In this paper, we present a novel class of long quasi-cyclic low-density parity-check (QC-LDPC) codes. Each of the codes in this class has a structure formed by concatenating single-parity-check codes and QC-LDPC codes of shorter lengths, which allows for efficient, high throughput encoder/decoder implementations. Using a code in this class, we design a forward error correction (FEC) scheme for optical transmission systems and present its high throughput encoder/decoder architecture. In order to demonstrate its feasibility, we implement the architecture on a field programmable gate array (FPGA) platform. We show by both FPGA-based simulations and measurements of an optical transmission system that the FEC scheme can achieve excellent error performance and that there is no significant performance degradation due to the constraint on its structure while getting an efficient, high throughput implementation is feasible.

'Super Hi-Vision' (SHV) is promising as a future form of television. It is an ultra-high definition TV system that has 16 times the number of pixels of HDTV and employs a 22.2 multichannel sound system. It offers superior presence and gives the impression of reality. The information bitrates of the current prototypes range from 24 to 72 Gbit/s, and a fiber optic transmission system is needed to transfer even just one channel. This paper describes the optical transmission technologies that have been developed for SHV inter-equipment connects and links between outdoor sites and broadcasting stations.

In this paper, we use frequency-domain equalization (FDE) to create coherent optical single-carrier (CO-SC) transmission systems that are very tolerant of chromatic dispersion (CD) and polarization mode dispersion (PMD). The efficient transmission of a 25-Gb/s NRZ-QPSK signal by using the proposed FDE is demonstrated under severe CD and PMD conditions. We also discuss the principle of FDE and some techniques suitable for implementing CO-SC-FDE. The results show that a CO-SC-FDE system is very tolerant of CD and PMD and can achieve high transmission rates over single mode fiber without optical dispersion compensation.

We have developed a novel railway signal control system that operates as a distributed system. It consists of a central control unit (called LC) and terminal devices (called FC) that are distributed at the railroad wayside and operate signal devices. The Internet technologies and optical LAN technologies have been used as communication methods between the LC and the FCs. While handling enormous amount of electric cables may cause human errors, the system is expected to reduce troubles of the current signal system at construction works thanks to the Internet technologies. The FC is a distributed terminal device that has its own processor and placed at the railroad wayside to control the field signal devices. The LC is a centralized computer device that has software arranged by the function of the field devices. An optical network system and multiple communication paths between the LC and the FCs realize durable transmissions. Moreover, the assure performance of controls and transmissions have been investigated, and the autonomous distributed signal control system is also discussed as the next steps of the system.

This paper describes the distortion properties created by self-phase modulation in super wideband FM converted 40 AM/30 64-QAM CATV and super-high-frequency RF converted 8 BS/12 CS TV signal transmission based on the optical SSB modulation scheme.

Application of microwave and millimeter-wave circuit technologies to InGaP-HBT ICs for 40-Gbps optical-transmission systems is demonstrated from two aspects. First, ICs for various important functions -- amplification of data signals, amplification, frequency doubling, and phase control of clock signals -- are successfully developed based on microwave and millimeter-wave circuit configurations mainly composed of distributed elements. A distributed amplifier exhibits ≥164-GHz gain-bandwidth product with low power consumption (PC) of 71.2 mW. A 20/40-GHz-band frequency doubler achieves wideband performance (40%) with low PC (26 mW) by integrating a high-pass filter and a buffer amplifier (as a low-pass filter). A compact 40-GHz analog phase shifter, 20- and 40-GHz-band clock amplifiers with low PC are also realized. Second, a familiar concept in microwave-circuit design is applied to a high-speed digital circuit. A new approach -- inserting impedance-transformer circuits -- to enable 'impedance matching' in digital ICs is successfully applied to a 40-Gbps decision circuit to prevent unwanted gain peaking and jitter increase caused by transmission lines without sacrificing chip size.

The performance of a new APSK receiver is analyzed using numerical simulation. The proposed receiver eliminates the penalty caused by SPM-induced phase-shift of optical pulses by employing three sub-modules and an amplitude-pattern controlled switch for each DPSK tributary. The interplay between SPM, IXPM, and XPM determines the performance of the proposed receiver for single-channel and WDM transmission.

