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 degrees 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. (c) 2005 Elsevier B.V. All rights reserved.