Author_Institution :
OFS Labs., Somerset, NJ, USA
Abstract :
Investigation and application of the high Q-factor optical microresonators became an interesting and rapidly developing field of modern optics. Special attention is given to the Fabry-Perot, ring, disk, sphere, and toroid microresonators as well as more recently introduced bottle, coil, and capillary microresonators. Optical microresonators are demonstrated as super-perceptive physical, chemical and biological sensors, microlasers, and have promising applications in cavity quantum electrodynamics, cavity optomechanics, and other areas of fundamental and applied research and development. This presentation reports recent demonstration of a new type of optical microresonator - a silica microbubble resonator. The fabrication method of this resonator is based on blowing a microbubble using the stable radiative CO2 laser heating rather than the unstable convective heating in a flame or furnace. Microbubbles are created along a microcapillary and are naturally opened to the input and output microfluidic or gas channels. The demonstrated optical microbubble resonators have a few hundred micron diameter and around one micron wall thickness. The resonant properties of a microbubble are studied by coupling it to a microfiber. A biconical taper with a microfiber waist is fabricated from a conventional single mode fiber by adiabatic tapering using the CO2 laser indirect heating method. The measured Q-factor of a microbubble resonator exceeds 106 (limited by the resolution of the measurement device used). The transmission spectrum of an empty microbubble is compared to the spectrum of the same microbubble filled with ethanol. As an application, the mechanical tunability of a microbubble resonator was experimentally investigated by stretching it with a PZT. Previously, both thermal and mechanical tuning of high Q-factor microresonators has been considered. However, the full tunability (i.e. the tunable range exceeding the azimuthal free spectral ra- - nge of a microresonator) has not been achieved. Here, a fully tunable silica MBR having a tuning range more than two times larger than the azimuthal free spectral range of this resonator is demonstrated. This is the largest tuning range ever achieved for the high Q-factor microcavities (microspheres, microspheroids, microtoroids, etc.) significantly exceeding the record result obtained previously. Tunability of a microbubble resonator is accomplished with a much smaller stretching force than that needed for a similar bulk microresonator.
Keywords :
Q-factor; micromechanical resonators; optical resonators; biconical taper; high Q-factor optical microresonators; laser heating; optical microbubble resonator; Biomedical optical imaging; Fabry-Perot; Heating; Laser tuning; Microcavities; Optical resonators; Optical sensors; Q factor; Silicon compounds; Tunable circuits and devices; high Q-factor optical resonators; optical fiber devices; optical microresonators; optical sensors; tunable microresonators;
