|
This paper reports a compact yet highly sensitive all-optical acoustic pressure sensor which is designed to operate under a pre-designed resonant mode, targeting to achieve ultra-high sensitivity for underwater applications. It consists of a micro-opto-mechanical silicon cantilever beam which is fabricated by a CMOS-compatible process flow based on a silicon-on-insulator (SOI) substrate, and integrated with a rib waveguide located on the top of the cantilever beam. Two grooves are created on the same substrate and aligned in line with the rib waveguide. Two optical fibers are then fixed into the pre-aligned two grooves on both sides of the rib waveguide, separately, for optical signal coupling in and out. The deflection of the cantilever beam caused by the acoustic waves is transferred to a variation of the output optical intensity from the optical fiber due to the fiber-to-waveguide end coupling strategy. For proof of concept, a silicon cantilever beam with a length of 9.5 mm, a width of 2.5 mm and a thickness of 10 μm is fabricated to provide an ultra highly sensitive acoustic sensor operating at the frequency of 150 Hz. The results show that an acoustic pressure detection sensitivity of 8.34 V/Pa with the minimum detectable acoustic pressures of 35 nPa/Hz1/2 at the designed frequency is successfully demonstrated. The proposed acoustic pressure sensor may be useful in particular applications such as defense and security equipment, as it is different from most existing acoustic pressure sensors which pursue a compromise between high sensitivity and wide working bandwidth.
|
