Light scattering and Fano resonances in high-Q photonic crystal nanocavities

Abstract

The authors show that light scattering from high-Q planar photonic crystal nanocavities can display Fano-like resonances corresponding to the excitation of localized cavity modes. By changing the scattering conditions, we are able to tune the observed lineshapes from strongly asymmetric and dispersivelike resonances to symmetric Lorentzians. Results are interpreted according to the Fano model of quantum interference between two coupled scattering channels. Combined measurements and line shape analysis on a series of silicon L3 nanocavities as a function of nearby hole displacement demonstrate that Q factors as high as 1.1×105 can be directly measured in these structures. Furthermore, a comparison with theoretically calculated Q factors allows to extract the rms deviation of hole radii due to weak disorder of the photonic lattice.

Ultra-subwavelength phase-sensitive Fano-imaging of localized photonic modes

“…The spectrum displays two resonances corresponding to the two lower energy modes (M1 and M2) and includes both positive and negative values because the experimental background signal (which is spatially averaged in a region at approximately 2 mm away from the cavity) has been subtracted from the raw data. Both resonances exhibit a dispersive-like line shape, whose intensity F as a function of energy is well reproduced (see Figure 2a) by the Fano formula 26,29 :…”

“…In fact, using a far-field setup equivalent to the one of Ref. 26, we obtain Q 5 2650 for M1. In the SNOM measurement, we observed a Q reduction in the range of 5%-20% of the original value, i.e., the perturbation is strong enough to provide a detectable spectral shift but still not so large to alter the localized mode spatial distribution.…”

Quantum dot micropillar cavities with quality factors exceeding 250,000

“…This leads to an interference effect, which is manifested by the Fano-lineshape of the reflection spectrum. While similar effects caused by a mode mismatch between the incoming laser beam and the resonator have been observed in photonic crystal nanocavities [20,21], we note that a fully microscopic understanding of the origin of the Fano-effect in our device requires advanced numerical simulations, which is beyond the scope of this paper. We can reproduce the reflection-spectrum by the formula:…”

“…The width of the resonance is then directly determined by the photon lifetime in the resonator. Recently, reflectance measurements of photonic crystal nanoresonators have revealed strong Fano-features in the lineshape as a result of the interference between an effective two level photonic system and continuum modes [20,21]. Here, we carry out a comparative investigation of micropillar cavities with ultra-high quality factors via micro-photoluminescence (µPL) and micro-photoreflectance (µPR) with respect to their quality factor as well as the shape of the resonance.…”

Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances

“…Such angular sensitivity prevents miniaturization of photonic crystal devices 22,26,32 and imposes severe restrictions on the angular divergence of the incident light beams. While highly collimated laser beams have been used for interrogating high-Q photonic crystal structures in the visible and telecommunication spectral ranges 25,26,31,33 , the angular divergence of incoherent beams used for mid-infrared spectroscopy is typically prohibitively high for utilizing GRMs supported by photonic crystals. Note that high angular sensitivity is also typical for the frequency-selective surfaces 34 that can be thought of as microwave predecessors 1 of metasurfaces.…”