光纤通信系统 顾畹仪 李国瑞课后习题
光纤通信第二版答案光纤通信顾畹仪答案
光纤通信第二版答案光纤通信顾畹仪答案1．纤光信通的缺点优各是么？什答：点有优带宽：资源丰，通信富量大；容损低耗中，距继长离无串音干；，扰密性保好适应能；力强；积小体、量轻、重便于工维护；原施料材源丰富来，潜价在低格廉。
等缺点有接：口昂贵，度差，强不能传送力，需电要专门的具工、备以及设训，未经受长培时的间验检等2。
光．纤信系通由统几哪部分成组各部分？功的能什么？是答：纤通信光系统由部三组分成：光射发机、接光机和收纤光路。
链发射机由光模或拟数字接电口电压—电、流动驱路和光电组件组源。
光成源件包括光组、光源源—光耦纤合和器一光纤（尾纤或段纤跳线光组）。
成模拟数或电字接作用是实现口的抗阻配匹和信号电平匹配（限输入制信号振的）作用幅光。
源是L DE LD 或这两，种二管极光功率与的动电驱流成比。
电压正—流驱电电动是输路电路入光源间的与电接口，用来将输入信号的压电换转成流电以驱动光源光。
—源纤光合器耦作的是用光源把发的光出合到光耦纤或光缆中。
光接收机光由检测器组、件放电路和模大拟数或字接电口成。
光检组测组器包件括段一光纤（纤或光尾纤跳）线、纤—光检光波器耦器合光、检器和测电流—压电换转器光。
检器测光将号转信为化流电信号常用的器件有。
PIN 和PD。
然A后再过电流—电通压转器换变，电成信压号出。
输拟或数模电接字对输出电路其口阻抗配匹信号和电匹平配用。
光作链路纤光由光纤、光缆连纤器、光缆终端接盒、光缆路盒线和继中1器组成等。
光光缆由纤英或塑石料光纤、属金包层和套外组管。
成光线缆盒：路缆生产厂家光产的光缆一般生2为mk一，盘而因如，光发送与光接果之收间的离超距2多k m，时隔每2mk 将要需用缆线光路把盒缆连光起接。
来缆终端盒：光主要于用将光从户缆（外或内）引户入户到内或（户）外，光将缆的中纤光光缆中从分来，出一放置在般光设备机房内光。
连纤器接：主用于要将光发机送或（接光收）机与光缆终端盒出来的分光纤连起接，即来接连光纤线跳光与缆中光纤的3．。
顾婉怡光纤通信答案
顾婉怡光纤通信答案Fiber optic communication, people's post office answer fiber communication after classChapter one basic theory1, what is the principle of single mode transfer of the first step refractive index fiber?A: angelica sinensis, a frequency V is smaller than that of the second order mode LP11 normalized cut-off frequency, 0 < V < 2.40483, namely There is only one transfer mode in the pipeline, that is single mode transmission.How does the loss of the pipeline and dispersion affect the optical fiber communication system?A: in optical fiber communication systems, optical fiber loss is one of the important factors that restrict WuZhongJi communication distance, to a large extent determines the transmission system of relay distance; The dispersion of the optical fiber causes the distortion of the transmission signal, reducing the communication quality, thereby limiting the communication capacity and the communication distance.What kind of dispersion is in the fiber optic? Explain what it means.Answer: (1) the mode dispersion: there are many in the multimode fiber transmission mode, different mode along the fiber axial transmission speed is different, the time arrived at thereceiving end, and the mode dispersion.(2) the material dispersion: due to the refractive index of optical materials is the nonlinear function of wavelength, so that the transmission speed changes over the wavelength of light, the resulting dispersion is called the material dispersion.(3) the waveguide dispersion: the phase constant of the uniform mode is changed with the wavelength, the group velocity varies with the wavelength, and the resulting dispersion is called the waveguide dispersion.How does the fiber optic nonlinear effect affect the optical fiber communication system?Answer: the nonlinear effect of optical fiber in optical fiber communication system has both positive and negative influence, on the one hand, can cause additional