Abstract
A subwavelength electromagnetic diode scheme in a microwave waveguide system is proposed by using an asymmetric photonic crystal (PC) cavity side-coupled with electromagnetically induced transparency like (EIT-like) metamaterials. It is found that the composite PC-EIT configuration can generate tenfold <i>Q</i>-factor enlargement, accompanied with enhanced nonreciprocal electromagnetic localization simultaneously. Further study of the measured one-way response exhibits excellent electromagnetic diode performance including 19.7 dB transmission contrast and 7 dBm operating power at a working frequency of 1.329 GHz. We emphasize that such high-contrast transmission and low-threshold diode actions are not at costs of greatly increasing volume and drastically reducing transmission. Our findings may benefit the design of compact nonreciprocal devices in the integrated optical nanocircuits.
Highlights
A subwavelength electromagnetic diode scheme in a microwave waveguide system is proposed by using an asymmetric photonic crystal
cavity side-coupled with electromagnetically induced transparency
It is found that the composite photonic crystal (PC)-EIT configuration can generate tenfold Q-factor enlargement
Summary
双明模耦合的双波段类电磁诱导透明研究 Electromagnetic induction-like transparency in dual-band with dual-bright mode coupling 物理学报. 基于石墨烯振幅可调的宽带类电磁诱导透明超材料设计 Tunable grapheme amplitude based broadband electromagnetically-induced-transparency-like metamaterial 物理学报. 基于非对称结构全介质超材料的类电磁诱导透明效应研究 Research on analogue of electromagnetically induced transparency effect based on asymmetric structure all-dielectric metamaterial 物理学报. 里德伯电磁感应透明中的相位 Phase in Rydberg electromagnetically induced transparency 物理学报. 近年来, 量子光学中的电磁诱导透明 (electromagnetically induced transparency, EIT) 现象受 到了国内外科学家的广泛关注 [23−40]. 最后, 通过加 载非线性材料 (变容二极管), 并且改变输入信号功 率, 从实验上观察到电磁波正、反向入射内嵌类 EIT 超材料的一维非对称 PC 谐振腔结构时的非线性 相移不同. 在频率为 1.329 GHz 下, 得到了高达 19.7 dB 的透射对比度, 相应的输入功率强度仅为 7 dBm. 值得一提的是, 引入类 EIT 超材料并没有 大幅增加器件体积和剧烈降低信号透过率. 作 为 “暗态”的 SRR 大小为 6.4 mm × 6.4 mm, 线宽为 1.5 mm, 开口狭缝为 1.0 mm, 与微带线的距离为 10.2 mm, 与梳状线的距离为 0.3 mm. 根据上述所选定的结构 参数, 梳状线与 SRR 共振频率相同, 同时类 EIT 超材料与 (AB)2D(BA)2(BBAA) 的工作频率一致. 透射谱线, 如图 2(a) 所示. 其中, (AB)2(BA)[2] 在 0.95 GHz 和 1.65 GHz 之间存在一个明显的光子带 隙. 当引入谐振腔 D 时, 在光子禁带中 1.374 GHz 频率处会出现一个谐振腔模. 当在 (AB)2D(BA)[2] 右侧引入光子壁垒 BBAA, 由于谐振腔反射壁的 厚度增加, 谐振腔的透射发生微小的下降. 图 2(b) 给出了不同方向入射 (AB)2D(BA)2(BBAA) 时的 反射谱线. 可以明显看出, 正向入射和反向入射结 构时的反射率是不一样的. 这里我们假定从左侧入 射为正向入射, 而从右侧入射为反向入射. 对于正 向入射情形, 在腔模处的反射为–7.8 dB; 然而对于 反向入射情形, 在腔模处的反射仅为–2.5 dB. 由于 一维非对称光子晶体谐振腔的透射率不依赖于入 射方向, 所以也就是说, 正、反向入射结构时总吸 收是不同的. 而结构的吸收是由电磁场局域强弱决 定的, 因此可知正向入射时腔模处的电磁场局域要 强于反向入射时的情形
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