Boffin’s beamforming kit opens the door to holograms • The Register

An MIT-led research team has developed a novel kit that can dramatically increase the speed and power of optical beam-shaping technology and is easy to manufacture at scale.

If commercialized, the team’s new type of spatial light modulator (SLM) could pave the way for super-fast LiDAR imaging for autonomous vehicles, improved medical scanners, and even the development of free-standing 3D holograms resembling those seen in Star Wars. Admittedly, we’ll be waiting for the latter for a while.

According to MIT, the project was a four-year endeavor that resulted in an article published in Nature in this week. The lead author Dr. Christopher Panuski described the results as “a major step towards the ultimate goal of complete optical control – both spatially and temporally – for the myriad applications that use light”.

An SLM upgrade

SLMs are devices that modulate the wavelengths of light rays to create colors or shapes; The most basic example of this is the overhead projector transparency.

More advanced SLMs use two-dimensional arrays of things like liquid crystals and digital micromirrors to change the colors of the light passing through them, but these are still limited in bandwidth and pixel density. To circumvent these limitations, the MIT team opted for a series of “photonic crystal microcavities” they call PhC-SLM. According to the researchers, their design achieves a tenfold improvement over older 2D SLMs.

Cavities in the PhC-SLM capture light for about half a nanosecond – just long enough for the cavity to be tuned to manipulate it. To maximize the effectiveness of the PhC-SLM, the team designed an algorithm to determine the best way to form a narrow beam of light.

“We want the reflected light from each cavity to be a focused beam as this improves the beam steering performance of the final device. Our process essentially yields an ideal optical antenna,” said Panuski.

A micro LED array is used to drive the PhC-SLM, with each cavity paired with a single LED. The LEDs, in turn, are used to modulate laser beams, and since all the work is done by LEDs, there are no wires in the system – it’s entirely optical. This means, according to Panuski, that the devices can be placed incredibly close together without loss of absorption.

Commercially usable research results?

While the MIT team gave no indication that commercialization of their product is imminent, Panuski said manufacturability of the PhC SLMs is an important part of the project. Since each cavity is only about a micron in size, and an entire PhC SLM is fabricated on a 12-inch silicon wafer, any small deviation in manufacturing could affect performance.

To circumvent this problem, the team developed a “vision-based holographic trimming” method, which uses a superheated laser to create a layer of silicon dioxide on the surface of each cavity. MIT said the laser was designed to hit all of the cavities simultaneously, ensuring the silicon dioxide aligns the resonances of each cavity.

The MIT team now plans to build larger devices to test some of the many potential applications of their new SLMs. As for the Star Wars holograms, “high-resolution, high-frame-rate holographic displays” that enable “full DoF spatiotemporal modulation” could also be created with the technology, the team said in the paper, but with some limitations like the one need for a reflector.

Still, it’s a first step toward creating the rapid and precise control of light required for this and other photonic wonders.

No word on whether this new beamformer could also be used to help create that other long-sought piece of Star Wars technology that relies on shaping light into spatiotemporal controlled beams, so put those Jedi Ambitions back for now. ®