An optical fiber communication system for transmitting information-bearing optical signals over an optical fiber transmission line includes a signal generator coupled to the transmission line for introducing information-bearing optical signals thereonto, preferably as wavelength modulated signals, and one or more optical amplifiers for periodically, collectively amplifying the transmitted signals to overcome the effects of attenuation. Wavelength modulation is achieved by altering the resonant characteristics of an optical resonator, optically coupled to a gain medium so as to provide an output that varies between a first and second wavelength. The optical amplification is achieved by injecting, preferably via lateral optical fiber couplings, pumping beams into the optical fiber so as to effect an increase in the amplitude of the information-bearing signals by stimulated Raman scattering.

Optical communications system using raman repeaters and components therefor

Recent research on long-wavelength lightwave communication utilizing the wavelength region between 1.3 and 1.6 µm is reviewed with an eye toward future system development. The attraction of the long-wavelength region is the availability of the ultimately low-loss and wide-band features of the silica fiber, where minimum loss is 0.27 dB/km at a wavelength of 1.3 µm and 0.16 dB/km at 1.55 µm. The single-mode fiber has found its first significant applications in long-wavelength systems. The specific characteristics of lightwave components are discussed with focus on physical fundamentals. The practical performance of fibers and lightwave devices is surveyed. The dynamic properties of long-wavelength laser diodes are discussed in relation to fiber characteristics. The noise characteristics of long-wavelength detectors are considered for the purpose of specifying the repeater spacing. Some system studies are reviewed, for example, 1.3-µm-wavelength lightwave systems, which have demonstrated bandwidth-distance products of about 40 GHz ċ km. Various approaches to extend the capacity of long-wavelength lightwave transmission are given. In the future, the 1.5-µm wavelength system could operate at the lowest loss wavelength region extending from 1.5 to 1.65 µm. Much higher performance, for example, bandwidth-distance products of 185 GHz ċ km, achieved by further continuation of research and development on lightwave sources as well as fibers. Because of the author's familiarity with work in Japan, that work is emphasized and most frequently cited.

Long-wavelength optical fiber communication

The systems and operational requirements, reliability, and cost estimates for several undersea fiber optic cable communications systems of varying capacities, data transmission rates, and link distances are analyzed in detail to highlight relevant design tradeoff parameters. It is shown that systems with a high data rate per fiber are more economical and reliable than low data rate systems with multiple fibers. This study concludes that undersea optic cable systems can soon provide reliable broad-band digital services.

Undersea fiber optic cable communications system of the future: Operational, reliability, and systems considerations

The objective of this study is to look at fiber optics networks in a predominately functional domain and to assess their potential survivability advantages from that point of view. As a consequence, service survivability is emphasized far more than physical survivability, although physical existence of facilities is a definite prerequisite for all telecommunications services.

The need for a quantitative (or formal, or unique, or numerical) definition of the term "survivability" is addressed. The report proposes a partial solution to this problem. It introduces a network–related quantity, defined with the moments of the connectivity cross section histograms, that appears to possess many of the properties wanted for measuring and comparing survivability of different topologies. For lack of a better name, that quantity may be called the effective topological survivability index.

The fiber advantage of large data throughput, typically in tens of Mb/s, must be exploited when connectivity or other network status is in doubt. This is part of the network reconstitution or restoration issue. Outlines of procedures, protocols, and formats are given to achieve comprehensive network–wide restoral for small but still realistic networks. The information fields of extensive reconstitution data arrays are possible and advisable. If transmitted, received, and stored rapidly, and not processed in a lengthy manner, these data arrays are shown to offer unprecedented restoral opportunities. Through locally or regionally focused restoration processes the methods appear practicable even for very large networks.

The conclusion is that full–scale automation is essential. It should be distributed to all nodes of the network and its implementation should be with the very highest speed parallel processors. Any node that survives should be capable of both initiating and participating in the network restoration sessions. Thus, centralized hierarchical controls are to be avoided.

Fiber Optic Networks and Their Service Survival

n a recent Special Issue on Optical Fiber Communications (PROCEEDINGS OF THE IEEE, October 1980), S.E. Miller, the Guest Editor, said “ . . . The era of experi~ mental and trial installations appears to be near an end, and customers are ready for standard commercial offerings.” This is indeed the case for most of the optical fiber systems: short-haul and intraoffice systems, on-premises applications, data links, etc. However, there remain certain pro,blems to be solved in such systems as ubscriber loops and long-haul and undersea transmission systems.  The long-haul  system involves technical difficulties because it necessarily demands the use of single mode fibers. The optical undersea system ~~~ ~~ ~ ~~ ~~ ~~

M. Koyama

Papers

Present and future of large capacity optical fiber transmission