Suppression of phase-induced intensity noise in optical delay-line signal processors using a delayed differential technique

In this paper, a new technique that can suppress the dominant phase-induced intensity noise (PIIN) in general delay-line signal processor structures is presented. It is based on a delayed differential technique using a complementary output electro-optic modulator together with appropriate time delay and polarization effects to cancel the PIIN noise at the filter passband frequency. Experimental results using the delayed differential technique demonstrate a PIIN noise reduction of 19 dB at the filter passband for an amplified recirculating delay-line bandpass filter, together with a fourfold increase in the free spectral range and a 10 dB increase in the bandpass filter rejection level.