Foundry manufacturing of octave-spanning microcombs

TL;DR

This paper demonstrates the manufacturing of octave-spanning soliton microcombs using silicon-nitride photonics foundry, enabling compact, chip-based optical frequency combs for metrology with optimized design and fabrication considerations.

Contribution

It introduces a foundry-compatible process for producing octave-spanning microcombs with tailored dispersion and low power operation, advancing integrated photonics for optical metrology.

Findings

Successful fabrication of octave-spanning microcombs in a foundry environment.

Controlled soliton spectra through waveguide dispersion engineering.

Microcombs operate at low pump power with detectable offset frequency.

Abstract

Soliton microcombs provide a chip-based, octave-spanning source for self-referencing and optical metrology. We explore use of a silicon-nitride integrated photonics foundry to manufacture octave-spanning microcombs. By group-velocity dispersion engineering with the waveguide cross-section, we shape the soliton spectrum for dispersive-wave spectral enhancements at the frequencies for f-2f self-referencing. With the optimized waveguide geometry, we control the carrier-envelope offset frequency by adjusting the resonator radius. Moreover, we demonstrate the other considerations for octave microcombs, including models for soliton spectrum design, ultra-broadband resonator external coupling, low-loss edge couplers, and the nonlinear self-interactions of few-cycle solitons. This design process permits highly repeatable creation of soliton microcombs optimized for pump operation less than 100 mW, an electronically detectable offset frequency, and high comb mode power for f-2f detection. However, these design aspects must also be made compatible with the foundry fabrication tolerance of octave microcomb devices. Our experiments highlight the potential to manufacture a single-chip solution for an octave-spanning microcomb, which is the central component of a compact microsystem for optical metrology.