Pruszyńska-Karbownik Emilia, Janczak Mikołaj, Czyszanowski Tomasz
Institute of Physics, Lodz University of Technology, ul. Wólczańska 217/221, 93-005, Łódź, Poland.
Nanophotonics. 2021 Nov 23;11(1):45-52. doi: 10.1515/nanoph-2021-0478. eCollection 2022 Jan.
Bound states in the continuum (BICs) are observed in optical cavities composed of a high refractive index periodic structure embedded in significantly lower refractive index surroundings, enabling vertical confinement of the grating modes. Here, we propose a vertically nonsymmetric configuration, implemented on a high refractive index bulk substrate with a one-dimensional grating positioned on a distributed Bragg reflector (DBR). In this configuration, the grating modes are leaky, which could prohibit the creation of a BIC if the grating was implemented on uniform substrate. However, the judiciously designed DBR on which the grating is implemented reflects nonzero diffraction orders induced by the grating. We found that the laterally antisymmetric optical modes located at the center of the Brillouin zone of this structure create BICs that are robust against changes in the grating parameters, as long as the DBR reflects the diffraction orders. The configuration enables a high degree of design freedom, facilitating the realization of very high quality factor cavities in conventional all-semiconductor technology.
在由嵌入折射率显著较低的周围环境中的高折射率周期性结构组成的光学腔中观察到连续统中的束缚态（BIC），这使得光栅模式能够实现垂直限制。在此，我们提出一种垂直非对称配置，在具有位于分布式布拉格反射器（DBR）上的一维光栅的高折射率块状衬底上实现。在这种配置中，光栅模式是泄漏的，如果光栅是在均匀衬底上实现的，这可能会阻止BIC的形成。然而，在其上实现光栅的经过精心设计的DBR会反射由光栅引起的非零衍射级次。我们发现，只要DBR反射衍射级次，位于该结构布里渊区中心的横向反对称光学模式就会产生对光栅参数变化具有鲁棒性的BIC。这种配置实现了高度的设计自由度，有助于在传统全半导体技术中实现非常高的品质因数腔。
