1.Make a choice（共十题 每题1分）10p

(1).Which of the following dispersion dose not exist in single-mode optical fiber? （ D ）

(2).The unit of the fiber attenuation coefficient is (C)

(3).the bands of Optical fiber communication is (B)

(4).If the optical input power of a Optical amplifier is 10mW，and the optical output power is 100mW as well ,then its output gain level is (A)

(5)In order to make sure of the system BER conditions , if the minimum optical input power of the receiver is 1 uW, the sensitivity of the receiver must be

(6)The principal light sources used for fiber optical communications applications are ：

(7)laser action is the result of three key process，which one of the following is not be included？

(8) A single mode fiber usually has a core diameter of

(9)To make sure that the APD photo-detector works properly, a sufficiently is applied across the p-n junction.

(10) When DFA fiber amplifier uses as light Repeaters, its main effect is

A. amplifying and regenerating the signal

(11) In graded-index optical fiber, the numerical aperture NA can be expressed as

(12) In practical SMFs, the core diameter is just below the cutoff of the first higher-order mode; that is, for V slightly

(13) It is well known that the total dispersion in the single-mode regime is composed of two components:

(14) At present, erbium doped fiber amplifier’s maximum small signal gain is around

A. 40 dB

(15) Which of the following doesn’t belong to passive optical components

(16) The mode has no cut off and ceases to exist only when the core diameter is zero.

A. HE11

(17)When the phase difference is an integral multiple of A, the two modes will beat and the input polarization state will be reproduced.

(18)which one of the following mode can transmit in the single-mode optical fiber ?(A)

A.HE11

(19)Light attenuation in an optical fiber is caused by ( B )

(20)Which of the following will reduce the attenuation of fiber-optic cable assembly?

(21)Increasing a fiber’s length can

(22)What is the least important characteristic of a fiber-optic light source?

(23)Which of the following codes cannot be transmitted in fibers?

(24)Dispersion-shifted fiber (DSF) is a type of single-mode fiber designed to have zero dispersion near ___nm.

(25) In graded-index optical fiber, the numerical aperture NA can be expressed as

2. Write the full name of the following acronym

(1)OTDM: optical time-division multiplexing

(2)DTM: Dynamic Synchronous Transfer Mode

(3)DWDM: Dense wavelength division multiplexing

(4)DFF: Dispersiion-flattened fiber

(5)AWF: All wave fiber

(6)EPON: Ethernet Passive Optical Network

(7)ARQ: automatic reapt request

(8)SDH: Synchronous digital hierarchy

(9)SONET: synchronous optical network

(10)TDMA: time-division multiple access

(11)ISDN: integrated services digital network

(12)FDM: frequency-division multiplexing

(13)SIOF: step index optical fiber

(14)ATM: asynchronous transfer mode

(15)SOA: Semiconductor optical amplifier

(16)APD: Avalanche Photo Diode

(17)WDM: wavelength-division multiplexing

(18)PCM: pulse-code modulation

(19)NRZ: nonreturn-to-zero

(20)DSF: dispersion shift fiber

(21)TLLM: transmission-line laser model

(22)ONSL: optical network simulation layer

(23)OVPO: outside vapor-phase oxidation

(24)VAD: vapor-phase axial deposition

(25)MCVD: modified chemical vapor deposition

(26)EDFA: erbium-doped fiber amplifier

(27)FDDI: fiber distributed data interface

(28)GIOF: graded index optical fiber

(29)SQW: single quantum-well

(30)FEC: forward error correction

(1) The transmission distance of any fiber-optic communication system is inherently limited by ?

(2) The role of the optical transmitter is to convert the ( ) into the corresponding (optical signal) and then launch it into the ( ) serving as a communication channel.

(3) The LED structures being used for fiber optics can be classified as ( ) or ( ).

(4) The two basic LED configurations being used for fiber optics are ( ) and ( ).

(5) The three main components of the optical transmitter are ( ), ( ), ( ).

(6) The role of the optical receiver is to convert the ( ) back into ( ) and recover the data transmitted through the ( ).

(7) The design of the front end of receiver requires a trade-off between ( ) and ( ).

(8) The two fundamental noise mechanisms responsible for current fluctuations in all optical receivers are the ( ) and ( ).

(9) From an architectural standpoint, fiber-optic communication systems can be classified into three broad categories-point-to-point links, ( ), and ( ).

(10) Optical amplifiers are often cascaded to overcome ( ) in a long-haul lightwave system.

