View metadata, citation and similar papers at core.ac.uk brought to you by CORE SCIENCE & TECHNOLOGY TRENDS QUARTERLY REVIEW No.15 / April 2005 4 Trends in Optical Fiber Communication Technology and Industry, and Proposals for Future Directions — Towards the Fusion of Seeds and Needs — KIMIO TATSUNO Information and Communications Research Unit has been increasing since immediately after the 1 Introduction collapse of the optical communication bubble. Led by peer-to-peer sending and receiving of Optical fiber communication technology motion pictures, the conversion of the work enables ultrahigh-speed, high-capacity, of business and national and local government long-distance transmission. Because there is no is gradually spreading through e-commerce, alternative technology, it is indispensable basic e-government, e-education, e-medicine, and so infrastructure supporting society’s information on. These add up to the working of synergies that and communication functions. The spread and are peculiar to the Internet. improved performance of photonic infrastructure Therefore, at some point in the near future therefore has a major influence on a country’s we may awake to find that traffic is congested overall social life. For example, mobile telephones at various points in society. The reliability and using wireless utilize wireless communication to safety of communication may be damaged, and reach nearby antenna stations, but the stations declining quality of service (QoS) may become utilize photonic networks among themselves, a major social issue. In other words, bottlenecks and optical-fiber cables on the ocean floor enable may occur in the photonic networks that form real-time communication with people all over the backbone of communications infrastructure. the globe. In addition, while the asymmetrical For that reason, we must not relax research and digital subscriber lines (ADSL) now widely used development efforts directed towards future for the Internet use metal wires, station-to-station photonic technology. transmission utilizes photonic networks, Based on the current awareness and future connecting the world’s personal computers. The vision described above, this article discusses scale of the world market for the photonic device questions such as the following. (1) What is industry that utilizes this technology as its core the background of the optical communication is ¥10 trillion. If optical fibers are connected not recession, and why did it occur? (2) In relation only to backbones but also to ordinary homes as to the continuously increasing volume of exemplified by “fiber to the home” (FTTH) and traffic, what will the next bottleneck in to information devices, the scale of the photonic photonic technology be? (3) Is a structure device industry’s market can expand even in place for creative research into new further. communications services actively utilizing However, for the past several years the optical broadband infrastructure made possible by communication industry has been confronted photonic technology? In addition, the article with the collapse of the IT or dot-com bubble, offers proposals regarding the direction of and with the world in the throes of a recession R&D designed to fuse the seeds of optical led by North America, demand for backbone communication infrastructure with the needs in particular has cooled off and the market has that require it. stagnated. Meanwhile, traffic over Internet lines 50 51 SCIENCE & TECHNOLOGY TRENDS QUARTERLY REVIEW No.15 / April 2005 Figure 1 : Optical fiber transmission loss bands and optical fiber amplifier operation frequency Figure 2 : Principles of optical communication 2 Optical fiber communication technology 2-1 Optical communication principles and wavelength division multiplexing Within photonic technology there are modes such as the propagation of light through space, but this article discusses optical fiber communications utilizing optical fibers of glass materials with silicon oxide (SiO2) as the signal transmission medium. For the sake of simplicity, the article will refer to this as “optical communication.” Figure 1 shows transmission loss characteristics of optical wavelengths on currently installed typical optical fibers[1]. The strength of that light is digitized as an electrical peak in the center is the absorption band created signal that modulates on/off. The modulated by the harmonics of the OH base of residual light signals are propagated in the optical fibers, moisture inside the fiber. Ordinarily, optical but absorption and dispersion in the optical communication utilizes the wavelength bands, fibers cause loss of data and attenuation. For called “windows,” that avoid the peak. The long-distance communications, therefore, wavelength used