Study Of Tunable Optical Filters Based On Liquid Crystals

With the development of the modern information society,Tunable optical devices also become an indispensable performance optimization of all-optical networks.Tunable filters,which can screening the signal of one or more wavelengths at any time,and it also can be used for wavelength conversion,transmission performance monitoring and reconfigurable optical add drop multiplexer.In order to adapt to the development of the dense wavelength division multiplexing,and to make it reduce the photoelectric conversion link communication at the same time,the technology of optical filter is also in constant development to more perfect following DWDM technology.Optical tunable filter is an important component of all-optical networks in the future.Because the liquid crystal is a kind of optical materials with anisotropy,Birefringent characteristics makes it be sensitive to the changes of the external parameters,Such as electromagnetic field,temperature,pressure etc.So we choice the liquid crystal as the material composition of tuanable optical filter,it has much more prominent feature,Such as easy integration,small volume,high stability,low power consumption.In addition,the price of liquid crystals is cheap,and easily available.Therefore,it has important theoretical and practical significance that we choice liquid crystal as raw materials of filters.This paper is based on liquid crystal to study the fabrication about bandpass filter and bandstop filter.At first,I research the tuanble temperature-controlled optical filters based on different configurations with cholesteric liquid crystals.I study the deepen bandgap and broaden bandgap filters.For deepen bandgap,the transmission is reduced from 45%to 3.2%,the central wavelength is shifted 42nm to short wave,and for broaden bandgap filter,the bandwidth is broadend by 50%compared to single cell.Then we study the electronic-controlled experiment,and put forward a new structure of electric field to adapt to the helical structure of liquid crystal.The electric-controlled expriment based on new liquid crystal cell,which improve the threshold voltage of liquid crystal,make the shifting range central position of central wavelength larger than before.At last,by the way of simulation,we confirm implementation of tunable filter based at the end face of fiber end-coated chosing the air and liquid crystal as defect layer.Then we chose the air layer as the defect layer in the experiment.Through tuning the thickniess of air layer,we can make shift the centre of transmission spectrum,the moving range is about 60nm.