Study Reveals Optimal Waveguide Designs for Photonic Ultrasound Sensors

A recent study conducted by researchers from various institutions, including IHP – Leibniz-Institute for High Performance Microelectronics and Technische Hochschule Wildau, has delved into the realm of photonic ultrasound sensors based on silicon waveguides. This study aimed to compare and analyze three different design approaches for pressure-sensitive waveguide architectures on SOI platforms.

The first approach, designated as (A), involved a flexible silicon membrane placed above a silicon waveguide, where the detection mechanism relied on the geometrical change induced by an applied pressure. The study revealed that this design approach offered the highest sensitivity limit, with the TM mode exhibiting almost three times higher sensitivity compared to the TE mode.

In contrast, design approach (B) utilized a silicon waveguide positioned on top of a silicon dioxide membrane (BOX). Although this approach showed the lowest sensitivity values, it demonstrated simplicity in processing, making it a feasible option for sensor development.

Design approach (C) incorporated a polymer cladding, specifically PDMS, covering the silicon waveguide. This approach leveraged the strong photoelastic response of the cladding material, resulting in significantly higher sensitivity values compared to approach (B). Interestingly, the TM mode within a strip waveguide exhibited about twice the sensitivity of the TE mode.

The study also investigated the sensitivity of the example micro-ring resonator (MRR) configurations, considering dispersive coupling conditions. The results indicated that the SOI platform serves as a suitable foundation for miniaturized ultrasound sensors, with silicon nitride waveguides showing slight variations in sensitivity compared to silicon waveguides.

Overall, the simulation-based analysis provided valuable insights into the comparative performance of the different design approaches, aiding in the selection of optimal waveguide geometries for future advancements in photonic integrated ultrasound sensor technologies. The research sheds light on the potential for enhanced sensitivity, bandwidth, and integration capabilities in biomedical imaging and other ultrasound sensing applications.