光纤通信 1.Fiber Optic Communications System.ppt

Fiber Optic Communications,Fiber Optic Communications.Fifth Edition.Joseph C.Palais,Fiber Optic Communications,Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber.The light forms an electromagnetic carrier that is modulated to carry information.First developed in the 1970s,fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age.,Fiber Optic Communications,Because of its advantages over electrical transmission,optical fibers have largely replaced copper wire communications in core networks in the developed world.Optical fiber is used by many telecommunications companies to transmit telephone signals,Internet communication,and cable television signals.Due to much lower attenuation and interference,optical fiber has large advantages over existing copper wire in long-distance and high-demand applications.,Chapter 1:Fiber Optic Communication Systems Chapter 2:Optics ReviewChapter 3:Lightwave Fundamentals Chapter 4:Integrated Optic WaveguidesChapter 5:Optic Fiber Waveguides Chapter 6:Optical Source and Amplifiers Review,Fiber Optic Communications,Chapter 1 Fiber Optic Communications System,In this chapter,we define the subject of fiber optic communications and explain our approach to this subject.We review the many advantages over alternative technologies and discuss significant applications.These includes fibers,optics,communications,optic communications and complete fiber optic communications systems.,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,1.2 The Basic Communications System,1.3 Nature Of Light,Chapter 1 Fiber Optic Communications System,1.4 Advantages Of Fibers,1.5 Applications Of Fiber Optic Communication,1.6 Summary And Discussion,Please read the paragraphs from“light was always been with us”to“In fact,any type of indicator lamp is basically an optic communications system”When you are reading,please think about two questions:How many kinds of traditional communication systems it has introduced?2.whats the common disadvantage of these communication systems?,1.1 Historical Perspective,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,source,Light has always been with us.Communications using light occurred early in our development,when human beings first communicated by using hand signals.This is obviously a form of optic communications,Chapter 1 Fiber Optic Communications System,During the day,the sun is the source of light for this system.The information is carried from the sender to the receiver on the suns reflected radiation.Hand motion modifies,or modulates,the light.The eye is the message-detecting device,and the brain processes is this message.Information transfer by such a system is slow,the transmission distance is limited,and the chances for error are great.,1.1 Historical Perspective,Chapter 1 Fiber Optic Communications System,source,Human first communicated by using hand signal.,Chapter 1 Fiber Optic Communications System,How can it work in darkness?,1.1 Historical Perspective,A later optic system,useful for longer transmission paths,was the smoke signal.The message was sent by varying the pattern of smoke rising from a fire.This pattern was again carried to the receiving party by reflected sunlight.This system required that a coding method be developed and learned by the communicator and receiver of the message.This is comparable to modern digital systems that use pulse codes.,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,In 1880:Alexander Graham Bell invented a light communication system-photophone,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,It used sunlight reflected from a thin voice-modulated mirror to carry conversations.At the receiver,the modulated sunlight fell on a photo-conducting selenium(硒)cell,which converted the message to electrical current.A telephone receiver completed the system.The photophone never achieved commercial success,although it worked rather well.,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,After the advent of lamps,simple optic-communications systems appeared,such as blinker lights for ship-to-ship and ship-to-shore links,automobile turn signals,and traffic lights,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,In fact,any type of indicator lamp is basically an optic-communications systems.,Other TraditionalOptic Communication Systems?,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,Chinese traditional communication systems,Setting beacon(烽火)fire to make fun of dukes,Message with a feather attached as a sign of urgency,Low information capacities,Chapter 1 Fiber Optic Communications System,hand signal,blinker lights,Smoke signal,Disadvantage,photophone,1.1 Historical Perspective,Please continue to read the paragraphs from“All these systems have low information capacities”to the end of section 1.1.When you are reading,please think about three questions:Whats the disadvantage of the atmosphere system?What is the major breakthrough that led to high-capacity optic communications?How about the history of the fibers?,1.1 Historical Perspective,Chapter 1 Fiber Optic Communications System,Solution-It provided a narrowband source of optic radiation suitable for use as a carrier of information,Chapter 1 Fiber Optic Communications System,Laser,1.1 Historical Perspective,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,Unguided optic communications-atmospheric laser system-were developed shortly after the discovery of the laser.Communications over light beams traveling through the atmosphere was easily accomplished.The disadvantages of these systems include dependence on a clear atmosphere,the need for a line-of-sight path between transmitter and receiver,and the possibility of eye damage to persons who unknowingly look into the beam.,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,Although somewhat limited in their use,these early applications aroused interest in optic systems that would guide the light beam and thus overcome those disadvantages.In addition,guided beams could bend around corners and could be buried in the ground.The early work on atmosphere laser systems provided much of the fundamental theory and many of the actual components required for communications over fibers.Ironically,(讽刺的是)it is now known that laser sources are not required for all fiber systems.In many cases the broader band light-emitting diode(LED)is suitable.,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,In 1960s:An efficient fiber was missing.Although light could be guided by glass fibers,those available attenuated light by far（非常）too large an amount.Glass produced by the ancient Egyptians(埃及人)was opaque(不透明).The artisans(工匠)of Venice fabricated glass of much greater purity in the Middle Ages.Venetian glass was moderately(适度地)transparent,but still orders of magnitude too lossy for modern long-distance communications.,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,It was not until 1970 that the first truly low-loss fiber was developed and fiber optic communications became practical.This occurred just 100 years after John Tyndall,a British physicist,demonstrated to the Royal Society that light can be guided along a curved stream of water.Guiding of light by a glass fiber and by a stream of water are evidence of the same phenomenon(total internal reflection).,Chapter 1 Fiber Optic Communications System,1.1 Historical Perspective,“光纤之父”高锟博士早期关于光纤的实验,1966年，高锟发表了一篇题为光频率介质纤维表面波导的论文，开创性地提出光导纤维在通信上应用的基本原理，描述了长程及高信息量光通信所需绝缘性纤维的结构和材料特性。