1、Unit Communication TechnologyLesson 17 Optical Fiber CommunicationsNew Words convey knvei vt. 搬运, 传达, 转让 transfer trnsf: n. 移动, 传递, 转移 superimpose ,sju:primpuz v. 添加, 双重 microwave maikruweiv n. 微波 conversion knv:n n. 变换, 转化 semiconductor ,semikndkt n. 半导体 diode daiud n. 二极管 photodiode ,futudaiud n.
2、光敏二极管, 光电二极管 phototransistor ,fututrnzist n. 光电晶体管, 光敏晶体管 photoconductor ,futukndkt n 物 光电导体,光电导元件 discrete diskri:t a. 不连续的, 离散的 implement implimnt, impliment n. 工具, 器具 vt. & v. 贯彻, 实现, 执行 encode enkud vt. 编码 equalizer i:kwlaiz n. 均衡器, 平衡装置 decode ,di:kud vt. 解码, 译解Phrases and Expressions optical f
3、iber n. 光纤 electromagnetic wave n. 电磁波 avalanche photodiode (APD) n. 雪崩发光二极管 front-end amplifier n. 前置放大器Notes1.by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal. 介词by + 动名词短语充当状语； which 引导定语从句，修饰wave。2.This modulated carr
4、ier is then transmitted to the required destination where it is received and the original information signal is obtained by demodulation. 过去分词短语required 充当定语，where it is by demodulation是定语从句，两者均修饰destination。3.by using electromagnetic carrier waves operating at radio frequencies as well as microwave
5、 and millimeter wave frequencies. 介词by + 动名词短语充当状语； as well as 意思是“以及”，相当于and，常用于句中，下文中仍有这种用法。再如：He can speak English as well as Chinese。请比较：He can speak English, and he can speak Chinese as well (as well 用于句末，相当于too)。 4.However,“communication”may also be achieved by using an electromagnetic carrier
6、 which is selected from the optical range of frequencies. Which引导定语从句，修electromagnetic carrier。5.In this case the information source provides an electrical signal to a transmitter comprising an electrical stage which drives an optical source to give modulation of the lightwave carrier. in this case：
7、“在这种场合下，既然这样”；which引导定语从句。6.to provide gain as well as linear signal processing and noise bandwidth reduction. 此为不定式短语，充当目的状语。Translation of TextsLesson 17 Optical Fiber Communications Communication may be broadly defined as the transfer of information from one point to another. When the information
8、 is to be conveyed over any distance a communication system is usually required. Within a communication system the information transfer is frequently achieved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal. 第第17课课 光纤通信光
9、纤通信 广义地说，把信息从一点传送到另一点就称为通信。当信息跨越一段距离被传送时，就需要一个通信系统。在通信系统中，信息传送是通过把信息叠加在电磁波上或对电磁波进行调制来实现的，电磁波起着载送信号的作用。 This modulated carrier is then transmitted to the required destination where it is received and the original information signal is obtained by demodulation. Sophisticated techniques have been devel
10、oped for this process by using electromagnetic carrier waves operating at radio frequencies as well as microwave and millimeter wave frequencies. However, “communication” may also be achieved by using an electromagnetic carrier which is selected from the optical range of frequencies. 这一经过调制的载波随后被传送到
11、要求到达的目的地，在那里被接收，并且通过解调还原成原始信息。在运用电磁载波的领域，高新技术得到进一步的发展，比如射频、微波以及毫米波的频率都被用来作为载波频率。在通信中，也可选择光波的频率作为载波频率。 Typical optical fiber communications system is shown in Fig.20-1. In this case the information source provides an electrical signal to a transmitter comprising an electrical stage which drives an op
12、tical source to give modulation of the lightwave carrier. The optical source which provides the electrical-optical conversion may be either a semiconductor laser or light emitting diode (LED). 典型的光纤通信系统如图171所示。信源提供电信号给发射机，发射机组成一个电子平台来驱动光源以完成对光载波的调制。光源是由发光二极管或半导体激光管构成的，它完成光电变换。传输媒介由光纤（缆）组成。 The trans
13、mission medium consists of an optical fiber cable and the receiver consists of an optical detector which drives a further electrical stage and hence provides demodulation of the optical carrier. Photodiodes (p-n, p-i-n or avalanche) and, in some instances, phototransistor and photoconductors are uti
