Caltech Develops Chip-Scale Frequency Comb Using Topological Solitons

New approach allows for more compact and practical frequency comb sources.

Mar. 26, 2026 at 3:57am

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Caltech scientists have developed a new way to produce optical frequency combs - important tools in devices that keep time and measure distances very precisely - at the chip scale. The approach uses a robust class of light pulses called topological solitons, which had been previously predicted but largely unexplored until now. The new device, called a degenerate optical parametric oscillator (DOPO), exploits strong quadratic nonlinearity in lithium niobate to generate frequency combs more easily than previous methods that relied on weaker cubic nonlinearity.

Why it matters

Frequency combs are critical tools in many applications like spectroscopy, telecommunications, and astronomical research, but current frequency comb sources are often bulky tabletop laser systems. Caltech's new chip-scale approach using topological solitons could make frequency combs more compact, practical, and accessible for a wider range of uses outside the lab.

The details

The DOPO device generates the frequency comb by exploiting quadratic nonlinearity in lithium niobate, which is much stronger than the cubic nonlinearity used in many previous chip-scale frequency comb approaches. This allows the device to produce the nonlinear effects needed for the comb with a lower quality resonator that is easier to fabricate. The DOPO also generates the comb at half the frequency of the input light, enabling access to the important mid-infrared spectral region. The team demonstrated both a two-soliton comb state and a "soliton crystal" state with 16 evenly spaced dark pulses.

  • The research paper was published online on March 25, 2026.

The players

Alireza Marandi

Professor of electrical engineering and applied physics at Caltech and the lead author of the study.

Nicolas Englebert

Postdoctoral scholar at Caltech and one of the lead authors of the study, along with Robert M. Gray.

Robert M. Gray

PhD student at Caltech at the time of the study, now at ETH Zurich.

Caltech

The university where the research was conducted.

Kavli Nanoscience Institute

The institute at Caltech where the DOPO device was fabricated.

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What they’re saying

“Our new approach allows us to explore a completely different path. It promises that many of the challenges we have faced with other on-chip methods for generating frequency combs may be avoided.”

— Alireza Marandi, Professor of electrical engineering and applied physics at Caltech

“Thanks to the DOPO, this topological frequency comb forms at half the frequency of the input light. This is particularly exciting since it allows for generating combs in the hard-to-access mid-infrared spectral region, starting from readily available integrated near-infrared lasers.”

— Nicolas Englebert, Postdoctoral scholar at Caltech

What’s next

The team plans to further characterize the behaviors of the topological soliton states in the DOPO and explore potential applications beyond frequency comb sources.

The takeaway

Caltech's development of a chip-scale frequency comb using topological solitons represents an important advance that could make these critical tools more compact, practical, and accessible for a wider range of applications outside the lab setting.