A novel all-optical akinetic ultrasound sensor, consisting of a rigid, fiber-coupled Fabry-Pérot 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-Pérot 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 20 MHz measurement bandwidth (without signal averaging), while maintaining a flat frequency response, and a detection bandwidth up to 22.5 MHz (-6 dB). The measured large full field of view of the sensor is 2.7 mm × 1.3 mm and the dynamic range is 137 dB/ √ Hz or 63 dB at 20 MHz bandwidth. For different required amplitude ranges the upper amplitude detection limit can be customized from at least 2 kPa to 2 MPa 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. functional photoacoustic microscopy of mouse brain in action," Nat. Methods 12, 407-410 (2015). 7. L. Xi, C. Song, and H. Jiang, "Confocal photoacoustic microscopy using a single multifunctional lens," Opt. Lett. 39, 3328-3331 (2014). 8. J. Gateau, A. Chekkoury, and V. Ntziachristos, "Ultra-wideband three-dimensional optoacoustic tomography," Opt.Lett. 38, 4671-4674 (2013). 9. C. Zhang, T. Ling, S.-L. Chen, and L. J. Guo, "Ultrabroad bandwidth and highly sensitive optical ultrasonic detector for photoacoustic imaging," ACS Photonics 1, 1093-1098 (2014). 10. E. Zhang, J. Laufer, and P. Beard, "Backward-mode multiwavelength photoacoustic scanner using a planar Fabry-Pérot polymer film ultrasound sensor for high-resolution three-dimensional imaging of biological tissues," Appl. Opt. photoacoustic microscopy using a digital micromirror device," Opt. Lett. 38, 1683-2686 (2013).