Variable optical attenuator for perfluorinated gradual index polymer optical fiber using a polymer dispersed liquid crystal cell

Abstract

A Variable Optical Attenuator (VOA) based on a Polymer-Dispersed Liquid Crystal (PDLC) Cell is presented. The VOA's developed prototype has been successfully tested at 660nm, 850nm and 1300nm. This ability makes it strongly recommended for networks using Perfluorinated Gradual Index Polymer Optical Fiber (PF GI-POF) technology. The prototype has revealed a better than 12dBs dynamic range and losses of <1.2dB. In addition, the VOA presents a very low power consumption and non-dependendence with polarization. In order to avoid the dependence with temperature, an electrooptical feedback is incorporated to the device, by means of a microcontroller system. Electrically controllable intermediate transmission levels can be selected this way. The response time is in the milisecond range. The present feedback prototype, developed with POF technology, includes lenses, PDLC, 1x2 POF couplers and fotodiodes in the optical part, and a microcontroller system where the feedback processing is carried out. No polarizers are required so that optical losses are minimal. Polymer-Dispersed Liquid Crystals are formed by microdroplets of liquid crystal embedded in a flexible matrix, and sandwiched between transparent electrodes. This structure scatters strongly the light. When an AC electrical field is applied to the film the material becomes transparent. A largest dynamic range could be achieved designing conveniently the radius of the microdroplets. No-dependence with polarization, high transmittance when activated, and large dynamic range within a wide range of optical wavelengths make PDLC the most appropriate liquid crystal technology for VOAs fabrication.