Untangling the potential of frequency-modulated combs

David Burghoff

A frequency comb is a laser with a twist that emits many uniformly spaced optical wavelengths. The regularity of the spacing between lines — the comb’s teeth — serves as a ruler for measuring light frequencies.

David Burghoff, assistant professor of electrical engineering, developed a technique that showed that many lasers act as frequency-modulated combs. His research group Quantum and Nonlinear Optoelectronics also has demonstrated the first laser-based terahertz combs and the first deliberately designed combs in semiconductor lasers.

Burghoff is now the first to demonstrate that the light in many lasers obeys the same nonlinear equation that describes systems such as electrons in atoms and waves in narrow channels. His paper, “Unraveling the origin of frequency-modulated combs using active cavity mean-field theory,” was recently published in Optica, the Optical Society’s online journal.

“Frequency-modulated (FM) comb states have been observed in many systems and have been numerically described, but not analytically,” Burghoff said. “It turns out FM comb states can be described quite simply, but instead of having a potential proportional to intensity, FM combs obey one with a potential proportional to phase.”

“The active-cavity mean-field theory was critical for getting results,” said Burghoff. “Using it, we were able to pare down the multiple complicated equations necessary down to one equation, which for the first time allows us to write the solution.

“Now that we understand these combs at such a deep level, we can start engineering them to make better, more stable combs with broader bandwidths to help perform specific function.”

Potential applications for chip-scale frequency combs range from light detection measurement for self-driving cars to spectroscopy for chemical sensing and optical communications.

Burghoff’s work is funded in part by the Air Force Office of Scientific Research through its Young Investigator Program.

Originally published by the College of Engineering on January 13, 2021.