UNIT I
1. Explain the intermodal and intramodal dispersion. What are draw back of
dispersion .and how can we minimize dispersion? Compare dispersion
shifted and dispersion flattened fiber.
2. Explain the following terms related to optical laws:(a) Snell’s Law
(b) Critical Angle
(c) Total Internal Reflection
(d) Refractive Index
(e) Numerical Aperture
3. Classify fibers based on modes of propagation & index profiles of various
types of fibers. Enumerate their application.
4. Write short note :(a) Fiber Fabrication
(b) Fiber Materials
5. A typical single mode fiber has a zero-dispersion wavelength of 1.31µm
with a dispersion slope of 0.09 ps nm-2km-1 compare the first order
dispersion for the fiber at the wavelengths of 1.28µm & 1.55 µm. When the
materials & profile dispersion at the latter wavelength are 13.5psmm-1km1
&0.4ps nm-1km-1, respectively, determine the waveguide dispersion at this
wavelength.
UNIT II
1. Explain the structure, materials characteristics & modulation of an LED used
as a optical source.
2. Explain the general principle of operation of LASER diode &
characteristics.
3. List the common LED structures & explain the surface emitter LED
structure with suitable diagram.
4. Write short note :(a) LED Material (b) Hetrostructures
5. A GaAs injection laser has an optical cavity of length 250µm & width 100
µm. At normal operating temperature the gain factor is 21×10-3Acm-3& the
loss coefficient per cm is 10.
Determine the threshold current density & hence the threshold current for
the device. It may be assumed that the cleaved mirrors are uncoated & that
the current is restricted to the optical cavity .The refractive index of GaAs
may be takes as 3.6.
UNIT III
1. Difference between a PN diode, a PIN diode and an APD.
2. Explain the physical principle of PIN photo detector using schematic
circuit diagram. Also show the quantum efficiency & responsively.
3. (a) Explain construction & working of APD with the help of suitable
diagram.
(b) What is silicon reach through APD?
(c) What are the benefits and drawbacks of APD?
4. Write short note on:
(a) Optical operation
(b) Responsivity & Quantum efficiency
5. Photodiode has a quantum efficiency of 65% when photon of energy
1.5×10-19J are
incident (h= 626×10-34Js).
(1) At what wavelength is the photodiode operating.
(2) Calculate the incident 2.5µA when the photodiode is operating as
described above.
UNIT IV
1. Explain the link design for optical communication system .Give brief
description of the losses to be counted in link design. What are two main
budget equations used for link design?
2. Write short note on the following
(a) Fiber splicing
(b) Fiber connectors
3. Describe Wavelength Division Multiplexing (WDM) principle &
specifications.
4. How would you couple a source to fiber and what are the various factors
to be taken to account while coupling ?
5.
A step index fiber has a core refractive index of 1.5 and a core diameter
of 50µm. the fiber is jointed with a lateral misalignment between the
core axes of 5 µm. Estimate the insertion loss at the joint due to the
lateral misalignment assuming a uniform distribution of power between
all guided modes when
(a) There is a small air gap at the joint
(b) The joint is considered index matched
UNIT V
1.) Write a short note on measurement of attenuation.
2.) Write a short note on measurement of refractive index profile.
3.) Write a short note on measurement of numerical aperture .
4.) Explain the time domain inter modal and frequency domain intermodal
dispersion measurement with the help of test set up diagram.
5.) Explain the OTDR (optical time domain reflectrometry).