Enhanced Underwater Acoustic Detection via Microring Resonators on a Multiscale MEMS–Nanoimprint Platform

Microring resonators (MRRs) offer the advantages of easy integration and broad bandwidth for acoustic sensing applications, but they face challenges such as low sensitivity and complex, high-cost fabrication processes. In this paper, we propose polymer-based MRRs using a composite diaphragm to enhance the underwater acoustic sensitivity, based on the significant geometrical deformation of the MRR on the acoustic-sensitive composite diaphragm, along with a polymer refractive index change induced by the photoelastic effect. The devices are manufactured via a novel multiscale fabrication platform that synergizes MEMS techniques for micron-scale diaphragm patterning with high-throughput nanoimprint lithography (NIL), potentially enabling nano-scale optical waveguide features at wafer-level scalability and much lower cost than conventional deep-ultraviolet (DUV) and E-beam lithography approaches. Experimental results show that the sensors effectively respond to underwater acoustic waves ranging from 10 Hz to 10 kHz. They exhibit an average acoustic pressure sensitivity level of −185.9 dB re 1 V/μPa from 10 Hz to 1 kHz, with a flatness of 2.6 dB, representing a ∼32.1 dB improvement compared to traditional devices. The noise equivalent pressure (NEP) is 95.5 dB re 1 μPa/√Hz, corresponding to a minimum detectable pressure of 59.8 mPa/√Hz at 1 kHz. These miniature optical acoustic sensors show great potential for accurate underwater target detection and positioning for future underwater vehicles and robotics.