Performance of a 45 Mb/s optical DFSK system using self-heterodyne detection

An optical differential frequency shift keying (DFSK) system with self-heterodyne detection (SHD) operating at 45 Mb/s is demonstrated. One of the major advantages of the DFSK system is that it does not require an optical local oscillator (laser diode) at the receiver. This reduces the complexity of the receiver design and lowers the system cost. It is shown that the system can tolerate a source linewidth-to-bitrate ratio of 0.5. The bit error rate (BER) is obtained as a function of received average DC optical power for different transmitted sequences, and the effect of long strings of zeros and ones in the data stream on receiver performance is analyzed. The effect of laser phase noise (linewidth) on broadening of the intermediate frequency (IF) spectrum is investigated by determining the BER characteristics for two IF filters with 3-dB bandwidths of 300 MHz and 500 MHz. For a 101010 . . . data sequence, a BER of less than 10/sup -9/ is obtained.<>