Temperature stability analysis of a Ti:LiNbO₃ optical waveguide electric field sensor

The output static optical power of the developed <i>y</i>-cut <i>z</i>-propagation <i>T</i><i>i</i>:<i>L</i><i>i</i><i>N</i><i>b</i><i>O</i>₃ optical waveguide electric field sensor has been tested under the temperature changes from 5°C to 35°C. The results show that the static optical power has decreased for 866.6 µW, corresponding to a change of 32.79° in the static operating point <i>φ</i>_B and an electric field measurement error exceeding 10%. Based on the finite element method, the light wave modes in the optical waveguide have been simulated. The results reveal that there is a small <i>E</i>_z component in both the quasi-TE and TM modes, causing <i>φ</i>_B to be affected not only by the thermal expansion effect but also by the thermal-optic effect. It has been calculated that the effects of thermal-optic and thermal expansion on <i>φ</i>_B are approximately -0.3301^∘/^∘<i>C</i> and 0.0087°/°C, respectively, resulting within 5-35°C, the static optical power variation is approximately -267.94µ<i>W</i>, with a rate of change is -8.93µ<i>W</i>/^∘<i>C</i>. Furthermore, the influence of temperature on the birefringence of the sensor output polarization-maintaining fiber (PMF) has been considered and analyzed. It has been found that the phase difference of the slow and fast light waves changes by -3.050<i>r</i><i>a</i><i>d</i>/<i>K</i> when the length of the PMF is 1488 mm. As a result, considering the effects of thermo-optical and thermal expansion as well as the influence of the PMF, the sensor output static optical power changes -868.86µ<i>W</i>, with temperature changes from 5°C to 35°C, which is consistent with the experiment results.