Bidirectional Optical Fiber SSB Data Communication System Constructed Using a Pair of Edge-Emitting LED Modules and a Pair of Wire-Cable SSB Data Transmitters

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  • 通信線搬送装置を用いた双方向SM光ファイバSSBデータ通信システム
  • ツウシンセン ハンソウ ソウチ オ モチイタ ソウホウコウ SM ヒカリ ファ

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Abstract

This paper describes a bidirectional single-mode (SM) optical fiber SSB data communication system consisting of a pair of optical transmitters, each transmitter constructed using an edge-emitting LED (ELED), a pair of optical receivers, a pair of single-mode optical fibers, each having a length of 12km, and a pair of wire-cable SSB data communication systems for use with coaxial cables. A pair of 12 channels are assigned to SSB data at frequencies of 12kHz through 60kHz in the lower frequency band on the up-going link, and of 72kHz through 120kHz in the higher frequency band on the down-going link, respectively. In each optical transmitter, SSB data is fed to the squarewave frequency (SWIM) modulator constructed using a voltage controlled oscillator (VCO) having a center frequency of 3.7MHz. The output of the SWFM modulator is fed to the edge-emitting LED (ELED) module through the ELED drive circuit. The light beam of the ELED module is fed to the SM optical fiber. In each optical receiver, the light beam received through the SM optical fiber is detected by the PIN photodiode module, and fed to the SWFM detector consisting of a digital delay circuit and an EX-OR gate, which converts the SWFM signal voltage into the double pulse frequency modulation (DPFM) signal voltage which includes the baseband component of SSB data. The DPFM signal voltage at the output of the SWFM detector is fed to the lowpass filter (LPF) where SSB data is obtained. The optical transmitter and receiver, whose power is supplied from a DC-DC converter, are housed in a transmitter-receiver unit. When the transmission was experimentally carried out, spurious was as low as -50 to -70dB on each channel, and SNR was as high as more than 65 to 70dB. The proposed optical communication system was improved when the transmission signal quality was compared with that of the coaxial cables system, and the construction was simple at low cost because of the use of the ELED instead of the LD.

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