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New device can control light at unprecedented speeds

Crystal Modulator. Image by Sampson Wilcox

A programmable optical device for high-speed beam steering has been developed in research involving the University of Strathclyde.

The researchers have demonstrated a programmable, wireless device that can control light, such as by focusing a beam in a specific direction or manipulating the light’s intensity and do so in orders of magnitude more quickly than commercial devices.

They also pioneered a fabrication process that ensures the device quality remains near-perfect when it is manufactured at scale. This would make their device more feasible to implement in real-world settings.

Known as a spatial light modulator, 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. It could also accelerate brain scanners, which use light to ‘see’ through tissue. By being able to image tissue faster, the scanners could generate higher-resolution images which are not affected by noise from dynamic fluctuations in living tissue, like flowing blood.

The paper is a collaboration led at MIT and also involving Flexcompute Inc, the State University of New York Polytechnic Institute, Applied Nanotools Inc, the Rochester Institute of Technology and the U.S. Air Force Research Laboratory. It has been published in the journal Nature Photonics.

Professor Michael Strain, of Strathclyde’s Institute of Photonics, the University’s lead in the project, said: “This application of high-speed LED-on-CMOS displays as micro-scale optical pump sources is a perfect example of the benefits of integrated photonic technologies and open collaboration. We have been thrilled to work with the team at MIT on this ambitious project.”

A spatial light modulator (SLM) is a device that manipulates light by controlling its emission properties. Similar to an overhead projector or computer screen, an SLM transforms a passing beam of light, focusing it in one direction or refracting it to many locations for image formation.

Inside the SLM, a two-dimensional array of optical modulators controls the light but light wavelengths are only a few hundred nanometres, so to control light precisely at high speeds, the device needs an extremely dense array of nanoscale controllers.

The researchers used an array of photonic crystal microcavities to achieve this goal; these photonic crystal resonators allow light to be controllably stored, manipulated, and emitted at the wavelength-scale.

When light enters a cavity, it is held for about a nanosecond, bouncing around more than 100,000 times before leaking out into space. While a nanosecond is only one billionth of a second, this is enough time for the device to manipulate the light precisely. By varying the reflectivity of a cavity, the researchers can control how light escapes. Simultaneously controlling the array modulates an entire light field, so the researchers can quickly and precisely steer a beam of light.

The device demonstrated near-perfect control — in both space and time — of an optical field with a joint “spatiotemporal bandwidth” 10 times greater than that of existing SLMs. Being able to control precisely a huge bandwidth of light could enable devices that can carry massive amounts of information extremely quickly, such as high-performance communications systems.

Now that they have perfected the fabrication process, the researchers are working to make larger devices for quantum control or ultrafast sensing and imaging.

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