Fiber Optics: Theory And Applications Question Paper

Fiber Optics: Theory And Applications

Course:Bachelor Of Science (Computer Science)

Exam Year:2006

FIBER OPTICS: THEORY AND APPLICATIONS
SECTION A (30marks)
Q1.(a) i.Draw a well labeled diagram of an optical fiber communication system.(5marks)
ii.Give any three examples that illustrate and emphasize the reasons for using optical fiber.(3marks)
(b)Give the definition of dielectrics.(2marks)
(c)State two factors that determine the waveguide forms(2marks)
(d)i.With the aid of a well labeled diagram explain the meaning of TEM wave (4marks)
ii.Derive the formula for the cutoff wavelength, in a standard rectangular waveguide, for the TE1,0 mode.(2marks)
(e) If the transmission power is 2Mw and the minimum required received power is 0.1µW,calculate
i.the power budget in dB(2marks)
ii.the new transmission power if the power budget is decreased by 3 db while the received power remained uncharged.(2marks)
(f) Define dispersion in optical fiber.(2marks)
(g)Give three reasons why photodiodes are operated at reverse bias for detection in optical communication systems.(6marks)
SECTION B(20 marks each)

Q2.(a) i.State the difference between phase and group velocities of an electromagnetic wave.(2marks)
ii.Define the term dominant mode of operation for a waveguide.(2marks)
(b) With the aid of sketches explain the plain wave representation of both TE and TM modes in a parallel-plate waveguide.(8marks)
(c)A 6-GHz signal is propagated in a parallel-plane waveguide whose plane separation is 3cm.Considering TEmo modes,calculate
i.the cutoff wavelength(?o) of the dominant mode (2marks)
ii.the wavelength of the dominant mode (?p) in the waveguide(2marks)
iii.the corresponding group and phase velocities (4marks)

Q3.(a) State any two main functions of the optical fiber coating material(2marks)
(b) With the aid of sketches explain how a graded-index fiber can be used to reduce dispersion as opposed to the multimode step index fiber.(10marks)
(c)For a step index fiber with a core refractive index n1=1.47 and cladding refractive index n2=1.465.Calculate
i.the critical angle (2marks)
ii.the numerical aperture (2marks)
iii.the range of the propagation velocity along the fiber(4marks)

Q4.(a) State two main similarities and two main differences between semiconductor lasers and solid-state lasers.(4marks)
(b) With the aid of sketches describe the principle of operation of the semiconductor laser.(10marks)
(c) Calculate the ratio of stimulated emission rate to that of spontaneous emission rate at 300K thermal equilibrium in the absence of external pumping if photon wavelength is 1.5 µm in a semiconductor laser diode.(2marks)
(d) An inGaAsP laser diode measuring 100 µm long,5µm wide and 0.1µm thick.The spontaneous emission rate of InGaAsP laser is given by A21 No, with No being a constant around the doping concentration.Assuming that A21=109 sec-1 and No=10241/m3.Calculate
i.the pumping rate required for population inversion(2marks)
ii.the minimum injection current required (2marks)

Q5.(a) List three main characteristics of photo detectors.(3marks)
(b) With the aid of sketches describe the principle of operation of P-1-N photodiode(10marks)

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