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Recent Progress on PSK Coherent Systems at Fujitsu Laboratories

PSK coherent systems are very attractive because of their highly sensitive characteristics and widely applicable features. In this paper, our recent progress on various modulation/demodulation schemes of optical PSK /DPSK systems are described. High receiver sensitivities of -46.9 dBm for 1.2 Gb/s DPSK, -52.5 dBm for 560 Mb/s DPSK and -51.6 dBm for 560 Mb/s carrier recovery PSK have been achieved using external fiber cavity DFB-LD modules and a balanced optical receiver. Transmission experiments over 200 km of single mode fiber have been performed using these systems. To overcome the signal fading caused by polarization fluctuation in the transmitting fiber, a polarization diversity receiver was developed and demonstrated for 1.2 Gb/s DPSK transmission over 100 km of single mode fiber. A phase-noise-canceling demodulator using carrier recovery was also developed and an effective suppression of the laser phase noise by this demodulator was confirmed. This scheme is applicable to a demodulator for multi-value PSK transmission. Also described are a multi-channel transmission of HDTV signals using a DPSK polarization diversity tunable receiver, and an image rejection receiver for optical frequency division multiplexing heterodyne transmission.