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

A new technique that can suppress the dominant phase-induced intensity noise (PIIN) in photonic signal processors is presented. It is based on a novel topology for the processor structure that enables bi-directional operation to be obtained, which enables the use of differential detection to be employed for suppressing the PIIN. This technique is simple and it does not affect the signal-processor RF response. Experimental results demonstrate a large phase-noise reduction of 36.7 and 16.5 dB in the passive and active recirculating delay-line filters, respectively. This is the first demonstration of PIIN reduction in multiple-tap recirculating delay-line signal processors.