Tuneable liquid crystal Fabry-Perot filters

In this paper tuneable optical filters based on liquid crystal Fabry-Perot interferometers (LCFPI) are presented. Liquid crystal (LC) devices are lightweight and suitable for compact arrays with a large number of pixels, as shown in high resolution flat panel displays. The fabricated filters offer a high finesse (119) and a wide tuning range (> 60 nm). The devices are coupled to standard single mode fibers by fiber collimators. For all filters the layer structure of a standard passive LC display is used, adding only two reflective layers. Dielectric mirrors (R = 0.98) are used to achieve high finesse and low insertion losses (-4.8 dB). The cost can be further reduced by using thin gold layers, acting as electrodes and mirrors (R = 0.9) at the same time. The finesse of the Gold-FPIs is about 30 and the measured insertion loss is -10 dB. Additionally, a twisted nematic (TN) structure is investigated. Using this orientation, the polarization dependence of the device is reduced with increasing tuning voltage.