Fig. 9.

Mode splitting in an Ultrahigh-Q microresonator. (a) Schematic of the experimental setup. DMA, differential mobility analyser; PD, photo-diode. The inset shows an SEM image of a microtoroid. (b) Illustration of the coupled nanoparticle–microtoroid system. k₁, microtoroid–taper coupling rate; k₀, intrinsic damping rate (material and radiation losses); g, coupling coefficients of the light scattered into the resonator; GR, additional damping rate due to scattering losses. CW, clockwise modes; CCW, counter-clockwise modes. (c) Series of normalized transmission spectra taken at a 1550 nm wavelength band and the corresponding optical images recorded without nanoparticles (top trace) and with four successive depositions of KCl nanoparticles. The spectral baseline is vertically shifted for clarity. (d) Normalized splitting 2g/ω_c (2g, splitting frequency; ω_c, resonance frequency) versus particle number for KCl nanoparticles. Each discrete step corresponds to a single nanoparticle binding event. The inset shows an enlarged plot for nanoparticles of R = 40 nm. Adapted from ref. 101. © 2010 Macmillan Publishers Ltd: Nature Photonics.