Exploring Polymer geometries for integrated Photonics Ultrasound Sensors

Abstract

Silicon Photonics is a dynamic field of research for developing new sensing technologies. In the domain of biomedical imaging, much effort is put to design photonic sensors as an alternative to commonly used piezo transducers for detecting ultrasounds. Piezo transducers are popular due to their cost effectiveness but they have some disadvantages such as limited bandwidths, difficulty of miniaturisation for achieving higher image resolutions and high sensitivity to electromagnetic noise. On the other hand, photonic sensors can achieve much higher bandwidths, be easily miniaturised and are more energy efficient. The most common photonic sensing device is the micro ring resonator (MRR). When a laser light propagates inside them, for certain laser wavelengths, resonance occurs and causes a sharp change of light intensity. Whenever an ultrasound wave hits the ring resonator, deformation occurs and causes a shift of the resonant frequency. This amount of shift is tracked to characterise the ultrasound wave. Currently, MRRs are not sufficiently sensitive for detecting weak ultrasounds. Therefore, this project was aimed at improving ring resonator sensitivity to ultrasounds by applying a patterned polymer layer on top of a MRR.

To study the effect of a patterned polymer on ultrasound sensitivity: First a FEM simulation was conducted to compute MRRs sensitivity to ultrasounds with different polymer configurations. Then multiple fabrication methods were tested to produce a polymer pattern on top of a MRR. Finally, an ultrasound characterisation was done with the fabricated patterns to determine and compare sensitivity results with the simulation and conclude about the patterning effect.