Temperature response of a fiber end-face integrated lithium niobate crystal probe based on pyroelectric and thermo-optic effects via polarization state modulation

This paper presents the temperature response in a fiber end-face integrated lithium niobate (LN) crystal probe. It is a reflective probe. The fiber end-face integrated with components such as a focusing lens, a quarter waveplate, a cube of LN crystal and a gold mirror. Thanks to the pyroelectric and thermo-optic effects of the LN, the temperature response with a steep change in a narrow range of temperature is observed and it might be exploited in temperature measurement applications. The ambient temperature is mapped to the output light via polarization state modulation (PSM) method. Experimentally, the change of exit beam polarization is measured as the variation of the S1. The experimental results show that the variation of the S1 per unit interaction length which is the sensitivity reaches 5.37 K-1cm-1 in the temperature range of 309.95 K to 316.15 K. It is 447 times higher than that in a polarization-maintaining fiber (PMF). The temperature accuracy is 0.86 K in the range of 311.15 K to 316.15 K which is estimated via the standard deviation between the experimental data and fitting cure. In terms of size, the sensitive material lithium niobate cube has a side length of 2 mm and the total length including all the assembled optical components is 1.7 cm. Due to the compact size and optic signal transmission, the probe might be used in biological domain such as measuring core temperature and in industrial fields such as remote monitoring.