The construction of an optical subscriber loop and its operation system will be one of the most important infrastructures for the information society of the future. This paper presents a discussion of current and future service trends, the evolution of fiber-optic systems in the loop, and subscriber loop operation systems. Several operation technologies are also discussed which will enable the operation systems described in this paper to be constructed. Of these, the key technologies are an operation system architecture with flexibility, software technologies based on object-oriented design and programming, and automatic operation modules.

Fiber-optic local area networks (LANs) with Fiber Distributed Digital Interface (FDDI) protocol have come into use as backbones connecting other small LANs. This paper describes the current status of LANs, reviews a number of issues that stand in the way of further development and look at the future of LANs. Demands for wide-area networks (WANs) connecting LANs and multimedia LANs including voice and image capability has been extremely strong, spurring progress in geographical expansion and throughput increase, now over 100Mbit/s. The logical choice of transmission medium for next-generation systems is single-mode optical fiber, not only for backbone LANs but also, eventually, for floor LANs.

Single-mode fibers with intentionally induced periodical residual strains (IIPRS) along the fiber length are proposed for the suppression of the stimulated Brillouin scattering (SBS). A change of the residual strain along a fiber will change the Brillouin frequency shift, resulting in a broadening of the Brillouin gain profile. Such an increase of the line-width of the gain profile will cause a decrease of the gain coefficient which will raise the threshold power of the stimulated Brillouin scattering in optical fibers. Two types of the IIPRS fibers were fabricated. The residual strain of one IIPRS fiber is modified rectangularly while that of the other is changed triangularly. The measured spectra of the SBS are compared with that of a fiber with a constant strain. Using a novel mathematical model presented in this report, the possible improvements of the threshold powers for these two IIPRS fibers over the constant-strain fiber can be assessed through the SBS spectra. Finally, the achieved improvements are confirmed with the experimental results. The estimated improvement of the threshold for the IIPRS fiber with the rectangular profile is 2.9dB while the measured is 2.4dB. In case of the IIPRS fiber with a triangular profile, the improvement of the threshold is 5.4dB by estimation and is 5.1dB by experiment. While the limit of the threshold improvement for rectangular IIPRS fibers is 3dB, the threshold improvement for triangular IIPRS fibers is limited only by the allowable deviation of the tension applied during the drawing of fibers. It is estimated that a 5dB improvement is not difficult to realize.

This report will present an expression for the mechanical behavior of a drum-wound dual coated fiber and an analytical expression for the microbending loss in single mode dual coated fibers. These analytical expressions are then compared with experimental drumwinding microbending loss results to determine their validity.

To construct a Fiber-To-The-Home network, high count optical fiber cables are needed. The requirements for these cables are small diameter, light weight, and high capacity. We studied the cable structures for ribbon fiber, which are useful for quick splicing. We calculated the diameter of three types of cables: a slotted rod cable, a loose tube cable and a newly developed U-groove cable. When the same ribbons are cabled with the same clearance, the cross sectional area of the U-groove cablet is about 27% less than that of the other two cables. No problems with the manufactured 1500-fiber U-groove unit cable are detected by the conventional cable testing.

Improvement of fatigue behavior of a fusion spliced portion on a carbon-coated fiber is achieved by recoating carbon using a thermal-CVD process with a CO₂ laser as a local heat source. The fatigue parameters, so-called n-values, of 121 and 94 are obtained on the non-spliced portion and the spliced portion, respectively. Assuming a life time prediction model, these high values have been proved to have an advantage in a long-term reliability and to be sufficient in a practical submarine cable use.

The 22 mechanical optical switch for single mode fiber (SMF) is reported. By using the precision grinding and molding techniques all-plastic multiple-fiber connector, 22 pin-referenced indirect slide switch is developed. The characteristics and the reliability test's results of this optical switch are also reported. Evaluations confirm that the switch has low insertion loss, high-speed switching, stable switching operations and reliability in practical applications.

By optimizing the structure of erbium-doped fibers, high efficiency such as a gain coefficient of 6.3dB/mW, or a slope efficiency of 92.6% have been realized with very flat wavelength dependence. Though the optimized structure has high NA, the splice loss with standard fibers can be lowered by the additional arc technique. The carbon coated fiber with a fatigue parameter over 150 guarantees the reliability, even when wounded on a small coil. In-line isolators and WDM couplers have been also developed. An amplifier module has been assembled, resulting in an output power more than +16dBm owing to the high performance of each component.

