Optical Fibre Communication (EC-801) - Important Questions

Calculate numerical aperture, critical angle at core-cladding interface, and acceptance / maximum entrance angle for a given step-index fiber with core index $n_1$ and cladding index $n_2$.

Derive the expression for numerical aperture (and acceptance angle) of a step-index optical fiber in terms of core and cladding refractive indices.

Explain ray theory transmission in step-index optical fiber.

Explain the different types of optical fibers, their structure and waveguiding fundamentals with diagrams.

Explain the modes in a planar optical waveguide.

Derive an expression for the numerical aperture (and acceptance angle) of a step-index optical fiber.

Calculate normalized frequency (V-number) and number of guided modes for a step-index fiber given core radius, refractive indices and wavelength.

Derive an expression for the modes propagating in a step-index fiber.

Elaborate differences between step-index and graded-index optical fiber.

Calculate the acceptance angle from given numerical aperture, core/cladding indices and outer medium refractive index.

Introduce normalized frequency and derive its expression.

What is OTDR? Explain its working principle and its applications in measurement of fiber losses and faults.

Discuss absorption losses in optical fibers including intrinsic and extrinsic mechanisms and how absorption can be reduced.

Numerically estimate the critical radius of curvature for large bending losses in a multimode step-index fiber.

Explain the Modified Chemical Vapour Deposition (MCVD) technique of optical fiber fabrication.

Draw the optical fiber attenuation vs wavelength characteristic and explain the different wavelength windows.

Explain the Vapour-phase Axial Deposition (VAD) method of optical fiber fabrication.

Explain bending losses and core-cladding losses and how they can be reduced.

Discuss in detail the intermodal dispersion with relevant expressions and diagrams.

Discuss attenuation in optical fiber communication due to scattering and absorption.

Explain scattering and bending losses in optical fiber with suitable diagram.

Explain how signal is degraded in optical fiber due to dispersion.

Write short notes on any two topics including LED, splicing techniques, Raman amplifier and passive optical networks.

What is quantum efficiency? Derive its expression in terms of recombination lifetime.

Calculate the number of longitudinal modes and their frequency separation for a ruby laser given crystal length, refractive index and peak emission wavelength.

Explain the principle and working of a PIN diode with suitable diagram.

What is an Avalanche Photodiode (APD), its impact ionization gain mechanism, and comparison of PIN vs APD performance, advantages and disadvantages?

Describe the principle, construction and working of a laser diode and explain various laser structures used in optical sources.

Explain the basic principle of photodetection and the construction and working of a PIN photodiode.

Explain the basic principle and working of lasers.

Derive an expression for the internal optical power generated in LEDs.

Explain the Avalanche photodiode.

What is the resonant frequency of a laser? Derive the expression for wavelength spacing between two longitudinal modes.

How is modulation of a laser diode done? Explain with a suitable diagram.

Explain link power budget analysis for optical link design, deriving the power budget equation including source power, fiber attenuation, connector and splice losses, receiver sensitivity, and system margin

Calculate the maximum bit rate that may be achieved on the fiber link length of 50 km without repeaters and using NRZ format. Transmitter rise time is 4 ns. Intermodal rise time is 5 ns. Intramodal rise time 1 ns. Receiver rise time is 2 ns.

Explain the different types of optical fiber connectors used, their characteristics and insertion loss.

Explain the steps involved in splicing optical fibers and classify and explain the various splicing techniques employed between two fibers.

Explain the following in respect of digital link:

Explain how the eye pattern is useful in analyzing the performance of optical transmission.

Derive a relation for digital receiver performance.

Explain the architecture and working of SONET and SDH.

Explain the working principle of EDFA.

Explain the operational principle of a Raman Amplifier. Contrast its working mechanism, bandwidth capabilities, and noise characteristics with those of an EDFA.

Explain the concept and operating principle of WDM with a neat diagram and its applications.

Write short notes on any two of the following:

Derive the expression for EDFA conversion efficiency and amplifier gain.

Explain the layers of SONET with neat sketches.

Explain optical coupler parameters: splitting ratio, excess loss, insertion loss, and crosstalk

Write short notes on EDFA, Optical Fiber Connector, Raman Amplifier, Single Mode Fibers, SONET, and Fiber Joints

Discuss MEMS technology and explain how it is beneficial for WDM.