A multi-wavelength source based on Sagnac loop and semiconductor optical amplifier

Abstract

This dissertation studies the performance and application of Semiconductor Optical Amplifiers (SOAs) as the linear gain medium of Multiwavelength Fibre Laser (MWFL) in conjunction with a Polarization Maintaining Fibre (PMF) based Sagnac Loop Mirror (SLM). Multiwavelength sources such as these are highly useful as signal sources for their low cost-per-wavelength and their compatibility with the normal silica-based optical fibres used for transmission in modern optical networks. Furthermore, the SOA is an inhomogeneous gain medium and thus the OAbased MWFL does not suffer from the effects of mode-competition and suppression, as compared to Erbium Doped Fibre Amplifier (EDFA)-based MWFLs where the EDFA used as the linear gain medium has the disadvantage of being a homogenous gain medium and thus susceptible to the effects of mode-competition. The SOA is characterised for small (-30 dBm) and large (0 dBm) signal gains and it is determined that the best gain obtainable is 20 dB with a noise figure of 6.5 dB for the small signal and a gain of 10 dB and noise figure of 7 dB for the large signal while the peak ASE power obtained is – 23 dBm. The optimum length of the PMF to create the SLM is determined to be 2.86 m to create a MWFL with a channel spacing of 2.00 nm and a PMF length of 3.81 m to create a MWFL with a channel spacing of 1.50 nm. The SOA based MWFL is tested with a linear and ring cavity. The linear cavity can generate up to 6 dominant and well tructured lasing wavelengths at a channel spacing of 2.40 nm and 9 dominant and well structured lasing wavelengths at a channel spacing of 1.67 nm, with both sets of wavelengths having a Signal-to-Noise Ratio (SNR) of above 35 dB. The ring cavity MWFL also generates up to 6 dominant and well structured lasing wavelengths at a channel spacing of 2.40 nm and but at a channel spacing of 1.67 nm 10 dominant and well structured lasing wavelengths are obtained. Both sets of wavelengths have an SNR of above 35 dB. The linear and ring cavity MWFLs are also examined using the EDFA as the gain medium, and in this configuration the SNR of the output multiwavelength comb drops to 18 dB, although the channel spacing is unchanged from that of the SOA based MWFL.