We report in this paper the principal function of the electrically controlled variable optical attenuator (VOA) using polymer dispersed liquid crystal (PDLC) and describe the fabrication procedure on silicon v-groove. We have fabricated three VOA with a pitch of 2 mm on a single silicion v-groove chip with total dimensions of 12 mm x 10 mm. We have achieved a cell-dependent contrast ratio from 8 dB to 14 dB by applying a control voltage URMS (squared wave voltage, f = 10 kHz) from 0 to 30 V. We measured also a cell-dependent polarization dependent loss (PDL): < 3.6 dB for two cells and < 1.6 dB for one cell depending on the control voltage. The strong variation of the PDL and contrast ratio is due to the non-optimized PDLC processing parameters. Due to the large pitch size there is no crosstalk. The estimated power consumption is very low (< 1 μW), so the described fabrication procedure meets the requirements low cost, small power consumption and compact size. We have used this three VOA and proper chosen delay lines to build up a liquid crystal phase shifter (LCPS) for optically generated RF-signals at fRF = 2 GHz. Using the vector sum of two signals a continuously 360° phase shift of the RF-signal is demonstrated. We will present the theory and measurement results of 360° phase shifting. This LCPS can be used to control individually the phase and amplitude of each antenna element.
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. 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.