Abstract
The thermal stability of monolithic optical microresonators is essential for many mesoscopic photonic applications such as ultrastable laser oscillators, photonic microwave clocks, and precision navigation and sensing. Their fundamental performance is largely bounded by thermal instability. Sensitive thermal monitoring can be achieved by utilizing cross-polarized dual-mode beat frequency metrology, determined by the polarization-dependent thermorefractivity of a single-crystal microresonator, wherein the heterodyne radio-frequency beat pins down the optical mode volume temperature for precision stabilization. Here, we investigate the correlation between the dual-mode beat frequency and the resonator temperature with time and the associated spectral noise of the dual-mode beat frequency in a single-crystal ultrahigh-Q MgF2 resonator to illustrate that dual-mode frequency metrology can potentially be utilized for resonator temperature stabilization reaching the fundamental thermal noise limit in a realistic system. We show a resonator long-term temperature stability of 8.53 μK after stabilization and unveil various sources that hinder the stability from reaching sub-μK in the current system, an important step towards compact precision navigation, sensing, and frequency reference architectures.
Highlights
High-precision clocks and oscillators are cornerstones for global navigation to provide accurate timing and distance information, via satellite-to-satellite or satellite-toground communications, for the synchronization of electronic device communications and for quantum information processing using atomic qubits[1,2,3]
Theoretical model of dual-mode temperature stabilization The resonator is made from a z-cut magnesium difluoride (MgF2) single crystal
MgF2 is a birefringent crystal with ne = 1.382 and no = 1.37, where (o) represents the ordinary polarized light or polarized with a transverse magnetic (TM) mode and (e) represents the extraordinary polarized light or polarized with a transverse electric (TE) mode, for the z-cut resonator
Summary
High-precision clocks and oscillators are cornerstones for global navigation to provide accurate timing and distance information, via satellite-to-satellite or satellite-toground communications, for the synchronization of electronic device communications and for quantum information processing using atomic qubits[1,2,3]. Frequency communications have limited data transfer rates largely due to the available spectral bands, and often require large antenna sizes and high power consumptions due to diffraction, which naturally demands higher frequency carriers. The oscillators based on electronics attain their spectral purity from the high-quality factor of the resonator circuit, which usually degrades with increasing frequency. This design, potentially increases the size and the power consumption and the complexity of the signal generation subsystems. Free-space low-noise optical carrier networks provide an alternative with compact footprints for high-precision timing synchronization and high data rate links[4,5,6]
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