Optical frequency combs are broadband sources that offer mutually coherent, equidistant spectral lines with unprecedented precision in frequency and timing for an array of applications1. Frequency combs generated in microresonators through the Kerr nonlinearity require a single-frequency pump laser and have the potential to provide highly compact, scalable and power-efficient devices2,3. Here we demonstrate a device—a laser-integrated Kerr frequency comb generator—that fulfils this potential through use of extremely low-loss silicon nitride waveguides that form both the microresonator and an integrated laser cavity. Our device generates low-noise soliton-mode-locked combs with a repetition rate of 194 gigahertz at wavelengths near 1,550 nanometres using only 98 milliwatts of electrical pump power. The dual-cavity configuration that we use combines the laser and microresonator, demonstrating the flexibility afforded by close integration of these components, and together with the ultra low power consumption should enable production of highly portable and robust frequency and timing references, sensors and signal sources. This chip-based integration of microresonators and lasers should also provide tools with which to investigate the dynamics of comb and soliton generation.
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The data that support the findings of this study are available from the corresponding authors on reasonable request.
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We are grateful to S. Miller, C. Joshi, T. Lin, U. Dave and J. Jang for discussions and to M. Yu for help with soliton simulations. We also thank M. C. Shin and O. Jimenez for packaging advice. This work was supported by AFRL programme award number FA8650-17-P-1085; the ARPA-E ENLITENED programme (DE-AR0000843); the Defense Advanced Research Projects Agency (DARPA) under the Microsystems Technology Office Direct On-Chip Digital Optical Synthesizer (DODOS) program (N66001-16-1-4052) and the Modular Optical Aperture Building Blocks (MOABB) programme (HR0011-16-C-0107); the STTR programme (N00014-16-P-30); and the Air Force Office of Scientific Research (AFOSR) (FA9550-15-1-0303). X.J. acknowledges the China Scholarship Council for financial support. This work was performed in part at the Cornell NanoScale Facility, an NNCI member supported by NSF grant ECCS-1542081.
Nature thanks W. Freude and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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Extended data figures and tables
Shown is the simulated optical spectrum of a soliton comb generated with 700 µW optical pump power (Pin) in the bus waveguide before the microresonator. The microresonator dimensions used in the model are 730 nm × 1,800 nm with a radius of 120 µm, corresponding to a 194 GHz FSR.
a, Simulation of a single-soliton comb generated with 2 mW optical pump power in the bus waveguide before the microresonator (1.66 mW after the microresonator). The microresonator dimensions used in the model are 730 nm × 1,800 nm with a radius of 120 µm, corresponding to a 194 GHz FSR. b, Optical spectrum of a measured single-soliton comb (from Fig. 3c) with 1.66 mW pump power in the bus waveguide after the microresonator. The sech profile and comb bandwidth qualitatively match those of the simulated comb.
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Stern, B., Ji, X., Okawachi, Y. et al. Battery-operated integrated frequency comb generator. Nature 562, 401–405 (2018). https://doi.org/10.1038/s41586-018-0598-9
- Frequency Comb
- Comb Generation
- Equidistant Spectral Lines
- Reflective Semiconductor Optical Amplifier (RSOA)
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