High-speed Tunable Liquid Crystal Optical Filter For WDM Systems

One of the key components in future wavelength-division-multiplexed (WDM) networks is a tunable optical filter. Desirable characteristics for a commercially successful filter include: fast tuning speed, wide tuning range (30-40 nm for systems combining doped fiber amplifiers), low power consumption, and low cost. As an inherently inexpensive technology with low power consumption, liquid crystals (LCs) have the potential to fulfill all of the above req.uirements. Tunable LC Fabry-Perot (FP) filters have been demonstrated using nematic LCs as the active cavity material[l,2]. These filters have a tuning range of -100 nm, however their tuning speed ranges from a few milliseconds to hundreds of milliseconds [:3], which is too slow for packet-switched systems. Another class of LCs, chiral smectic A* LCs, have microsecond and submicrosecond switching speeds, allowing for three orders of magnitude faster tuning over nematic LC filters.