Design of a gain-controlled tuneable comb filter for multi-wavelength fibre lasers

This paper describes the design and operation of a birefringent Sagnac loop filter (SLF) to select a comb of uniformly spaced wavelength channels. A SLF is designed with a 100 GHz channel spacing and it is shown that by placing a polarization controller (PC) at one end of the SLF, both gain and channel wavelengths of the comb filter can be controlled. The filter is also used in a fibre ring laser to produce a tuneable multi-wavelength spectrum which can find potential applications in optical communication and fibre optic sensing.