Scientists at Harvard have developed a new way to produce extremely precise patterns of laser light on a tiny chip, a breakthrough that could shrink advanced optical technologies into much smaller and more efficient devices.
The research, led by Professor Marko Lončar at the Harvard John A. Paulson School of Engineering and Applied Sciences, shows how a special material called lithium niobate can generate evenly spaced colors of light known as an optical frequency comb.
An optical frequency comb is a laser source whose colors are arranged at perfectly regular intervals, like the teeth of a comb.
These combs are essential for technologies that require extreme precision, including atomic clocks, environmental sensors, and high-speed communication systems. Traditional versions are large and expensive, relying on bulky fiber lasers.
Researchers have long sought to shrink them onto tiny photonic chips, creating so-called microcombs that use less power and can be integrated into portable devices.
The Harvard team used thin films of lithium niobate, a crystal known for its ability to control light with electricity.
This material has become increasingly important in photonics, the science of using light to process information.
However, making microcombs with lithium niobate has been difficult because of a phenomenon called the Raman effect. When the crystal is pumped with a laser, vibrations inside the material scatter the light and produce a single color instead of the desired evenly spaced pattern.
To overcome this problem, the researchers designed a new type of tiny ring-shaped device, similar to a racetrack, that suppresses the unwanted scattering.
By carefully choosing the orientation of the crystal, they were able to produce stable microcombs on the chip. In their latest work, they generated a special kind called a normal dispersion Kerr microcomb, which efficiently converts laser power into many evenly spaced light signals.
These signals are especially useful for sending large amounts of data through optical communication systems.
During the experiments, the team made an unexpected discovery.
A small amount of the Raman effect still remained, but instead of ruining the comb, it interacted with the light in a helpful way. This created a new hybrid comb that spans a wider range of colors and could be even more useful for applications that require coverage of hard-to-reach wavelengths.
Computer simulations confirmed that this new comb remains stable and coherent across its full range.
The ability to generate these precise light patterns on a chip could transform many technologies. For example, compact spectroscopic sensors could detect gases or chemicals by analyzing how they absorb specific colors of light. Improved communication systems could transmit data faster using multiple light channels at once.
Because the comb generator is only about a millimeter in size, it can be built alongside other optical components on the same chip, paving the way for fully integrated photonic systems.
Researchers say the work demonstrates that lithium niobate is a powerful platform for the next generation of light-based technologies.
By combining comb generation and electrical control on a single chip, the breakthrough moves scientists closer to miniaturized devices that were once only possible in large laboratory setups.
Source: KSR.
