Over the past several decades, researchers have been making rapid progress in harnessing light to enable all sorts of scientific and industrial applications. From creating stupendously accurate clocks to processing the petabytes of information zipping through data centers, the demand for turnkey technologies that can reliably generate and manipulate light has become a global market worth hundreds of billions of dollars.
Over the past several decades, researchers have been making rapid progress in harnessing light to enable all sorts of scientific and industrial applications. From creating stupendously accurate clocks to processing the petabytes of information zipping through data centers, the demand for turnkey technologies that can reliably generate and manipulate light has become a global market worth hundreds of billions of dollars.
One challenge that has stymied scientists is the creation of a compact source of light that fits onto a chip, which makes it much easier to integrate with existing hardware. In particular, researchers have long sought to design chips that can convert one color of laser light into a rainbow of additional colors—a necessary ingredient for building certain kinds of quantum computers and making precision measurements of frequency or time.
Now, researchers at JQI have designed and tested new chips that reliably convert one color of light into a trio of hues. Remarkably, the chips all work without any active inputs or painstaking optimization—a major improvement over previous methods. The team described their results in the journal Science on Nov. 6, 2025.
The new chips are examples of photonic devices, which can corral individual photons, the quantum particles of light. Photonic devices split up, route, amplify and interfere streams of photons, much like how electronic devices manipulate the flow of electrons.
„One of the major obstacles in using integrated photonics as an on-chip light source is the lack of versatility and reproducibility“, says JQI Fellow Mohammad Hafezi, who is also a Minta Martin professor of electrical and computer engineering and a professor of physics at the University of Maryland. „Our team has taken a significant step toward overcoming these limitations.“
The new photonic devices are more than mere prisms. A prism splits multicolored light into its component colors, or frequencies, whereas these chips add entirely new colors that aren’t present in the incoming light. Being able to generate new frequencies of light directly on a chip saves the space and energy that would normally be taken up by additional lasers. And perhaps more importantly, in many cases lasers that shine at the newly generated frequencies don’t even exist.
The ability to generate new frequencies of light on a chip requires special interactions that researchers have been learning to engineer for decades. Ordinarily, the interactions between light and a photonic device are linear, which means the light can be bent or absorbed but its frequency won’t change (as in a prism). By contrast, nonlinear interactions occur when light is concentrated so intensely that it alters the behavior of the device, which in turn alters the light. This feedback can generate a panoply of different frequencies, which can be collected from the output of the chip and used for measurement, synchronization or a variety of other tasks.
Unfortunately, nonlinear interactions are usually very weak. One of the first observations of a nonlinear optical process was reported in 1961, and it was so weak that someone involved in the publication process mistook the key data for a smudge and removed it from the main figure in the paper. That smudge was the subtle signature of second harmonic generation, in which two photons at a lower frequency are converted into one photon with double the frequency. Related processes can triple the frequency of incoming light, quadruple it, and so forth.
Since that first observation of second harmonic generation, scientists have discovered ways to boost the strength of nonlinear interactions in photonic devices.
