I. Introduction
When the linearly polarized light transmits some transparent medium, the polarization plane of the incident light will rotate along the propagation direction, which is called optically active phenomenon [1]. The polarimeter is an instrument used to measure optical rotation angles. With the development of polarization measurement technology, the polarimeter is widely used in such as health care, biomedical analysis, and sugar industry [2]. Usually, a polarized rotation measurement is based on extinction method, and some movable optics are required to determine the maximum or minimum extinction position, either manually or mechanically. For example, a stepping motor is employed in a polarimeter to rotate the polarizer to get the maximum extinction position for an optical rotation angle detection [3]. It is simple and low cost but low sensitivity and poor precision as well, and it cannot realize a high-speed real-time measurement. A methodology based on photo-elastic modulation (PEM) [4] is a manual one, and its stability and accuracy are badly sensitive to birefringence and light loss. What’s worse, a polarimeter with movable optics rotated has defects of poor accuracy and short service life. To avoid any component rotation, some novel methods have been put forward. A Mueller matrix polarimeter using dual PEMs [5] is applied for measuring glucose concentration in the presence of a scattering effect, but it is hard to meet the requirement of two PEMs with identical optical characteristics. A real-time, closed-loop, and dual-wavelength polarimetric system [6]–[8] with high sensitivity is proposed for ascertaining the blood glucose levels, but it requires too many optical devices and makes the system too complicated. Based on the birefringent prisms and diode lasers [9] a polarimeter achieves over ±45° rotation angle measurement, but it has a defect of optical power dependence, so the measurement is easily affected by the fluctuation of the light source. A heterodyne polarimeter [10] and an internal reflection-based polarimeter [11] are compact and simple, but their resolution is as low as 10−2deg/mm.