Modeling and Demonstration of Thermally Stable High-Sensitivity Reproducible Acoustic Sensors

Abstract

A thermally stable high-sensitivity compact fiber acoustic sensor with a large bandwidth and a high dynamic range is introduced. The device is based on a photonic crystal fabricated on a compliant single-crystal silicon diaphragm, which is placed near the metalized end of a single-mode fiber to form a Fabry–Perot (FP) cavity. High reproducibility in operating wavelength ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex></formula> 1 nm) is enabled by assembling the sensor in a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{SiO}_{2}$</tex></formula> chip using room-temperature sodium silicate oxide bonding. We demonstrate ten FP sensors with measured displacement sensitivities within <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex></formula> 0.6 dB. The response is shown to be polarization independent and thermally stable, with a thermal coefficient of the operating wavelength of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$2.9\ \hbox{pm}/^{\circ}\hbox{C}$</tex></formula> over more than 50 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula> . An experimental sensor is shown to measure acoustic pressures down to a record low of 5.6 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{Pa}/\surd\hbox{Hz}$</tex> </formula> at 12.5 kHz with a flatband response greater than 8 kHz and a sensitivity extending down to at least 100 Hz. The dynamic range in pressure is greater than 100 dB. An electromechanical model of the device response is presented and shown to be in good agreement with experimental results. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hfill$ </tex></formula> [2011-0381]