Liquid-crystal birefringent filter-based Wavelength Blocker/Channel Equalizer for reconfigurable optical networks

Abstract

This paper discusses the design of a Wavelength Blocker/Channel Equalizer (WB/CE) based on stacked liquid-crystal birefringent blocks. Each block, which is optimized to control a predefined channel wavelength, consists of three components. The wavelength blocking/transmitting and the equalizing actions are provided by the liquid-crystal cell (LCC) whose optical path difference varies between two particular values when its birefringence is electrically controlled. Preliminary experimental tests show that for a sample block which is optimized for a channel wavelength λ = 1.55 µ;m, the power transmissivity can readily be equalized. When the LCC is switched to be a half wave plate at λ (VLCC = 10V), then the channel wavelength λ is fully transmitted, whereas when the LCC is switched to have zero phase shift (VLCC = 42V), channel wavelength λ is then blocked. However, if the LCC is tuned to have an intermediate state, the λ-power transmissivity is equalized. The benefit of such a polarization-based WB/CE is that it operates without free space demultiplexing optics and with no moving parts. It can be used as a ROADM subsystem in CWDM or DWDM broadcast and select architectures.