Liquid refractive index measurement system by adaptive lens

Refractive index is an important optical parameter of the liquids. Conventional liquid refractive index measurement instruments can be classified into refractometers and interferometers according to measurement methods. These methods are relatively simple. However, the liquid in the measurement instrument is usually in contact with air and is not suitable for measuring volatile and toxic liquids. In this paper, we propose a liquid refractive index (LRI) measurement instrument based on electrowetting lens. The instrument is composed of a light source, a collimating lens, a liquid measurement chamber, an electrowetting lens and an image sensor which is integrated in a cylindrical cavity. After adding the measured liquid, the refractive index of the measurement chamber changes, and the incident light cannot be focused on the image plane. By adjusting the driving voltage of the electrowetting lens, the curvature of the liquid-liquid interface changes to focus the incident light on the image plane. According to the voltage value, we can measure the refractive index of the liquid. The proposed LRI measurement instrument has no mechanical moving parts and the imaging surface remains stationary, which can make the measurement simply and accurately. The experiments show that the measurement range can be turned from ∼1.3300 to ∼1.4040. The instrument can be used to measure the optical properties of liquids and has widely potential applications in chemical reagent detection and pharmaceutical testing.