All-optical highly sensitive akinetic sensor for ultrasound detection and photoacoustic imaging

A novel all-optical akinetic ultrasound sensor, consisting of a rigid, fiber-coupled Fabry-Perot etalon with a transparent central opening is presented. The sensing principle relies exclusively on the detection of pressure-induced changes of the refractive index in the fluid filling the Fabry-Perot cavity. This enables resonance-free, inherently linear signal detection over a broad bandwidth. We demonstrate that the sensor achieves a exceptionally low peak noise equivalent pressure (NEP) values of 2 Pa over a 20MHz measurement bandwidth (without signal averaging), while maintaining a flat frequency response, and a detection bandwidth up to 22.5MHz (-6 dB). The measured large full field of view of the sensor is 2.7mm x 1.3mm and the dynamic range is 137 dB/root Hz or 63 dB at 20MHz bandwidth. For different required amplitude ranges the upper amplitude detection limit can be customized from at least 2 kPa to 2MPa by using cavity mirrors with a lower optical reflectivity. Imaging tests on a resolution target and on biological tissue show the excellent suitability of the akinetic sensor for optical resolution photoacoustic microscopy (OR-PAM) applications. (C) 2016 Optical Society of America