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Fiber-Optic Communication Systems

Govind P. Agrawal

Chapter 1

Introduction - all with Video Answers

Educators

Chapter Questions

01:18

Problem 1

Calculate the carrier frequency for optical communication systems operating at $0.88,1.3$, and $1.55 \mu \mathrm{m}$. What is the photon energy (in eV ) in each case?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
01:02

Problem 2

Calculate the transmission distance over which the optical power will attenuate by a factor of 10 for three fibers with losses of $0.2,20$, and $2000 \mathrm{~dB} / \mathrm{km}$. Assuming that the optical power decreases as $\exp (-\alpha L)$, calculate $\alpha$ (in $\mathrm{cm}^{-1}$ ) for the three fibers.

Ajay Singhal
Ajay Singhal
Numerade Educator
01:11

Problem 3

Assume that a digital communication system can be operated at a bit rate of up to $1 \%$ of the carrier frequency. How many audio channels at $64 \mathrm{~kb} / \mathrm{s}$ can be transmitted over a microwave carrier at 5 GHz and an optical carrier at $1.55 \mu \mathrm{m}$ ?

Anand Jangid
Anand Jangid
Numerade Educator
03:11

Problem 4

A 1-hour lecture script is stored on the computer hard disk in the ASCII format. Estimate the total number of bits assuming a delivery rate of 200 words per minute and on average 5 letters per word. How long will it take to transmit the script at a bit rate of $1 \mathrm{~Gb} / \mathrm{s}$ ?

Averell Hause
Averell Hause
Carnegie Mellon University

Problem 5

A $1.55-\mu \mathrm{m}$ digital communication system operating at $1 \mathrm{~Gb} / \mathrm{s}$ receives an average power of -40 dBm at the detector. Assuming that 1 and 0 bits are equally likely to occur, calculate the number of photons received within each 1 bit.

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Problem 6

An analog voice signal that can vary over the range $0-50 \mathrm{~mA}$ is digitized by sampling it at 8 kHz . The first four sample values are $10,21,36$, and 16 mA . Write the corresponding digital signal (a string of 1 and 0 bits) by using a 4 -bit representation for each sample.

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Problem 7

Sketch the variation of optical power with time for a digital NRZ bit stream 010111101110 by assuming a bit rate of $2.5 \mathrm{~Gb} / \mathrm{s}$. What is the duration of the shortest and widest optical pulse?

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Problem 8

A $1.55-\mu \mathrm{m}$ fiber-optic communication system is transmitting digital signals over 100 km at $2 \mathrm{~Gb} / \mathrm{s}$. The transmitter launches 2 mW of average power into the fiber cable, having a net loss of $0.3 \mathrm{~dB} / \mathrm{km}$. How many photons are incident on the receiver during a single 1 bit? Assume that 0 bits carry no power, while 1 bits are in the form of a rectangular pulse occupying the entire bit slot (NRZ format).

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Problem 9

A $0.8-\mu \mathrm{m}$ optical receiver needs at least 1000 photons to detect the 1 bits accurately. What is the maximum possible length of the fiber link for a $100-\mathrm{Mb} / \mathrm{s}$ optical communication system designed to transmit -10 dBm of average power? The fiber loss is $2 \mathrm{~dB} / \mathrm{km}$ at $0.8 \mu \mathrm{m}$. Assume the NRZ format and a rectangular pulse shape.

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Problem 10

A $1.3-\mu \mathrm{m}$ optical transmitter is used to obtain a digital bit stream at a bit rate of $2 \mathrm{~Gb} / \mathrm{s}$. Calculate the number of photons contained in a single 1 bit when the average power emitted by the transmitter is 4 mW . Assume that the 0 bits carry no energy.

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