Using hybrid integrated InP-Si3N4 diode lasers for the generation of sub-GHz repetition rate frequency combs

A. Memon*, A. van Rees, J. Mak, Y. Fan, P.J.M. van der Slot, H.M.J. Bastiaens, K.-J. Boller

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review

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Optical frequency combs based on broadband-gain bulk lasers, due to the low intrinsic linewidth and sub-GHz repetition rates, have gained tremendous interest for applications such as high-resolution spectroscopy, dual-comb spectroscopy or LIDAR. However, susceptibility to mechanical and acoustic perturbations, the complexity of optical pumping and the larger physical size of these lasers has motivated research toward chip-based integrated extended cavity diode lasers with low-loss Si3N4 waveguide feedback circuits for low repetition rates. In diode lasers, mode-locking via saturable absorbers is generally used for generating frequency combs, however, the short upper-state carrier lifetime results in repetition rates of at least a few GHz. Here, we demonstrate absorber-free, passive mode-locking as well as hybrid mode-locking at sub-GHz repetition rates using a long Si3N4 feedback circuit with three highly frequency-selective microring resonators for extending the cavity roundtrip length to more than 0.6 m. This enables frequency-domain mode-locking in the form of a continuous wave, with a line spacing of around 500 MHz. Hybrid mode-locking, in addition to passive mode-locking, is demonstrated by adding a weak AC drive current with a frequency close to 500 MHz. This stabilizes the repetition rate and reduces the Gaussian component of the laser’s RF linewidth attaining a negligible Lorentzian component. Our numerical simulations predict that further lowering of the repetition rate and line spacings might be achievable with further cavity length extension.
Original languageEnglish
Title of host publicationIntegrated Optics
Subtitle of host publicationDevices, Materials, and Technologies XXVII
EditorsSonia M. Garcia-Blanco, Pavel Cheben
ISBN (Electronic)9781510659537
Publication statusPublished - 17 Mar 2023
EventSPIE Photonics West 2023 - The Moscone Center, San Fransisco, United States
Duration: 31 Jan 20232 Feb 2023


ConferenceSPIE Photonics West 2023
Country/TerritoryUnited States
CitySan Fransisco
Internet address


  • Optical Frequency Combs
  • Mode-locked Lasers
  • Passive Mode-Locking
  • Hybrid Mode-locking
  • Hybrid Integrated Diode Lasers
  • Extended Cavity Diode Lasers
  • Fourier Domain Mode-Locking
  • Low Repetition Rate

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