This paper starts by describing the advantages of cascaded modulation, i.e., using multiple concatenated external modulators to modulate CW (Continuous Wave) light. Next, the paper examines computer simulations of the resulting modulated light waveform shapes and intermodulation distortion values to elucidate the basic modulation characteristics of a cascaded modulation scheme. Examples of applying cascaded modulation to a multi-channel optical signal transmission system are shown, and the characteristics are clarified by optical transmission experiments. For example, the dependency of the signal quality on the modulation depth values of each external modulator is clarified. Moreover, experiments show that cascaded modulation permits the remote insertion of local broadcast programs into wide area broadcast programs. Last, the paper shows that cascaded modulation offers better modulation properties than the conventional single modulation approach.

Ultrahigh-speed fiber lasers operating at up to 40 GHz offer a clean longitudinal comb and a narrow linewidth. This makes them suitable for applications including optical comb generation, ultrahigh-speed optical pulse transmission including PSK, and as opto-microwave oscillators. In this paper, we describe recent progress on ultrafast fiber lasers and their applications to optical metrology.

We propose a scheme by which Broadcast Satellite/Communication Satellite- radio frequency (BS/CS-RF) converted TV signals are transmitted over optical fiber, and also propose a simultaneous Frequency Modulation (FM) converted CATV and BS/CS-RF converted TV optical transmission system as one of its applications. To confirm the proposals, we demonstrate the simultaneous transport of FM converted CATV signals and BS/CS-RF converted TV signals over a single optical fiber. In the experiments, 40 carriers of AM-VSB CATV channels, 30 carriers of 64-QAM digital TV channels, 8 carriers of FM/TC8PSK BS-TV channels, and 12 carriers of QPSK CS-TV channels are simultaneously transmitted. For optical access network application, the practical transmission length of 15 km over 1.3 µm-zero-dispersion optical fiber can be achieved by using dispersion compensation fiber (DCF).

Various mixed-signal very-high-speed integrated circuits have been developed using InP DHBTs. These circuits have been designed for fiber-optic 43 Gbit/s transmissions applications. They include: on the transmitting side, a clocked driver and an EAM driver, as well as a PSBT/DQPSK precoder; on the receiving side, a sensitive decision circuit, a limiting amplifier and an eye monitor. System experiments made possible by these circuits include a 6 Tbit/s transmission on >6000 km distance.

This study is a detailed numerical investigation on the relations between the performance of the RZ format single-channel transmission, and the chromatic dispersion of transmission fiber and pre-compensation ratio. We observed the transition from the SPM dominant low dispersion region to the intra-channel nonlinearities dominant high dispersion region, and found that the EOP is very sensitive to the pre-compensation ratio when the dispersion assumes a intermediate value. Furthermore, by analyzing the optical power-dependence of the EOP and other nonlinear impairments, we found that the amplitude fluctuation resulting from IFWM is dominant in determining the EOP in the transmission systems employing highly dispersed pulses.

This paper describes design optimization and performances of hybrid optical transmission lines consisting of effective-area-enlarged pure silica core fiber and dispersion compensating fiber. As a result of the design optimization, considering low nonlinearity and good bending characteristic, the developed fibers exhibit a span average loss of 0.208 dB/km, a span average dispersion slope of 0.02 ps/nm2/km and low nonlinearity with an equivalent effective area of 60 µm2. Further optimization of the relationship among the nonlinearity, the dispersion slope and the bending characteristic enables perfectly dispersion-flattened hybrid optical transmission lines exhibiting a low transmission loss of 0.211 dB/km, low nonlinearity with an equivalent effective area of 60 µm2 and small dispersion deviation of 0.03 ps/nm/km in a wavelength band wider than 40 nm.

Today, an ultra-high capacity transmission system based on N40 Gb/s channel rate is the most promising approach to achieve multi-terabit/s of capacity over a single fiber. We have demonstrated 5.12 Tbit/s transmission of 128 channels at 40 Gbit/s over 3100 km and 10.24 Tbit/s transmission of 256 channels at 42.6 Gbit/s (using FEC) over 100 km, based on four main technologies: 40 Gbit/s electrical time-division multiplexing (ETDM), vestigial sideband demultiplexing (VSB), advanced amplifier technology including Raman amplification and TeraLightTM fiber. A record spectral efficiency of 1.28 bit/s/Hz is applied to achieve 10.24 Tbit/s transmission within the C- and L-band.

