A highly reliable and available network which automatically can restore itself from failures is an important concept for the future high capacity broadband networks. Self-healing algorithm, restoring the failed VPs (Virtual Paths) in the backbone ATM networks, is an indispensable technique to meet these requirements. In this paper we propose a coordination-based restoring self-healing algorithm called C-TRUS, which meets different requirements of service classes of survivability by using a simple rerouting and capacity reserving protocols. The simulation results show that the proposed algorithm can restore VPs quickly and improve the restoration time in case of multi-failures by using network resources very efficiently. Furthermore, C-TRUS outperforms the combination method in both restoration ratio and restoration time. In addition, the significant improvement of restoration ratio in the multi-failure scenario has been achieved.

A 161 km non-repeatered transmission and a 216 km transmission with a linear repeater have been achieved at 10 Gbit/s using Er3+-doped fiber amplifiers. It is also verified that GaAs-IC technology is applicable to 10 Gbit/s optical transmission systems.

A wavelength demultiplexer made of 2-D photonic crystal capable of simultaneously separating many channels from WDM light is analyzed in order to study the properties and clarify the design parameters. Numerical analyses are carried out for the optical filter structure and the demultiplexer structure which consists of several filters and waveguides carved in the crystal. The results of this paper show the considerations regarding the frequency tuning, the device size, the bandwidth and integration of filters. Further more, for a photonic crystal filter, a method for realizing a flat-top pass-band generally required from the dense-WDM systems is presented and its property is shown. The calculation method is the scattering matrix method which is proper to the analysis of the frequency domain in a 2-D photonic crystal with finite size and with some defects.

Basic characteristics of Erbium-doped fiber laser amplifier (EDFA) pumped by laser diodes with oscillating wavelength of 1.48µm are measured. Unsaturated gain of 26 dB, 3 dB saturation output power of 1 mW, and noise figure of 5.5 dB are obtained. As a result of transmission experiment using the EDFA at 1.8 Gbit/s over 210 km, linear repeater gain of 20 dB is achieved by considering loss of optical band pass filter and power penalty due to degradation of extinction ratio. By using the basic parameters obtained experimentally, maximum regenerative repeater spacing are calculated in a direct detection transmission system with EDFA repeaters. It is clarified that theoretical regenerative repeater spacing of 5000 km can be achieved by using 50 amplifiers with gain of 20 dB and noise figure of 6 dB, including coupling loss of 0.5 dB, at a bit rate of 2 Gbit/s.

A 400 Mb/s optical fiber fransmission system was designed for field trial using single-mode fibers. The system is targeted to 20 km repeater spacing using InGaAsP/InP DH laser diode (LD) and Ge-APD as an optical device. This paper describes the design philosophy for the single-mode fiber transmission system and the field trial results. The error rate performance is expressed by signal to noise ratio (SNR) for practical high-speed digital optical repeater, putting emphasis on LD mode partition noise. Based on the SNR analysis and results obtained from several preliminary experiments, the design procedures for the 400 Mb/s transmission system were clarified. Through the field trial, it has become clear that the 400 Mb/s optical transmission system is practically applicable to long-haul transmission systems.

Modulator output and fiber transmission characteristics of optical single sideband (SSB) modulations are analyzed under the assumption that SSB modulators are constructed using Mach-Zehnder (MZ) interferometers. The fiber input signal and the detected signal are derived theoretically for SSB modulation with and without an optical carrier. Optical SSB fiber transmission simulations show that the received signal waveform is degraded by harmonic components due to non-linear switching curve of MZ interferometer as a component of SSB modulators even if the Hilbert transformers is ideal for the definition. The optical SSB suppressed carrier is preferred to the SSB with an optical carrier from a viewpoint of waveform degradation.

