Reduction of mode partition noise by using semiconductor optical amplifiers

Multi-wavelength light sources by narrow-band spectral filtering of multi-mode lasers have been studied for wavelength division multiplexing (WDM) applications. Long-wavelength Fabry-Perot (FP) semiconductor lasers provide many modes, whose mode spacing can be fixed with precise frequency by using a mode locking technique. However, increased intensity noise has been observed in the spectral filtering of multi-modes generated by mode-locked semiconductor lasers. This is known as mode partition noise. The noise appears as an extreme increase in the relative intensity noise (RIN) spectrum in low frequency regions. This limits transmission applications because of degradation of signal to noise ratio (SNR). In the paper, we demonstrate reduction of the mode partition noise by using a semiconductor optical amplifier (SOA). 16-dB SNR recovery is reported for spectral filtering of FP lasers.