Researchers develop programmable optical device for high-speed beam steering
Scientists have developed a programmable, wireless spatial light modulator that can manipulate light at the wavelength scale with orders-of-magnitude faster response than existing devices. Credit: Sampson Wilcox

In a scene from "Star Wars: Episode IV -- A New Hope", a hologram of Princess Leia is making a desperate plea for help. Even today, we don't have the technology to create realistic holograms like that one.

It would take a lot of precise and fast control of light to create a 3D hologram.

The problem of high-speed optical beam forming has been tackled by an international group of researchers. They have demonstrated a wireless device that can control light in a variety of ways, such as focusing a beam in a specific direction or manipulating the light's intensity.

The fabrication process they pioneered ensures the device quality remains near- perfect when it is manufactured. It would be possible to implement their device in real world settings.

The device could be used to create super-fast lidar (light detection and ranging) sensors for self- driving cars, which could image a scene about a million times faster than existing mechanical systems. Light can be used to see through tissue. Higher-resolution images that aren't affected by noise from fluctuations in living tissue, like flowing blood, could be generated by being able to image tissue quicker.

Since antiquity, we've focused on controlling light. Christopher Panuski is the lead author and recently graduated with his PhD in electrical engineering and computer science.

Researchers from MIT, Flexcompute, Inc., the University of Strathclyde, the State University of New York Polytechnic Institute, and the Rochester Institute of Technology collaborated on the paper. An associate professor of electrical engineering and computer science at MIT is the senior author. The research is in a journal.

Light being manipulated.

A spatial light modulator is a device that works with light. Similar to an overhead projector or computer screen, an SLM transforms a passing beam of light into an image.

The light is controlled by an array of optical modulators. To control light at high speeds, a dense array of nanoscale controllers is needed. This goal was achieved using an array of crystal microcavities. Light can be stored, manipulated, and emitted at a wavelength.

Light bounces around more than 100,000 times before hitting the ground. There is enough time for the device to precisely manipulate the light. Researchers can control how light escapes by changing the reflectivity of the building. The researchers can steer a beam of light if they control the array simultaneously.

The device has an engineered radiation pattern. The beam-steering performance of the final device can be improved by focusing the reflected light from each cavity. Panuski says that their process is an ideal optical antenna.

The researchers were able to achieve this goal by using a new method to design crystal devices that form light into a narrow beam.

It is possible to use light to control light.

The team used a small display. A single microcavity is made possible by the fact that the LEDs line up with the crystal on the chip. When a laser hits that activated microcavity, the cavity responds in a different way.

This application of high-speedLED-on-CMOS displays as micro-scale optical pump sources is a perfect example of the benefits of integrated optical technologies. Michael Strain is a professor at the Institute of Photonics of the University of Strathclyde.

Panuski says that the array is completely wireless because of the use of LEDs.

All-optical control is what it is. We can place devices closer together without worry about absorption losses.

It took a long time to figure out how to make such a device. The device could be mass produced using the same techniques that were used for computers. Huge fluctuations in performance can be caused by tiny deviations in the fabrication process and by the size of the chips.

The researchers collaborated with the Air Force Research Laboratory to create a mass-manufacturing process that stamps billions of cavities onto a 12-inch Silicon wafer. They put in a post-processing step to make sure the microcavities all work at the same wavelength.

One of the biggest challenges at the beginning was getting a device architecture that would be manufacturable. Chris invented a new technique for machine vision-based holographic trimming because he worked with a wonderful team of engineers and scientists.

The researchers use a laser to trim the microcavities. The laser creates a substance called Silicon dioxide, or glass. A layer of glass was added to align the natural frequencies at which the cavities vibrate.

Modifications to the fabrication process allowed us to make world-class devices in a process that had good uniformity. figuring out how to make these manufacturable is one of the major aspects of this work.

In both space and time, the device demonstrated near perfect control of an optical field with a joint "spatiotemporal bandwidth" 10 times greater than that of existingSLMs Being able to control a huge bandwidth of light could allow devices that can carry a lot of information quickly.

Researchers are working to make larger devices for quantum control now that they have perfect fabrication.

Christopher L. Panuski and his colleagues wrote about a full degree-of-freedom spatio-temporal light modulator. The DOI is 10.1038/s.

Journal information: Nature Photonics

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