高锟是继李政道、杨振宁、丁肇中、李远哲、朱棣文、崔琦及钱永健之后，第八位获得诺贝尔科学奖的华裔科学家。,Chapter 1 Fiber Optic Communications System,光纤,For groundbreaking achievements concerning the transmission of light in fibers for optical communication,BL product,Development of optical fiber communication system,Development of optical fiber communication system,Please continue to read the paragraphs from“A basic communications system”to“lay the foundations for further discussions”.When you are reading,please think about two questions:How does every part of the basic communications system work?What are the advantages of guided channel over unguided waveguide?,Chapter 1 Fiber Optic Communications System,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Transmitter,Information Channel,Receiver,1.2 The Basic Communication system,The message is generated and put into a form suitable for transfer over the information channel,Transmitter,Information Channel,Receiver,The information travels from the transmitter to the receiver over this channel,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Two-Wire Line;Coaxial Cable;Rectangular Waveguide,Transmitter,Information Channel,Receiver,The message extracted from the information channel and put into its final form,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Guided channel,Unguided channel,Information Channels,Atmospheric channel,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Guided channels include a variety of conducting transmission structures,including two-wire line,coaxial cable,and rectangular waveguide.Guided channels cost more to manufacture,install,and service than do atmospheric channels,but it have the advantages of privacy,weather independence,and the ability to convey messages within,under,and around physical structures.Fiber waveguides have these advantages and others.We enumerate(列举)them in this chapter.,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,A more detailed,but still quite general block diagram appears in Fig.1.3.A brief discussion of each block in this figure gives us a good feel for the main elements of a communications system.Descriptions of these element emphasize those suitable for fiber systems.Many of the concise descriptions given in this section are expanded later.For now,we present an overview of the subject and lay the foundations for further discussions.,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Message origin,generalized fiber optic communication system,Information channel,category 种类 relay 转播，接替rectangular 矩形的 rectangle ncoaxial 共/同轴的 co-协同，合作 waveguide 波导 privacy 隐私 convey 传送 emphasize 强调transmitter 发送机 channel 信道weather independence 与天气无关的enumerate 列举 计算 extract 抽取，榨取 schematic 图表 illustration 插图,New words,Please read this section,then think about the question:What form does the information must be before transmission for either electronic or optical communications?,1.2.1 Message origin(信源),Message origin,generalized fiber optic communication system,Information channel,The message origin may take several physical forms.Quite often it is a transducer that converts a non-electrical message into an electrical signal.Common examples include microphones for converting sound waves into currents and video(TV)cameras for converting images into currents.In some cases,such as data transfer between computers or parts of a computer,the message is already in electrical form.This situation also arises when a fiber link constitutes a portion of some larger system and fibers used in relaying cable television signals.In any case,the information must be in electrical form before transmission for either electronic or optical communications.,1.2.1 Message origin,Please read this section,then think about the questions:What are the two main functions of the modulator?What are the two distinct categories of modulation?Whats the difference between the two kinds of modulation?,1.2.2 Modulator(调制器),messageorigin,The modulator has two main functions.First,it converts the electrical message into the proper format;second it impresses this signal onto the wave generated by the carrier source.,generalized fiber optic communication system,1.2.2 Modulator,messageorigin,Two distinct categories of modulation format are analog and digital,generalized fiber optic communication system,1.2.2 Modulator,Soundamplitude,0,current,current,Chapter 1 Fiber Optic Communications System,1.2 The Basic Communication system,1.2.2 Modulator,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Soundamplitude,0,current,current,The analog modulation need not change the format of the signal,It just amplify the signal to be strong enough to drive the carrier source,1.2.2 Modulator,An analog signal is continuous and reproduces the form of the original message quite faithfully.For example,suppose a sound wave containing a single tone is to be transmitted.The electrical current produced when a microphone picks up this wave has the same shape as the wave itself.This relationship is illustrated in Fig1.4.In this case,the modulator need not change the format of the signal.It could be appropriate to amplify this signal,however,so that the signal will be strong enough to drive the carrier source.,Chapter 1 Fiber Optic Communications System,1.2.2 Modulator,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,Soundamplitude,0,current,current,Digital modulation involves transmitting information in discrete form.The signal is either on or off.The on state represents a digital 1,the off state a digital 0.These states are the binary digits(or bits)of the digital system.The data rate is the number of bits per second transmitted.,1.2.2 Modulator,The sequence of on and off pulses might be a coded version of an analog message.An analog-to-digital converter develops the digital sequence from the analog message.The reverse process occurs at the receiver,where the digital signal is returned to its analog form.To impress a digital signal onto a carrier,the modulator need only turn the source on or off at the appropriate times.The ease of constructing digital modulators makes this format very attractive for fiber systems.,1.2 The Basic Communication system,Chapter 1 Fiber Optic Communications System,1.2.2 Modulator,The choice of format must be made very early in the design of any system.Other considerations and comparisons between analog and digital systems are discussed in more detail later in this and succeeding chapters.At the end of this chapter is a list of the decisions a designer faces in the construction of a complete system.We explain the items in this table throughout the book.Later,we are more specific in describing the available choices,and we add a list of advantages,disadvantages,and primary applications appropriate to each choice.,1.2.2 Modulator,oscillate 振荡，振动 oscillator 振荡器moderate 中等的，适度的，适中的a moderate price，a moderate climateproportion 比例，均衡，面积，部分positive 肯定的，实际的，积极的。电 正的，阳的negative 否定的，消极的，负的，阴性的linearity 线性，直线性DC bias