We present three high finesse tunable monolithic fiber Fabry-Perot cavities (FFPCs) with high passive mechanical stability. The fiber mirrors are fixed inside slotted glass ferrules, which guarantee an inherent alignment of the resonators. An attached piezoelectric element enables fast tuning of the FFPC resonance frequency over the entire free-spectral range for two of the designs. Stable locking of the cavity resonance is achieved for sub-Hertz feedback bandwidths, demonstrating the high passive stability. At the other limit, locking bandwidths up to tens of kilohertz, close to the first mechanical resonance, can be obtained. The root-mean-square frequency fluctuations are suppressed down to ∼2% of the cavity linewidth. Over a wide frequency range, the frequency noise is dominated by the thermal noise limit of the system’s mechanical resonances. The demonstrated small footprint devices can be used advantageously in a broad range of applications like cavity-based sensing techniques, optical filters or quantum light-matter interfaces.

Fabry–Perot interferometers have stimulated numerous scientific and technical applications ranging from high-resolution spectroscopy over metrology, optical filters, to interfaces of light and matter at the quantum limit and more. End facet machining of optical fibers has enabled the miniaturization of optical Fabry–Perot cavities. Integration with fiber wave guide technology allows for small yet open devices with favorable scaling properties including mechanical stability and compact mode geometry. These fiber Fabry–Perot cavities (FFPCs) are stimulating extended applications in many fields including cavity quantum electrodynamics, optomechanics, sensing, nonlinear optics and more. Here we summarize the state of the art of devices based on FFPCs, provide an overview of applications and conclude with expected further research activities.

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