Integrated nonlinear photonics.

Optical frequency combs revolutionized precision measurement — a breakthrough recognized by the 2005 Nobel — by providing an exquisitely stable ruler for measuring optical frequencies.

The traditional version relies on big, complex femtosecond laser systems. The push of the past decade has been to shrink that capability onto a chip — combining the topological lattice from the previous page with the right kind of nonlinearity, so that one color of laser light, sent in, comes out as many.

Pump the lattice with a single color of laser light. Out comes a comb — many colors at once.

The lattice does the work. As the pump circulates, the Kerr nonlinearity in each ring couples it to its neighboring frequencies, building up a comb of optical lines below.

And here's the twist

Look closely at one tooth of that comb. Zoom in. What looks like a single spectral line at one scale turns out to be — at finer resolution — another comb.

This is the heart of nested frequency-phase matching: combs within combs, on multiple timescales simultaneously. A coarse comb sets the rhythm; inside each tooth, a finer comb follows. Both lock to the chip; both stay phase-coherent.

Why this matters

Each comb tooth is, in principle, a usable channel — for telecommunications, for sensing, for clocks. A nested comb gives you orders of magnitude more channels from the same chip area, with the matching conditions engineered in by the lattice geometry rather than tuned painstakingly after fabrication. That's the door this work opens, and it's why most of my recent papers live here.