Diffractive Beam Splitter – The Magic Behind Apple’s FaceID

Diffractive Beam Splitter

So, like many of us who watched the Apple iPhone event live or perhaps caught the highlights, you may have noticed something rather unfamiliar, rather off-the-beaten-path, rather unusual called a “diffractive beam splitter” highlighted by Phil Schiller, Apple’s Sr. VP of WW Marketing, at the recent iPhone launch event. And, if you’re not a research scientist, you perhaps scratched your head and wondered what role a diffractive beam splitter played in the front camera assembly of the iPhone.

Diffractive Beam Splitter

Simply put, a beam splitter separates a single beam of light into two or more beams of light. Light can be split by percentage of overall intensity, wavelength, or polarization state but it retains the same optical characteristics as the input beam. Beam splitters often form the common components in high-power lasers and illumination systems. They are used in spectroscopy, fluorescence applications, optical interferometry, life science, instrumentation and, of course, in the iPhone X (S).

faceidWell, as it turns out, a beam splitter plays a critical role in the iPhone’s front camera system and is part of its Dot Projector assembly. They are credited for enabling FaceID. The dot projector projects 30,000 invisible dots of light to map your face. This information then passes through (in the form of light) to the diffractive beam splitter which then creates a terrain of pixels that match the contours of your face helping the phone essentially map every nook and cranny of your face. And, then voila! With a few algorithm-driven tricks performed by the A12 Bionic and you’re in.

Types of Beamsplitters

Plate Polka Dot Dichroic Transmission Grating
Plate beam splitter broadband polka dot beam splitter dichroic beamsplitter transmission grating beam splitter

Plate Beam Splitter –
Used in many life sciences, imaging, or laser applications, as well as in the entertainment and design industry.

Polka-Dot Beam Splitter – Near constant reflection to transmission ratio with minimal angle sensitivity. As the name suggests, “polka dots” are created from the combination of a photolithography process and the vacuum deposition of aluminum (Al). The result is a precise pattern of small aluminum “dots” on the glass substrate. The beam is split by reflection from the aluminized dots and transmission through the non-aluminized portion of the substrate.

Dichroic Beam Splitters – Optimized to provide high transmission of one spectral band, while reflecting a second spectral band, with a very sharp transition slope between these two bands.

Transmission Grating Beam Splitter – Commonly used for laser beam division and multiple laser line separation in visible wavelengths. They are designed for the useful division of He-Ne (Helium-Neon) lasers, and multiple laser line separation.

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