萨那蒙法测量纤维双折射中应该注意的问题

PROBLEMS IN MEASURING FIBRE BIREFRINGENCE BY SENARMONT'S METHOD

纤维双折射的测量有许多方法,但萨那蒙法是最常用方法之一。它只需要λ/4波片和检偏器的转动,就能完成其他方法中专用补偿器的作用。而检偏器转过的角度θ理论上等于相位差角δ的一半(θ=δ/2)。由于萨那蒙法主要是测量非整数部分的相位差值;整数部分由纤维斜切面上干涉条纹数确定,故测量中限制少、精度高。加上光学器件配置简单,使该方法具备方便,快速和精确的特点。但多年来人们认为相位差随纤维厚度变化的单调性,而在实测中忽略了①纤维和光学器件放置方向与检偏器转动方向的关系;②纤维本身结构对补偿转动方向的影响;③纤维和光学器件单一放置测量中的非对称性误差等问题。本文从实验和理论上对这些问题给予必要的讨论。认为由于纤维性质和结构的复杂性,运用萨那蒙法时,应首先已知光学器件和纤维的放置方向,才能正确地判断补偿角的正负性,使测量结果准确无误。同时,通过纤维呈正交的二种放置的实测,证实可消除光路中的非对称影响,使结果更为精确。

Senarmont's method is one of most commonly used methods in measuring fibre birefringence. It only needs a quart wavelength plate and analyzer to make a function of compensator. The rotated angle of the analyzer, in theory, is equal to half of the phase difference. So the birefringence of fibers can be obtained conveniently and accurately by the method. But, up to now, there have been some problems ignored, such as 1) the relationship between the rotating direction of analyzer and the setting direction of a fibre and optical elements, 2) the influence of fibre structure itself on rotating direction of analyzer and 3) how to decrease the asymmetry error caused by the single arrangement of optical elements and a fibre in measurement. In the paper ,these problems are discussed systematically. In my opinion,on using Senarmont's method ,the direction setting optical elements and fibers should be known at first in order to measure correct reults of compensated angles and birefringences. Meanwhile, the experimental results show that the influence of asymmetry in optical way can be reduced by using the two setting way of the fibre, i e. in horizontal and vertical position of the fibre axis.