Dynamic release of trapped light from an ultrahigh-Q nanocavity via adiabatic frequency tuning

Adiabatic frequency shifting is demonstrated by tuning an ultrahigh-Q photonic crystal nanocavity dynamically. By resolving the output temporally and spectrally, we showed that the frequency of the light in the cavity follows the cavity resonance shift and remains in a single mode throughout the process. This confirmed unambiguously that the frequency shift results from the adiabatic tuning. We have employed this process to achieve the dynamic release of a trapped light from an ultrahigh-Q cavity and thus generate a short pulse. This approach provides a simple way of tuning Q dynamically.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

High-Q coupled resonances on a PhC waveguide using a tapered nanofiber with high coupling efficiency

We experimentally demonstrate high-Q cavity formation at an arbitrary position on a silicon photonic crystal waveguide by bringing a tapered nanofiber into contact with the surface of the slab. An ultrahigh Q of 5.1 x 10^5 is obtained with a coupling efficiency of 39%, whose resonant wavelength can be finely tuned by 27 pm by adjusting the contact length of the nanofiber. We also demonstrate an extremely high coupling efficiency of 99.6% with a loaded Q of 6.1 x 10^3. In addition, we show that we can obtain an all-pass filter type coupled resonator system, which has the potential to be used for slow light generation.Comment: 8 pages, 7 figures. The following article has been submitted to Optics Express. After it is published, it will be found at https://www.osapublishing.org/oe/home.cf

Polygonal silica toroidal microcavity for controlled optical coupling

We fabricated polygonal silica toroidal microcavities to achieve stable mechanical coupling with an evanescent coupler such as a tapered fiber. The polygonal cavity was fabricated by using a combination of isotropic etching, anisotropic etching and laser reflow. It offers both high and low coupling efficiencies with the cavity mode even when the coupler is in contact with the cavity, which offers the possibility of taking the device outside the laboratory. A numerical simulation showed that an octagonal silica toroidal microcavity had an optical quality factor of 8.8\times10^6.Comment: 13 pages, 4 figure

Mechanically actuated Kerr soliton microcombs

Mode-locked ultrashort pulse sources with a repetition rate of up to several tens of gigahertz greatly facilitate versatile photonic applications such as frequency synthesis, metrology, radar, and optical communications. Dissipative Kerr soliton microcombs provide an attractive solution as a broadband, high-repetition-rate compact laser system in this context. However, its operation usually requires sophisticated pump laser control to initiate and stabilize the soliton microcombs, particularly in millimeter-sized ultrahigh-Q whispering-gallery resonators. Here, we realize a mechanically actuated soliton microcomb oscillator with a microwave repetition rate of 15 GHz. This enables direct soliton initiation, long-term stabilization, and fine tuning, where the operation now lifts the prerequisite pump laser tunability that must be relaxed if the technology is to be widely used outside the laboratory environment. We reveal the prospects for using this method with a wide range of applications that would benefit from mechanical soliton actuation such as optical clocks, spectral extension, and dual-comb spectroscopy