loss of transmission signal of the crosstalk between channels in WDM system and mobile signal carrier and so on, on the other hand, can be used to develop new devices such as amplifier, modulator.What kinds of single mode fiber?Answer: the single mode fiber can be divided into four categories: the dispersion-shifted single-mode fiber, dispersion-shifted single-mode optical fiber, cutoff wavelength displacement single-mode optical fiber, nonzero dispersion displacement single-mode fiber.What are the parts of the cable?Answer: strengthen piece, cable core, exterior guard layer.*, the advantages of fiber optics: great bandwidth (200THz), small loss of transmission, light weight, electromagnetic interference, and metal saving.*, optical fiber loss: the attenuation of optical fiber by optical fiber. Causes of fiber loss: the loss, manufacturing loss, and the added loss. *, optical fiber dispersion: due to the optical fiber transmission signal is carried by the different frequency components and different model components, different frequency components and different model components of transmission speed is different, lead to signal distortion. The cause of optical fiber dispersion: the light signal is not a single color, the optical fiber is the dispersion effect of the light signal. Dispersion type: pattern dispersion (different modes of wavelength), material dispersion (refractive index), waveguide dispersion (same pattern, phase constant).Single mode fiber: the optical fiber that transmits a single base mode at a given working wavelength.Chapter ii light source and light transmitterWhat are the three basic processes of light and matter? What are their respective characteristics?Answer: (1) spontaneous radiation: the spontaneous behavior ofhigh level electrons has nothing to do with whether there are external incentives; Spontaneous radiation can occur in a range of levels, and the spectrum of emission from this material is wide; Even if the transition process to meet the same energy level difference, and they are independent, the random radiation, the photon energy is the same and have nothing to do with each other, each column of light waves can have different phase and polarization direction, and spread to all aspects of space, is a kind of incoherent light.(2) stimulated radiation: the energy of the induced photon is the difference between the energy levels of the downward transition; The photons that are generated by the stimulated radiation are all the same photons, and they are coherent; The stimulated radiation process is essentially a magnifying process of external incident light.