NOVEL OPTICAL FREQUENCY-DISCRIMINATOR FOR FM NOISE-REDUCTION OF SEMICONDUCTOR-LASERS

A compact and highly-reliable optical frequency discriminator is proposed for the FM noise reduction of semiconductor lasers. This discriminator provides the error signal for locking laser frequency to the center of a resonant spectral profile of a Fabry-Perot interferometer (FPI) without any modulation techniques. The gain of this discriminator is 10 dB larger than that of other discriminators using the slope of a resonant profile of a FPI. The phase delay of the discriminator is only 90-degrees. For the high-gain and fast electrical negative feedback loop, these properties are superior to those of the others. To demonstrate the feasibility of this discriminator, the spectral linewidth of a semiconductor laser was reduced from 6 MHz to 250 kHz.