A polarimetric glucose sensor using a liquid-crystal polarization modulator driven by a sinusoidal signal

Rather than using a conventional Faraday modulator, this study adopts a liquid-crystal based rotator to modulate the azimuth of the linear polarized light in a sinusoidal signal for the measurement of glucose concentrations. The tilt angle of the LC director would vary as a sinusoidal-like function; however the modulating frequency in the sensing system is the double of the driving signal. A new signal demodulation algorithm, therefore, is developed that enables the polarization rotation angle corresponding to the glucose concentration to be derived. The standard deviation in rotation angle level of 0.00551° has been obtained, with a 0.998773 correlation coefficient between the reference and the measured values. The proposed measurement method has a minimum resolvable concentration of 0.2 g/dl. Compared to its conventional counterparts, the developed polarimeter potentially has a simpler structure, fewer optical elements, and a cheaper modulator component.