(3) stimulated absorption: external light energy needs to be consumed when stimulated absorption; The stimulated absorption process corresponds to the absorption of the photon, which generates the photoelectric conversion process of the electron.What is a population inversion?A: the number of particles in a high energy state is greater than the number of particles in the lower energy state.How to achieve light amplification?Answer: make the electron density on the medium and high energylevel is greater than the low level of electron density, the stimulated radiation dominate, light passes through a medium strength according to the index law growth, waves are amplified, then realize the optical amplification.What are the functional components that constitute a laser?Answer: the source area, the light feedback device, the frequency selection element, the direction of the beam, the light waveguide.What are the methods for optical cavity? What are the corresponding laser types?Answer: (1) the crystal natural cleavage plane form method in - perot cavity (F - P cavity), when the light in the cavity to satisfy a certain phase and resonance conditions, to establish a stable light oscillation;(2) using periodic corrugated structures on one side of the source region to provide optical coupling to form optical oscillations.*, the general conditions of ejection: (1) there are sufficient number of population inversion distributions in active regions;(2) there is an optical resonance mechanism, and a stable laser oscillation is established in the active areaChapter iii optical receiverAnalyze the working principle of photodiode and APD.Answer: photodiode: stimulated absorption, electron - hole pair movement; APD: electrons - holes cause avalanches in multiple collisions.Analyze the similarities and differences between photodiode and APD performance parameters.A: APD is a gain of the photodiode, requiring higher in optical receiver sensitivity, with APD is beneficial to extend the transmission distance of the system, and the sensitivity requirement is not high, generally with no gain PIN photoelectric detector.Chapter iv fiber optic communication systemWhat is SDH? Describe the main featuresAnswer: (1) the SDH technology is in the information structure level, overhead, synchronous multiplexing mapping structure, pointer position adjustment and network node interface standard, mainly USES the optical fiber transmission medium (a small amount of microwave and cable) digital transmission technology.(2) features (advantages) : a unified standard light interface; The cost of bits is rich; To use digital synchronous reuse; The digital subdivision multiplexing is directly up and down2Mbit/s; Digital cross-linking increases network flexibility;The "self-healing" capability of the loop network.What are the composition of the frame structure of the SDH? What is the role of the various parts?Answer: the frame structure of SDH is composed of three parts:(1) the stm-n net load: the blocks of user information sent by stm-n.