HIGH-SPEED CONTINUOUSLY TUNABLE LIQUID-CRYSTAL FILTER FOR WDM NETWORKS

We describe a high-speed wavelength tunable liquid crystal filter whic h can be utilized as the tuning element at the receiving end of wavele ngth division multiaccess (WDMA) optical networks, The filter uses chi ral smectic A electroclinic liquid crystals as the active cavity mater ial in a Fabry-Perot etalon in order to obtain a microsecond switching speed. Using the commercially available BDH764E liquid crystal materi al, we demonstrate a tunable optical filter both in a bulk Fabry-Perot and a fiber Fabry-Perot (FFP) configuration, A bandwidth of about 0.7 nm and effective finesse of 70 were obtained in the FFP configuration , A FFP tuning range of 13 nm with a switching time of less than 10 mu s were measured at the operating wavelength of 1.55 mu m. A theoretic al analysis of the expected filter performance in the FFP configuratio n is given, Diffraction in the Fabry-Perot cavity is identified as the dominant loss factor, resulting in reduced throughput and finesse bro adening, It is calculated theoretically that an effective finesse of 1 30 and a throughput loss of 2.2 dB are achievable for a mirror finesse of 200 and a liquid crystal cavity thickness of 5 mu m, A short waveg uide piece is assumed to be included in the cavity, Other expected los s sources for the filter in the FFP configuration have been calculated , showing negligible effect on the filter performance.