Scientists at the California Institute of Technology (Caltech) have developed a method for creating ultra-low-loss optical paths directly on silicon wafers. The new technology allows light to be guided with losses approaching those of optical fiber, particularly in the visible wavelength range.
The researchers used germanosilicate glass—the same material found in optical fiber. The waveguides are formed into spirals so that light travels a long path within a compact chip area of just a couple of centimeters. This is reminiscent of winding fiber onto a spool, but at the nanoscale.
In the visible spectrum, the new platform outperforms silicon nitride—the standard material for photonic integrated circuits—by a factor of 20. Losses are reduced to such an extent that lasers based on these waveguides demonstrate more than a hundredfold improvement in light coherence.
Project lead Kerry Vahala notes that the method brings the manufacturing advantages of optical fiber to standard 8- and 12-inch silicon wafers. Co-authors of the study, postdoctoral scholar Hao-Jing Chen and graduate student Kellan Colburn, emphasize that surface smoothness is achieved through "reflowing" in a furnace down to the atomic level.
The results have been published in the journal Nature. The devices have already been tested in ring resonators, various types of lasers, and nonlinear resonators. Potential applications include chip-scale atomic clocks, gyroscopes, quantum systems, and energy-efficient communications in AI data centers.
How will this impact the development of miniature sensors and quantum technologies in the coming years? One thing is clear for now: low losses pave the way for more coherent and economical photonic circuits that previously seemed unattainable on silicon.
The work was funded by DARPA, the U.S. Air Force, and other organizations. The scientists emphasize that this is only an intermediate stage—significant progress lies ahead.
