Fig. 5: Single-sideband (SSB) phase noise of the dual-mode beat frequency, Allan deviation, and their enhancement at different proportional feedback gains. | Light: Science & Applications

Fig. 5: Single-sideband (SSB) phase noise of the dual-mode beat frequency, Allan deviation, and their enhancement at different proportional feedback gains.

From: Probing 10 μK stability and residual drifts in the cross-polarized dual-mode stabilization of single-crystal ultrahigh-Q optical resonators

Fig. 5

a SSB phase noise measurements of the dual-mode beat frequency at 5.953 GHz. Inset: the stabilized dual-mode beat frequency spectrum at 5.953 GHz. b Measured TM laser frequency in time with the two different feedback gains. The frequency drifts estimated with a linear function fitting show two examples at 11.8 kHz min−1 (navy) and 0.54 kHz min−1 (green), respectively. The red line is the unlocked (open-loop) TM laser frequency for comparison. c TM laser frequency Allan deviations with different feedback gains. By lowering the proportional gain, the long-term stability is improved, illustrating that the radio-frequency reference noise could be responsible for the frequency drift. d The lower proportional gain makes the enhancement slower along the integration time, but the enhancement roll-off is avoided with the higher gain. The enhancement factor at 1000 s integration time is 51.78

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