Cable TV has been playing an auxiliary part so far in video distribution services, or in broadcasting systems. Recently however, cable TV is reappreciated for its capability of not only distributing economically multi-channel video signals but also realizing two-way transmission. And moreover toward the construction of a new broadband optical network, cable IV has attracted special interest. This paper describes briefly the process of development of cable TV systems in Japan and a meaning of introduction of optical transmission technology into them. Then some examples of recent optical cable TV systems developed in USA and Japan are shown. Finally remaining problems for further study are discussed.

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To introduce digital video services into demand-access optical CATV systems, we apply 16-QAM (80 Mbps) it and experiment with 16-QAM/FM multichannel hybrid optical trunkline transmission. Multiplexed 16-QAM and FM signals, all with the same optical modulation depth of 4.72% per channel, are transmitted by modulating the intensity of a LD (Laser Diode). The BER performance of the 16-QAM signal is below 1 × 10^<-9> and the CNR of the FM signals is 30.3dB with an optical received power of -7dBm. Experimental results show that the BER performance and error continuity of a 16-QAM signal with Intermodulation Products are the same as in the case with random noise.

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In this study, we present experimental results og bit error rate (BER) characteristics of 6Mbps QPSK signal and 16Mbps 16QAM signal, in this condition of various CTBs induced under fifty one VSB-AM channels optical hybrid transmission. We make clear the following items. (1)BER dependency of CTB cannot be specified by average CTB values. (2)In the case that maximum CTB values are considered, amplitude probability distribution of CTB should be taken into account. (3)Amplitude probability distribution of CTB changes depending on modulation depth of CTB.

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It has been reported that in AM/QAM hybrid subcarrier multiplexed (SCM) optical transmission systems. LD clipping causes serious degradation on QAM transmission characteristics. In this paper, the mechanism of the clipping induced degradation was investigated through experiments. As a result, it was confirmed that impulsive distortion due to the clipping degrades bit error rate of QAM signals. Furthermore, novel frequency allocations were proposed, which can suppress the clipping induced degradation.

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Both domestic and overseas CATV operators are intending to offer new multi-media services with compressed digital video, utiiizing the existing equipment. In response to this, an AM/QAM hybrid optical transmission system for compressed digital video signals has been developed which is compatible with the existing coaxial CATV systems. This optical transmission system can transmit 70 AM signals and 80 16QAM signals simultaneously in one optical fiber. Also, the design method for this hybrid system has been established through the study and analysis of the influence of clipping in laser diode on the 16QAM BER, which is major problem of this system.

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156Mbit/s fiber-optic Video Transmission Equipment has been development. It can transmit 1channel NTSC signal of contribution quality and 4channel audio signals. It can easily construct video transmission system by connecting to SDH(Synchronous Digital Hierarchy) Network. The interface of a video signal has a resolution of 10bit per sample. The S/N of the video signal is more than 60dB. In addition, it can simultaneously transmit audio signals with the quality as CD or DAT. By using SDH interface LSIs and an integrated optical transceiver, small size and low power consumption is realized.

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In optical multiple-access networks using subcarrier multiplexing (SCM), performance degradation due to beat noise is a severe problem. In this paper, the authors propose a beat-noise-free SCM optical multiple-access network using subcarrier multiplexing repeaters. Low-cost and long-distance systems are possible using the proposed network. Furthermore, fundamental characteristics have been estimated. Results indicate that in a wide-area monitoring system, 20 local nodes (LNs) with Fabry-Perot (FP) LDs and 200 LNs with DFB LDs can be connected, respectively.

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Recently, fiber-radio systems have been reported worldwide. It is very important for fiber transmission to meet a dynamic range required radio systems. This paper describes an overview of technologies to increase the dynamic range, especially FM double modulation. Optically controlled MES-FET is also discussed in order to improve optical receiver sensitivity.

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Recently, there has been stronger demands for wireless indoor data networks, which offer flexible interconnections. Optical wireless transmission is expected to be an attractive alternative to wired networkes, because of its high capacity and high flexibility. In this report, we theoretically investigate the signal transmission characteristics of optical wireless indoor transmission, and propose optical wireless indoor communication system that can accomplish high speed transmission by combining optical fiber communication with optical wireless transmission techniques.

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The deterioration of bit error rate is measured when 2 or 3 QPSK signals with various frequency interval are transmitted through nonlinear circuit.

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