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

doi:10.1117/12.2661210

17 March 2023 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

Author Affiliations +

Proceedings Volume 12424, Integrated Optics: Devices, Materials, and Technologies XXVII; 124240H (2023) https://doi.org/10.1117/12.2661210
Event: SPIE OPTO, 2023, San Francisco, California, United States

Abstract

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.

Conference Presentation

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A. Memon, A. van Rees, J. Mak, Y. Fan, P. J. M. van der Slot, H. M. J. Bastiaens, and K.-J. Boller "Using hybrid integrated InP-Si₃N₄ diode lasers for the generation of sub-GHz repetition rate frequency combs", Proc. SPIE 12424, Integrated Optics: Devices, Materials, and Technologies XXVII, 124240H (17 March 2023); https://doi.org/10.1117/12.2661210

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