Analysis of Embedded Optical Interferometry in Transparent Elastic Grating for Optical Detection of Ultrasonic Waves

Abstract

In this paper, we propose a theoretical framework to explain how the transparent elastic grating structure can be employed to enhance the mechanical and optical properties for ultrasonic detection. Incident ultrasonic waves can compress the flexible material, where the change in thickness of the elastic film can be measured through an optical interferometer. Herein, the polydimethylsiloxane (PDMS) was employed in the design of a thin film grating pattern. The PDMS grating with the grating period shorter than the ultrasound wavelength allowed the ultrasound to be coupled into surface acoustic wave (SAW) mode. The grating gaps provided spaces for the PDMS grating to be compressed when the ultrasound illuminated on it. This grating pattern can provide an embedded thin film based optical interferometer through Fabry–Perot resonant modes. Several optical thin film-based technologies for ultrasonic detection were compared. The proposed elastic grating gave rise to higher sensitivity to ultrasonic detection than a surface plasmon resonance-based sensor, a uniform PDMS thin film, a PDMS sensor with shearing interference, and a conventional Fabry–Perot-based sensor. The PDMS grating achieved the enhancement of sensitivity up to 1.3 × 10−5 Pa−1 and figure of merit of 1.4 × 10−5 Pa−1 which were higher than those of conventional Fabry–Perot structure by 7 times and 4 times, respectively.

Tunable Optical Diffusers Based on the UV/Ozone-Assisted Self-Wrinkling of Thermal-Cured Polymer Films

“…To our knowledge, UV/ozone-assisted thermal-cured self-wrinkling micropatterns for the application of tunable optical diffusers have not been studied, which is promising for stretchable optoelectronics. In this regard, ubiquitous PDMS is an ideal flexible optical device substrate because of its exceptional light transparency, stretchability and oxidizability [ 23 , 24 ].…”

Fabry–Perot Resonance in 2D Dielectric Grating for Figure of Merit Enhancement in Refractive Index Sensing

“…In recent years, optical resonators [ 1 , 2 ] are one of the favored structures in sensors for sensing applications, such as biomedical sensing [ 3 ], refractive index sensing [ 4 ], and ultrasonic detection [ 5 , 6 , 7 ] due to their high-quality factor (Q factor) of the narrow resonant mode [ 8 ], which arises from resonant cavity [ 9 ].…”