We report on Brillouin optical-fiber time domain reflectometry (BOTDR) for distributed temperature or strain measurement along a single-mode optical fiber. BOTDR uses Brillouin scattering in optical fibers, whose Brillouin frequency shift increases in proportion to temperature or strain induced in the fiber. This method requires access to only one end of a fiber, as with conventional optical time domain reflectometry (OTDR) which uses Rayleigh scattering in optical fibers. In BOTDR, a coherent optical detection method is used as a backscattered light detection technique. This technique can achieve both high sensitivity and high frequency resolution and easily separate a weak Brillouin line from a strong Rayleigh scattering peak and Fresnel reflected light. Experimental results show the potential for measuring temperature and strain distribution with respective accuracies of 3 or 0.006%, and a spatial resolution of 100m in an 11.57km long fiber.

We propose an integrated smart cable operation system and its architecture for the future cable network. In the proposed architecture, an application programs and various modules are loosely coupled using a cable operation system platform. We anticipate the task flows for the future optical cable network operation in order to realize the proposed system and architecture. Each task flow is broken down into "atomic tasks." The task flow can be changed easily by combining these atomic tasks. We use an object-oriented design for designing the cable operation system platform. As a first step towards the construction of the proposed system a pre-prototype system was constructed and the results are shown.

This paper proposes a surveillance system concept, which includes the analysis of fiber fault factors and monitored items, the architecture for diagnosing fiber degradation and the system configuration. Fiber faults are classified into two types. One is fiber failure caused by fiber axial tensile strain and the other is fiber loss increase caused by fiber bending and the absorption of hydrogen molecules. It was found that there is an urgent need for fiber axial strain monitoring, sensitive loss monitoring operating at longer wavelengths and water sensing, in order to detect the origin and early indications of these faults before the service is affected. Moreover, an algorithm for predicting and diagnosing fiber faults based on the detected results was investigated and systematized.

Optical soliton transmissions at 10 and 20Gbit/s over 1000km with the use of erbium-doped fiber amplifiers are described in detail. For the 10Gbit/s experiment, a bit error rate (BER) of below 110^-13 was obtained with 2²⁰-1 pseudorandom patterns and the power penalty was less than 0.1dB. In the 20Gbit/s experiment optical multiplexing and demultiplexing techniques were used and a BER of below 110^-12 was obtained with 2²³-1 pseudorandom patterns under a penalty-free condition. A new technique for sending soliton pulses over ultralong distances is presented which incorporates synchronous shaping and retiming using a high speed optical modulator. Some experimental results over 1 million km at 7.210Gbit/s are described. This technique enables us to overcome the Gordon-Haus limit, the accumulation of amplified spontaneous emission (ASE), and the effect of interaction forces between adjacent solitons. It is also shown by computer runs and a simple analysis that a one hundred million km soliton transmission is possible by means of soliton transmission controls in the time and frequency domains. This means that limit-free transmission is possible.

Subjective quality tests have proven that embedded adaptive differential PCM (ADPCM), known to tolerate information loss through bit dropping, does not maintain sufficient speech quality when directly applied to asynchronous transfer mode (ATM) due to the fixed-length cell transmission scheme unique to ATM. We propose a coding and transmission scheme which enhances the performance by adjusting the embedded ADPCM coding rate according to input speech characteristics, thereby taking advantage of the ATM environment, where the transmission of variable rate sources is feasible. By varying the number of code bits of an embedded ADPCM coder from 6bits per sample, or 48kbps, for blocks of speech with a high prediction gain, to 2bits, or 16kbps, for silent blocks, a good compromise between coding bit rate and speech quality with gradual degradation due to information loss is achieved. The results of subjective evaluation tests showed the speech quality of the proposed scheme to be over 3.5 mean opinion score (MOS) on a scale of 1 to 5 at a cell loss rate of 10%. A prototype of the codec and the ATM cell assembly/disassembly functions were also fabricated using 3 conventional digital signal processors (DSPs) for real-time conversation tests.

The transmission of HDTV signals on digital networks requires adoption of sophisticated compression techniques to limit the bit-rate requirements and to provide a high-quality and reliable services to customers. This paper describes system design and transmission characteristics of an adaptive subband DCT codec that can encode original 1.2Gb/s HDTV signals at 156Mb/s. The performance of the codec was evaluated using motion picture signals. The characteristics obtained with the codec was found to maintain good picture quality.

The path diversity improvement inherent in direct sequence spread spectrum (DS/SS) signalling under multi-path propagation environments is investigated for mobile/personal radio communications systems that employ DPSK modulation. The bit error rate (BER) performance of post-demodulation selection diversity reception is theoretically analyzed in the presence of noise-only-paths in the time window for diversity combining. Results of laboratory experiments conducted to evaluate the BER performance are also presented. It is shown that the experimental results agree well with the theoretical BER.