Optical Microcavity: Sensing down to Single Molecules and Atoms

Abstract

This review article discusses fundamentals of dielectric, low-loss, optical micro-resonator sensing, including figures of merit and a variety of microcavity designs, and future perspectives in microcavity-based optical sensing. Resonance frequency and quality (Q) factor are altered as a means of detecting a small system perturbation, resulting in realization of optical sensing of a small amount of sample materials, down to even single molecules. Sensitivity, Q factor, minimum detectable index change, noises (in sensor system components and microcavity system including environments), microcavity size, and mode volume are essential parameters to be considered for optical sensing applications. Whispering gallery mode, photonic crystal, and slot-type microcavities typically provide compact, high-quality optical resonance modes for optical sensing applications. Surface Bloch modes induced on photonic crystals are shown to be a promising candidate thanks to large field overlap with a sample and ultra-high-Q resonances. Quantum optics effects based on microcavity quantum electrodynamics (QED) would provide novel single-photo-level detection of even single atoms and molecules via detection of doublet vacuum Rabi splitting peaks in strong coupling.

Photonic bandstructure engineering of THz quantum-cascade lasers

“…18 The sensor has shown a sensitivity S 0 of 0.025 defined as S 0 ¼ À1/ f df/dn, where f is the frequency and n the refractive index. 19 This sensitivity is comparable to PhC sensors in the visible. 20 Based on the same principle and using our device in the second photonic band leads to an S 0 of 0.17 at the M1-point.…”

On-chip High-finesse Fabry-Perot Microcavities for Optical Sensing and Quantum Information

“…Thus, the practical limit of detection for a microcavity sensor scales inversely with both Q and Γ, at least up to a point. For Q exceeding some maximum value (typically 10 5 -10 6 [39,40]), wavelength noise (in part arising from thermally induced variations in the resonant wavelength of the microcavity [31,41]) becomes the limiting parameter. In other words, practical limitations of interrogation instruments (e.g.…”

Terahertz Sensor Using Photonic Crystal Cavity and Resonant Tunneling Diodes

“…THz sensing using metamaterial metallic resonators has been widely studied for high-sensitivity applications [8][9][10][11]. However, the minimum detectable refractive index change Δn [7], which is important for practical, highly sensitive microanalysis, is limited by the low Q factors of the metamaterial metallic resonators (approximately 10-70) due to ohmic loss. In the light wave region, high sensitivities have been reported using a high Q factor photonic crystal (PC) cavity [12][13][14][15][16][17].…”

“…The use of a resonator can improve the sensitivity [7]. In refractive index sensing, the change in resonant frequency due to a specimen being added to the resonator is measured.…”