Tiny 'Ski Jumps' on a Photonic Chip Beam Thousands of Laser Points into Open Air
Massachusetts Institute of Technology
Thirty thousand pixels in the space occupied by two on a smartphone display. That is the pixel density achievable with a new photonic chip platform developed by researchers at MIT, MITRE, Sandia National Laboratories, and the University of Arizona. The technology, published in Nature, uses arrays of microscopic structures that physically curl upward from the chip surface to beam laser light into open air, solving a long-standing challenge in photonics: getting light off the chip efficiently and controllably.
The trapped-light problem
Photonic chips process data using light instead of electricity, which offers faster communication speeds and greater bandwidth. But most of that light stays confined within the chip's optical waveguides, the equivalent of tiny wires for photons. Extracting it into free space, where it can interact with the outside world, has been a persistent engineering bottleneck. Existing methods for broadcasting and steering light off a photonic chip typically handle only a few beams at once and cannot scale to the thousands or millions of independently controlled beams that advanced applications demand.
The motivation for solving this problem came from quantum computing. The work grew out of the Quantum Moonshot Program, a collaboration between MIT, the University of Colorado at Boulder, MITRE, and Sandia National Laboratories, aimed at building a novel quantum computing platform using diamond-based qubits (quantum bits). These qubits are controlled by laser beams, and the research team needed a way to interact with potentially millions of them simultaneously.
How the 'ski jumps' are made
The solution is elegantly physical. The researchers fabricated two-layer microstructures from silicon nitride and aluminum nitride, two materials with different thermal expansion rates. During the high-temperature fabrication process, both materials expand. As the chip cools to room temperature, the difference in how much each layer contracts causes the entire structure to curl upward off the chip surface, much like a bimetallic strip in an old-fashioned thermostat.
The result is thousands of tiny curved structures that the researchers describe as resembling miniature ski jumps. Waveguides on the chip funnel laser light to each structure, and a series of modulators allows rapid, independent control over how light is emitted from each one. The structures can broadcast light at different colors, and by adjusting the frequencies, the team can control the density and pattern of the emitted light.
The system proved remarkably stable. According to co-lead author Henry Wen, a visiting research scientist at MIT's Research Laboratory of Electronics, the emitted pattern remains perfectly still without error correction. The team simply calculates which lasers need to be active at a given moment and turns them on.
Projecting full-color images half the size of a salt grain
To demonstrate the platform's capabilities, the researchers used the chip to project detailed, full-color images that measure roughly half the size of a grain of table salt. Each pixel sits at the physical limit of how small a pixel can be, determined by the wavelength of the light itself. This gives the platform a pixel density roughly 15,000 times greater than that of a typical smartphone display.
The approach essentially allows the chip to paint pictures in free space using light, creating what amounts to an optical engine at the smallest possible scale. For augmented reality, this could mean lightweight glasses with displays far sharper than anything current technology permits.
Quantum computing and beyond
The original quantum computing motivation remains central. Diamond-based qubits require precise laser control, and this platform can generate thousands of individually addressable beams from a single chip. Scaling to millions, the number needed for practical quantum computers, would require arrays of multiple chips working together, which the researchers plan to explore.
The technology also has potential applications in Lidar (light detection and ranging) systems. Current Lidar units are bulky, but a photonic chip that can steer beams rapidly across a wide area could shrink the technology enough to fit on small robots or drones. In 3D printing, where lasers cure layers of resin to build objects, the platform's rapid beam switching could significantly accelerate fabrication speeds and enable more complex geometries.
What needs to happen next
The platform is at a proof-of-concept stage. The researchers demonstrated the principle with thousands of emitters, but scaling to the millions needed for quantum computing remains an engineering challenge that has not been addressed experimentally. The fabrication innovation, combining silicon nitride and aluminum nitride on a single chip, was enabled by pioneering work at Sandia National Labs, and reproducing it at commercial scale will require further development.
Durability is another open question. The team acknowledges the need for robustness testing to determine how long the curled structures maintain their shape and optical properties under real-world conditions. The thermal-mechanical principle that creates the curl is the same one that could, over many temperature cycles, cause material fatigue.
The work also does not address integration with existing photonic ecosystems. Getting light off a chip is one half of many applications; the other half involves detecting, processing, or using that light after it enters free space, which introduces its own set of challenges depending on whether the end use is a display, a quantum computer, or a Lidar system.
But as a fundamental platform technology, the ski jump architecture opens a path that previous photonic approaches could not. The ability to project thousands of independently controlled laser beams from a single chip, with pixel-level precision and without active stabilization, is a capability the field has lacked. What gets built on that foundation remains to be seen.