Real-time ultrasound sensing with a mode-optimized photonic crystal slab

TL;DR

This paper presents a mode-optimized photonic crystal slab sensor with enhanced sensitivity and real-time ultrasound detection capabilities, suitable for medical diagnostics and tissue monitoring.

Contribution

It introduces a low-loss polymer cladding and mode optimization in PCS to improve ultrasound sensing performance and scalability.

Findings

Achieved a noise equivalent pressure of 170 Pa.

Demonstrated real-time ultrasound sensing with high sensitivity.

Enabled potential for scalable 2D ultrasound sensor arrays.

Abstract

Integrated photonic sensors can provide large scale, flexible detection schemes. Photonic crystal slabs (PCS) offer a miniaturized platform for wideband, sensitive ultrasound detection by exploiting the photoelastic effect in water. However, poor modal overlap with the sensing medium and non-negligible absorption loss of the aqueous medium have previously limited PCS sensor performance. In this study, we detail the development and optimization of a PCS-based acoustic sensor, by adding to it a low-loss high-index polymer cladding layer. Exploiting a mode-optimized TM-like optical resonance present in a PCS, with high bulk index sensitivity (>600 nm/RIU) and quality factor Q (>8000), we demonstrate real-time ultrasound-sensing at a noise equivalent pressure (NEP) of 170 Pa (1.9 Pa/rt Hz). The PCS sensor is backside-coupled to optical fiber which, along with its intensity-based ultrasound-sensing architecture, will allow us to scale up easily to a 2D array. This work paves the way to a sensitive compact ultrasound detector for photoacoustic-based diagnostics and monitoring of tissue.