Forget LEDs, researchers from the University of Michigan have developed a new type of incandescent light bulb. The device is capable of emitting elliptically polarized light, described as "twisted" light.
The word "twisted" (aka "chiral") describes the clockwise and counterclockwise rotation of the light's electric waves that mirror each other as it travels. By contrast, traditional light sources emit unpolarized light or linearly polarized light.
It sounds weird, but this new design has the potential to transform optics and photonics.
The bulb produces this twisted form of polarized light due to the intricate engineering of the filament itself. By integrating micro- and nanoscale twists into the tungsten filament structure, the light wave inherits that helical shape, effectively making it elliptically polarized.
Changing the light's polarization characteristics in this manner mimics things found in nature, like the ridiculously sophisticated and specialized vision of the mantis shrimp. With 12 types of photoreceptors (compared to humans' piddly three – red, green, and blue), mantis shrimp can see all the colors, including parts of the ultraviolet and infrared spectrum. They can even detect circular polarized light. All of this excellent visual information makes them lethal underwater hunters (not to mention they can punch about 100 times harder than a human, but that's for another story, another time).
What is polarized light?
We've all heard of polarized sunglasses, and the consensus is generally that they're better than non-polarized sunglasses. Yes and no, depending on your usage.
Polarized light is simply the waves of light oscillating in a specific direction. Direct sunlight is usually scattered in all directions, but when sunlight hits water, the light reflects linearly and the waves travel to your eyes from the water's surface in a mostly uniform fashion, making it seem brighter or harsher to your eyes. The glassier the water or more reflective the surface, the more uniform the polarization goes straight into your eyeballs. This is why polarized sunglasses work so much better at the beach or lake or while driving.
Next time you're wearing your polarized sunglasses – which are generally designed for horizontal polarized light – look at a reflective window, then turn your head 90-degrees sideways and you'll see how they work in action.
But back to why this old tech with a new twist is cool ... As mentioned earlier, certain animals are sensitive to polarized light. Bees, ants and birds, among others, use it for navigation. Octopi, fish and more use it to hunt or hide. The list goes on.
One of the most promising uses of this twisted light technology is in robotic vision systems, giving robots the ability to see in spectrums similar to these specialized animals.
Elliptically polarized light can better a robot's ability to interpret its environment far better than scattered light, by providing more layers of information. For example, it could improve object detection and surface texture recognition by providing more contrast. If you've ever used a camera with autofocus and you just couldn't seem to get it to focus on something plain or flat, it's usually because there isn't enough contrast for the sensor to distinguish how far away it is.
The better that robotic vision systems can see, the better the results for activities like autonomous navigation or machine learning. Twisted light would be like throwing a 3-dimensional grid onto an object that robotic vision could map with far better precision. And mantis shrimp.
"These findings, for example, could be important for an autonomous vehicle to tell the difference between a deer and a human, which emit light with similar wavelengths but different helicity because deer fur has a different curl from our fabric," said Nicholas Kotov, Professor and director at the NSF Center of Complex Particles and Particle Systems, and co-author of the study.
Robotics aside, this type of light has the potential for improving other imaging technologies such as more detailed medical diagnostics and materials science images.
Communication system improvements are equally significant. Polarized light is already used in fiber optics and data transmission to carry more data on a single line. The ability to control light polarization with such precision could lead to more channels on existing infrastructure, making data rates faster and more secure.
Incandescent lights, seemingly old and obsolete in the age of LEDs, have found purpose again to potentially brighten our future. But don't go digging out your hundred-year-old light bulbs from the closet just yet, there's still more work to be done.
Source: University of Michigan
