Self-aligned optical microcomb emerging between octave separated lasers

TL;DR

This paper presents a novel integrated microcomb architecture that uses two octave-separated pump lasers to generate a self-aligned, octave-spanning optical frequency comb, enabling robust, compact, and versatile applications in precision metrology.

Contribution

The authors introduce an architectural inversion where microcombs form between two pump lasers, overcoming previous limitations and enabling stable, octave-spanning combs on-chip with simplified stabilization.

Findings

Successfully generated octave-spanning combs from telecom to visible wavelengths.

Achieved robust self-alignment and synchronization with pump lasers across multiple devices.

Demonstrated core OFC tasks: frequency synthesis, millimeter-wave generation, and optical clock readout.

Abstract

Optical frequency combs (OFCs) are frequency rulers essential for precision metrology, next generation navigation, and testing of fundamental physics. Despite intense efforts, chip-integrated OFCs remain laboratory-bound, unable to fulfill their promise of compact and cost-effective deployment. While improvement in fabrication and integration are important, a conceptual limitation has fundamentally stymied progress: on-chip OFC architectures have aimed to miniaturize their table-top counterparts and relied on cascading outward from (i.e., spectrally broadening) a single pump. In integrated platforms, this approach does not readily allow for the generation of strong and low-noise octave-spaced signals that are crucially needed for robust zero-frequency offset detection. Here, we overcome this limitation via an architectural inversion where an optical microcomb forms by filling the spectrum between two octave-separated pump lasers. The two pumps generate a parametrically driven cavity soliton (PDCS) in an integrated $\chi^{(3)}$ resonator, which robustly self-aligns to (i.e., synchronizes with) the pump lasers across multiple foundry-fabricated devices and operating configurations. This produces a single octave-spanning comb extending from telecom to visible wavelengths, whose zero-frequency offset is completely defined by the two harmonically-related pump lasers, and can therefore be reliably detected and stabilized. We showcase our platform's capabilities by executing all of the three core tasks of OFC metrology: optical frequency synthesis, low-noise millimeter-wave generation, and integrated optical clock readout, using the same self-aligned microcomb with only its input locks changed.