A Cascadable Approach to Produce Widely Selectable Spectral Spacing in Birefringent Comb Filters

We demonstrate an approach that allows a good flexibility in controlling the spectral spacing in a birefringent comb filter. Our scheme exploits the bidirectional transit of light in a polarization-maintaining fiber (PMF). The light polarization between the two transits is adjusted to change the equivalent propagation distance. The number of achievable spectral spacings is substantially larger than those demonstrated by previous approaches. Using two segments of PMFs, 12 different spacings that span from 0.27 to 6.08 nm have been demonstrated. The experimental data agree well with our calculated results. The approach is easily cascadable and the number of combinations scales up very rapidly with the fiber segments used in the setup