Performance of an optical DFSK system using optical self-heterodyne detection

The performance of an experimental 45 Mb/s optical differential frequency shift keying (DFSK) system using optical self-heterodyne detection (OSHD) has been evaluated. In OSHD, the intermediate frequency is obtained by mixing the received optical signal with its delayed version. Therefore, in such a receiver, an optical local oscillator is not required, which greatly simplifies the receiver design. It has further been demonstrated that a DFSK system can use transmitting laser diodes with linewidths up to 0.5 times the bit rate. A two-channel DFSK system has also been studied; the two channels were wavelength division multiplexed using an optical coupler. The bit error rate as a function of received optical power has been measured for a one-channel and a two-channel DFSK system.