.Suppose 0.5?w of optical power produces a multiplied photocurrent of 10?A,find the primary photocurrent and the multiplication factor.(6 marks) 4 (a) List and sketch the different types spiciling techniques and connectors.(8 marks) 4 (b) What are the priciple requirements of a good connector design?(6 marks) 4 (c) A single mode fiber has a normalized frequency V=2.40, a core RI n₁=1.47,a cladding RI of n₂=1.465 and a core diameter of 9?m.Find the inseration loss of a fiber joint,if the lateral offset is 1?m.Also find the loss,if there is an angular misalignment of 1° at a 1300_nm wavelenghth.(6 marks) 5 (a) Expalin with a neat digram,the basis section and operation of an optical receiver.(6 marks) 5 (b) Brifly explain the 'quntum limits'(4 marks) 5 (c) Dervie the equation for the perfomance fidelity of an analog receiver.substains that for large optical signals.SNR represents the quantum limit for receiver sensitivity(10 marks) 6 (a) With a relvent diagram,discuss the subcarrier multiplexing techniques(6 marks) 6 (b) Discuss the various parameters involved in optical link power budget,with the relvent equation.(6 marks) 6 (c) write shorts note on:
Mode-parition noise
Charping(8 marks) 7 (a) describe the operational principles ofWDM ,depictim the implmentation of a typical WDM networks containg various types of optical amplifires(8 marks) 7 (b) Explain brifly the working of thin -film resonant cavity fiter.what is the application ? (6 marks) 7 (c) What is MEMS technology?with an example,explain a MEMS actuation method.(6 marks) 8 (a) with relevent schematics diagram,explain the three possible configuration of a EDFA(6 marks) 8 (b) Discuss the physical layer aspects os SONET,expalning the basic structure of an STS-L SONET frame(6 marks) 8 (c) What is the difference between fixed OADM and ROADM ?list the features of ROADM.(8 marks)