Investigations On Optical Homogeneity And Temperature Characteristic Of Magneto-optical Medium Used In Faraday Bias Element

Laser gyro as an ideal apparatus in strap-down inertial navigation system has been widely used in this field. Four-mode differential gyro is the representation of the next generation laser gyro, whose kernel is the Faraday bias element based on Faraday effect. Differential gyro has strict requirements on its elements. Most domestic researches on enhancing the precision of this type of gyro only focus on the characteristics of the laser resonant cavity, but few on the effect induced by characteristics of Faraday bias element. So it is necessary to make investigations on the inner characteristics of Faraday bias element to improve the resolution further.In this thesis, two research subjects are involved: one is the optical homogeneity of magneto-optical medium used in Faraday bias element, and the other is its temperature characteristic. The main works are as follows:(1) A new method for optical homogeneity measurement based on laser resonant cavity theory is put forward and the theoretical model is given. By the use of resonant cavity, not refractive index difference but frequency difference is measured. Using this method, two samples are measured and the order of magnitude of 10^-5 in optical homogeneity is achieved depending on existing experimental equipment. Error analyses to experiment results and factors affecting the results are discussed in detail. The order of magnitude of 10^-6 or higher in optical homogeneity may be achieved depending on more fine F-P scanning interferometer. Compared with the precision of holographic interferomtory, two or more orders of magnitude are improved. The measurement demand to the optical homogeneity of magneto-optical medium can be satisfied easily in Faraday bias element in differential gyro.(2) A temperature-controlled setup is designed and actualized. The eigen rotation and the Verdet constant of the paramagnetic terbium glass Tb20 are measured in 293K-343K. With the temperature goes higher, the eigen rotation increases, ard the explanation for which is given. The theoretical model of the Verdet constant of paramagnetic medium presented by Liu Gongqiang is validated by the phenomenon in experiment that in some temperature range the Verdet constant of the sample decreases with increase of temperature. In addition, the Verdet constant of the terbium glass sample rebounds when the temperature goes higher than 333K, which is out of accord with the theoretical model and need to be further researched. It is found in the experiment result that the Verdet constant of the terbium glass sample in 333K is about 20% less than which in 293K. So temperature compensation must be taken when the terbium glass is used as Faraday bias element medium.(3) Errors in output signal induced by the optical homogeneity and temperature characteristic of the magneto-optical medium used in Faraday bias element in differentialgyro are calculated separately and quantificationally. It is shown that both the two aspects will affect the resolution of gyro, and the aspect of temperature takes worse effect. Therefore, it is very important to choose a kind of medium with high quality to improve the resolution, and the strict temperature compensation to specific kind of medium is also needed.