Invented by Garcia Salazar; Ofir, Suski; Matthew D, Song; Yu, Yu; Caroline

Head-mounted devices are becoming a big part of our daily lives, from smart glasses to virtual reality headsets. But making these devices work well has many hidden challenges, especially when it comes to sensing the world around us. Today, we’ll explore a new patent application for a smart way to block and manage stray light in these devices. This technology helps keep the device sensors accurate and reliable. Let’s break down what’s happening, why it matters, and how this invention changes things.

Background and Market Context

Wearable technology, especially head-mounted devices like smart glasses, virtual reality (VR), and augmented reality (AR) headsets, is quickly changing how we interact with digital and real worlds. These devices use sensors and cameras to capture, understand, and respond to our environment. Some help us play games, others help workers in factories, doctors in hospitals, or drivers on the road. But to do all this, they need to “see” what’s around us. That’s where light sensors come in.

When devices try to sense what’s outside, they often use invisible light, such as infrared. The device sends out a light beam, and a sensor receives the reflection. This tells the device if something is in front of it, how far away it is, or even what it looks like. These abilities power features like gesture control, eye tracking, object detection, and more.

But there’s a big challenge just beneath the surface: not all light behaves as we want it to. Sometimes, instead of going straight out and bouncing off what’s in front of you, light bounces around inside the device’s protective glass or plastic layer. This is called “stray light.” If stray light reaches the sensors, it can trick the device, making it think there’s something there when there isn’t. This can lead to errors in tracking, misinterpreted gestures, and even security risks, especially when the device is supposed to collect sensitive data or help with safety.

As AR and VR become more mainstream, these problems matter more. Users expect accuracy, privacy, and comfort. Businesses want devices that work everywhere, from bright sunny days outdoors to dim indoor rooms. At the same time, device makers want to keep things light, slim, and stylish—nobody wants a bulky headset. So, the market is hungry for solutions that make sensors smarter and more reliable, without making devices bigger or more expensive.

This is where the patent we’re looking at comes in. It introduces stray light redirecting structures—a clever way to keep unwanted light out of the sensors. This means better performance, safer experiences, and more trust in the technology, which is key as more people and industries depend on these devices.

Scientific Rationale and Prior Art

To understand why this invention matters, let’s talk about how light works in these devices. When a headset or smart glasses have a transparent cover (like glass or plastic), this layer separates the inside of the device (where the sensors are) from the outside world. When the device sends out a beam of light (often invisible infrared), it wants that beam to go out, hit an object, and then return to the sensor. If everything goes perfectly, the sensor only sees the light that bounced off the real-world object.

But here’s the problem: glass and plastic can act like mirrors inside. This effect is called “total internal reflection.” When light hits the inside of the glass at a certain angle, instead of escaping, it gets trapped and bounces around inside. If there are tiny scratches, dust, or even design features not meant for guiding light, some of the outgoing light reflects sideways and travels within the glass or plastic layer. This stray light can end up at the sensor, just like the real reflected signal from outside. The sensor can’t tell the difference between the “real” signal and the stray one.

For years, engineers and scientists have tried to reduce this problem. Some old solutions include:

– Making the glass or plastic as perfect and clean as possible, so there are fewer places for light to bounce around. But this is hard and expensive.

– Adding coatings that absorb or scatter light, but these can make the device less clear or harder to make.

– Using barriers or black paint around the sensors, but this can make the device look bad or block too much light.

In the past, most devices just tried to live with some stray light. They used software tricks to ignore it or made the sensors less sensitive. But as we want more from these devices—like tracking tiny eye movements, reading gestures, or even recognizing faces—these tricks aren’t enough. Tiny errors from stray light can cause big problems, and as devices get thinner and more stylish, there’s less room for old solutions.

