Photonic microchips are small semiconductors that use light rather than electricity to carry information. Light travels through tiny channels called waveguides that are only micrometers wide. These chips support the high-speed data handling needed in telecommunications, large artificial intelligence centers, and quantum technologies.
Engineers normally design each part of such a chip by starting with a known shape and adjusting it by hand. This process is slow. Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences and the Max Planck Institute for the Science of Light took a different approach. They used a computer method known as inverse design. In this method the desired behavior of the light is stated first. The computer then searches many possible shapes until it finds one that produces exactly that behavior. The resulting shapes often look irregular, with holes and ridges, yet they guide light precisely in a space much smaller than the width of a human hair.
Toward higher-performance photonics
The work focused on silicon nitride, a material that loses little light and can help generate clean light of many colors. Three types of components were created, fabricated, and tested. Wavelength splitters separate different colors of light. Spatial mode sorters divide light into different spatial paths. Mirrors reflect light.
Compact mirrors only a few micrometers across reflect up to 98.5 percent of the light that reaches them while blocking unwanted paths. When two such mirrors face each other they form an optical cavity, a small region where light bounces more than one hundred times before leaving. Each of these components is about five hundred times smaller than conventional versions and can be made with standard commercial manufacturing processes.
The next step is to combine the new components with nonlinear optical circuits. In those circuits intense light can produce optical frequency combs, which are precise sets of many evenly spaced colors of light used in measurement, telecommunications, and quantum work. The same design method can create several different functions on one chip, opening a route to more compact and higher-performance light-based technology.
This research is published in Nature Communications.