Study On Frequency And Temperature Characteristics Of Elastic-optic Crystal Lithium Niobate

Photo-elastic modulation interferometer, as the core component of photo-elasticmodulation Fourier transform spectrometer, consists of photo-elastic modulator which iscomposed of photo-elastic crystal and piezoelectric crystal. As part of photo-elastic modulator,elastic-photo crystal has a wide selection, among which lithium niobate crystal has theproperties of stable mechanical properties, high temperature resistance, corrosion resistance,excellent nonlinear optical effect, photo-elasticity and piezoelectricity, as well as easyproducing crystal with large size, easy processing and low cost, thus is widely applied inphoto-elastic modulator. However, resonance characteristics of photo-elastic modulatorcauses the drift of temperature-frequency of crystal, thus resulting in instability when systemis running. Therefore lowering the temperature coefficient of lithium niobate crystal is animportant problem demanding prompt solution.To solve the problem of higher temperature coefficient of lithium niobate crystal,meanwhile controlling and compensating for temperature in elastic-optic modulator,according to the characteristics of the properties of lithium niobate crystal relate to crystalcut ,the present study analyzes the frequency temperature characteristic of lithium niobatecrystal resonator in (xyt)φ1cut-length extension vibration mode, deduces the relationshipof temperature with Density of lithium niobate crystals, young’s modulus and expansioncoefficient, and figures out the level temperature coefficient of elasticity, level coefficient oflinear expansion and level density temperature coefficient. The results show that thehigher-order frequency- temperature coefficient can be ignored compared with level-ordertemperature coefficient. Besides, the study gets relationship of first temperature coefficient offrequency of lithium niobate crystal a0and tangent anglesφ1by combining frequency temperature characteristic equation with the frequency equation in (xyt)φ1cut-lengthextension vibration mode. By analysing this curve, the author gets the conclusion that thereexists no zero temperature coefficient in (xyt)φ1cut-length extension vibration mode, whichprovides a theoretical basis for the further study of cut type of lithium niobate crystal,elastic-optic modulator control and compensation of temperature, as well as the eliminatingthe drift of frequency temperature.