(11) A fiber Bragg grating acts as an optical filter because of the existence of a ( ), the frequency region in which most of the incident light is reflected back.

(12) The electromagnetic energy of a guided mode is carried partly in the ( ) and partly in the ( ).

(13)The basic attenuation mechanisms in a fiber are ( ), ( ) and ( ) of the optical waveguide.

(14) The two main optical amplifier types can be classified as ( ) and ( ).

(15) The two most common samples of these spontaneous fluctuations are ( ) and ( ).

(16)According to the refractive index of the core, the fiber can be divided into ( ) fiber and ( ) fiber .

(17)The total dispersion in single-mode fibers consists mainly of

(18) The most meaningful criterion for measuring the performance of a digital communication system is the

(19) The simplest transmission link is a.

(20)Absorption is related to the fiber material, whereas scattering is associated both with the (fiber material) and with (structural imperfections) in the optical waveguide.

4. Give a brief description of following terms and questions（共5题 每题3分）15p

(1) Please write three main factors that influence the sensitivity of the optical receiver.

1) Noise: shot noise and thermal noise

2) Extinction Ratio

3) Fiber dispersion

(2) Briefly describe there major goals of SDH.

1) Avoid the problems of PDH

2) Achieve higher bit rates

3) Better means for operation, administration and Maintenance

(3) List at least three advantages of optical fiber in fiber communication.

1) Wide bandwidth

2) Anti-interference

3) Low loss

4) Large capacity

(4) List at least three advantages of SOA.

1) Small size, and easy to be integrated with semiconductor circuits.

2) Fabrication is simple and with low power consumption, long life-span and low cost.

3) Gain response is very quick and well suited for switching and signal processing in optical networks application.

4) Can amplify optical signal and process signal in the same time such as switch, so can be used in wavelength converting and optical switch.

(5) List more than three disadvantages of SOA.

1) The coupling loss with optical fiber is too large

2) Sensitive to polarization

3) Noise figure is high(~8 dB)

4) crosstalk

5) Easy to be affected by temperature, low stability

(6)BER

Bit-Error rate, defined as the probability of incorrect identification of a bit by the decision circuit of the receiver.

(7) What conditions should be met to achieve a high signal-to-noise ratio?

1) The photodetector must have a high quantum efficiency to generate a large signal power.

2) The photodetector and amplifier noises should be kept as low as possible.

(8) Please write the three basic categories of degradation of light sources

1) internal damage

2) ohmic contact degradation

3) damage to the facets of laser diodes

(9)List the three factors largely determining the frequency response of an LED

1) the doping level in the active region

2) the injected carrier lifetime Ti in the recombination region

3) the parasitic capacitance of the LED.

(10) Please write the three different mechanisms causing absorption briefly

1) Absorption by atomic defects in the glass composition.

2) Extrinsic absorption by impurity atoms in the glass material.

3) Intrinsic absorption by the basic constituent atoms of the fiber material.

(11) The disadvantage of Raman amplifier

Need large output power pump laser. As Raman Scattering, the energy is transferred from high frequency to low frequency. Cross talk will affect signal.

(12) Dynamic Range

System dynamic range is the maximum optical power range to which any detector must be able to respond.

(13) List at least three advantages of fiber amplifiers in fiber communication

1) low insertion loss

2) large bandwidth

3) low noise

4) low crosstalk

5) high gain

(14) List at least three factors of attenuation in fiber communication

1)material absorption

2)Rayleigh scattering

3)mie scattering

4)connection losses

5. Figure（共1题 每题5分）5p

（1）Please draw the basic step for an automatic-repeat-request (ARQ) error-correction scheme.

Solution:

(2)Please draw out the basic elements of the optical receiver.(5p)

Solution:

(3)Please draw out the basic elements of an analog link and the major noise contributions.

Solution:

(3) consider the encoder shown in Fig.1that changes NRZ data into a PSK waveform.using this encoder,draw the NRZ and PSK waveforms for the data sequence 0001011101001101.

Fig.1

Solution:

6. Calculation Problems(共3-4题，统计40分) 40p

(1) A wave is specified by,where y is expressed in micrometers and the propagation constant is given in.Find (a) the amplitude,(b) the wavelength,(c) the angular frequency, and (d) the displacement at time and.

Solution:

The general form is:

y = (amplitude).Therefore

(a) amplitude

(b) wavelength: so that

(c)

(d) At and we have

(2) A certain optical fiber has an attenuation of 0.6dB/km at 1300nm and 0.3dB/km at 1550nm.Suppose the following two optical signals are launched simultaneously into the fiber: an optical power of 150 at 1300nm and an optical power of 100 at 1550nm. What are the

Solution:

power levels in of these two signals at (a) 8km and (b) 20km?

