Research On Narrow Pass-band Tunable Filters Work In Broad Spectral Range

A narrow pass-band tunable filter working in relative wide spectral range is a key component in spectral imaging instruments. Especially, the development of two-dimension tunable filter is very important for fabricating staring high (hyper) resolution spectral imaging technology. The tunable filter on the development history and research status has done a brief overview, and by comparing the characteristics of several typical filters to confirm the research topics at the focus to birefringence liquid crystal tunable filter (LCTF) and the FP-cavity tunable filter.Birefringence LCTF is the use of nematic liquid crystal cell as a variable phase retarder to build a Lyot-type and Solc-type filter, and these are the two classical types of birefringent filter. Two calculation methods of the birefringent filter were used to elaborate the basic principles of Lyot and Solc filter, and write the computer simulation program to calculate the transmission of the birefringent filter. The filters were designed by theoretical calculation and simulation; the production of liquid crystal cells and the development of control circuit composed the experimental system of the filters; the performance of the filters was measured by associating with the spectrophotometer. Actually, a 3-stage Lyot LCTF, a Solc LCTF and a Lyot and Solc Hybrid LCTF were developed. The encountered or occurred issues in experiments were discussed and some improvements were proposed in this paper.FP-cavity tunable filter with its simple composition, high spectral resolution and other advantages is another important research point of the subject. As the space length of FP cavities is equal to several microns, the phase shift on reflection of mirror need to be considered critically. Through the phase analysis point of view, a study of the spectral characteristics of FP-cavity filters has been done. The required characteristics of the FP cavity-type filter can be obtained rely on the selection of space length and the optimization of high reflection coatings. Then the multi-stage FP-cavity filter system would be designed. The preparation of multi-stage FP-cavity tunable filter simulation program is available and convenient to design multi-stage FP-cavity filters. And a three-stage FP-cavity filter system was proposed for the first time, and the actual device of a three-stage FP-cavity LCTF system was built.Finally the research work was summarized, and some suggestions on tunable filters for further developments and applications were advanced.