Research Of Tunable Optical Filter Based On LCOS

With the development of intelligent optical network, multi-rate tunable all-opticalnetwork is becoming a hot research topic, which needs support of tunable optical filter withvariable center wavelength and the bandwidth and other core optoelectronic devices. LiquidCrystal on Silicon (LCOS) technology in the application of tunable optical filter become oneof the main characters, it provides advanced programmable functions in computer, and canimprove channel filtering characteristics with the specific applications. By theoretical andexperimental analysis, the LCOS-based tunable optical filter is studied in this thesis, asfollows:By studying the principle of electric-control phase delay of liquid crystal molecules andliquid crystal phased array, implement methods of discrete steering angle and continuoussteering angle are obtained. Angle of discrete beam steering is limited and uneven distributed,while in the circumstances of continuous beam steering, the number of steering angle issharply increased and deflection precision is greatly improved. And then, two models forcharacterizing the spectral respond of the passband of LCOS are presented, in the commonlyused approach of supergaussian model, fitting routine only guarantees that the data points atthe m-dB bandwidth are met, but does not match the slope of the curve, we must sweep theparameter of gaussian-order and then determine the best fit to measurement. In the approachof error function model, the optical transfer function (OTF) bandwidth ultimately determinesseveral of the key parameters for the final device filter shape, error function model offers amore complete match to measured results.Light path of1×4LCOS-based optical filter is designed in detail, parameters of thefilter system, such as loss, crosstalk, receiving efficiency, input and output fiber arraystructure and so on are calculated. From the result of calculation, continuous beam steeringbased on LCOS has the advantage of achieving precise coupling. Then the experiments ofthe LCOS-based optical filter are done, the experimental results show that single channelloss is less than6dB, crosstalk is below-36dB, from which we can see the obvious effectof wavelength selection.The implement of LCOS for2-dimensional beam steering is presented. Based onthe theoretical analysis, a novel LCOS-based optical filter which can realize4×4 demultiplexing in space division multiplexing(SDM) and wavelength division multiplexing(WDM) transmission system is proposed.