超材料（Metamaterials）是由人工“原子”周期或无序地排列而成，人工“原子”的尺寸要大于自然原子的尺寸，从而有利于我们自由调控其性能。通过调节人工“原子”的形状、尺寸和性能参数，我们可以设计出自然界中不存在的具有超常电磁响应的人工材料。利用超材料来制备吸波材料和光开关器件因其具有重大的应用价值而引起了广泛的关注，然而目前大部分吸波超材料和光开关超材料都是基于金属结构人工“原子”实现的。介质超材料的Mie谐振为超材料的设计提供了新的思路，有望进一步提高吸波材料和光开关器件的性能，本课题致力于研究探索利用介质超材料来设计制备单频、双频和宽频吸波材料以及低阈值、高响应速度的光开关器件。设计制备出单频吸波铁电介质超材料，其在8.96 GHz的吸收率达到99%。在8.96 GHz处其介电常数和磁导率近似相等，使该铁电介质超材料的阻抗接近于1，满足了阻抗匹配条件，从而得到吸收率接近100%的吸收峰。该吸收峰对入射波的偏振方向和入射角不敏感，吸收峰的位置会随铁电体人工“原子”边长或介电常数的减小向高频移动。研究了基于不同边长和介电常数铁电体人工“原子”的双频吸波材料和基于双级Mie谐振的双频吸波材料。三种双频吸波材料均实现了两个频段吸收率接近100%的吸收峰。双频吸收峰均对入射波的偏振方向和入射角不敏感，通过改变介质超材料的尺寸和介电参数可以单独或同时调控两个吸收峰的频率和强度。研究了基于铁电体人工“原子”尺寸渐变和介电常数渐变的宽频吸波材料和基于高阶Mie谐振峰耦合的宽频吸波材料。三种宽频吸波材料均实现了吸收峰的宽化，且吸收峰的宽化程度可以人工调控。设计了基于铁电介质超材料谐振热效应的全光开关器件，通过改变调控电磁波的强度，信号电磁波从没有信号通过的光开关的“关”状态，变为有信号通过的“开”状态。实现了利用不同频率的调控电磁波来控制信号电磁波的功能。模拟设计出基于金属结构超材料和介质超材料模态转换的全光开关器件，模态转换的速度在光速量级，因而实现了全光开关的超快响应。且全光开关的工作频率可以通过调节金属结构超材料和介质超材料的尺寸性能参数来任意调控。
Metamarials are composed of artificial “atoms” periodically or disorderly. The size of artificial “atoms” is much bigger than that of natural atoms. It helps us to control its properties freely. We can design artificial materials with abnormal electromagnetic properties by modulating the shape, size and property parameters of artificial “atoms”, the artificial materials may not exist in nature. Utilizing metamaterials to realize absorber and optical swiching has aroused wide attention due to its significant application. However, so far most of the absorber metamaterials and optical switching metamaterials are based on metal structure artificial “atoms”. Actually, the Mie resonances of dielectric metamaterials provide a new way to build metamaterials. It may further improve the performance of absorber and optical switching devices. This article is focused on studying single band, dual-band and wide band absorbers and optical switchings with low switching energy and high switching speed based on dielectric metamaterials. We design and fabricate a single band absorber based on ferroelectric metamaterials. Its absorptivity is 99% at 8.96 GHz. Both the permittivity and permeability spectra of this metamaterial have resonance around 8.96 GHz, and the value of permittivity is approximately equal to that of the permeability at 8.96 GHz, resulting in the impedance of the metamaterial to be 1. The impedance match condition has been satisfied. Therefore, we achieve near 100% absorptivity. The absorption band is insensitive to the polarization and incident angles of the electromagnetic waves. The absorption band will shift to higher frequency when we decrease the size or permittivity of the artificial “atoms”. We have studied dual-band metamaterial absorbers based on different cube size and different permittivity of ferroelectric artificial “atoms”, and dual-band metamaterial absorbers based on two Mie resonances. All these three dual-band metamaterial absorbers have two absorption bands with near 100% absorptivity. Also, both two absorption bands are insensitive to the polarization and incident angles of the electromagnetic waves. The frequency and intensity of the absorption bands can be tuned separately or simultaneously by modulating the size and property parameters of artificial “atoms”. We have studied wide band metamaterial absorbers based on ferroelectric artificial “atoms” with gradient size and permittivity, and wide band metamaterial absorber based on the coupling of higher order Mie resonances. All these three absorbers achieved wide band absorption, and the width of the band can be modulated artificially.We design an all-optical switching device based on the thermal effect of Mie resonances of ferroelectric metamaterials. The signal wave can be swith from “close” state to “open” state by modulating the intensity of control wave. Controlling electromagnetic wave by another electromagnetic wave with different frequency can be realized. We also design all-optical switching devices based on modes transform of metal structure and dielectric metamaterials. The speed of modes transform in metal structure and dielectric metamaterials is equal to the speed of light. Therefore, we have achieved ultrafast response of all-optical switching. The working frequency of the all-optical switching can be tuned by modulating the size and property parameters of artificial “atoms” in metal and dielectric metamaterials.
