| Birefringent filter is an important tunable optical element, It is an improved version of Lyot filter. When it is placed in a resonant cavity of laser with Brewster angle, its tunable range will larger, tuning facilitates, insertion loss will lower and Anti-damage threshold will become bigger. So it is widely used in Ti: sapphire laser and dye lasers. However, previous studies have focused on tunable wavelength, transmission and narrow spectral width. The research on the other characteristics of BF is short, so there are some limitations to play the full functions of the BF. This paper from the temperature and dispersion characteristics of quartz crystal, analysis the vary law of transmission of BF, then further analysis the temperature effect of BF, to provide the basic theory for the precision design and perfect application of filters.The article is divided into four chapters: Chapter I introduction. Mainly to sum up the development history and current status of the application of Lyot filter, in order to highlight the significance of the issues.Chapter II the basic theory of the quartz crystal birefringent filter. The design structural and working principle of two different types Lyot BF are introduced in the chapter II. There are some theoretical analysis and calculation to solve the various options of each parameter. The transmission equations of two units BF and the transmission formula of the combination BF are presented. The transmission curve is plotted for comparing the transmission spectrum line-width and free spectral range. The perfect tuning and filtering function of the birefringent filter can be seen from the transmittance curve.Chapters III, introduce the temperature and dispersion characteristics of quartz crystal. The temperature properties and the dispersion characteristics of the quartz crystal were analyzed in Chapter III. Since the refractive index of quartz crystal will change follow with the temperature changes, in order to analysis the changing tendency in detail, the dispersion characteristics of the quartz crystal must be solved. The modified Sellmeier equation is used to analysis the dispersion characteristics. The relation equation and the cure between wavelength and refractive index are given. The dispersion characteristics at different temperature can be tested and the changing relation equation between refractive index and temperature can be gotten, above these can provides some theoretical basis for studying the temperature effects of the birefringent filter.Chapter IV the temperature effect of the quartz crystal birefringent filter. The temperature effect of quartz BF is studied in Chapter IV. We can learn from the previous chapter that the refractive index of quartz crystal changes follow with the temperature changes, which Moreover, the line degrees of the filter also changes, all these resulting in the phase retardation changes. The result will enable the central wavelength of transmission belt shift, the center wavelength transmission rate fall down, and introduce an increase of transmission bandwidth. So it is great significance to study quartz BF for correct designing and applying filter.The principle of the units' quartz crystal is equivalent to a delay device, from change phrase retardation to achieve tunable aim, so we can from the temperature effects of retarder to analysis the BF. Firstly we use numerical analysis method to deduce the basic equation between retardation and temperature, and analysis each factor which changing with temperature, then apply software to plot correspond cure chart. In experiment, we put one temperature control device in the spectrophotometer to operate. We can control the voltage to vary temperature environment of filter and change transmission spectra, then the different groups' related data and transmission curves could be obtained.The major working and innovation of the paper consists there parts: Firstly, the temperature and the disperse characteristics of the quartz crystal are comprehensively analyzed, there is a preliminary settlement for the defect of the past without accurate dispersion formula for quartz crystal. And use the dispersion curve to prediction the characteristics of quartz crystal, in order to provide reference for the proper use and design of devices. Then the temperature coefficients and temperature curve of quartz crystal are obtained on the basis of the laboratory tests. From the data's and curves reflect the relations between refractive index of quartz crystal and wavelength, when the temperature is changed.Secondly,on the basis of the first, the principle of temperature effect is applied on the birefringent filter, and the method of numerical analysis is used to study the filter. The relation formulas are introduced, from that the line expansion rate and the impact of temperature coefficient of birefringent index to phase delay also can be gotten, and the linear expansion coefficient of different temperature and different axis orientation are tested. The impact of temperature alteration to transmission of filter can be completely reflected by integrated the phase delay with above two points.Thirdly, we mainly use the spectrophotometer which can be placed a temperature control device to accommodate kinds of filters to operate; the shortcoming of single-source is overcame. The transmission spectrum of filter in different temperature environment is obtained by controlled the voltage, then got different group data and related curve.Major test conducted in the following areas: (1), at the room temperature, the transmission spectrum of unit BF between 400-1200nm, 400-800nm and 880-1500nm dividedly. (2), at the high temperature, the transmission spectrum vary tendency of unit BF between 400-800nm, 880-1500nm dividedly.From theoretical analysis and spectrum, we can see that the thin filter will cause larger line-width at room temperature. With the increasing of thickness, the line-width decrease, and this tendency will remain at high temperature. From the experiment, we can see that the birefringence will change apparently when the temperature higher than 50℃. With the temperature varying, the transmission spectrum will shift from long-wave to the shorter wavelength orientation, and transmission has dropped. The thickness BF will be impacted very obvious, there is larger vary in the transmission spectrum. Compared experimental results with previous theoretical analysis, we can see that the theory match with experiment very well. |
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