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Tunable All-Dielectric Metasurfaces for Phase-Only Modulation of Transmitted Light Based on Quasi-bound States in the Continuum
ACS Photonics ( IF 6.5 ) Pub Date : 2020-06-10 , DOI: 10.1021/acsphotonics.0c00554 Mohammad Mahdi Salary 1 , Hossein Mosallaei 1
ACS Photonics ( IF 6.5 ) Pub Date : 2020-06-10 , DOI: 10.1021/acsphotonics.0c00554 Mohammad Mahdi Salary 1 , Hossein Mosallaei 1
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Phase-only modulators are of great importance for dynamic control over the wavefront of light in a wide range of applications where high efficiency and uniform amplitude are required. Electro-optical tuning approaches based on electro-refraction induced by free carrier effects are of particular interest for developing phase-only modulators due to offering high speed and low power consumption. Here, an electro-optically tunable all-dielectric metasurface is proposed operating in the near-infrared frequency regime for dynamic control over the phase retardation of transmitted light while maintaining a high amplitude with minimal variations over the phase modulation range. The metasurface consists of a zigzag array of elliptical silicon nanodisks connected in each column via silicon nanobars serving as biasing lines. The constituent elements of the metasurface are configured as multijunction p–n structures with moderate doping levels whose multigate biasing enables modulation of carrier concentrations. Due to broken symmetry in the zigzag arrangement, the symmetry-protected bound states in the continuum supported by the metasurface collapse into Fano resonances with extremely high quality-factors under normal incidence. The spectral overlap of excited electric and magnetic quasi-bound states in the continuum is exploited to establish a Huygens’ regime with maximal transmission and highly steep spectral phase agility of 2π. The electro-optical shift of the Huygens mode via the electro-refraction induced by carrier accumulation in multijunction p–n structures under applied bias voltage yields a wide dynamic phase span of 240° while maintaining an average transmission amplitude of 0.77. The performance manifests a substantially enhanced tunability afforded by a weak electro-refraction of Δn = 4 × 10–3 which is attributed to the ultrahigh Q-factors of the quasi-bound states in the continuum leading to the significant increase in the lifetime of photons and field confinement within the active regions of resonators. The potential application of such a multifunctional transmittive metasurface is numerically demonstrated in two different areas, namely dynamic polarization control and tunable pulse compansion.
中文翻译：
基于连续态中的准束缚态的可调谐全介电超表面，仅用于透射光的相位调制。
仅相位调制器对于需要高效率和均匀振幅的广泛应用中的光波前动态控制至关重要。由于提供了高速度和低功耗，基于自由载流子效应引起的电折射的电光调谐方法对于开发仅相位调制器尤为重要。在此，提出了一种在近红外频率范围内工作的电光可调谐全介电超表面，用于动态控制透射光的相位延迟，同时在相位调制范围内以最小变化保持高振幅。超表面由通过用作偏置线的硅纳米棒在每列中连接的椭圆形硅纳米盘的锯齿形阵列组成。超表面的组成元素被配置为具有中等掺杂水平的多结p–n结构，其多栅极偏置可实现载流子浓度的调制。由于之字形排列中对称性的破坏，在垂直入射下，由超表面支撑的连续体中受对称保护的结合态塌陷为Fano共振，具有极高的品质因数。利用连续谱中激发的电和磁准束缚态的光谱重叠来建立具有最大透射率和2π的高陡光谱相位捷变的惠更斯状态。惠更斯模通过在施加偏置电压下由多结p–n结构中的载流子积累引起的电折射产生的电光位移产生240°的宽动态相位跨度，同时保持0.77的平均透射幅度。该性能表明，弱电折射可提供显着增强的可调性。Δn = 4×10 –3，这归因于连续谱中准结合态的超高Q因子，从而导致光子寿命的显着增加和谐振器有效区域内的场约束。在两个不同的领域，即动态极化控制和可调脉冲扩展，在数值上证明了这种多功能透射形超表面的潜在应用。
更新日期：2020-07-15
中文翻译：
基于连续态中的准束缚态的可调谐全介电超表面，仅用于透射光的相位调制。
仅相位调制器对于需要高效率和均匀振幅的广泛应用中的光波前动态控制至关重要。由于提供了高速度和低功耗，基于自由载流子效应引起的电折射的电光调谐方法对于开发仅相位调制器尤为重要。在此，提出了一种在近红外频率范围内工作的电光可调谐全介电超表面，用于动态控制透射光的相位延迟，同时在相位调制范围内以最小变化保持高振幅。超表面由通过用作偏置线的硅纳米棒在每列中连接的椭圆形硅纳米盘的锯齿形阵列组成。超表面的组成元素被配置为具有中等掺杂水平的多结p–n结构，其多栅极偏置可实现载流子浓度的调制。由于之字形排列中对称性的破坏，在垂直入射下，由超表面支撑的连续体中受对称保护的结合态塌陷为Fano共振，具有极高的品质因数。利用连续谱中激发的电和磁准束缚态的光谱重叠来建立具有最大透射率和2π的高陡光谱相位捷变的惠更斯状态。惠更斯模通过在施加偏置电压下由多结p–n结构中的载流子积累引起的电折射产生的电光位移产生240°的宽动态相位跨度，同时保持0.77的平均透射幅度。该性能表明，弱电折射可提供显着增强的可调性。Δn = 4×10 –3，这归因于连续谱中准结合态的超高Q因子，从而导致光子寿命的显着增加和谐振器有效区域内的场约束。在两个不同的领域，即动态极化控制和可调脉冲扩展，在数值上证明了这种多功能透射形超表面的潜在应用。
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