Other inventions tried using special shapes or materials inside the glass, but they often came with trade-offs: maybe the device got heavier, thicker, or harder to manufacture. Or maybe the solution worked for visible light but not for the invisible infrared used by many sensors. Clearly, a new approach was needed—one that could fit inside slim devices, work with invisible light, and be easy for manufacturers to use.

Invention Description and Key Innovations

This new patent brings a fresh solution: stray light redirecting structures built right into the transparent layer of the device. These structures can be formed in several different ways, but they all aim to do one thing—get rid of the stray light before it reaches the sensor.

Let’s look at how this technology works, step by step.

First, the device’s transparent layer (like the front glass or plastic of a headset) has a special window. This window lines up with where the light source (such as an infrared LED) sends its light out. The sensor, which wants to receive reflections from outside, is also lined up behind this transparent layer.

The clever part is what’s added around this window: the stray light redirecting structure. There are a few ways to build this structure, each with its own benefits.

– The structure can be a recess—a small groove or dip in the glass or plastic, partially or completely surrounding the window. This groove interrupts the smooth surface inside the transparent layer. When stray light tries to travel sideways inside the glass, it hits this groove and is forced out of the glass instead of continuing on its path. The groove can be just 10% as deep as the thickness of the glass, so it doesn’t make the device bulky.

– Instead of a groove, the structure might be a protrusion—a tiny bump or ridge. This works much like the groove, redirecting the stray light out of the glass and away from the sensor.

– Another approach is to use a gap—two separate pieces of clear material with a tiny space between them. This gap acts as a barrier, so stray light can’t keep traveling inside the glass.

– The structure could also be a textured region, like a patch of roughness on the inside surface. This texture scatters the stray light, breaking up its path so it doesn’t reach the sensor.

– Micro-bubbles can be added—tiny air pockets inside the glass or plastic. These bubbles scatter and redirect stray light in all directions, sending it out of the transparent layer.

– A special thin coating, made from a polymer that matches the glass’s properties, can also help. Because the coating “matches” the glass, it doesn’t affect how the device looks or feels, but it helps send stray light away from the sensor.

All these structures are placed so that they at least partially surround the light source window. This way, any stray light that tries to sneak through the glass or plastic is stopped before it can reach the critical sensors.

To make the system even better, an opaque masking layer can be added on top of the structure. This is a thin film of dark or light-absorbing material, like ink or dye, that soaks up any stray light that gets redirected out of the glass. The device designer can choose to use this extra layer wherever more stray light needs to be blocked.

What’s really smart is that these structures don’t just block light—they can also help the device in other ways. For example, the grooves or bumps can be shaped to act as tiny lenses, focusing the outgoing light from the source so it works even better. And because these features are built into the glass or plastic itself, they don’t add much weight or thickness.

The invention is flexible: the structures can be made with simple manufacturing steps, like molding, etching, laser processing, or adding coatings. They can be used for visible or invisible light, and they work in all sorts of devices, from glasses to car dashboards, phones, or even gaming controllers.

By getting rid of stray light, this invention lets sensors work with much higher accuracy. It improves the device’s ability to track objects, hands, or eyes, even in tricky lighting conditions. This means better user experiences, fewer mistakes, and more trust in the device. It also helps keep the design sleek and modern, which people want in wearable tech.

Conclusion

The battle against stray light has always been a silent one, but its outcome shapes how well our head-mounted devices and other smart gadgets work. This new patent for stray light redirecting structures is a leap forward, offering a simple yet powerful way to keep unwanted light away from sensitive sensors. By building these features right into the transparent layer, the invention lets devices stay slim, stylish, and accurate—without big changes to how they’re made.

As we move into a world where smart glasses, AR headsets, and other wearable devices are everywhere, technologies like this will be key. They solve hidden problems that users never think about, but that make all the difference in how these devices see, sense, and interact with the world. For anyone designing the next generation of wearable tech, understanding and using innovations like stray light redirecting structures will be essential for creating products that truly work.

Click here https://ppubs.uspto.gov/pubwebapp/ and search 20250216682.