Optical Communication — Summer 2018

Explain the basic principal of Optical Fiber. Compare Optical Fiber with Co-axial cable as a communication channel.

What is normalized frequency? Astep index fiber in air has a numerical aperture of 0.16, core refractive index 1.45, and core diameter 60 micro meter. Assume that wavelength is 0.1 micrometer. Determine normalized frequency for fiber.

Define and explain following terms: 1) Critical Angle 2) Numerical Aperture 3) Meridional Ray 4) Dark Current 5) Bending Losses 6) Response Time 7) Monochromatic Source Astep

Discuss linear scattering losses in optical fiber with respect to, (1) Rayleigh Scattering (2) Mie Scattering

Explain the importance of cladd i n g i n o p t i c a l f i b e r 0 communication. Justify the statement: “Light travels faster in cladding than core.”

What is dispersion? Discuss various types of dispersions and their effect on performance of optical fiber. Derive the equation for intermodal dispersion.

Discuss in detail, different types of Attenuation Losses related to optical fiber communication.

What is graded index fiber? How it is superior to step index fiber?

Calculate the rms pulse broadening per km due to intermodal dispersion for the multimode step index fiber of 6 km optical link with the 86.7 ns rms pulse broadening for an optimum near parabolic profile graded index fiber with the 1.5 core axis refractive index and 1% relative refractive index difference.

List the important parameters of photo detectors. Briefly explain the principal of optical detection. Discuss the major advantages of APD over P-i-n photodiode.

Technically explain the term spontaneous emission and stimulated emission.

Ap-n photodiode has a quantum efficiency of 50% at a wavelength of 0.9 micro meter. Calculate: (1) Its responsivity at 0.9 micrometer. (2) The received optical power if the mean photocurrent is 10-6 A.

Define quantum efficiency. Derive an expression for responsivity and prove that responsivity is directly proportional to the quantum efficiency at a particular wavelength.

Explain population inversion.

Define and explain following with reference to LASER. (1) Mode Hoping (2) Frequency Chirp

Describe the working principal and functioning of Raman amplifier with neat diagram.

Define and explain internal quantum efficiency and differential quantum efficiency of a LASER.

Compare LASER and LED as an optical Source.

Discuss and compare link power budget and rise time budget methods for design of optical link.

List the major types of optical couplers and explain any one.

Determine the power internally generated within the device when the peak emission wavelength is 0.87 micrometer at a drive current of 40 mA. The internal quantum efficiency of the device is 0.625.

What is splicing? Explain various fiber splicing techniques in detail.

Explain the basic principles of WDM and DWDM with respect to optical fiber system.

What is the use/application of OADM, optical circulators, wavelength converter and OTDR in optical communication?

Write a technical note on optical receivers.