There have been multiple suggestions that Apple plans to adopt under-screen Touch ID for the iPhone 13, given that masks have greatly reduced the usefulness of Face ID. The company already has a bunch of patents for different ways to pull this off, and has today applied for an interesting new one.

Apple explains that optical fingerprint reading can be unreliable for two reasons, and explains how it would address these …

The patent application spotted by Patently Apple explains how optical under-screen Touch ID could work.

In an under-display fingerprint-sending system, 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.

There are, however, two problems with this approach. First, there’s a limit to how much of the light reaches the fingertips – typically, significantly less than is the case with standalone optical fingerprint readers.

Second, the display layers tend to result in the light being diffracted, which further limits the reliability of the scan.

Apple explains how its invention would solve this.

To overcome this problem, the subject disclosure 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. 

One way to achieve this is via prisms.

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 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 with respect to the normal to the plane of the optical coupling layer. 

The application does, however, outline alternative methods.

Apple has largely solved the mask problem for Apple Watch owners in the betas of iOS 14.5 and watchOS 7.4.

To enable the Unlock with Apple Watch feature, open the Settings app on your iPhone, then look for the “Face ID & Passcode” setting. Once you flip this toggle, your Apple Watch will be able to authenticate your iPhone as long as the following conditions are met:

  • Face ID detects a mask

  • Your Apple Watch is nearby

  • Your Apple Watch is on your wrist

  • Your Apple Watch is unlocked

  • Your Apple Watch has a passcode enabled

I’ve found this to work really well, but that still leaves everyone else without a solution.

Photo by Habib Dadkhah on Unsplash

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Ben Lovejoy

Ben Lovejoy is a British technology writer and EU Editor for 9to5Mac. He’s known for his op-eds and diary pieces, exploring his experience of Apple products over time, for a more rounded review. He also writes fiction, with two technothriller novels, a couple of SF shorts and a rom-com!

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