For Better AR Cameras, Swap Plastic Lenses for Silicon Chips

Metalenz adds the power of polarization to its innovative PolarEyes chips

5 min read
Silicon Nanostructures

Metalenz uses standard semiconductor manufacturing processes to build metasurfaces comprising nanostructures that control light, with one chip replacing multiple traditional camera lenses.

Metalenz

This week, startup Metalenz announced that it has created a silicon chip that, paired with an image sensor, can distinguish objects by the way they polarize light. The company says its “PolarEyes” will be able to make facial authentication less vulnerable to spoofing, improve 3D imaging for augmented and virtual reality, aid in telehealth by distinguishing different types of skin cells, and enhance driving safety by spotting black ice and other hard-to-see road hazards.

The company, founded in 2017 and exiting stealth a year ago, previously announced that it was commercializing waveguides composed of silicon nanostructures as an alternative to traditional optics for use in mobile devices.

Metalenz recently began a partnership with ST Microelectronics to move its technology into mass production and expects to be shipping imaging packages sometime in the second quarter of this year, according to CEO Robert Devlin.

IEEE Spectrum spoke with Devlin last week to find more about the company’s technology and what it will be able to do when it gets into consumer hands.

Before we talk about your new polarization optics, briefly help us understand how your basic technology works.

Robert Devlin: We use standard semiconductor lithography on 12-inch wafers to create nanostructures in the form of little pillars. These structures are smaller than the wavelength of light, so by changing the radius of the pillars, we can use them to control the length of the optical path of the light passing through. For the first generation of this technology, we are working with near-infrared wavelengths, which transmits through silicon, rather than reflecting as visible light would do.

What’s the advantage of using nanostructures over traditional lenses?

Devlin: Our technology is flat, for one. When you are using a curved lens to put an image on a flat sensor, you have to make all sorts of corrections using multiple lenses and finely controlling the spacing between the lenses to make it work; we don’t have to do that. We also can bring the functions of multiple traditional lenses onto one chip . And we can manufacture these lenses in the same semiconductor foundries as the image sensors and electronics used in camera modules.

The iPhone face ID system, for example, has three lenses: one diffractive lens, for splitting infrared light being projected onto your face into a grid of dots, and two refractive, for collimating the lasers to project onto the face. Some of these modules have an optical path that’s folded by mirrors, because otherwise they would be too thick to fit into compact spaces required for consumer devices. With the single-chip flat optics, we can shrink the overall thickness, and don’t need folded optical paths or mirrors in even the most space-constrained applications.

3D mapping is another infrared imaging application that uses multiple lenses today. Augmented reality systems need to create a 3D map of the world around them in real time, in order to know where to place the virtual objects. Today, these use a time-of-flight system—again, working in the infrared part of the spectrum—which sends out pulses of light and times how long they take to get back to the image sensor. This system requires several refractive lenses to focus the outgoing light and a diffractive lens to multiply the light to a grid of points. They also require multiple lenses on the imaging side to collect the light from the scene. Some of the lenses are needed to correct for the curvature of the lenses themselves, some are needed to make sure the image is crisp across the entire field of view. Using nanostructures, we can put all of these functions onto one chip.

So that’s what the chips you announced do?

Devlin: Yes, and the first product to use our technology, shipping in the second quarter of this year, will be a module for use in 3D imaging.

Initially for mobile phones?

Devlin: For consumer devices generally but also for mobile phones.

What about AR?

Devlin: Of course, everyone is eagerly waiting for AR glasses, and the form factor remains a problem. I think what we are doing—simplifying the optics—will help solve the form-factor problem. People get suspicious if they see a big camera sitting on someone’s face. Ours can be very small, and, for this application, infrared imaging is appropriate. It allows the system to understand the world around it in order to meld the virtual world with it. And it isn’t affected by changes in lighting conditions.

Okay, let’s talk about what you’re announcing now, the polarization technology, your PolarEyes.

Devlin:When we spoke a year ago, I talked about Metalenz wanting to not just simplify existing mobile-camera modules, but to take imaging systems that have been locked away in scientific laboratories because they are too expensive, complex, or big, and combine their optics into a single layer that would be small enough and cheap enough for consumer devices.

One of those imaging systems involves the polarization of light. Polarization is used in industrial and medical labs; it can be used to see where cancerous cells start and end, it can in many cases tell what material something is made of. In industry, it can be used to detect features of black objects, the shape of transparent objects, or even scratches on transparent objects. Today, complete polarization cameras measure around 100 by 80 by 80 millimeters, with optics that can cost hundreds of dollars.

gif of four views of face with and without masks showing different polarizations of lightThe PolarEyes chip from Metalenz sorts light by its polarization, allowing the pixels of images captured to be color-coded by polarization. In this case, the difference in polarization between materials makes it obvious when a mask obstructs skin.Metalenz

Using metasurface technology, we can bring the size down to 3 by 6 by 10 mm and the price down to [US] $2 to $3. And unlike many typical systems today, which take multiple views at different polarizations sequentially and use them to build up an image, we can use one of our chips to take those multiple views simultaneously, in real time. We take four views—that turns out to be the number we need to combine into a normal image or to create a full map of the scene color-coded to indicate the complete polarization at each pixel.

Besides the medical and industrial uses you mentioned, why else are polarized images useful?

Devlin: When you get these into mobile devices, we will likely find all sorts of applications we haven’t thought of yet, and that’s really exciting. But we do have an initial application that we think will help get the technology adopted—that’s in facial recognition. Today’s facial recognition systems are foiled by masks. That’s not because they couldn’t get enough information from above the mask to recognize the user. They use a high-res 2D image that provides enough data to the algorithms to do that. But they also use a 3D imaging system that is very low resolution. It’s meant to make sure that you’re not trying to spoof the system with a mask or photograph, and that’s what makes facial recognition fail when you are wearing a mask. A polarization imaging module could easily distinguish between skin and mask and solve that problem.

The Conversation (1)
FB TS21 Jan, 2022
INDV

IMHO one of the best applications for lensless flat surface digital cameras could be both ground & space telescopes!

Imagine being able to create telescopes of any size by simply joining together flat panels!

The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
Vertical
A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay
Blue

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.

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