Angular displacement-enhanced heterodyne polarimeter for the measurement of optically active media

We have developed an angular displacement-enhanced polarimeter to measure optically active media such as blood glucose. Traditionally, optical angular displacement induced by optically active media is based on the measurement of intensity change. Instead, we measure phase change. In addition, the phase change is enhanced using the null-detection technique, which is achieved by incorporating a retardation-tunable wave-plate and an analyzer into a custom-made common-path heterodyne polarimeter. The optical common-path setup for the interference of TE and TM waves in our system is employed to reduce noise from the environment. The enhancement of this system can reach to two orders in amplitude when the retardation of the retardation-tunable wave-plate is set to approach 180°. With this polarimeter, the measurement of optical angular displacement with a resolution of 1 × 10−4° has been experimentally demonstrated, corresponding to a 2.5 mg/dl concentration resolution. This approach, based on our knowledge, appears to be the most accurate for phase measurement and has the potential to be a tool for noninvasive glucose monitoring.