Analysis of direct-discrimination of FSK modulated optical signal using injection-locked DFB lasers

Direct discrimination of FM and FSK optical signals using injection-locked DFB semiconductor lasers is analysed. The demodulation efficiency is found to be independent of the optical injection level in the steady state. However, the optical injection level is important in determining the dynamic response. There exists an optimum optical injection rate to achieve the highest demodulation speed. The noise analysis revealed that the signal to noise ratio of this method is of the same order as that of the passive interferometer demodulation method