Since the attenuations are given in dB/km, first find the power levels in dBm for

100 and 150. These are, respectively,

P(100) = 10 log (100 /1.0 mW) = 10 log (0.10) = - 10.0 dBm

P(150) = 10 log (150 /1.0 mW) = 10 log (0.15) = - 8.24 dBm

(a) At 8 km we have the following power levels:

P1300(8 km) = - 8.2 dBm – (0.6 dB/km)(8 km) = - 13.0 dBm = 50

P1550(8 km) = - 10.0 dBm – (0.3 dB/km)(8 km) = - 12.4 dBm = 57.5

(b) At 20 km we have the following power levels:

P1300(20 km) = - 8.2 dBm – (0.6 dB/km)(20 km) = - 20.2 dBm = 9.55

P1550(20 km) = - 10.0 dBm – (0.3 dB/km)(20 km) = - 16.0 dBm = 25.1

(3) A double-heterojunction InGaAsP LED emitting at a peak wavelength of 1310nm has radiative and nonradiative recombination times of 25 and 90ns, respectively. The drive current is 35mA.

(a) Find the internal quantum efficiency and the internal power level.

(b) If the refractive index of the light source material is n=3.5, find the power emitted from the device.

Solution:

(a) From Eq., the internal quantum efficiency is

，

and from Eq. the internal power level is

(b) From Eq.,

(4) An LED with a circular emitting area of radius 20 has a lambertian emission pattern with a 100axial radiance at a 100mA drive current. How much optical power can be coupled into a step-index fiber having a 100 core diameter and NA=0.22? How much optical power can be coupled from this source into a 50 core-diameter graded-index fiber having and?

Solution:

The source radius is less than the fiber radius,

so Eq. holds:

From Eq.

(5)Suppose an avalanche photodiode has the following parameters:, and.Consider a sinusoidally varying 850nm signal, which has a modulation index m=0.85 and an average power level, to fall on the detector at room temperature. At what value of M does the maximum signal-to-noise ratio occur?

Solution:

Using Eq. we have

The value of M for maximum S/N is found from Eq., with x = 0.5:

Moptimum = 62.1.

(6)An LED operating at 1300 nm injects 25 of optical power into a fiber. If the attenuation between the LED and the photodetector is 40 dB and the photodetector quantum efficiency is 0.65, what is the probability that fewer than 5 electronhole pairs will be generated at the detector in a 1-ns interval ?

Solution:

From,the average number of electron-hole pairs generated in a time t is

Then,from Eq.(7-2)

(7) An engineer has the following components available:

(a) GaAlAs laser diode operating at 850 nm and capable of coupling 1 mW (0 dBm) into a fiber.

(b) Ten sections of cable each of which is 500 m long, as a 4-dB/km attenuation, and has connectors on both ends.

(c) Connector loss of 2dB/connector.

(d) A pin photodiode receiver.

(e) An avalanche photodiode receiver.

Using these components, the engineer wishes to construct a 5-km link operating at 20 Mb/s. If the sensitivities of the pin and APD receivers are -45 and -56 dBm, respectively, which receiver should be used if a 6-dB system operating margin is required?

Solution:

(a)Use，to analyze the link power budget.(a) For the pin photodiode,with 11 joints

Which gives L=4.25km. the teansmission distance cannot be met with these components.

(b)For the APD

Which gives L=7.0km. the transmission distance can be met with these components.

(8) Suppose we want to frequency-division multiplex 60 FM signals. If 30 of these signals have a per-channel modulation index =3 percent and the other 30 signals have =4 percent, find the optical modulation index of the laser.

Solution:

The total optical modulation index is

(9) An optical transmission system is constrained to have 500-GHz channel spacings. How many wavelength channels can be utilized in the 1536-to-1556-nm spectral band?

Solution:

In terms of wavelength,at acentral wavelength of 1546nm a 500-GHz channel spacing is

The number of wavelength channels fitting into the 1536-to-1556 spectral band then is

(10) The output saturation power is defined as the amplifier output power for which the amplifier gain G is reduced by 3 dB (a factor of 2) from its unsaturated value. Assuming >>1, show that in terms of the amplifier saturation power, the output saturation power is

Solution:

Let and.then Eq.(11-15) yields

Solving for and with,we have

武汉理工 2012-1013光纤通信复习题增加- 副本