BCS-Assignmnet questions

1. Describe with aid of a neat diagram the basic principle of Total Internal
Reflection for a fiber to work as light conduit
Pg no:-16(BCS) pg no :-13(BCS PPT)
2. Compare Step index and Graded index fiber
Pg no:-28(BCS) pg no :-22(BCS PPT)
3. A light wave is travelling in a semiconductor medium (GaAs) of refractive
index 3.6.it is incident on a different semiconductor medium (AL GaAs ) of
refractive index 3.4 and the angle of incidence is 80 o will this
result in Total internal reflection

pg no:-15(BCS PPT)
4. Determine the cut off wavelength of a step index fiber to exhibit single mode
operation when the core refractive index is 1.48 and radius is 4.5 micrometer
respectively, refractive index difference being 0.25%

pg no:-28(BCS PPT)
5. Describe causes of attenuation in optical fiber and their mechanisms

Pg no:-37(BCS) pg no :-37(BCS PPT)

6. Describe effects of macrobending and microbending

pg no:-46(BCS PPT)
7. The radiative and non-radiative recombination lifetimes of the minority
carriers in the active region of a double heterojunction LED are 50ns and 110ns
respectively. Determine the total carrier recombination lifetime and the power
internally generated within the device when the peak emission wavelength
is0.87micrometer at a drive current of 40 mA

pg no:-62(BCS PPT)
8. How does APD internally multiplies the current

pg no:-85(BCS PPT)
9. A given APD has a quantum efficiency of 65% at wavelength of 900 nm
. if 0.5 micro watt of optical power produces a multiplied
photocurrent of 10micro A find the multiplication factor M

pg no:-86(BCS PPT)
10. Following are the parameters of a point to point optical link Optical
power launched 3dBm, sensitivity of detector: -32, source connector loss
:1dB each, length of optical cable :60km, cable Attenuation
:3.3dB/km,jumper cable loss:3dB assume two jumper cables at two ends
of transmission fiber
Compute the power margin of the link using spread sheet method
 pg no:-93(BCS PPT)

11. The 10-90% rise times for possible components to be used in D-IM analog
fiber link are specified as
LED source :10 ns
Fiber cable: Intermodal:9ns/km Intramodal
:2ns/km
APD detector:3ns
The desired link length without repeaters is 5km and the required BW 6 Mhz.
Determine the above combination of components give an adequate
response
pg no:-96(BCS PPT)
12. Briefly explain WDM standards

pg no:-105(BCS PPT)
13. Describe EDFA architecture
pg no:-115(BCS PPT)

14. Describe working principle of EDFA

pg no:-114(BCS PPT)
15.

Calculate the output power at port 3? incoming

power =1mw

Splitting ratio of each coupler=9:1

Excess loss of each coupler=0.3 dB the coupler is joined by connectors with an

insertion loss of 0.2 dB each

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16.
List the orbital Elements and their significance in orbital maintenance
pg no:-133(BCS PPT)
17.
Considering the space shuttle circular orbit height,h=250kmand earth radius
=6378km,obtain:

a)orbit period b) Average linear velocity

pg no:-135(BCS PPT)
18.
Describe Orbital Perturbations
pg no:-140(BCS PPT)
19.
Discuss how the Altitude control subsystem takes care of the orientation of
satellite in its respective orbit
pg no:-148(BCS PPT)
20.
Describe Telemetry and Command subsystem
pg no:-149(BCS PPT)
21.
How precise ranging is done through Spread spectrum Technique for Tracking
subsystem
22.
Find number of cells required to generate end of life power of 6000 W
,Assume solar flux density 1200 W/m2 ,solar cell efficiency at EOL of 13%,29%
loss due to shield and cell area of 8cm 2
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23.
The earth subtends an angle of 150 when viewed from geostationary orbit. what
are the dimensions and gain of a horn antenna that will provide global
coverage at 4GHz

pg no:-160(BCS PPT)
24.
A C-band earth station has an antenna with a transmit gain of 54 dB. The
transmitter output power is set to 100 W at a frequency of 6.100 GHz. The
signal is received by a satellite at a distance of 37,500 km by an antenna with
a gain of 26 dB. The signal is then routed to a transponder with a noise
temperature of 500 K, a bandwidth of 36 MHz, and a gain of 110 dB.

a. Calculate the path loss at 6.1 GHz. Wavelength is 0.04918 m.

b. Calculate the power at the output port (sometimes called the output
waveguide flange) of the satellite antenna, in dBW

. c. Calculate the noise power at the transponder input, in dBW, in a bandwidth of

36 MHz.

pg no:-200(BCS PPT)
25.
This sequence of questions requires you to design a communication link
through a geostationary satellite to meet a C/N and link margin

specification. Use these constants: Boltzmann's constant k = -

228.6 dBW/K/Hz

Path length to satellite = 38,500 km Satellite:

Geostationary at 73o W longitude.

