Apple has been working on under-display fingerprint technology since at least 2013 (published in 2015) and since then there have been a great number of patents related to this future feature (01, 02, 03, 04, 05 and more).
In June 2021 Ming-Chi Kuo changed his forecast for Apple's under-display fingerprint feature to 2022. Then a rumor surfaced earlier this year claiming, without a source, that Apple has abandoned this feature. To date, other smartphone companies have successfully implanted under-display fingerprint authentication. Samsung, according to Chrome Unboxed, is one that has perfected this technology on their Galaxy S22+.
The biggest complaint about Apple's latest iPhone SE (3) is that the design has passed its time. Introducing a larger display with under-display Touch ID for the next-gen iPhone SE would certainly add some needed pizzazz. Whether Apple will make that leap is still unknown at this time.
Today the US Patent & Trademark Office published granted patent 11,281,884 titled "Under-Display Fingerprint Sensing based on Off-Axis Angular Light."
Apple's granted patent covers an under-display fingerprint-sending system wherein the display consists of active red-green-blue (RGB) pixels that emit light and illuminate the finger placed on top of the display. The light reflected from the finger passes through the openings between the display pixels and is captured by the sensor beneath the display.
The contact and noncontact regions between the finger skin and the display's glass plate generate different light intensity, which thus forms the ridge-valley contrast of the fingerprint. Due to the low-light throughput and diffraction caused by the display stack, the fingerprint image may suffer from low contrast and low signal-to-noise ratio (SNR).
To overcome this problem, Apple's granted patent provides a method to capture the off-axis angular light from the finger by insertion of angle-dependent filtering options between the display and the sensor. This method can improve the contrast of fingerprint impressions and maintain the compactness of the entire sensing system.
In some aspects, the subject technology is directed to an apparatus for under-display fingerprint sensing based on off-axis angular light. The apparatus includes a light-emitting layer, an optical coupling layer, a collimator layer and a pixelated image sensor.
The light-emitting layer is covered by a transparent layer and illuminates the surface touching the transparent layer and allows transmission of reflected light rays from the surface to underlying layers including the optical coupling layer, the collimator layer and the pixelated image sensor.
The optical coupling layer directs the reflected light rays at an angle to the collimator layer, which includes a number of apertures and can collimate the directed reflected light rays. The pixelated image sensor can sense collimated light rays.
In one or more implementations, the optical coupling layer is an optical layer made of a planar array of Fresnel prisms. The apparatus further includes a polarizer, including a linear polarizer and one or more circular polarizers.
The angle at which the optical coupling layer directs the reflected light rays is about 42.degree. with respect to the normal to the plane of the optical coupling layer. The collimator layer can be a tilted collimator with aperture walls at nearly 42.degree. with respect to the normal to the plane of the optical coupling layer.
Apple's patent FIG. 1 below is a diagram illustrating an example of an under-display optical fingerprint-sensing device based on off-axis angular light; FIG. 2 is a diagram illustrating an example of an under-display optical fingerprint-sensing device including two polarizer layers; FIG. 3 is a diagram illustrating an example of an under-display optical fingerprint-sensing device including three polarizer layers.
Apple's patent FIG. 4 below is a diagram illustrating an example of a simulated angular distribution of light intensity corresponding to the three polarizer layers of FIG. 3; FIG. 5 is a diagram illustrating an example of a simulated angular distribution of light intensity corresponding to the two polarizer layers of FIG. 2.
Apple's patent FIG. 6 above is a diagram illustrating an example of an under-display optical fingerprint-sensing device based on off-axis angular light including blazed gratings; FIG. 8 is a diagram illustrating an example of an under-display optical fingerprint-sensing device based on off-axis angular light including holographic gratings.
For more details, review Apple's granted patent number 11,281,884.
It should be noted that the patent doesn't restrict Touch ID to an iPhone. Apple Watch is another device that could utilize this feature which is presented in another granted patent today.