Q-factor limits for far-field detection of whispering gallery modes in active microspheres

Abstract

This paper investigates the Q-factor limits imposed on the farfield detection of the whispering gallery modes of active microspherical resonators. It is shown that the Q-factor measured for a given active microsphere in the far-field using a microscope is significantly lower than that measured using evanescent field collection through a taper. The discrepancy is attributed to the inevitable small asphericity of microspheres that results in mode-splitting which becomes unresolvable in the far-field. Analytic expressions quantifying the Q-factor limits due to small levels of asphericity are subsequently derived.

Whispering-gallery-mode emission from biological luminescent protein microcavity assemblies

“…The measured Q-factor was 460, lower than the theoretical radiation-loss-limited Q-factor of 4,300 for a droplet of the size (22 μm). This discrepancy is reasonable considering the possible un-resolvable mode splitting due to droplet deformation [20] and possibly scattering loss at contacts with other smaller lipid droplets in the cytoplasm. In contrast to the GFP-ABHD5-transduced cells, GFP-transduced 3T3-L1 cells showed uniformly dispersed GFP molecules in the cytosol and failed to produce any noticeable cavity-modified spectral feature in fluorescence (Fig.…”

Optical-resonance-assisted generation of super monodisperse microdroplets and microbeads with nanometer precision

“…The deformation manifested as WGM line broadening, with full width half maximum of the peaks being 0.4 nm, which matches with the observed magnitude of the deformation. 31 We were able to produce solid beads in the diameter range from 5 μm to 50 μm (Fig. S2 †).…”

Dynamic Self-Referencing Approach to Whispering Gallery Mode Biosensing and Its Application to Measurement within Undiluted Serum

“…Fluorescent or active resonators are particularly interesting in this context as they allow remote excitation of the resonator, thereby alleviating some of the practical limitations of passive resonator configurations 9,[23][24][25] . Active resonators do display lower Q-factors 26 in comparison with passive resonators 27,28 , however, techniques exist that can facilitate in improving the Q-factor such as operating the resonator within the stimulated emission regime 29 or breaking the symmetry of the resonator by placing it onto the tip of a microstructured optical fiber (MOF) 30 . This second technique has the additional advantage of creating a robust and easy to use dip-sensing architecture 1 .…”