Fiber-taper coupling to Whispering-Gallery modes of fluidic resonators embedded in a liquid medium
Citation
Hossein-Zadeh, Mani, and Kerry J. Vahala. “Fiber-Taper Coupling to Whispering-Gallery Modes of Fluidic Resonators Embedded in a Liquid Medium.” Optics Express, vol. 14, no. 22, 30 Oct. 2006, pp. 10800–10.
Keywords
- Optofluidics
- Whispering-Gallery (WG) Modes
- Droplet Resonator
- Fiber-Taper Coupling
- Liquid Cladding
- Phase Matching
- Critical Coupling
- Quality Factor (Q-factor)
- Azimuthal Modes
- Reconfigurability
Brief
The article discusses a novel technique for efficient optical coupling to Whispering-Gallery modes of a droplet resonator immersed in liquid, highlighting its advantages for optofluidic applications.
Summary
This article, published in 2006, details a novel technique for coupling light into a liquid droplet resonator. The sources identify two primary challenges in optical analysis of droplet resonators: stabilizing the droplet and efficiently coupling light into it. To circumvent these issues, the authors immerse the droplets in an immiscible liquid "cladding" with a lower refractive index than the droplet. This cladding serves to prevent evaporation, dampen mechanical vibrations and, with careful material matching, enable phase-matched coupling to the droplet.
Previous methods of free space coupling with a Gaussian beam have proven inefficient due to phase mismatch and minimal spatial overlap with the desired optical mode. The article details the experimental success of using a fiber-taper coupler to excite whispering-gallery modes (WGMs) within a water droplet. This waveguide coupling method is presented as an efficient alternative to free space coupling.
The authors present two successful trials: coupling light into a 1 mm diameter droplet and a 600 μm diameter droplet. In both cases, critical coupling to the fundamental WGMs was achieved at a wavelength of 980 nm. Analysis of the transmission spectrum, free-spectral range, and quality factors show strong agreement between the experimental results and theoretical calculations. The smaller droplet demonstrated the added benefit of allowing observation of the over-coupled regime.
The article concludes by highlighting several benefits and future applications of this technique, noting the potential for droplet resonators in optofluidics and sensing applications.
Origin: https://opg.optica.org/oe/fulltext.cfm?uri=oe-14-22-10800&id=116603