High-performance electro-optically tunable birefringent interleaver filters

Abstract

Tunable interleaver filters are very important in DWDM applications. To be effective, it is required that the filters must possess wide passband (or stopband) width, high isolation, small channel spacing, high tuning speed an so on simultaneously. Whereas, for the small birefringence of all the natural crystals and synthesized crystals, it is quite difficult for the available birefringent interleavers to have the channel spacing smaller than 50GHz and other properties mentioned above simultaneously. This paper proposes a novel electro-optically tunable birefringent interleaver filter, which solves the problem successfully. It is based on cascaded analog birefringent structures. The filter of this configuration can achieve small channel spacing (≤50GHz), wide passband and stopband width (>1/5 period) and high isolation (<-30dB). When voltage is applied on electro-optical crystal plates in analog birefringent structures, the filter also possesses the function of high-speed (submicrosecond) center-frequency tunability simultaneously. A most efficient electro-optic configuration, which needs the lowest operating voltage and has not walk-off effect of extraordinary ray in the crystals, is proposed and analyzed. A prototypical experiment verifies the electro-optic tunability of this filter as well.