This report describes AlGaAs/GaAs HBT ICs for 20-Gb/s optical transmission, the preamplifier and optical modulator driver circuits, and those ICs for 10-Gb/s clock extraction circuits, the rectifier and phase shifter circuits. These ICs were fabricated using our developed hetero guard-ring fully self-aligned HBT (HG-FST) fabrication process. The Pt-Ti-Pt-Au multimetal system was also used as a base ohmic metal to reduce base contact resistance, and a high fmax of 105 GHz was obtained. Good results in the HBT IC microwave performances were achieved from the on-wafer measurements. The preamplifiers exhibited the broad bandwidth of 20. 9 GHz. The optical modulator driver performed a sufficiently large output-voltage swing of 4-VP-P at a 20-Gb/s data rate. The rectifier and the phase shifter circuits achieved good operations at 10-Gb/s. These results suggest that these HBT ICs can be applied to 20-Gb/s optical transmission and 10-Gb/s clock extraction systems.

We study nonlinear pulse propagation in an optical transmission system with dispersion compensation. This is particularly important for designing an ultra-fast long-haul communication system in the next generation. There exists a quasi-stationary pulse solution in such a system whose width and chirp are rapidly oscillating with the period of dispersion compensation. This pulse also has several new features such as enhanced power when compared with the soliton case with a uniform dispersion and a deformation from the sech-shape of soliton. We use the averaging method, and the averaged equation to describe the core of the pulse solution is shown to be the nonlinear Schrodinger equation having a nontrapping quadratic potential. Because of this potential, a pulse propagating in such a system eventually decays into dispersive waves in a way similar to the tunneling effect. However in a practical situation, the tunneling effect is estimated to be small, and the decay may be neglected.

This paper surveys low-power design techniques for Si bipolar Gbit/s LSIs. First, a total strategy for power reduction in bipolar LSIs is described. The power dissipation of Si bipolar LSIs can be minimized by reducing the supply voltage, switching and driving currents, the power of input and output circuits, and the equivalent "on" ratio. Widely spread activities from device to architecture levels are indispensable and each of the low-power techniques reduces power by a factor of about 0.5 to 0.7. The integration of these techniques is very important, and as a certain example of their effectiveness, an SOH signal processing LSI is demonstrated with a reduction factor of 1/10. Comparisons with other device technologies for low power characteristics reveal the low-power potential of bipolar LSIs in the Gbit/s region.

This paper presents the performance of a proposed GaAs MESFET photodetector with wide drain-to-gate distances for improving the optical coupling efficiency in subcarrier optical transmission. Principle and design parameters of the proposed MESFET are described. Link gain, CNR, and BER, are experimentally investigated as functions of the drain-to-gate distance. It is experimentally found that the proposed MESFET improves the link gain by 8.5 dB compared to the conventional structure at the subcarrier frequency of 140 MHz. Discussions are also included compared to PIN-PD.

This paper overviews fiber-oriented wireless communication systems, particularly in the area of microcell systems. The benefits of fiber-oriented wireless systems are discussed focusing on an application board scheme to facilitate new service deployment in light of intelligent networks. Dynamic range improvement technologies to remove interference are highlighted. Overall system performance is calculated for an economical FP-LD. Furthermore, effective modem use and a potential diversity technique are introduced. This strategy will play a role in realizing flexible fiber-optic subscriber networks.

This paper presents the performance of optically controlled MESFETs as photodetectors. The optical performance characteristics such as optic-to-electric responsivity, and BER for a π/4-QPSK signal are experimentally investigated. Measurements are performed by using MMIC compatible MESFETs. Experimental results are also evaluated in comparison with calculated PIN-PD limit. Optic-to-electric responsivity has high gain at lower received optical powers. It is shown experimentally that MESFET photodetectors improve the permissible optical power by 6 dB compared to the PIN-PD limit. Optically controlled MESFETs will provide a novel receivers for fiber-optic systems.