1. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Chapter 1 Historical Development and Recent Situation of Optical Communications 1.1 Historical Development of Optical Communications 1.2 General Optical Fiber Communication Systems 1.3 Advantages of Optical Fiber Communications 1.4 Applications of Optical Fiber Communications

2. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.1 Historical Development of Optical Communications T The use of light for communication purposes dates back to antiquity if we interpret optical communications in a broad sense. Most civilizations have used fire and smoke signals to convey a single piece of information (such as victory in a war). Essentially the same idea was used up to the end of the 18th century through signaling lamps, flags, and other semaphore devices. The advent of telegraphy in the 1830s replaced the use of light by electricity and began the era of electrical communications.

3. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The bit rate B could be increased to ~ 10 b/s by the use of new coding techniques such as the Morse code. The use of intermediate relay stations allowed communication over long distances (~1000 km). Indeed, the first successful transatlantic telegraph cable went into operation in 1866. The invention of the telephone in 1876 brought a major change inasmuch as electric signals were transmitted in the "analog" form through a continuously varying electric current. 1.1 Historical Development of Optical Communications

4. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The development of worldwide telephone networks during the 20th century led to many advances in the design of electrical communication systems. The first coaxial-cable system, put into service in 1940, was a 3-MHz system capable of transmitting 300 voice channels or a single television channel. The bandwidth of such systems is limited by the frequency-dependent cable losses which increase rapidly for frequencies beyond 10 MHz. 1.1 Historical Development of Optical Communications

5. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 This limitation led to the development of microwave communication systems in which an EM carrier wave with frequencies ~1-10 GHz is used to transmit the signal by using suitable modulation techniques. The first microwave system operating at the carrier frequency of 4 GHz was put into service in 1948. The most advanced coaxial system, put into service in 1975, operates at a bit rate of 274 Mb/s. 1.1 Historical Development of Optical Communications

6. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.1 Historical Development of Optical Communications Microwave communication systems generally allow larger repeater spaces, but their bit rate is also limited by the carrier frequency of such waves. T The capacity of a communication system is often measured through the bit rate-distance product BL, where B is the bit rate and L is the repeater spacing.

7. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Fig. 1.1 Increase in bit rate-distance product during 1850-2000. 1.1 Historical Development of Optical Communications

8. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 It was realized during the second half of the 20th century that an increase of several orders of magnitude in the BL product would be possible if optical waves were used as carrier. However, neither a coherent optical source nor a suitable transmission medium was available during the 1950s. The invention of the laser and its demonstration in 1960 solved the first problem. 1.1 Historical Development of Optical Communications

9. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Attention was then focused on finding ways for using the laser light for optical communications. Many ideas were advanced during the 1960s, the most noteworthy being the idea of light confinement by using a sequence of gas lenses. It was suggested in 1966 that optical fibers might be the best choice, as they are capable of guiding the light in a way similar to the guiding of electrons in copper wires. 1.1 Historical Development of Optical Communications

10. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The main problem was the high loss of optical fibers; fibers available during the 1960s had losses in excess of 1000 dB/km. A breakthrough occurred in 1970 when the fiber loss could be reduced to about 20 dB/km in the wavelength region near 1-  m. At about the same time, GaAs semiconductor lasers, operating continuously at room temperature, were demonstrated. The simultaneous availability of a compact optical source and a low-loss optical fiber led to a worldwide effort for developing fiber-optic communication systems. 1.1 Historical Development of Optical Communications

11. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Figure 1.2 shows the progress in the performance of lightwave systems realized after 1974 through five generations of development stages. Fig. 1.2 Progress in lightwave communication technology over the period 1974-1992. 1.1 Historical Development of Optical Communications

12. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The commercial deployment of lightwave systems followed the research and development closely. After many field trials, the first generation lightwave systems operating near 0.8  m began to be deployed in 1978. They operated at a bit rate in the range 50-100-Mb/s range and allowed a repeater spacing of about 10 km [BL ~ 500 (Mb/s)-km]. It was clear during the 1970s that the repeater spacing could be increased considerably by operating the lightwave system in the wavelength region near 1.3  m. 1.1 Historical Development of Optical Communications

13. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Furthermore, optical fibers exhibit minimum dispersion in this wavelength region. This realization led to a worldwide effort for the development of InGaAsP semiconductor lasers and detectors operating near 1.3  m. Such a laser was demonstrated in 1977. The second generation of fiber-optic communication systems became available in the early 1980s and allowed a repeater spacing in excess of 20 km. 1.1 Historical Development of Optical Communications

14. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 A laboratory experiment in 1981 demonstrated 2-Gb/s transmission over 44 km of single-mode fiber. The introduction of commercial systems soon followed. By 1987, second-generation 1.3  m lightwave systems operating at bit rates up to 1.7 Gb/s with a repeater spacing of about 50 km were commercially available. The repeater spacing of the second-generation lightwave systems is limited by the fiber loss at the operating wavelength near 1.3  m (typically 0.5 dB/km). 1.1 Historical Development of Optical Communications

15. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The introduction of third-generation lightwave systems operating at 1.55  m was considerably delayed by large fiber dispersion near 1.55  m. Conventional InGaAsP semiconductor lasers could not be used because of pulse spreading occurring as a result of simultaneous oscillation of several longitudinal modes. By 1985 the laboratory transmission experiments showed the possibility of communicating information at bit rates up to 4 Gb/s over distances in excess of 100 km. 1.1 Historical Development of Optical Communications

16. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The third-generation 1.55-  m systems operating at 2.4 Gb/s became available commercially in 1990. Such systems are capable of operating at bit rates in excess of 10 Gb/s with a careful design of semiconductor lasers and optical receivers. The development of 10-Gb/s lightwave systems is under way in several laboratories. 1.1 Historical Development of Optical Communications

17. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Coherent systems have been under development worldwide during the 1980s, and their potential advantage has been demonstrated in many system experiments. In one experiment 100 channels of 622 Mb/s were multiplexed by using a star coupler and transmitted over 50 km of fiber length with negligible interchannel crosstalk. The use of coherent detection is not a prerequisite for lightwave systems employing optical amplifiers. 1.1 Historical Development of Optical Communications

18. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 These devices were originally fabricated from alloys of AlGaAs which emitted optical wavelength. Recently this wavelength range has been extended to the region 1.1-1.6  m by the use of other semiconductor alloys. The light emitting diodes (LEDs) and photodiodes (PDs) also contributed to the realization of optical fiber communication systems. 1.1 Historical Development of Optical Communications

19. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 The radio communication was developed to higher frequencies leading to the introduction of the even higher. The relative frequencies and wavelengths of these types of electromagnetic wave can be observed from the electromagnetic spectrum. In additional benefit of the use of high carrier frequencies is the general ability of the communication system. 1.1 Historical Development of Optical Communications

20. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 Optical communication systems were developed with the invention of the solid state laser. This device provided a coherent light source together with the possibility of modulation at high frequency. The invention of the laser instigated a tremendous research effort in the study of optical components to achieve reliable information transfer using a lightwave carrier. 1.1 Historical Development of Optical Communications

21. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.2 The General Optical Fiber Communication Systems T The optical fiber communication systems are similar to all the other communication systems. In general, the communication systems therefore consist of a transmitter, the transmission medium, and a receiver. F For optical fiber communication system, the information source provides an electrical signal to a transmitter comprising optical source and optical modulator.

22. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.2 The General Optical Fiber Communication Systems T The transmission medium may consist of a pair of wires, a coaxial cable or a radio link through free space down which the signal is transmitted to the receiver. I In any transmission medium the signal is attenuated and is subject to degradations due to contamination by random signals and noise. I In any communication system there is a maximum permitted distance between the transmitter and the receiver.

23. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.2 The General Optical Fiber Communication Systems T 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. T Thus the analog optical fiber communication links are generally limited to shorter distances and lower bandwidths than the digital optical fiber communication links.

24. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.2 The General Optical Fiber Communication Systems O Optical communication systems differ in principle from other communication systems only in the frequency range of the carrier wave used to carry the information. T The optical carrier frequency is typically ~100 THz, which should be compared with the microwave carrier frequency of ~1-10 GHz.

25. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.2 The General Optical Fiber Communication Systems Fig. 1.3(a) The general communication system

26. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.2 The General Optical Fiber Communication Systems Fig. 1.3(b) The optical fiber communication

27. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.3 Advantages of Optical Fiber Communications Low Loss Now the losses optical fibers have been achieved as low as 0.2dB/km. It increases the repeater spacing of optical fiber communication systems. Broad Band The frequency of optical carrier in the range 10 to 10 Hz. The information-carrying capacity of optical fiber systems is already proving far superior to the best copper cable systems.

28. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.3 Advantages of Optical Fiber Communications Electrical Isolation Optical fibers are fabricated from glass sometimes a plastic polymer. Small Size And Light Weight When such fibers are covered with protective coatings they are far smaller and much lighter than the corresponding copper cables. Non-crosstalk Characteristic The operation of an optical fiber communication system is unaffected by transmission.

29. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.3 Advantages of Optical Fiber Communications FFlexibility The coated optical fibers are manufactured with high tensile strengths. The coated fibers may also be bent to quite small radii or twisted without damage. Nature Resource Conservation The optical fiber is made from sand. So, in comparison with copper conductors. In the future it will become as cheap to use optical fibers with their superior performance than almost any type of electrical conductor.

30. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.4 Applications Of Optical Fiber Communications VVoice Communication Application The first applications were for public and private telephone communication system links. The expanded service and the suitability of optical fibers are for the voice communication to the design and test of telephone equipments. VVideo Communication Application Optical Visual Information System (OVIS ) Cable Television (CATV) System.

31. 教育部顧問室光通訊系統教育改進計畫 高應大 副教授 吳曜東 編撰 1.4 Applications Of Optical Fiber Communications DData Communication Application Connections between the central processing unit (CPU) and terminal equipments and between CPUS can be made a local area network (LAN). SSensor Application The application of optical fibers in sensing external stimuli such as current, pressure, temperature, rotations electric and magnetic fields.