Polarization-independent tunable fiber comb filter

We have demonstrated a polarization-independent tunable fiber comb filter by using both polarization-diversity loop technique and birefringence tuning technique. The proposed apparatus consists of one polarization beam splitter, polarization-maintaining fibers, and three waveplates (one quarter-wave plate and two half-wave plates). The capability of continuously tuning the output spectrum was theoretically analyzed and then experimentally verified.