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Moiré Quasibound States in the Continuum
Physical Review Letters ( IF 8.1 ) Pub Date : 2022-06-21 , DOI: 10.1103/physrevlett.128.253901 Lei Huang 1 , Weixuan Zhang 1 , Xiangdong Zhang 1
Physical Review Letters ( IF 8.1 ) Pub Date : 2022-06-21 , DOI: 10.1103/physrevlett.128.253901 Lei Huang 1 , Weixuan Zhang 1 , Xiangdong Zhang 1
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The novel physics of twisted bilayer graphene has motivated extensive studies of magic-angle flat bands hosted by moiré structures in electronic, photonic, and acoustic systems. On the other hand, bound states in the continuum (BICs) have also attracted great attention in recent years because of their potential applications in the field of designing superior optical devices. Here, we combine these two independent concepts to construct a new optical state in a twisted bilayer photonic crystal slab, which is called as moiré quasi-BIC, and numerically demonstrate that such an exotic optical state possesses dual characteristics of moiré flat bands and quasi-BICs. To illustrate the mechanism for the formation of moiré flat bands, we develop an effective model at the center of the Brillouin zone and show that moiré flat bands could be fulfilled by balancing the interlayer coupling strength and the twist angle around the band edge above the light line. Moreover, by decreasing the twist angle of moiré photonic crystal slabs with flat bands, it is shown that the moiré flat-band mode at the Brillouin center gradually approaches a perfect BIC, where the total radiation loss from all diffraction channels is significantly suppressed. To clarify the advantage of moiré quasi-BICs, enhanced second-harmonic generation (SHG) is numerically proven with a wide-angle optical source. The efficiency of SHG assisted by designed moiré quasi-BICs can be greatly improved compared with that based on dispersive quasi-BICs with similar quality factors.
中文翻译：
连续体中的莫尔准束缚态
扭曲双层石墨烯的新颖物理学激发了对电子、光子和声学系统中由莫尔结构承载的魔角平带的广泛研究。另一方面，连续谱中的束缚态（BIC）近年来也因其在设计优质光学器件领域的潜在应用而引起了极大的关注。在这里，我们结合这两个独立的概念，在扭曲的双层光子晶体板中构建了一个新的光学状态，称为莫尔准BIC，并通过数值证明这种奇异的光学状态具有莫尔平带和准- BIC。为了说明莫尔扁平带的形成机制，我们在布里渊区中心开发了一个有效的模型，并表明通过平衡层间耦合强度和光线上方带边缘周围的扭曲角可以实现莫尔平坦带。此外，通过减小具有平带的莫尔光子晶体板的扭转角，表明布里渊中心的莫尔平带模式逐渐接近完美的BIC，其中所有衍射通道的总辐射损失被显着抑制。为了阐明莫尔准 BIC 的优势，增强的二次谐波产生 (SHG) 用广角光源进行了数值证明。与基于具有相似品质因数的色散准BIC相比，设计的莫尔准BIC辅助的SHG效率可以大大提高。
更新日期：2022-06-21
中文翻译：
连续体中的莫尔准束缚态
扭曲双层石墨烯的新颖物理学激发了对电子、光子和声学系统中由莫尔结构承载的魔角平带的广泛研究。另一方面，连续谱中的束缚态（BIC）近年来也因其在设计优质光学器件领域的潜在应用而引起了极大的关注。在这里，我们结合这两个独立的概念，在扭曲的双层光子晶体板中构建了一个新的光学状态，称为莫尔准BIC，并通过数值证明这种奇异的光学状态具有莫尔平带和准- BIC。为了说明莫尔扁平带的形成机制，我们在布里渊区中心开发了一个有效的模型，并表明通过平衡层间耦合强度和光线上方带边缘周围的扭曲角可以实现莫尔平坦带。此外，通过减小具有平带的莫尔光子晶体板的扭转角，表明布里渊中心的莫尔平带模式逐渐接近完美的BIC，其中所有衍射通道的总辐射损失被显着抑制。为了阐明莫尔准 BIC 的优势，增强的二次谐波产生 (SHG) 用广角光源进行了数值证明。与基于具有相似品质因数的色散准BIC相比，设计的莫尔准BIC辅助的SHG效率可以大大提高。
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