Investigation on Factors Influencing Flatness of a Bidirectional SOA-based Multiwavelength Fiber Laser

Abstract We investigate the flatness of the output spectrum in two multiwavelength fiber lasers (MWFLs) using two different configurations, unidirectional and bidirectional semiconductor optical amplifiers (SOAs). The most significant finding is the large variance in flatness values between the configurations where the unidirectional SOA is at 6.54 dB and the bidirectional SOA is at 1.45 dB. This is due to the lower total power and incomplete counter propagation in the cavity. The best SOA-based MWFL using a bidirectional SOA can generate 215 spectral lines within 5 dB uniformity. The multiwavelength spectrum is flat with a broad range, about 20 nm, owing to the property of spectral reshaping by the bidirectional amplification process in the SOA as well as complete counter propagation. Apart from the bidirectional SOA, the intensity-dependent loss mechanism also contributes to the multiwavelength spectrum flatness. The adjustment of the half-wave plate in the polarization controller affects the wavelength range and optical signal-to-noise ratio. The MWFL shows excellent power stability, with the highest power deviation being only 0.95 dB.