The recent development of ultrasound sensing using the silicon-photonics platform has enabled super-resolution optoacoustic imaging not possible by piezoelectric technology or polymeric optical microresonators. The silicon waveguide etalon detector (SWED) design exploits the sub-micrometer light confinement in the cross-section of a silicon strip waveguide to achieve a sensor aperture which is 13-fold to 30-fold smaller than the cutoff wavelength of the sensor. While its performance in near-field scanning optoacoustic imaging has been previously studied, the operational characteristics of this sensor as it relates to conventional optoacoustic imaging applications are not known. Here, for the first time, the application of the SWED in optoacoustic mesoscopy is investigated, the interaction of the sensor with ultrasound in the far-field is characterized, the acoustic point spread function up to a depth of 10 mm is measured, and 3D vasculature-mimicking phantoms are imaged. The measured point spread function of the sensor shows that surface acoustic waves can degrade the lateral resolution. Nevertheless, superior resolution is demonstrated over any state-of-the-art ultrasound sensor, over the whole range of imaging depths that are of interest to optoacoustic mesoscopy. Silicon photonics is proposed as a powerful and promising new platform for ultrasonics and optoacoustics.