【作者】 王昌辉；

【导师】 林列；

【作者基本信息】 南开大学 ， 光学工程， 2013， 博士

【摘要】 太赫兹波是指波长介于30～3000μm之间的电磁波。随着超快激光技术的发展,太赫兹波的产生和探测技术得到了快速发展,太赫兹技术正在日益走向应用。太赫兹波具有宽带宽,定向性好的优点,十分适合应用于卫星间以及地面短程宽带无线通信系统中,在这些应用系统中调制器、光开关、滤波器等太赫兹波功能器件是必不可少的。本文在对太赫兹光子晶体和超材料两种亚波长微结构人工电磁材料特性研究的基础上,重点分析了这两种微结构人工材料在太赫兹强度调制器和窄带谐振腔等中的应用。主要的工作内容和研究成果如下：1、搭建了透射式太赫兹时域谱系统。采用钛宝石飞秒激光泵浦光电导天线产生太赫兹脉冲,以碲化锌晶体电光取样探测太赫兹脉冲。用这套太赫兹时域谱系统测量了经过表面抛光处理的4mm厚的高密度聚乙烯(HDPE)和0.4mm厚的高阻硅(Si)平板的时域谱数据,经傅里叶变换后获得了两种材料在0-3THz波段的折射率,测量结果与文献报道的折射率数据相吻合。2、利用光子晶体线缺陷波导的慢光效应,设计了一种基于填充液晶的马赫-曾德尔干涉仪结构的太赫兹相位器件。马赫-曾德尔干涉仪由光子晶体线缺陷波导和光子晶体分光器组合构成。通过对不同晶格结构的光子晶体波导传输特性的分析发现正方晶格介质柱光子晶体和三角晶格空气孔光子晶体波导都具有明显的慢光效应,填充液晶后,线缺陷模色散曲线会随着液晶折射率改变而产生移动,在线缺陷模的慢光区域,色散曲线的移动使得波导内模式的有效折射率的变化幅度大于液晶折射率的变化幅度。慢光效应提高了这两种光子晶体线缺陷波导组成的马赫-曾德尔干涉仪的相位调制效率。计算表明这种液晶填充的光子晶体太赫兹马赫-曾德尔干涉仪的相位调制效率是纯液晶盒相位器件的1.8-5.7倍。3.、设计了一种由宽口径光子晶体线缺陷波导、光子晶体渐变锥形结构以及点缺陷构成的介质柱光子晶体窄带谐振腔结构。数值仿真分析表明光子晶体渐变锥形结构能减少宽、细两种不同口径线缺陷波导耦合过程中反射损耗、多模传输时的多模干涉损耗以及两种波导之间模式失配造成的损耗,有效地提高耦合效率。同时窄带谐振腔锥形耦合系统能大幅度提高窄带滤波效果,Q值为不通过锥形结构直接耦合时的2倍,便于在准波长尺度的点缺陷内形成强的太赫兹局域场。4、提出了一种能增强磁性感应的新型双开田谐振环结构的太赫兹超材料强度调制器。该超材料的谐振结构由两个通过金属连接起来的同心开口金属圆环构成,基底材料为本征砷化镓。数值仿真分析表明,与传统双开口谐振环结构的超材料相比,环间连接的开口环结构能有效提高在太赫兹波垂直入射时,由太赫兹波电场激励产生电容而引起的LC谐振的谐振强度。当波长为800nm的飞秒激光照射该超材料,本征砷化镓基底的自由电子浓度随飞秒激光的光强增加而增加,而双开口谐振环结构的LC谐振的电容效应将随自由电子浓度的增加而减弱,实现对透射光的光强调制。数值仿真结果表明环间连接的开口环结构对与LC谐振相同频率的太赫兹波能实现调制深度为40%的强度调制,而相同结构参数的传统双开口谐振环结构仅能实现深度为30%强度调制。更多还原

【Abstract】 Terahertz waves refer to the electromagnetic waves with wavelength range between30～3000μm. Due to the fast development of the technology of ultrafast lasers, there has been great interest in terahertz wave applications nowadays. With a wide bandwidth and an excellent linear propagation direction, terahertz waves are particularly suitable for the wireless communication. So the terahertz functional devices such as intensity modulators, optical switches, filters et al. are essential for the researches of terahertz waves.In this thesis, the study including theories and applications of two kinds of terahertz subwavelength microstructure, photonic crystals and metamaterials, are discussed. Respectively, terahertz modulators and narrow bandwidth cavities made by these two artificial materials are discussed. The major contents and results are shown as follows:1. A terahertz time domain spectroscopy (THz-TDS) has been set up. Terahertz transmitter is based on photoconductive antenna, and terahertz detector is based on electro-optic crystal ZnTe. The quart-optical path (4f) of terahertz waves is constructed by four paraboloidal mirrors, and the sample are assumed to put in the point of the second’focus point. Terahertz spectroscopy of HDPE and Si plates were measured by this THz-TDS, the results showed that the indices and the spectroscopy of the two samples agree well with the available datum.2. A novel tunable photonic crystal (PC) waveguide Mach-Zehnder interferometer (MZI) based on nematic liquid crystals (LCs)5CB is proposed, which is composed of the photonic crystal line defect waveguides and splitters. The line defect modes of the PC waveguide with different liquid crystals refractive indices are analyzed by using the plane wave expansion method. Owing to the slow group velocity region of the line defect mode, when the index of5CB is changing by rotating its derector, the variation of the line defect mode’s effective indices is larger than the variation of the indices of liquid crystals. As a conclusion, the slow light in the line-defect of PC promotes the phase modulating efficiency of MZI. The efficiencies of MZI are1.8-5.7times larger than the phase modulator made of liquid crystal box.3. A pillar photonic crystal (PPC) with a tapered waveguide and a point defect to highly confine Terahertz wave is demonstrated. A PPC taper can provide low loss connections between waveguides with different cross-sectional areas. Terahertz wave is first guided into the tapered waveguide, gradually compressed to its end, and finally confined in the point defect cavity. The numerical simulations indicate that narrow band Terahertz wave is highly confined in the point defect cavity with the quality factor twice the value of the cavity without the tapered structure. Also, the coupling process is greatly extended, so the slow light effect is extremely strong. The demonstrated device may be used as an antenna for enhancing light-matter interactions in the point defect cavity at terahertz frequencies and improving the sensitivity of terahertz near field microscopy.4. A novel terahertz double split-ring resonator (DSRR) metamaterial which can optically tune the transmission of the terahertz wave is presented and demonstrated. Unlike the traditional DSRR metamaterials, the DSRR discussed in this paper is constituted by two split rings connected by two bridges. Numerical simulations with finite integration technique (FIT) method reveal that the magnetic response of this DSRR with connecting bridges is stronger than the traditional DSRR. Then by increasing the carrier density of the intrinsic gallium arsenide (GaAs) substrate, the magnetic response of the original and complementary special DSRR metamaterial can be weakened or even turned off. This metamaterial structure is promised to be a narrow-band terahertz modulator with several nanoseconds response time.更多还原