Coherent FSK experiment using split-contact DFB transmitter laser

The authors report on a novel dual contact DFB laser with a `dog-leg´ p-contact. The FM-response of this laser was measured and found to be uniform from 100 kHz to >4 GHz (limited by measurement set-up). This flat low frequency response was confirmed by using the device as transmitter in a 622 Mb/s and a 1.8 Gb/s coherent FSK experiment where the pattern dependence of the device was compared to that of a commercial single contact device. It was found that at 622 Mb/s a pattern dependent penalty of only 2 dB was incurred for a PRBS of 2²³-1, and at 1.8 Gb/s a penalty of <1 dB was incurred. The lowest frequency component in a 622 Mb/s PRBS of length 2²³ -1 is <1 kHz which indicates that the device has a uniform FM response down to frequencies lower than 100 kHz. These results indicate that multi-electrode devices may be suitable for FSK coherent transmission systems where there is no coding on the transmitted data