Compact Optical Sensor For Fingerprint Detection

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. The optical sensor system is preferably configured such that light returned from the object can be focused by the microlens structure onto the sensor array through the transparent apertures.

1 . An optical sensor system for placement under a display panel for detecting and/or imaging light returned from an object 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 detector pixels facing the back side of the microlens structure, wherein each aperture is aligned with at least one of said optical detector pixels,   
       wherein the optical sensor system is configured such that light returned from the object can be focused by the microlens structure onto the sensor array through the transparent apertures. 
     
     
         2 . The optical sensor system according to  claim 1 , wherein the optical sensor system is configured such that light returned from the object within a predefined range of incident angles is focused by the microlens structure to the sensor array whereas light returned from the object outside said predefined range of incident angles is not detected. 
     
     
         3 . The optical sensor system according to  claim 2 , wherein the predefined range of incident angles is 40 degrees, or 30 degrees, or 20 degrees, or 16 degrees, or 10 degrees or 6 degrees. 
     
     
         4 . The optical sensor according to  claim 1 , wherein each focusing element is configured to focus and/or image light returned from the object to at least one corresponding pixel on the sensor array. 
     
     
         5 . The optical sensor system according to  claim 2 , wherein the microlens structure is configured to absorb at least part of the light returned from the object outside said range of incident angles. 
     
     
         6 . The optical sensor system according to  claim 2 , wherein the microlens structure is configured to reflect at least part of the light returned from the object outside said predefined range of incident angles. 
     
     
         7 . The optical sensor system according to  claim 1 , wherein reflective material is attached to the back side of the microlens structure to form the transparent apertures and such that light incident on the back side of the inside of the microlens is either transmitted through the transparent aperture or reflected by the reflective material. 
     
     
         8 . The optical sensor according to  claim 1 , wherein a metal foil is attached to the back side of the microlens structure such that the back side of the microlens structure is reflective towards the front side of the microlens structure. 
     
     
         9 . The optical sensor according to  claim 8 , wherein the transparent apertures are provided as holes in the metal foil. 
     
     
         10 . The optical sensor according to  claim 1 , wherein the sensor array comprises at least one pixel for each focusing element. 
     
     
         11 . The optical sensor according to  claim 1 , wherein a plurality of neighbouring pixels of the sensor array is assembled in groups, and wherein each group of pixels is configured to function as one active pixel such that the sensor array comprises only one active pixel for each focusing element. 
     
     
         12 . The optical sensor according to  claim 1 , wherein the distance between the front side and the back side of the microlens structure is less than 100 μm. 
     
     
         13 . The optical sensor according to  claim 1 , wherein the focusing elements have a diameter of less than 30 μm. 
     
     
         14 . The optical sensor according to  claim 1 , wherein the focusing elements is configured to have a back focal length of less than 15 μm. 
     
     
         15 . The optical sensor according to  claim 1 , wherein the apertures in the microlens structure have an area of less than 200 μm 2 . 
     
     
         16 . The optical sensor according to  claim 1 , wherein the sensor array is mounted with a predefined distance to the back side of the microlens array such that the sensor array is spaced from the apertures. 
     
     
         17 . The optical sensor according to  claim 1 , further comprising at least one infrared light source for transmitting light towards the front side of the microlens structure such that IR light is incident of an object on top of the display panel. 
     
     
         18 . The optical sensor according to  claim 1 , configured to utilize light from a light emitting display panel. 
     
     
         19 . The optical sensor according to  claim 1 , wherein the microlens structure is manufactured in a polymeric material by injection moulding or by film pressing. 
     
     
         20 . An image recognition device in the form of a fingerprint detector, comprising an optical sensor system according to  claim 1 , a storage unit for storing image information and a processing unit for processing the signal from the sensor array in order to recognize an image.