Chip-Scale Self-Referenced Optical Frequency Comb Sources

Project Information

REFOCUS

Grant agreement ID: 853522

DOI

10.3030/853522

Project closed

EC signature date 2 October 2019

Start date 1 January 2020

End date 30 June 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 487 597,00

EU contribution

€ 1 487 597,00

Coordinated by

DANMARKS TEKNISKE UNIVERSITET
Denmark

Periodic Reporting for period 3 - REFOCUS (Chip-Scale Self-Referenced Optical Frequency Comb Sources)

Reporting period: 2023-01-01 to 2024-06-30

Summary of the context and overall objectives of the project

Self-referenced frequency combs revolutionized metrology and enabled optical atomic clocks with unprecedented accuracy that benefit applications ranging from navigation and high-precision spectroscopy to telecommunications. Despite the outstanding performance, the application of such combs is limited to laboratories due to the prohibitively large size, weight, and power (SWaP) of a frequency comb system. Miniaturization of the comb systems will enable emerging applications such as LIDAR, chemical sensing, and medical imaging. This project aims to develop a chip-scale optical frequency comb source that can be self-referenced.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Octave-spanning frequency combs are the key to the realization of self-referencing. Although on-chip frequency comb generation has been demonstrated in nonlinear waveguides and microresonators based on the Kerr effects, it is still challenging to drive a broadband (octave-spanning) frequency comb with microwave repetition frequencies using on-chip lasers with limited output power. This project targets achieving broadband frequency combs and increasing the efficiency of the nonlinear processes for comb generation to bridge the broadband frequency comb with on-chip lasers. In this project, we carefully engineered the dispersion of nonlinear waveguides for octave-spanning dispersive wave generation. We demonstrated different microresonator dispersion designs to suppress the avoided mode crossing for easier soliton generation. We realized high-Q AlGaAs and SiC microresonators, enabling sub-milli-watt-level threshold Kerr comb generation.

Turn-key operation is another critical element for chip-scale frequency comb source. In this context, deterministic single soliton generation is highly desired but still elusive for octave-spanning microcombs. A delicate thermal equilibrium is required to trigger soliton generation for broadband operation. This project investigated how to achieve the athermal operation of microresonators for deterministic soliton generation. We engineered the dispersion of multi-mode microresonators and utilized a modified laser cooling technique to demonstrate deterministic single-soliton generation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

To bridge optical frequency and microwave frequencies, optical frequency combs should have octave-spanning bandwidths and microwave repetition rates. The required massive number of comb lines of such a broadband light source imposes a challenge in driving the combs and distributing sufficient power to the 1f and 2f comb lines for self-referencing using existing on-chip lasers (with state-of-the-art laser technologies). Therefore, a nonlinear process with extremely high efficiency needs to be developed. In this project, we also investigated a new method combining the AlGaAsOI waveguide's high nonlinearity and a seeded supercontinuum generation pump scheme. We demonstrated an octave-spanning comb with a microwave repetition rate using low-power picosecond pulses, which significantly relaxed the requirement for mode-locked lasers in supercontinuum generation and paved the way to the realization of chip-scale supercontinuum comb source.