at first was 0.85µm to the left repeaters are placed every few tens of kilometers of the peak. That was because the materials for to transmit optical signals over long distances. laser diodes of the time were GaAs-based. Later, On the receiving side, photodetectors and InP-based laser diodes were developed, and the electric amplifiers are in place, and the optical band from 1.3µm to 1.6µm, where transmission signal is converted into an electrical signal and loss is lowest, came into use. Furthermore, the original data are recovered. In conventional optical fibers are low cost at under ¥10 per single-wavelength mode, repeaters temporarily meter, they are long-lived and reliable, and their convert attenuated optical signals into electrical tensile strength is greater than that of steel. In signals, and reactivate a laser diode after electrical practice, such optical fibers (125µm diameter, amplification. In other words, each repeater must approximately 10µm core) are bundled by several perform photoelectric conversion and electrical hundred into optical fiber cables when installed. conversion. This conversion must be carried Figure 2(a) shows the basic structure of optical out for each wavelength channel, so utilizing communication utilizing optical fibers with wavelength division multiplexing with this characteristics like these. There is a laser diode method is difficult. light source on the data transmission end, and the In contrast, as shown in Figure 2(b), 50 51 SCIENCE & TECHNOLOGY TRENDS QUARTERLY REVIEW No.15 / April 2005 wavelength division multiplexing (WDM) passes by repeaters unnecessary. This is because these beams from multiple laser diodes for different optical amplifiers function like optically-pumped wavelengths through a coupler before inputting lasers, enabling them to amplify optical signals them into a single optical fiber. Therefore the in batches as light and on a relatively wide transmission capacity of a single optical fiber wavelength band. Furthermore, it is fortunate is the product of one wavelength channel’s that the operation frequencies of optical fiber transmission speed multiplied by multiple amplifiers, referred to as the S, C, and L bands, wavelengths. For example, if the interval between happen to be the optical fiber wavelength bands wavelength channels is 0.4nm, and the entire with the least loss, as can be seen in Figure 1. As wavelength used is 400nm, it can be multiplied depicted in Figure 3, the cable across the floor by 1,000 channels. If each wavelength channel of the Pacific Ocean has 180 repeaters equipped transmits 40Gbps, 40-Tbps ultrahigh-capacity with optical fiber amplifiers strung together optical communication becomes possible. If we about every 50 kilometers. explain this astonishing communications capacity in terms of digital versatile discs (DVDs), the 2-2 The structure of data stored in a two-hour movie on DVD is 4.7GB optical communication networks (about 40Gb), so the information stored in 1,000 As shown in Figure 4, the extremely high DVDs can be transmitted to a destination across performance optical communication method the Pacific in about one second. described above comprises a network Optical fiber amplifiers[1] such as erbium-doped constructed of a transmission system and fiber amplifiers (EDFAs) make this wavelength exchange node system that ties it together. The multiplexing transmission possible. Using them transmission system can be roughly divided into renders photoelectric and electrical conversion three layers, the backbone system (10-40Gbps) Figure 3 : Repeaters for the Transpacific Cable Figure 4 : Structure of the optical communications network 52 53 SCIENCE & TECHNOLOGY TRENDS QUARTERLY REVIEW No.15 / April 2005 connecting cities and undersea networks, the economic competition. Ports, canals, railroads, urban system (1G-10Gbps) inside cities, and superhighways, waterworks and sewers, and access system (0.1-1Gbps) exemplified by “fiber so on, were all invested in as infrastructure to the home (FTTH).” that would empirically increase national These transmission channels are connected competitiveness. A corporate investment of $100 to each other by exchange nodes. The exchange billion would be enough to lay optical fibers to nodes are equipped with routers, which they use every home, office, factory, school, library, and to control the destinations of traffic. If we liken hospital.” exchange nodes to an expressway, they are the Financial support for such expectations for equivalent of interchanges. With the increase in photonic technology began in 1990 with part traffic, faster switching throughput and higher of the surplus US military budget created by capacity processing scale are needed. As I will the end of the Cold War. This ample budget