All-optical control of ultrahigh-Q silica microcavities with iron oxide nanoparticles

We propose and experimentally demonstrate, to the best of our knowledge, the first all-optical control scheme of ultrahigh-quality (Q)-factor silica microcavities, which can maintain their Q factors over 10⁸ during the tuning process. For silica microcavities, the resonance tunability is very important and is also challenging for many applications. However, almost all previous works on resonance tuning deteriorate the Q factors of silica microcavities at different levels, and evidently these schemes are not suitable for applications in which ultrahigh Q factors are required. In this work, based on the proposed silica microbottle cavity and iron oxide nanoparticles, we realize all-optical control of the silica microcavity and maintain its Q factor of around 1.2×10⁸ during the tuning process. A tuning range of 85.9 GHz (0.68 nm) and a tuning sensitivity of 13.6 GHz/mW are obtained, and it is possible to realize full tunability by bridging the azimuthal free spectral range using six adjacent q-series modes. Moreover, all-optical control of the reflection spectrum is also carried out. This work will broaden the applications of ultrahigh-Q silica microcavities in nonlinear optics, microwave photonics, cavity optomechanics, and cavity quantum electrodynamics.