An initial trial of the optical fiber transmission system in NTT is reported in this paper. In NTT's transmission networks, the shorthaul application appears attractive in the near future. The laboratory test is primarily targeted to 32 Mb/s bit rate and 8 km long repeater spacing. We report here the design philosophy of step-index multimode fibers and repeaters for this trial. Through the design and manufacturing of fibers, the fundamental and common characteristics of fibers are clarified. Stable, compact and low power consuming optical repeaters are realized. Trere is no trouble of optical repeatered line and all repeaters in the line are operating with sufficient optical power margin. Multi-repeatered test has confirmed that experimental results are in good agreement with the design values.

We proposed and evaluated a speech packet loss concealment method which predicts lost segments from speech included in packets either before, or both before and after the lost packet. The lost segments are predicted recursively by using linear prediction both in the forward direction from the packet preceding the loss, and in the backward direction from the packet succeeding the lost segment. Predicted samples in each direction are smoothed by averaging using linear weights to obtain the final interpolated signal. The adjacent segments are also smoothed extensively to significantly reduce the speech quality discontinuity between the interpolated signal and the received speech signal. Subjective quality comparisons between the proposed method and the the packet loss concealment algorithm described in the ITU standard G.711 Appendix I showed similar scores up to about 10% packet loss. However, the proposed method showed higher scores above this loss rate, with Mean Opinion Score rating exceeding 2.4, even at an extremely high packet loss rate of 30%. Packet loss concealment of speech degraded with G.729 coding, and babble noise mixed speech showed similar trends, with the proposed method showing higher qualities at high loss rates. We plan to further improve the performance by using adaptive LPC prediction order depending on the estimated pitch, and adaptive LPC bandwidth expansion depending on the consecutive number of repetitive prediction, among many other improvements. We also plan to investigate complexity reduction using gradient LPC coefficient updates, and processing delay reduction using adaptive forward/bidirectional prediction modes depending on the measured packet loss ratio.

A wavelength demultiplexer made of 2-D photonic crystal capable of simultaneously separating many channels from WDM light is analyzed in order to study the properties and clarify the design parameters. Numerical analyses are carried out for the optical filter structure and the demultiplexer structure which consists of several filters and waveguides carved in the crystal. The results of this paper show the considerations regarding the frequency tuning, the device size, the bandwidth and integration of filters. Further more, for a photonic crystal filter, a method for realizing a flat-top pass-band generally required from the dense-WDM systems is presented and its property is shown. The calculation method is the scattering matrix method which is proper to the analysis of the frequency domain in a 2-D photonic crystal with finite size and with some defects.

We report here a pulsed lightwave frequency synthesizer system that is composed of a pulsed lightwave sweep frequency generator and a tracking generator. The key advance in the sweep generator is the use of a dynamically gain controlled EDFA. The combination of feedback and feed forward dynamic gain control effectively compensates EDFA gain fluctuation and equalizes fiber loop loss so that the initial pulse wave form and amplitude is retained in the loop at large circuit numbers. Over 1000 pulsed lightwave frequencies are synthesized in 250MHz steps by the sweep generator. Almost flat response (0.55dB variation) is realized up to 240GHz. The power spectrum decreases by 67% (1.7dB down) at 250GHz. The peak level of the pulses output from the loop is about -4dBm. Tracking generator and total synthesizer system performance are evaluated by (a) beat frequency between the tracking generator and the master lightwave source, (b) beat frequency between two tracking generators, and (c) a frequency chain between the master lightwave source and another HCN stabilized lightwave source via the synthesizer system. A continuous lightwave frequency locked to a frequency selected from the pulsed sweep frequency signal is demonstrated at over 200GHz to have an instability of 5MHz. Absolute accuracy of the lightwave frequency emitted from the synthesizer system is about 10MHz. Therefore, the relative accuracy of the lightwave frequency is as high as 510-8.

Optical fiber transmission systems have advanced rapidly with the advent of highly advanced electronic and optical devices. This paper introduces several IC technologies required for ultra-high-speed optical transmission and overviews current IC technologies used for the existing and developing optical fiber trunk transmission systems. Future trends in device technologies are also discussed.