Performance of heterodyne optical OOK systems with coding

The performance degradation of heterodyne optical OOK systems caused by additive receiver noise and phase noise can be substantially overcome by using coding techniques. Using two statistical descriptions of the filtered phase noise process, performance of the coded optical OOK system is evaluated. The results indicate that predictions based on the two phase models closely agree only for sufficiently small ratios of the overall laser linewidth β to the bit rate, namely when βT/M < 2 × 10−2, with T being the bit duration and M the IF bandwidth expansion factor. The analysis further shows that the coded OOK system can attain substantial coding gains; for instance, a coding gain of 10.5 dB is achieved for a rate-1/2 convolutional code of constraint length K = 7 with βT= 0.64 and M= 10.