Identification of Dielectric, Plasmonic, and Hybrid Modes in Metal-Coated Whispering-Gallery-Mode Resonators

Abstract

Making available and accessing in a controlled manner optical modes with largely disparate properties in a given system constitutes a prime challenge for different applications. Here, we propose, realize, and optically characterize a high-Q polymeric wedge-like whispering-gallery-mode resonator coated with a thin silver layer that supports pure surface plasmon polariton modes, pure dielectric modes, and hybrid photonic–plasmonic modes with Q-factors larger than 1000 and modal volumes as small as only a few cubic micrometers. We demonstrate both theoretically and experimentally that all three distinct kinds of cavity eigenmodes can be efficiently excited in the infrared via evanescent coupling to a tapered fiber. Performing finite-element simulations and coupled-mode theory, we develop an experimental procedure based on mode filtering to unambiguously identify the resonances observed in fiber transmission spectra. By controlling both the position of the tapered fiber with respect to the resonator and the input laser polarization, we successfully demonstrate that dielectric, plasmonic, and hybrid modes can be selectively excited, allowing for an explicit classification of the distinct cavity eigenmodes. Experimental results are in excellent agreement with the simulations.

Recent Progress on Optoplasmonic Whispering‐Gallery‐Mode Microcavities

“…Utilizing ultrahigh‐ Q dielectric microcavities as templates have been an efficient approach to realize high‐ Q SPP WGMs. [ 22,23,113,114 ] In a silver‐coated silica microdisk, B. Min et al. experimentally obtained SPP WGMs with Q factors exceeding 1000.…”

“…In addition to the IN and EX SPP WGMs, HPP WGMs and dielectric (DE) WGMs originating from the transverse‐magnetic (TM) and transverse‐electric (TE) modes in uncoated WGM microcavities, respectively, have also been investigated. [ 114,115 ] These are discussed in detail in Section 4. It is interesting to consider the strong coupling between the different types of modes as the mode indices come close to each other, for example, IN and EX, EX and HPP, as shown in Figure 3e,f.…”

“…Experimental realizations of the different types of HPP modes have also been discussed in previous reports. [ 114–116,119 ] In particular, the strongly hybridized HPP mode can hardly be generated in large and thick WGM microcavities except for rolled‐up microtube cavities. The microtube wall is scalable down to 100 nm, which satisfies well the hybridization requirements as discussed in the theoretical calculations.…”

Recent advances in the synthesis and application of Yb-based fluoride upconversion nanoparticles

“…WGMs refer to circular optical modes in resonators, in which the closed trajectories of light are supported by total internal reflections from boundaries of the curved and polygonal transparent dielectric structures, such as a ring, a cylinder, a disk or a sphere. [115][116][117][118] In a further development, Jin and co-workers realized ultraviolet B (UVB) microlasers with high gain coefficient at 288.6 nm by using LiYbF 4 :Tm@LiYbF 4 @LiLuF 4 UCNPs as the gain media. 119 The inner LiYbF 4 shell was designed to enhance the absorption of excitation light and subsequent energy transfer to Tm 3+ activators.…”

Microfluidic Whispering Gallery Mode Optical Sensors for Biological Applications

“…In recent years, hybrid plasmon-photonic WGM structures which combine the localization surface plasmon resonances (LSPR) with the WGM resonators have been proposed to effectively enhance the sensitivity. [41] The combination is usually realized through coating the resonator with a thin layer of metal [60][61][62] or attaching plasmonic nanoparticles to the resonator. [53,[63][64][65] Taking advantages of both the ultralow loss characteristics of WGMs and the strong field localization of LSPR modes, these structures normally contain high Q-factor as well as small modal volumes.…”