Free-space coupling efficiency in a high-Q deformed optical microcavity

Abstract

The free-space coupling technique provides a promising means to excite high-Q whispering gallery modes in deformed microcavities, but the precise quantification of the coupling efficiency remains challenging because of the non-Lorentzian spectral lineshape in the transmission and the partial collection in emission. Here, we experimentally identify the free-space coupling efficiency by measuring the threshold of stimulated Raman scattering in a slightly deformed microcavity. The measured efficiency is up to 30%. Furthermore, the dependence of the coupling efficiency on the incident angle is obtained by focusing the laser beam on the microcavity periphery, which is consistent with the prediction of the mode field distribution. Finally, it is experimentally demonstrated that free-space coupling efficiencies remain high even when the focusing beam has been translated several micrometers, both horizontally and vertically.

Advances in optoplasmonic sensors – combining optical nano/microcavities and photonic crystals with plasmonic nanostructures and nanoparticles

“…Stand-off biodetection with freespace coupled asymmetric microsphere cavities was demonstrated [83]. Efficient free-space coupling was reported, with coupling of up to 30% of the incident light [84].…”

Optofluidics Refractometers

“…Thin-wall cylindrical capillaries with spatial analyte-taper separation comprise an alternative scheme that is more convenient for optofluidic integration [ 42 , 43 ] ( Figure 4 a–d). Since high-Q WGMs in deformed microcavities can be excited by free space coupling [ 44 ] ( Figure 4 e), it is a feasible way to achieve high cavity coupling efficiency in microfluidic chips.…”

“…Copyright (2014) RSC; ( e ) Schematic diagram of the experimental setup for free-space coupling between a laser beam and a deformed toroidal microcavity. Reprinted with permission from [ 44 ]. Copyright (2016) OSA.…”

Highly Sensitive Cell Concentration Detection by Resonant Optical Tunneling Effect

“…Nowadays, most of the sensing mechanisms/structures of the RI sensors are based on near-field optics, such as optical fiber Bragg grating (FBG) ( Sun et al, 2017), long period fiber grating (LPG) (He et al, 2011;Rindorf et al, 2008), photonic crystal/photonic crystal fiber (PCF) ( Hoo et al, 2009;Wu et al, 2009), and whisper gallery mode (WGM) ( Luo et al, 2014;Scholten et al, 2014;Vollmer et al, 2002;Zhang et al, 2016;Zhi et al, 2017). Evanescent waves near the two-media interface are exploited for these detection methods.…”