(2) section overhead SOH: ensures that the information is required to be added to the running, management, and maintenance (OAM) bytes.(3) management unit pointer: the first byte to indicate the net load of the information in the stm-n frame.What is the speed rating of the SDH signal currently used?A: the speed rating of the SDH signal is defined on the basis of transmission lines, which can be light or microwave and satellite transmission channels.What are the types of fiber optic amplifiers?A: semiconductor optical amplifiers, erbium-doped light amplifiers, Raman amplifiers.Which band of light signals can be amplified by the EDFA? What is the structure of the EDFA? Working principle?Answer: (1) EDFA magnifies the light of the 1550nm band;(2) structure: made up of erbium-doped fiber, pump, wave separator, optical isolator and filter.(3) the principle: erbium absorbs pump light to produce stimulated radiation, amplifying the transmission signal light.What type of pump power conversion efficiency is high for the EDFA pump in 980nm pump and 1480nm pump? Which pump is less noisy? Why?Answer: (1) the EDFA power conversion efficiency of 980nm pump is up to 11dB/mW, while 1480nm is only 6.5 dB/mW.(2) the former has a low noise coefficient, only 3.2 dB to 3.4 dB,The latter minimum is about 4dB;(3) this is because of the high quantum conversion efficiency when pumping in the direction of 1480nm pump.What are the advantages of the Raman fiber amplifier?Answer: (1) the gain medium is a normal transmission fiber, and has good compatibility with optical fiber.(2) the gain wavelength is determined by the wavelength of the pump, and is not restricted by other factors;(3) high gain, small disturbance, low noise coefficient, wide spectrum, good temperature stability.For example, the application of optical fiber amplifier in optical fiber communication.A: (1) EDFA has played a large role in the extensive reuse of high-capacity optical fiber transmission, such as the application of DWDM systems and HFC systems.(2) the application of RFA: the independent Raman broadband amplifier, RFA + EDFA hybrid amplifiers, and RFA to make a source non-destructive device or dynamic equalizer device.Chapter v passive optical devices and WDM technologiesWhat are the functions of the analysis of optical couplers? How to achieve light coupling? How do you change the separation of the couplers?Answer: (1) function: the transmission of electrical signals by light is a good isolation for input and output electrical signals. To combine multiple light signals together; The light letters were assigned to multiple optical fibers;(2) : in the optical coupler input signal to light source, the light to the assembly together of shouguang, caused by the photoelectric effect should be the photocurrent, electricity by light