24 C band transponders, 28

Ku band transponders

3.2 kW RF power output

Antenna gain, on axis, C-band and Ku-band (transmit and receive) = 31 dB

Receive system noise temperature (C-band and Ku-band) = 500 K

Transponder saturated output power: C-band = 40 W

Transponder bandwidth: C-band = 36 MHz

Transponder saturated output power: Ku-band = 80 W

Transponder bandwidth: Ku-band = 54 MHz

Signals: FM-TV analog signal to be received in a bandwidth of 27 MHz

Multiplexed digital TV signals transmitted as QPSK with symbol rate

27 Msps using half rate FEC with coding gain 5.5 dB Minimum
permitted C/N overall = 9.5 dB

Question #Design a transmitting earth station to provide a clear air C/N of 26

dB in a C-band transponder at a frequency of 6.285 GHz. Use an uplink
antenna with a diameter of 9 m and an aperture efficiency of 68%, and find the
uplink transmitter power required to achieve the required C/N. The uplink
station is located on the 2 dB contour of the satellite footprint. Allow 0.5 dB for
clear air atmospheric attenuation and other losses

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 26. Suppose we have a 4GHzz receiver with the following gains and e
nois temperatures

Tin=50K GRF =23dB Gm =23 dB GIF =23dB

TRF= 50K

Tm=500k TIF=1000K

Calculate the system noise temperature

pg no:-168(BCS PPT)
1.For a 2x2 Fiber coupler ,input power is 200 microW ,through put power is 90 microW,coupled
power is 85 microW and cross talk power is 6.3 nanoW compute1)coupling ration 2)Excess
ratio
3)Insertion los
4)cross talk

pg no:-107(BCS PPT)

2.For a 2x2 Fiber coupler ,input power is 300 microW ,through put power is 150
microW,coupled power is 65 microW and cross talk power is 8.3 nanoW compute1)coupling
ration 2)Excess ratio
3)Insertion los
4)cross talk
pg no:-107(BCS PPT)

3.Calculate the output power at port 3?

4.
 sr.no Unit-2 numericals
1. The radiative and non-radiative recombination life times of minority carriers in the
active region of a double hetrojunction LED are 60 nsec and 90 nsec
respectively.Determine the total carrier recombination life time and optical power
generated internally if the peak emission wavelength is 870 nm and the drive current
is 40 mA

pg no:-62(BCS PPT)
2. Estimate the external power efficiency of a GaAs plannar LED when the
transmission factor of the GaAs-air interface is 0.68 and the internally generated
optical ower is 30% of the electrical power supplied .the refractive index of GaAs
may be taen as 3.6

pg no:-63(BCS PPT)
3. An optical transmitter uses a DH structure InGaAsP LED operating at a wavelength
of 1550 nm and τrr =25 nsec,τnr =90nsec if the LED is driven with a current of 35
mA.
1)find innternal quntum efficiency and the power generated internally
ifη=3.5 of the light source material,find the power emitted from the device

pg no:-64(BCS PPT)
4. A double hetrojunction In GaAsP LED operating at 1310nm has radiative and non
radiative recombination times of 30 and 100 ns respectively .the current injected is
40 mA calculate-1) bulk recombination life time2) internal quantum efficiency 3)
internal power level

pg no:-62(BCS PPT)
5. When 3x1011 photons each of wavelength of 0.85 μm are incident on a photodiode
,on average 1.2x1011 electrons are collected at the terminals of the device.Determine
the quantum effiency and responsitivity of the photodiode at 0.85μm

pg no:-78(BCS PPT)
6. A laboratory setup uses an inGaAsp hetrojunction photo transistor which has a
common emitter gain of 170 ,when operating at a λ=1300nm with an incident optical
power of 80μw.the base -collector quantum efficiency at this wavelength is 65%
estimate the collector current in the device.

pg no:-80(BCS PPT)
7. A p-i-n photodiode on average generates one electron-hole pair per three
incident photons at a wavelength of 0.8μm .assuming all electrons are collected
calculate: i) the quantum efficiency of the device 2)its maximum possible
bandgap energy
3) the mean output photocurrent when the received optical power is 10 -7 W

pg no:-80(BCS PPT)
8. A p-n photodiode has a quantum efficiency of 50% at a wavelengths of 0.9μm
calculate 1) its responsitivity at given wavelength2) the received optical power if the
mean photocurrent is 10 -6 A 3)the corresponding number of photons at this
wavelength

pg no:-81(BCS PPT)

1. 1 A typical relative index difference for an optical fiber designed for long distance
transmission is 1%.Estimate the NA and the solid acceptance angle in air for the
fiber when the core index is 1.48 further calculate the critical angle at the core
cladding interface within in the fiber
for small angles :the solid acceptance angle in air is given as ξ=π(NA) 2

pg no:-20(BCS PPT)
2. Light traveling through an optical fiber (n=1.44) reaches the end of the fiber and
exits into air.

