Abstract
Abstract The recently emerging all-dielectric optical nanoantennas based on high-index semiconductors have proven to be an effective and low-loss alternative to metal-based plasmonic structures for light control and manipulations of light–matter interactions. Nonlinear optical effects have been widely investigated to employ the enhanced interactions between incident light and the dielectrics at the Mie-type resonances, and in particular magnetic dipole resonances, which are supported by the semiconductor. In this paper, we explore the novel phenomenon of bound states in the continuum supported by high-index semiconductor nanostructures. By carefully designing an array of nanodisk structures with an inner air slot as the defect, we show that a novel high quality-factor resonance achieved based on the concept of bound state in the continuum can be easily excited by the simplest linearly polarized plane wave at normal incidence. This resonance further enhances the interactions between light and semiconductors and boosts the nonlinear effects. Using AlGaAs as the nonlinear material, we demonstrate a significant increase in the second-harmonic generation efficiency, up to six orders of magnitude higher than that achieved by magnetic dipole resonances. In particular, a second-harmonic generation efficiency around 10% can be numerically achieved at a moderate incident pump intensity of 5 MW/cm2.
Highlights
The use of resonating artificial structures such as nanoantennas to control light–matter interactions has been the subject of intense and continuous research interest over the past several decades [1]
Using AlGaAs as the nonlinear material, we demonstrate a significant increase in the second-harmonic generation efficiency, up to six orders of magnitude higher than that achieved by magnetic dipole resonances
To verify the huge enhancement of the second-harmonic generations (SHGs) obtained at the QBIC mode as compared to the SHG efficiency achieved by the magnetic dipole (MD) resonance, we further calculate the transmission spectrum and the SHG efficiency for the AlGaAs disk array with the same geometrical parameters as those given in Figure 2(a) except that the air slot is absent
Summary
The use of resonating artificial structures such as nanoantennas to control light–matter interactions has been the subject of intense and continuous research interest over the past several decades [1] These enhanced interactions can support a variety of novel applications, including optical detection of weak signals [2, 3], controlled spontaneous emission [4] and strong coupling [5], to name a few. Due to the extremely low nonlinear susceptibility of most materials, optically thick nonlinear materials are conventionally required to achieve a considerable nonlinear generation, and a careful structural design is important so that the nonlinear signals generated along the propagation path of the pump laser can add up constructively to achieve a maximum output This requirement restricts the occurrence of efficient nonlinear optical process at the nanoscale and the subsequent on-chip applications. One needs to use the complicated azimuthally polarized vector beam as the excitation
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