Fluorescent and lasing whispering gallery mode microresonators for sensing applications

Abstract

Whispering gallery modes (WGMs) have been exploited for a broad range of sensing applications. However, the vast majority of WGM sensors consist of passive resonators, requiring complex interrogation systems to be employed, ultimately limiting their practicality. Active resonators containing a gain medium, allowing remote excitation and collection of the WGM‐modulated fluorescence spectra, have emerged as an alternative to passive resonators. Although research is still in its infancy, recent progress has reduced the performance gap between the two paradigms, fueled by the potential for new applications that could not previously be realized. Here, recent developments in sensors based on active WGM microresonators are reviewed, beginning with a discussion of the theory of fluorescence‐based and lasing WGMs, followed by a discussion of the variety of gain media, resonator architectures, and emerging sensing applications. We conclude with a discussion of the prospects and future directions for improving active WGM sensors.

Optical bottle microresonators

“…[4,5] and a later progress in the field is reviewed in Ref. [10]. While these lasers have different geometry, the physical principles of their operation are similar.…”

“…Over the last decades, there has been a significant interest to the investigation and applications of dielectric optical microresonators. Several books, book chapters and review papers summarize the achievements in this research area (see e.g., [1][2][3][4][5][6][7][8][9][10]). The goal of the present review is to outline the major theoretical and experimental results in the development of the bottle microresonators [11] which were investigated in several research groups worldwide over the last decade and became of special interest for applications in photonics and adjacent disciplines.…”

“…These modes are propagating along the surface of these resonators and are analogous to acoustic WGMs discovered by Lord Rayleigh for acoustic waves a century ago [12] and proposed for fabrication of high Q-factor electromagnetic dielectric resonators by Richtmyer in 1939 [13]. The spherical microresonators since their experimental demonstration in paper [14] have a multidecade history of research and development [1][2][3][4][5][6][7][8][9][10]. The toroidal microresonators, which were introduced in papers [15,16], have found applications in optical linear and nonlinear signal processing, lasing, sensing, and quantum networking.…”

Luminescent Capillary‐Based Whispering Gallery Mode Sensors: Crossing the Lasing Threshold

“…When an integer number of wavelengths fits around the circumference, the light is amplified via constructive interference. A portion of the resonant electric field can extend into the channel region where it can sense the analyte, including specific surface binding events if the channel walls are appropriately functionalized . However, standard commercial microcapillaries do not work for WGM‐based optical sensors because they have relatively thick walls (tens to hundreds of micrometers) and therefore any WGM that propagates around the outer boundary will have its resonant field much too far away from the channel medium.…”

Surface nanoscale axial photonics (SNAP) at the silica microcapillary with ultrathin wall

“…Microfluidic sensing with optical WGMs circulating along the uniform capillary has been proposed and demonstrated in Ref. [8] and developed in numerous publications [9,10]. Employing a SNAP resonator at the capillary surface allows to significantly advance this method.…”