Research In The Spectral Transmittance Test System Of Liquid Crystal Tunable Filter Design

Optical filters are spectrum instruments which are used to intercept the spectrum band with a certain width from the continuous spectrum or extract some radiation lines from line spectrum. The liquid crystal tunable filter (LCTF) is an instrument whose transmit light wavelength can be adjusted, which is made basing on ECB and polarized-light interference theory. As the spectroscopy is developing, tunable filters have been widely used in physics, chemistry, biomedical, remote detection, military scouting and other research areas as an important tool for spectral analysis. Since the liquid crystal tunable filter (LCTF) have the advantages of simple principle, ascendant spectral properties and simple production equipment, research institutions in many countries attach great importance and do intensive study on it.In this paper we firstly introduce the principles, advantages and applications of tunable filters, analyzing the ECB, polarized-light interference theory and thoroughly illustrate the principle of LCTF which using a series of Lyot optical filters. We use MATLAB to simulate the transmittance curve of a six-staged Lyot LCTF. We have a deeper understanding of how the related LCTF structure parameters determines LCTF's FWHM(full width at half maximum) and FSR(free spectrum range) by comparing different transmittance curve under various structure parameters. Secondly, we designed a testing system of LCTF, checking the circuit by the testing plan design. The under-test circuit is composed of pre-filter amplification circuit, correlator, integrator, A/D module and microcontroller circuit. Thirdly, using the designed circuit building test system to test on the CRi VariSpec SNIR and VariSpec VIS and then sort out and analyze the experimental data.