Multi-wavelength fiber lasers have attracted a lot of interest, recently, because of their potential applications in
wavelength-division-multiplexing (WDM) systems, optical fiber sensing, and fiber-optics instruments, due to their
numerous advantages such as multiple wavelength operation, low cost, and compatibility with the fiber optic systems.
Semiconductor optical amplifier (SOA)-based multi-wavelength fiber lasers exhibit stable operation because of the SOA
has the property of primarily inhomogeneous broadening and thus can support simultaneous oscillation of multiple lasing
wavelengths. In this letter, we propose and experimentally demonstrate a switchable multi-wavelength fiber laser
employing a semiconductor optical amplifier and twin-core photonic crystal fiber (TC-PCF) based in-line interferometer
comb filter. The fabricated two cores are not symmetric due to the associated fiber fabrication process such as nonuniform
heat gradient in furnace and asymmetric microstructure expansion during the gas pressurization which results in
different silica strut thickness and core size. The induced asymmetry between two cores considerably alters the linear
power transfer, by seriously reducing it. These nominal twin cores form effective two optical paths and associated
effective refractive index difference. The in-fiber comb filter is effectively constructed by splicing a section of TC-PCF
between two single mode fibers (SMFs). The proposed laser can be designed to operate in stable multi-wavelength lasing
states by adjusting the states of the polarization controller (PC). The lasing modes are switched by varying the state of
PC and the change is reversible. In addition, we demonstrate a tunable multi-wavelength fiber laser operation by
applying temperature changes to TC-PCF in the multi-channel filter.