Polarization-independent all-fiber birefringent filter with adjustable wavelength spacing

Fiber filter has important applications in fiber sensor and optical fiber communication system.Especially,filter with all-fiber structure and tunable wavelength spacing is worth studying due to its unique characteristics.A polarization-independent all-fiber birefringent filter with adjustable wavelength spacing is proposed.The apparatus consists of a polarization beam splitter(PBS),two sections of polarization-maintaining fiber(PMF),and four half-wave plates(HWPs).The theoretical analysis shows that it operates as a polarization-independent multi-wavelength filter with good channel isolation and adjustable wavelength spacing by controlling the four HWPs in the loop.This filter is applicable for flexible multi-wavelength fiber laser and other optical fiber systems.