Phase-Preserving Amplitude Noise Compression of 40 Gb/s DPSK Signals in a Single SOA

Wavelength-preserving and wavelength-converting amplitude regeneration of 40 Gb/s DPSK data in a saturated semiconductor optical amplifier (SOA) with limited excess phase noise feature is reported and investigated. By injecting simultaneously in the amplifier the noisy data and a CW beam with proper power levels, both the pass-through (PT) signal and the wavelength-converted data by four-wave-mixing (FWM) can be regenerated. The strongest regenerative effect is observed for the converted FWM data. The effect of input power variations on the regenerative performance of the device is thoroughly investigated in terms of Bit-Error Rate (BER) versus threshold margin improvement. We observe that regenerative behavior is attained for different levels of the data and CW power levels at SOA input. Experimental investigation of small-signal amplitude and phase SOA response reveals indeed the role of data/CW power balance for reducing the impact of excess phase noise from the amplifier. The analysis also confirms the stronger regenerative capability of the FWM process due to the strong amplitude-limiting SOA response at lower input data power in respect to the PT signal. The scheme offers the advantages of simplicity, compactness, and low operating power levels, making it a practical candidate for all-optical regeneration of high-speed DPSK signals.