Impact of the frequency drift of a laser cooler on the phase noise of the microcomb repetition frequency
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Mahmood, Tanvir, James P. Cahill, Patrick Sykes, Curtis R. Menyuk, and Weimin Zhou. “Impact of the Frequency Drift of a Laser Cooler on the Phase Noise of the Microcomb Repetition Frequency.” In Laser Resonators, Microresonators, and Beam Control XXVII, 13349:20–23. SPIE, 2025. https://doi.org/10.1117/12.3043569.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
We study the repetition frequency phase-noise in an auxiliary laser cooler assisted soliton microcomb formed in a high-Q Si₃N₄ microresonator. We find that, below a 1-kHz offset from the carrier, this noise is dominated by the frequency drift of the laser cooler. We identify the dominant noise types in the phase-noise spectrum of the repetition frequency using the polynomial law and relate the underlying noise sources that lead to the phase instability. We find that the 1 𝑓³ ⁄ noise dominates the repetition frequency phase-noise over three decades, which we attribute to the frequency drift of the laser cooler and the uncompensated cavity-pump detuning. Since the laser cooler acts on the cavity-pump detuning via the thermo-optic effect, the thermal response time of the cavity limits the filtering of 1 𝑓³ ⁄ noise originating from the free-running pump laser. Hence, low-phase-noise operation that is obtained by using the auxiliary laser cooling scheme requires both the pump and cooler lasers to be locked to a stable frequency reference.