14、lized for the detection of the optical signal and the optical-electrical conversion. Thus there is a requirement for electrical interfacing at either end of the optical link and at present the signal processing is usually performed electrically. 光接收机由驱动后面电路平台的光探测器构成，用以完成对已调光载波的解调。用于检测光信号和进行光电转换的器件有：
15、光电二极管（P-N、P-I-N 或雪崩管）、发光三极管以及光敏电阻等。因此，在光系统链路的两端都要求有电接口，并且在现阶段，信号处理通常是通过电路实现的。 The optical carrier may be modulated by using either an analog or digital information signal. Analog modulation involves the variation of the light emitted from the optical source in a continuous manner. With digital modul
16、ation, however, discrete changes in the light intensity are obtained (i.e. on-off pulses). 模拟或数字的信号均可用来调制光载波。模拟调制是指从光源处发射的连续光强度的变化，而数字调制则不然，它是通过光强度离散的变化（比如，有无光脉冲）来实现的。 Although often simpler to implement, analog modulation with an optical fiber communication system is less efficient, requiring a far
17、 higher signal to noise ratio at the receiver than digital modulation. Also, the linearity needed for analog modulation is not always provided by semiconductor optical source, especially at high modulation frequencies. For these reasons, analog optical fiber communication link are generally limited
18、to shorter distances and lower bandwidths than digital links. 虽然简单易行，但模拟调制在光通信系统调制中调制效率较低，而且与数字调制相比，需要高得多的信噪比。模拟调制所必需的线性不总是来源于半导体光源，尤其是在高频调制中。基于上述原因，与数字光通信系统相比较，模拟光通信链路通常被限制使用在更短的通信距离和更窄的带宽上。 Initially, the input digital signal from the information source is suitably encoded for optical transmission
19、. The laser drive circuit directly modulates the intensity of the semiconductor laser with the encoded digital signal. Hence a digital optical signal is launched into the optical fiber cable. The avalanche photodiode (APD) detector is followed by a front-end amplifier and equalizer or filter to prov
20、ide gain as well as linear signal processing and noise bandwidth reduction. Finally, the signal obtained is decoded to give the original digital information. 首先，输入的信源数字信号被适当地编码以进行光传输。激光器的驱动电路通过这些已编码的数字信号来直接调制激光器的发光强度，然后数字光信号被注入光纤电缆。在接收端，信号通过雪崩发光二极管（APD）后进入前置放大器和均衡器或滤波器，放大器用来提供增益、滤波器用来对信号进行线性处理和减少噪声带
21、宽。最后，信号通过解码得到原始数字信号。Exercises1. Write T (True) or F (False) beside the following statements about the text.a. This modulated carrier is then transmitted to the required destination where it is received and the original information signal is obtained by modulation.b. Sophisticated techniques have bee
22、n developed for this process by using magnetic carrier waves operating at radio frequencies as well as microwave and millimeter wave frequenciesc.The information source provides an electrical signal to a transmitter comprising an electrical stage which drives an optical source to give modulation of
23、the lightwave carrier.d. The transmission medium consists of an optical fiber cable and the receivere. The optical carrier is modulated by using neither an analog nor digital information signal.f. With digital modulation, discrete changes in the light intensity are not obtained.g. Analog modulation
24、with an optical fiber communication system is more efficient, requiring a far lower signal to noise ratio at the receiver than digital modulation.h. The input digital signal from the information source is not suitably encoded for optical transmission.2. Fill in the missing words according to the tex
25、t.a. Within a communication system the information transfer is_ by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier.b. Photodiodes (p-n, p-i-n or avalanche) and _and _ are utilized for the detection of the optical signal and the optical-electrical con
26、version. c. The laser drive circuit directly modulates the intensity of the semiconductor laser with the encoded digital signal. Hence a _is launched into the optical fiber cable. d. There is a requirement for electrical interfacing at either end of the optical link and at present the _ is usually performed electrically.3. Translate the third paragraph into Chinese. End