output terminal lead, thus to realize optical coupling;(3) change the ratio of the spectra: by changing the length of the coupled regions, you can change the light power allocated by the coupling arm, thereby changing the spectral ratio.4, what is the working principle of fiber optic polarization controller and fiber Bragg grating?Answer: (1) fiber polarization controller: the optical fiber winding on the plate, fiber caused by the stress induced birefringence, make the input light in two polarization directions produces phase shift, polarizing control production use;(2) : optical fiber Bragg grating FBG provide periodic coupling points, in the single mode fiber into the club's fundamental mode according to the article determined and different transmission grating constant phase, can be coupled into the forward or backward transfer mode.Explain how the ring works. Give examples.Answer: (1) principle: light circulator USES the polarization phenomenon of light, the input and output relation of port is certain, and can only be transmitted. (2) the light signal that is reflected back by the optical isolator is used in the light division multiplexer to produce the WDM system with the fiber optic grating.What is the reference wavelength of the dense multiplexing system? What is the standard channel spacing?Answer: the reference wavelength is 1552.52 nm in DWDM system, channel interval is 0.8 nm (at the 1.55 um corresponding 10 GHZ frequency band interval) integer times.What is the difference between a DWDM open system and an integrated system?Answer: (1) the open system is a wavelength converter OUT in front of the wave division multiplexer, which converts the wavelength of the SDH non-standard to the standard wavelength.(2) integrated system is the standard light wavelength and meet the long-distance transmission light source in SDH, the whole system is simple, does not increase more than the equipment.What is the role of the monitoring channel in the WDM system? What are the requirements for it?Answer: (1) : reduce the probability of system failure, reduce troubleshooting time, enhance network survivability and robustness, and reduce the cost of operation, maintenance and management; (2) condition: the monitoring channel does not limit the wavelength of the optical amplifier pump. The monitoring channel should not limit the distance between the two circuit amplifiers. The monitoring path does not limit the future at 1310nm. The monitoring channel is still available when the line amplifier fails; (5) transmission should be segmented OSC has the function of 3 r and bidirectional transmission, on each optical amplifier Repeaters, information can be accepted by the right down, and can also attach a newmonitoring signal;6. Consider only on two optical fibers transmit bidirectional system, allowing the OSC two-way transmission, in case a single fiber after being cut off, monitoring information can still be accepted by lines.。
