A new technique to reduce the dominant phase-induced intensity noise (PIIN) in active high-Q recursive photonic signal processors is presented. This is based on using cross-gain-modulation effects in a semiconductor optical amplifier in the recursive loop of the processor. Two different laser sources are used, and no recombination of the optical power from the same laser source occurs in the optical domain, hence, PIIN generation is suppressed. The processor structure also features the advantage that it does not require an incoherent light source. Hence, the free spectral range of the processor is not limited by the coherence of the laser source, as in existing incoherent approaches. Experimental results for the new processor demonstrate a more-than-30-dB reduction in PIIN level for a high-Q bandpass filter, compared to the conventional approach for the same filtering parameters.
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