Pressure and Temperature Dependence of Optical Resonance Wavelength (ORW) of Large-Element Surface-Micromachined Optical Ultrasound Transducers (SMOUTs)

This paper investigates optical resonance wavelength (ORW) shifts in large-element, fiber-tip surface-micromachined optical ultrasound transducers (SMOUTs) induced by changes in ambient pressure and temperature. The displacement behavior of the SMOUT top membrane under varying pressure and temperature conditions is analyzed and modeled, and simulation results are presented for fiber-tip SMOUTs with four diameters (200, 400, 600, and 800 µm). Fabricated and assembled fiber-tip SMOUTs are experimentally characterized using two dedicated setups to measure their reflectivity spectra and ORW shifts over ambient pressures from 80 kPa to 120 kPa and temperatures from 25 °C to 45 °C. The experimental data show good agreement with the simulation results. These findings provide a solid basis for active control and compensation of ORW shifts via pressure and temperature adjustment. By stabilizing the reflectivity spectrum and minimizing ORW drift, the use of non-tunable high-power light sources to interrogate arrays of fiber-tip SMOUTs with enhanced operational stability and sensitivity is enabled.