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

Area of Science:

• Photonics and Waveguide Technology
• Optical Sensing and Metrology
• Materials Science (Titanium-indium-niobium-oxide)

Background:

• Titanium-indium-niobium-oxide (Ti:LiNbO3) optical waveguides are utilized in electric field sensing.
• Environmental temperature variations can affect sensor performance and accuracy.
• Understanding temperature-induced effects is crucial for reliable electric field measurements.

Purpose of the Study:

• To investigate the impact of temperature changes on the static optical power output of a Ti:LiNbO3 optical waveguide electric field sensor.
• To analyze the underlying physical mechanisms, including thermal expansion and thermo-optic effects, contributing to power variations.
• To evaluate the influence of polarization-maintaining fiber (PMF) birefringence on sensor performance across a temperature range.

Main Methods:

• Experimental testing of static optical power under controlled temperature changes (5°C to 35°C).
• Finite element method (FEM) simulations to model light wave modes and electric field components within the waveguide.
• Analysis of thermal expansion and thermo-optic effects on the static operating point (φB).
• Characterization of temperature-dependent birefringence in the sensor's output polarization-maintaining fiber (PMF).

Main Results:

• Static optical power decreased by 866.6 µW over the tested temperature range, causing a 32.79° shift in the static operating point (φB) and >10% electric field error.
• FEM simulations revealed a small Ez component in quasi-TE and TM modes, indicating that both thermal expansion and thermo-optic effects influence φB.
• Calculated contributions: thermo-optic effect (-0.3301°/°C) and thermal expansion (0.0087°/°C) resulted in a static optical power variation of -267.94 µW.
• PMF analysis showed a phase difference change of -3.050 rad/K for a 1488 mm fiber length.
• Combined effects predicted a total static optical power change of -868.86 µW, consistent with experimental findings.

Conclusions:

• Temperature variations significantly degrade the performance of Ti:LiNbO3 optical waveguide electric field sensors.
• Both thermal expansion and thermo-optic effects, along with PMF birefringence, are critical factors causing static optical power instability.
• Accurate electric field measurements require compensation strategies to mitigate temperature-induced errors in these sensors.