| Filter is used to transmit spectrum of definitive broadband in the continuous spectrum or to extract certain radiation in the line spectra. It has an important role in all domains of science and technology. Especially with the development of wavelength division multiplexing and dense wavelength division multiplexing systems which are to improve the transmission speed and capacity in optical fiber communication, tunable filter as an important device of such systems is caused attention by research department.The selection of the wavelength which is realized by the filter is the key function of most the system of wavelength division multiplexing. If certain wavelength can through the tunable filter and others are cut off, the data can be got correctly. If the tunable receiver is required, the filter must be tunable. So basing on diversity theory, there are diversified tunable filters.The mechanical tunable grating filter is realized by a grating and a rotary section. The angle between the incident light and grating is the decisive factor of the transmit wavelength. The tunable performance is obtained by rotating the grating. The disadvantages of the mechanical tunable filter are high control voltage, slow response time and big volume.The electro-optic tunable filters are obtained by the alteration of the birefringence of the electro-optic material applied voltage. The tunable performance can be realized by rotating the electro-optic material in the electric field. Now with the development of the crystal material science, the electro-optic tunable filters are used widely. Basing on the theory of Lyot filter and electro-optic effect of liquid crystal, tunable liquid crystal Lyot filter is designed and tested in this paper. It is proved that it has many attractive features(1) its applicable spectral range is broad, many liquid crystals have very large birefringence and good transparency in both near ultraviolet band, visible band and infrared band.(2) The tenability is determined by the birefringence of the liquid crystal, a large birefringence change can be obtained by a small voltage change.(3) The thickness of the liquid crystal and the arrangement of liquid crystal molecule are flexible, there are no deviation in the outgoing beams.(4) Its used area is wide, its fabrication is simple and its cost is low. Liquid crystal tunable filters as an important device of wavelengthdivision multiplexing and dense wavelength division multiplexing systems is caused attention by research department, especially many foreign research institute are studying it. but in our country its study is lag. and normal incidence of the crystal is almost the case, because the liquid crystal box is very thin, the field angle may be large and the pose of liquid crystal box may have impact on the measuring result .so, study in such subject ,especially the liquid crystal box's position angle, is academic and valuable.The paper has five sections include the basic knowledge and the experiment research, systematically analyses the impact of the liquid crystal box's position angle on the measuring result of liquid crystal Lyot filter and the practical significance of this work.The work of this paper maily includes five sections:(1) The related theory of the crystal birefringence is systemicly introduced in this paper;(2) The theory of the LC voltage-dependent birefringence is introduced;(3) No voltage applied,Changing curve between the transmission and the liquid crystal box direction is got from experiment;(4) Voltage applied, Changing curve between the transmission and the liquid crystal box direction is got from experiment;(5) Desired wavelength is extract from changing the direction of liquid box.Originality innovation of this paper is that the theory of the LC voltage-dependent birefringence is systemically introduced in this paper especially those related to voltage and direction. Changing curve between the transmission and the liquid crystal box direction... |
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