Abstract: The present disclosure relates to an optical sensor for use in an image recognition device, such as a fingerprint detector. The presently disclosed optical sensor has improved light transmittance in a compact and cost-efficient structure. In particular the presently disclosed optical sensor can be placed under a display panel of an electronic device, such as a smartphone. One embodiment relates to an optical sensor system for placement under a display panel for detecting/imaging light returned from a fingerprint on top of the display panel, the optical sensor comprising a microlens structure having a front side with an array of light focusing elements and an opaque back side with an array of optically transparent apertures aligned with the focusing elements, and a sensor array of optical detectors facing the back side of the microlens structure.