Abstract
Fiber-based optical microcavities exhibit high quality factor and low mode volume resonances that make them attractive for coupling light to individual atoms or other microscopic systems. Moreover, their low mass should lead to excellent mechanical response up to high frequencies, opening the possibility for high bandwidth stabilization of the cavity length. Here, we demonstrate a locking bandwidth of 44 kHz achieved using a simple, compact design that exploits these properties. Owing to the simplicity of fiber feedthroughs and lack of free-space alignment, this design is inherently compatible with vacuum and cryogenic environments. We measure the transfer function of the feedback circuit (closed-loop) and the cavity mount itself (open-loop), which, combined with simulations of the mechanical response of our device, provide insight into underlying limitations of the design as well as further improvements that can be made.
Highlights
High finesse Fabry-Perot cavities have extensive applications in spectroscopy [1, 2] and precision measurement [3, 4], as well as fundamental research in quantum optics [5, 6]
Fiber-based micro-mirrors [10] offer a promising technology for creating tunable, highfinesse optical micro-cavities. These cavities can achieve very small mode waists, which are advantageous for cavity quantum electrodynamics applications; so far, they have been coupled to atoms [11,12,13], ions [9, 14], optomechanical systems [15, 16], molecules [17], and crystalline defect centers [18,19,20]
An optimized design for a macroscopic Fabry-Perot cavity composed of two small free-space mirrors achieved a bandwidth of up to 180 kHz [23]. This result relied on the damping properties of lead inside the mirror mount to reduce the impact of low-frequency mechanical resonances on the feedback circuit, which limits its function to non-cryogenic applications
Summary
High finesse Fabry-Perot cavities have extensive applications in spectroscopy [1, 2] and precision measurement [3, 4], as well as fundamental research in quantum optics [5, 6]. Adding photothermal stabilization can further improve noise suppression for frequencies up to 500 kHz [21, 22] Such “self-stable" operation is achieved via intra-cavity heating of the mirror coatings by an incident laser; disturbances that change the length of the cavity affect the intra-cavity power, which in turn induces thermal expansion that stabilizes the effective length. An optimized design for a macroscopic Fabry-Perot cavity composed of two small free-space mirrors achieved a bandwidth of up to 180 kHz [23] This result relied on the damping properties of lead inside the mirror mount to reduce the impact of low-frequency mechanical resonances on the feedback circuit, which limits its function to non-cryogenic applications. With a combination of direct measurements of the system’s transfer function and finite-element simulations, we identify limiting features in the mechanical response associated with resonances in the mount, fiber, and epoxy, and provide an additional set of design considerations
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