LC-based Tunable Lyot Narrow-band Filter Work In Wide Spectrum Range

Optical filters are spectrum instruments which are used to intercept specified spectrum information from the continuous spectrum of a 2-D image. In early period, Optical filter was used in astronomic observation. But as developments took place in spectrum science, optical filters have been used in physics, chemistry, biomedical, remote sensing, military scouting, as important spectrum instruments. Birefringence interference filters (BIFs) have been given considerable attention by researching institutes in many countries, due to the advantages in simple principle, excellence spectrum performance and simple assembling. BIFs have been researched deeply in Europe and U.S, and products were developed and employed. But the researches in BIF haven't gone far enough in China. This paper is to design and assemble a tunable narrow band BIF which can work in whole visible spectrum.The first part of this paper introduces the principles and structures of kinds of optical filters. Tunable BIF systems were thoroughly introduced, including the Lyot type BIF and Sole type BIF. Tuning methods were also introduced, including mechanical rotating method and liquid crystal (LC) electronic controlling method. After comparison of these systems, and according to our school's technical foundation in LC research, LC based Lyot type tunable filter system was adopted because of its simplicity in assembling.The second part introduces the designing of this system, including optical elements designing and electronic circuit designing. In optical designing, a method was carried out aiming to make most use of LC birefringence to achieve best spectrum resolution performance. A six-stage Lyot tunable BIF was designed using this method, and was emulated by software. A circuit was design to achieve the ability of program controllable tuning, the main parts of this circuit are microcontroller and multi-way D/A converter.The third part introduces the assembling and testing of this system. Firstly, the assembling of six single-stage Lyot tunable BIFs is introduced, and experiment results were given. The results were analyzed, and the LC birefringence characteristic was achieved. Second, the six-stage Lyot tunable BIF was assembled and tested. A method using silicon oil to improve the system's transmission performance was introduced, and was proved by experiment.Finally, the whole work is summarized, and further improving direction was given.