Under display fingerprint sensor with improved contrast ratio

An under-display fingerprint sensor of generating a fingerprint image of a finger in contact with a glass cover disposed over a display panel, comprising:

• a light selection layer, being disposed under a display panel, configured for converting a downward circularly-polarized light that is reflected in a region below a valley of a fingerprint in contact with an upper surface of a glass cover into a downward linearly-polarized light, and configured for converting an unpolarized light that propagates downwardly from the display panel into a sensor linearly-polarized light, wherein a lower surface of the light selection layer is an interface between two media having different refractive indices, wherein the downward linearly-polarized light and the sensor linearly-polarized light perpendicularly incident on the lower surface of the light selection layer propagate in the perpendicular direction and the downward linearly-polarized light and the sensor linearly-polarized light incident on the lower surface of the light selection layer at the angle other than perpendicular are refracted at a refraction angle greater than an incidence angle;
• a plurality of lenses, being disposed apart from the light selection layer, configured for refracting the downward linearly-polarized light and the sensor linearly-polarized light that propagate in a perpendicular direction toward each focal point, and configured for deviating the downward linearly-polarized light and the sensor linearly-polarized light that propagate at an angle other than perpendicular from the focal point;
• and
• an image sensor having a plurality of light receiving units disposed at each focal point of the plurality of lenses to receive the downward linearly-polarized light and the sensor linearly-polarized light that are refracted toward each focal point.

An under-display fingerprint sensor of generating a fingerprint image of a finger in contact with a glass cover disposed over a display panel, comprising:

• a light selection layer, being disposed under a display panel, configured for converting a downward circularly-polarized light that is reflected in a region below a valley of a fingerprint in contact with an upper surface of a glass cover into a downward linearly-polarized light, and configured for converting an unpolarized light that propagates downwardly from the display panel into a sensor linearly-polarized light, wherein the light selection layer comprises:
• a first sensor retarder and a second sensor retarder having slow axes orthogonal to each other;
• and
• a first sensor polarizer disposed under the first sensor retarder and the second sensor retarder,
• wherein a combination of the first sensor retarder and the first sensor polarizer is a first light path, and a combination of the second sensor retarder and the first sensor polarizer is a second light path;
• a plurality of lenses, being disposed apart from the light selection layer, configured for refracting the downward linearly-polarized light and the sensor linearly-polarized light that propagate in a perpendicular direction toward each focal point, and configured for deviating the downward linearly-polarized light and the sensor linearly-polarized light that propagate at an angle other than perpendicular from the focal point;
• and
• an image sensor having a plurality of light receiving units disposed at each focal point of the plurality of lenses to receive the downward linearly-polarized light and the sensor linearly-polarized light that are refracted toward each focal point.