Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration,enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range....Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration,enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range.By comparing a star's spectrum to the astrocomb spectrum,minute radial velocity shifts indicative of an exoplanet's presence can be detected.The highest precision and accuracy astrocombs are generated by laser frequency combs.However,in the visible band,frequency comb calibrators have stringent operational lifetime limitations due to degradation of the supercontinuum-generating medium,and are thus typically used to calibrate FabryPérot etalons,which are then used for simultaneous observations with target stars.This work demonstrates a specially designed crystalline whispering-gallery-mode resonator(WGMR)that serves as an astrocomb etalon,featuring a coupling wavelength span of two octaves and a quasi-single-mode family.Several innovations have been incorporated into the system's compact design to achieve frequency stability,in addition to wide-range wavelength coupling.These include dual-mode thermometric frequency stabilization,in addition to vacuum packaging,effectively minimizing thermal and pressure-induced frequency drift.Long-term frequency stability,measured via a heterodyne RF beat note,exceeds 2×10-12,with a projected long-term modal frequency stability of≤10-10(equivalently 3 cm/s in Doppler velocity).This level of stability obviates the need for frequent cross-calibration with a laser reference,as was required with other astrocomb etalons.Overall,the architecture of the WGMR etalon provides a new and powerful capability,beyond what has previously been achieved by microresonator-based etalons,as a compact,ultra-wideband spectral reference for detecting small planets in long-period orbits around nearby stars.It also offers a path forward for a low size,weight,and power(SWaP)spectral reference appropriate for spaceflight.展开更多
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.T...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 dualmode 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 MgF_(2) 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 8.53μK 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.展开更多
基金Jet Propulsion Laboratory(80NM0018D0004,1654212,165880)National Aeronautics and Space Administration(NNH18ZDA001N-SAT,80NM0018D0004)。
文摘Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration,enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range.By comparing a star's spectrum to the astrocomb spectrum,minute radial velocity shifts indicative of an exoplanet's presence can be detected.The highest precision and accuracy astrocombs are generated by laser frequency combs.However,in the visible band,frequency comb calibrators have stringent operational lifetime limitations due to degradation of the supercontinuum-generating medium,and are thus typically used to calibrate FabryPérot etalons,which are then used for simultaneous observations with target stars.This work demonstrates a specially designed crystalline whispering-gallery-mode resonator(WGMR)that serves as an astrocomb etalon,featuring a coupling wavelength span of two octaves and a quasi-single-mode family.Several innovations have been incorporated into the system's compact design to achieve frequency stability,in addition to wide-range wavelength coupling.These include dual-mode thermometric frequency stabilization,in addition to vacuum packaging,effectively minimizing thermal and pressure-induced frequency drift.Long-term frequency stability,measured via a heterodyne RF beat note,exceeds 2×10-12,with a projected long-term modal frequency stability of≤10-10(equivalently 3 cm/s in Doppler velocity).This level of stability obviates the need for frequent cross-calibration with a laser reference,as was required with other astrocomb etalons.Overall,the architecture of the WGMR etalon provides a new and powerful capability,beyond what has previously been achieved by microresonator-based etalons,as a compact,ultra-wideband spectral reference for detecting small planets in long-period orbits around nearby stars.It also offers a path forward for a low size,weight,and power(SWaP)spectral reference appropriate for spaceflight.
基金support from DARPA and Air Force Research Laboratory under contract FA9453-14-M-0090.
文摘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 dualmode 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 MgF_(2) 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 8.53μK 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.
