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Optical Reference Cavity

Patent Number: 10,931,077


An optical reference cavity includes: a cell that includes: a cylindrical body; end faces; an optical canal having an interior cylindrical geometry; and an exterior surface having an exterior cylindrical geometry; mirrors disposed on the end faces; an aspect ratio that is less than 1; a compression clamp that holds the cell through compression and includes compression platens disposed on the end faces so that the compression platens exert a compressive force to the end faces at a radius from a central axis of the cell so that the cell is compressed by the compression clamp, and a length of the optical canal is unperturbed to first order with a magnitude of the compressive force; and a compression intermediary interposed between the compression platens and end faces, wherein the length of the optical canal is insensitive to vibration coupled to the cell by the compression clamp and compression intermediaries.

Patent Description

We have demonstrated an easy-to-manufacture 25-mm-long ultra-stable optical reference cavity geared toward transportable photonic microwave generation systems and mobile optical atomic clock applications. The cavity can be rigidly held in a way that is first-order insensitive to the squeezing force and with low vibration sensitivity. By locking a laser to the cavity resonance, we have demonstrated phase noise that is nearly thermal noise limited for three frequency decades (1 Hz to 1 kHz offset). The fractional frequency stability reaches 2 x 10^-15 at 0.1 s of averaging. Ongoing efforts have resulted in an improved design that relies on the same basic cylindrical geometry. The photograph below is the cavity and its Cavity Fastening Device (CFD).


While many passive optical reference cavity designs have been demonstrated, nearly all cavities capable of supporting sub-I Hz stabilization are large, not amenable to rigid holding, and, in some cases, operate at cryogenic temperatures. This invention enables a compact, rigidly held, vibrationally insensitive laser capable of operating at room temperature and outside the staid laboratory environment. Additionally, the geometries of other proposed or demonstrated rigidly held optical reference cavities are more complicated to manufacture. This inevitably introduces asymmetries that degrade the acceleration and holding force sensitivity. The simple cylindrical geometry of our design greatly increases the likelihood that it will be manufactured without undesirable asymmetries (at a concomitant lower cost).

Created March 24, 2021, Updated December 20, 2023