《光纤通信》课后习题标准答案
习题一1．光纤通信的优缺点各是什么？答：优点有：带宽资源丰富，通信容量大；损耗低，中继距离长；无串音干扰，保密性好；适应能力强；体积小、重量轻、便于施工维护；原材料来源丰富，潜在价格低廉等。
缺点有：接口昂贵，强度差，不能传送电力，需要专门的工具、设备以及培训，未经受长时间的检验等。
2．光纤通信系统由哪几部分组成？各部分的功能是什么？答：光纤通信系统由三部分组成：光发射机、光接收机和光纤链路。
光发射机由模拟或数字电接口、电压—电流驱动电路和光源组件组成。
光源组件包括光源、光源—光纤耦合器和一段光纤（尾纤或光纤跳线）组成。
模拟或数字电接的作用是实现口阻抗匹配和信号电平匹配（限制输入信号的振幅）作用。
光源是LED或LD，这两种二极管的光功率与驱动电流成正比。
电压—电流驱动电路是输入电路与光源间的电接口，用来将输入信号的电压转换成电流以驱动光源。
光源—光纤耦合器的作用是把光源发出的光耦合到光纤或光缆中。
光接收机由光检测器组件、放大电路和模拟或数字电接口组成。
光检测器组件包括一段光纤（尾纤或光纤跳线）、光纤—光检波器耦合器、光检测器和电流—电压转换器。
光检测器将光信号转化为电流信号。
常用的器件有PIN和APD。
然后再通过电流—电压转换器，变成电压信号输出。
模拟或数字电接口对输出电路其阻抗匹配和信号电平匹配作用。
光纤链路由光纤光缆、光纤连接器、光缆终端盒、光缆线路盒和中继器等组成。
光纤光缆由石英或塑料光纤、金属包层和外套管组成。
光缆线路盒：光缆生产厂家生产的光缆一般为2km一盘，因而，如果光发送与光接收之间的距离超多2km时，每隔2km将需要用光缆线路盒把光缆连接起来。
光缆终端盒：主要用于将光缆从户外（或户内）引入到户内（或户外），将光缆中的光纤从光缆中分出来，一般放置在光设备机房内。
光纤连接器：主要用于将光发送机（或光接收机）与光缆终端盒分出来的光纤连接起来，即连接光纤跳线与光缆中的光纤。
3．假设数字通信系统能够在高达1%的载波频率的比特率下工作，试问在5GHz的微波载波和1.55μm的光载波上能传输多少路64kb/s的音频信道？解：根据题意，求得在5GHz的微波载波下，数字通信系统的比特率为50Mb/s，则能传输781路64kb/s的音频信道。
《光纤通信》课后习题答案
第一章1．光纤通信的优缺点各是什么？答：优点有：带宽资源丰富，通信容量大；损耗低，中继距离长；无串音干扰，保密性好；适应能力强；体积小、重量轻、便于施工维护；原材料来源丰富，潜在价格低廉等。
缺点有：接口昂贵，强度差，不能传送电力，需要专门的工具、设备以及培训，未经受长时间的检验等。
2．光纤通信系统由哪几部分组成？各部分的功能是什么？答：光纤通信系统由三部分组成：光发射机、光接收机和光纤链路。
光发射机由模拟或数字电接口、电压—电流驱动电路和光源组件组成。
光源组件包括光源、光源—光纤耦合器和一段光纤（尾纤或光纤跳线）组成。
模拟或数字电接的作用是实现口阻抗匹配和信号电平匹配（限制输入信号的振幅）作用。
光源是LED或LD，这两种二极管的光功率与驱动电流成正比。
电压—电流驱动电路是输入电路与光源间的电接口，用来将输入信号的电压转换成电流以驱动光源。
光源—光纤耦合器的作用是把光源发出的光耦合到光纤或光缆中。
光接收机由光检测器组件、放大电路和模拟或数字电接口组成。
光检测器组件包括一段光纤（尾纤或光纤跳线）、光纤—光检波器耦合器、光检测器和电流—电压转换器。
光检测器将光信号转化为电流信号。
常用的器件有PIN和APD。
然后再通过电流—电压转换器，变成电压信号输出。
模拟或数字电接口对输出电路其阻抗匹配和信号电平匹配作用。
光纤链路由光纤光缆、光纤连接器、光缆终端盒、光缆线路盒和中继器等组成。
光纤光缆由石英或塑料光纤、金属包层和外套管组成。
光缆线路盒：光缆生产厂家生产的光缆一般为2km一盘，因而，如果光发送与光接收之间的距离超多2km时，每隔2km将需要用光缆线路盒把光缆连接起来。
光缆终端盒：主要用于将光缆从户外（或户内）引入到户内（或户外），将光缆中的光纤从光缆中分出来，一般放置在光设备机房内。
光纤连接器：主要用于将光发送机（或光接收机）与光缆终端盒分出来的光纤连接起来，即连接光纤跳线与光缆中的光纤。
3．假设数字通信系统能够在高达1%的载波频率的比特率下工作，试问在5GHz的微波载波和1.55μm的光载波上能传输多少路64kb/s的音频信道？解：根据题意，求得在5GHz的微波载波下，数字通信系统的比特率为50Mb/s，则能传输781路64kb/s的音频信道。
光纤通信课后答案
全书习题参考答案第1章概述1.1 填空题（1）光导纤维（2）掺铒光纤放大器(EDFA) 波分复用(WDM) 非零色散光纤(NIDSF) 光电集成(OEIC)（3）0.85µm 1.31µm 1.55µm 近红外（4）光发送机 光接收机 光纤链路（5）光纤 C=BW×log2(1+SNR) 信道带宽（6）大 大（7）带宽利用系数（8）可重构性可扩展性透明性兼容性完整性生存性1.2 解：利用光导纤维传输光波信号的通信方式称为光纤通信。
即以光波为载频，以光纤为传输介质的通信方式称为光纤通信。
1.3 解：（1）传输频带宽，通信容量大（2）传输距离长（3）抗电磁干扰能力强，无串音（4）抗腐蚀、耐酸碱（5）重量轻，安全，易敷设（6）保密性强(7) 原料资源丰富1.4 解：在光纤通信系统中，最基本的三个组成部分是光发送机、光接收机和光纤链路。
光发送机由电接口、驱动电路和光源组件组成。
其作用是将电信号转换为光信号，并将生成的光信号注入光纤。
光接收机是由光检测器组件、放大电路和电接口组成。
其作用是将光纤送来的光信号还原成原始的电信号。
光纤链路由光纤光缆、光纤光缆线路(接续)盒、光缆终端盒、光纤连接器和中继器等构成。
光纤光缆用于传输光波信息。
中继器主要用于补偿信号由于长距离传送所损失的能量。
光缆线路盒：将光缆连接起来。
光缆终端盒：将光缆从户外引入到室内，将光缆中的光纤从光缆中分出来。
光纤连接器：连接光纤跳线与光缆中的光纤。
1.5解：“掺铒光纤放大器(EDFA)+波分复用(WDM)+非零色散光纤(NIDSF)+光电集成(OEIC)”正成为国际上光纤通信的主要发展方向。
1.6 解：第一阶段（1966~1976年），实现了短波长（0.85µm）、低速（45或34 Mb/s）多模光纤通信系统，无中继传输距离约10km。
