Quasi-guided modes resulting from the band folding effect in a photonic crystal slab for enhanced interactions of matters with free-space radiations

Abstract

We elucidate that guided modes supported by a regular photonic crystal slab structure composed of a square lattice of air holes in a silicon slab will transition into quasi-guided (leaky) modes when the radius of every second column of air holes is changed slightly. This intentional geometric perturbation will lead to a doubling of the period in one direction and the corresponding shrinkage of the first Brillouin zone. Because of the translational symmetry in the k-space, leaky waves inheriting the spatial dispersion of the original guided modes, which do not interact with external radiation, will appear with the dispersion curves above the light cone. Our results show that ultrahigh Q-factor resonances with large operating bandwidth can be achieved. Interestingly, the perturbation in only one direction of the photonic lattice will lead to an in-plane wave number-dependent resonance characteristic in both directions. Our numerical results demonstrate a local enhancement of the electric field magnitude by the order of 102, which is even more significant than those in most plasmonic structures. These quasi-guided modes with superior properties will provide a new platform for efficient light–matter interactions.

Ultra-narrowband and rainbow-free mid-infrared thermal emitters enabled by a flat band design in distorted photonic lattices

“…1d , where the FBZ shrinks into a white rectangular region. This transformation folds the dispersion band of the GM along the XM direction in the original FBZ to the ΓY direction (i.e., QGM now) 45 in the new lattice, as shown by the red band in the ΓY direction in Fig. S4a .…”

Exploiting Zone-Folding Induced Quasi-Bound Modes to Achieve Highly Coherent Thermal Emissions

“…Another type of BMs, the guided modes (GMs), have broadband infinite Q factors, and its dispersion band can be folded into the continuum by introducing periodic perturbations to form quasi-GMs (QGMs). − Compared to QBIC, the QGMs have the Q factors inherently not sensitive to the wavevector/frequency, i.e., with robustness. The QGM inherits the steep dispersion of the original GM and thus have spectral tunability over the entire dispersion band while maintaining the high-Q characteristic. , This property enables good control over the spectral position by only varying the incident angle, with no negative influence to the Q. We note that both QBIC and QGM are collective behaviors in the periodic structures and require a large number of unit cells to achieve high Q values .…”

“…The QGM inherits the steep dispersion of the original GM and thus have spectral tunability over the entire dispersion band while maintaining the high-Q characteristic. 22,25 This property enables good control over the spectral position by only varying the incident angle, with no negative influence to the Q. We note that both QBIC and QGM are collective behaviors in the periodic structures and require a large number of unit cells to achieve high Q values.…”