(a) If the angle of incidence on the end of the fiber is 30 0, what is the angle of
refraction outside the fiber?
(b) How would your answer be different if the angle of incidence were 50 0?
(c) Is snells law statisfied?
(d) What are the conditions for Total Internal Reflection?

3. Estimate the critical bend radius of curvature at which large bending losses would
occur for a 62.5/125 μm
MMSI fiber with core refractive index of 1.5 relative refractive index difference
∆=3 % and operating wavelength of 820nm

pg no:-48(BCS PPT)
4. Describe the term critical bend radius with ference to optical fibers
5. −1
A 5 km optical fiber link uses fiber with a loss of 1.5 dB km . The fiber is jointed
every kilometer with connectors which give an attenuation of 0.8 dB each.
Determine the minimum mean optical power which must be launched into the
fibegr in order to maintain a mean optical power level of 0.3 μW at the detector.

6. For a single mode fiber with n1=1.49 and n2=1.47 find the following
1) cutoff wavelength of fiber if core rdius is 2micrometer
2)Maximum core diameter for single mode operation for λc=1310 nm
7. What is Dispersion ?explain intermodal dispersion and intramodal dispersion
8. Why Attenuation and Dispersion are to considered for fiber optics communication
9. A multimode step index fiber has a relative refractive index difference of 1% and a
core refractive index of 1.5 the number of modes propogating at a wavelength of
1.3μm is 1100 .Estimate the diameter of the fiber
10. Explain Total internal reflection inside optical fiber
 BBROADBAND COMMUNICATION SYSTEM

Assignment 2
1) A particular LED has a 5 ns injected carrier lifetime. When no modulation current is
applied to the device , the optical output power is 0.250mW for a specified dc bias.
Assuming parasitic capacitances are negligible , what are the optical outputs at
modulation frequencies of
(a)10 MHz (b)100 MHz

2) Consider an LED having minority carrier lifetime of 5ns. Find the 3dB optical Bandwidth
and 3 dB electrical Bandwidth.
3) A particular Ga1-xAlxAs Laser is constructed with a material ratio x=0.07. Find (a)the
bandgap of this material (b) the peak emission wavelength.(The band gap varies with x
as Eg=1.424+1.266 x+0.266 x2eV )
4) A particular Ga1-xAlxAs Laser is constructed for emitting a peak emission wavelength of 805
nm. Find (a)the bandgap of this material (b) Aluminium mole fraction x (.(The band gap
varies with x as Eg=1.424+1.266 x+0.266 x2eV )

5) A double heterojunction InGaAsP LED emitting at a peak wavelength of 1310 nm has

radiative and non radiative recombination times of 30 and 100 ns , respectively. The
drive current is 40mA. Find (a)the bulk recombination lifetime ;(b)the internal quantum
efficiency (c)the internal power level (d) the external power level if the material has
refractive index of 3.4
6) A photodiode has a quantum efficiency of 65% when photons of energy 1.5x10 -19 J are
incident upon it .
(a)At what wavelength is the photodiode operating?
(b)Calculate the incident optical power required to obtain a photocurrent of
2.5 µA when the photodiode is operating is operating as described
above .
7) Explain what is meant by long wavelength cutoff in a photodetector ? A material has
Bandgap energy 0f 1.51 eV . Determine the long wavelength cutoff of the photodetector
made up of the above mentioned material.
8) A p-i-n photodiode ceases to operate when photons with energy greater than 0.886 eV
are incident upon it. Calculate the band gap of such material .
9) A p-i-n photodiode on average generates one electron hole pair per three incident
photons at wavelength of 0.8µm. Assuming all the electrons are collected calculate :
(a)The quantum efficiency of the device
(b)Its maximum possible bandgap energy
(c)The mean output photocurrent when the received optical power is 10-7W
10) The quantum efficiency of a particular silicon RAPD is 80% for the detection of radiation
at a wavelength of 0.9 µm. When the incident optical power is 0.5µW, the output
current from the device (after avalanche gain ) is 11µA. Determine the multiplication
factor of the photodiode under these conditions .