第二阶段（1976~1986年），光纤以多模发展到单模，工作波长以短波（0.85um）发展到长波长，实现了波长为1.31µm、传输速率为140~165Mb/s的单模光纤通信系统，无中继传输距离为50~100km。
光纤通信课后第1章习题答案
第1章 复习思考题参考答案1-1 用光导纤维进行通信最早在哪一年由谁提出答：1966年7月英籍华人高锟提出用光导纤维可进行通信。
1-2 光纤通信有哪些优点光纤通信具有许多独特的优点，他们是： 1. 频带宽、传输容量大； 2. 损耗小、中继距离长； 3. 重量轻、体积小； 4. 抗电磁干扰性能好； 5. 泄漏小、保密性好；6．节约金属材料，有利于资源合理使用。
1-3 简述通信网络的分层结构构成通信网络的基础设施可用图1.1.3所示的分层模型来描述。
这种分层网络支持传统的电复用信号传输，但是也可以提供全光端对端透明连接。
在光层中传输的网络功能，如分插复用（ADM ）、交叉连接、信号存储以及业务调度均在光层中完成。
电交换/复接层( 层)LAN POTS CATVOXCOXCOXC业务和应用层光传送/网络层光接入声音视频网络管理OADMOADMOADM: OXC ：光分插复用光交叉连接SDH/ATM图 1.1.3 通信网络的分层结构1-4 比较光在空气和光纤中传输的速度，哪个传输得快答：当光通过比真空密度大的光纤时，其传播速度要减慢，如图1.2.3所示，减慢的程度与介质折射率n 成反比。
图1.2.3 光通过密度大的介质时传播速度要减慢1-5 简述抗反射膜的工作原理。
答：当光入射到光电器件的表面时总会有一些光被反射回来，除增加耦合损耗外，还会对系统产生不利的影响，为此需要在器件表面镀一层电介质材料，以便减少反射，如图1.3.6所示。
在该例中，空气折射率11=n ，器件材料是硅，5.33=n ，电介质材料选用43N Si ，其折射率9.12≈n ，在空气和硅器件折射率之间。
当入射光到达空气和抗反射膜界面时，标记为A 的一些光被反射回来，因为它是外反射，所以反射光与入射光相比有180o的相位变化。
该光波在电介质材料中传播，当到达抗反射膜和器件界面时，除大部分光进入器件外，一些光又被反射回来，标记为B 。
因为23n n >，还是外反射，B 光仍有180o 的相位变化，而且当它从抗反射膜出来时，已经受了2d 距离的传输延迟，d 为抗反射膜的厚度。
《光纤通信》课后习题答案
1．光纤通信的优缺点各是什么？答：优点有：带宽资源丰富，通信容量大；损耗低，中继距离长；无串音干扰，保密性好；适应能力强；体积小、重量轻、便于施工维护；原材料来源丰富，潜在价格低廉等。
缺点有：接口昂贵，强度差，不能传送电力，需要专门的工具、设备以及培训，未经受长时间的检验等。
2．光纤通信系统由哪几部分组成？各部分的功能是什么？答：光纤通信系统由三部分组成：光发射机、光接收机和光纤链路。
光发射机由模拟或数字电接口、电压—电流驱动电路和光源组件组成。
光源组件包括光源、光源—光纤耦合器和一段光纤（尾纤或光纤跳线）组成。
模拟或数字电接的作用是实现口阻抗匹配和信号电平匹配（限制输入信号的振幅）作用。
光源是LED或LD，这两种二极管的光功率与驱动电流成正比。
电压—电流驱动电路是输入电路与光源间的电接口，用来将输入信号的电压转换成电流以驱动光源。
光源—光纤耦合器的作用是把光源发出的光耦合到光纤或光缆中。
光接收机由光检测器组件、放大电路和模拟或数字电接口组成。
光检测器组件包括一段光纤（尾纤或光纤跳线）、光纤—光检波器耦合器、光检测器和电流—电压转换器。
光检测器将光信号转化为电流信号。
常用的器件有PIN和APD。
然后再通过电流—电压转换器，变成电压信号输出。
模拟或数字电接口对输出电路其阻抗匹配和信号电平匹配作用。
光纤链路由光纤光缆、光纤连接器、光缆终端盒、光缆线路盒和中继器等组成。
光纤光缆由石英或塑料光纤、金属包层和外套管组成。
光缆线路盒：光缆生产厂家生产的光缆一般为2km一盘，因而，如果光发送与光接收之间的距离超多2km时，每隔2km将需要用光缆线路盒把光缆连接起来。
光缆终端盒：主要用于将光缆从户外（或户内）引入到户内（或户外），将光缆中的光纤从光缆中分出来，一般放置在光设备机房内。
光纤连接器：主要用于将光发送机（或光接收机）与光缆终端盒分出来的光纤连接起来，即连接光纤跳线与光缆中的光纤。
3．假设数字通信系统能够在高达1%的载波频率的比特率下工作，试问在5GHz的微波载波和 1.55μm的光载波上能传输多少路64kb/s的音频信道？解：根据题意，求得在5GHz的微波载波下，数字通信系统的比特率为50Mb/s，则能传输781路64kb/s的音频信道。
《光纤通信》课后习题答案
《光纤通信》课后习题答案习题二1．光波从空气中以角度1θ=33°投射到平板玻璃表面上，这里的1θ是入射光与玻璃表面之间的夹角。
根据投射到玻璃表面的角度，光束一部分被反射，另一部分发生折射，如果折射光束和反射光束之间的夹角正好为90°，请问玻璃的折射率等于多少？这种玻璃的临界角又是多少？解：入射光与玻璃表面之间的夹角1θ=33°，则入射角57i θ=°，反射角57r θ=°。
由于折射光束和反射光束之间的夹角正好为90°，所以折射角33y θ=°。
由折射定律sin sin i i y y n n θθ=，得到sin /sin sin67/sin33y i y n θθ==（自己用matlab 算出来）其中利用了空气折射率1i n =。
这种玻璃的临界角为1arcsinc yn θ=（自己用matlab 算出来） 2．计算1 1.48n =及2 1.46n =的阶跃折射率光纤的数值孔径。
如果光纤端面外介质折射率1.00n =，则允许的最大入射角max θ为多少？解：阶跃光纤的数值孔径为max sin 0.24NA θ=允许的最大入射角()max arcsin 0.24θ=自己用matlab 算出来3．弱导阶跃光纤纤芯和包层折射率分别为1 1.5n =，2 1.45n =，试计算（1）纤芯和包层的相对折射率?；（2）光纤的数值孔径NA 。
解：阶跃光纤纤芯和包层的相对折射率差为2212210.032n n n -?=≈光纤的数值孔径为0.38NA =4．已知阶跃光纤纤芯的折射率为1 1.5n =，相对折射（指数）差0.01?=，纤芯半径25a m μ=，若01m λμ=，计算光纤的归一化频率V 及其中传播的模数量M 。
解：光纤的归一化频率002233.3V a n ππλλ==?=光纤中传播的模数量25542V M ≈=5．一根数值孔径为0.20的阶跃折射率多模光纤在850nm 波长上可以支持1000个左右的传播模式。