基于石墨烯纳米条波导边耦合矩形腔的等离子体诱导透明效应

为了减小器件尺寸、实现超快速响应和动态可调谐,研究了基于石墨烯纳米条波导边耦合矩形腔的单波段和双波段的等离子体诱导透明(PIT)效应,通过耦合模式理论和时域有限差分法从数值计算和模拟仿真两方面分析了模型的慢光特性.通过调节石墨烯矩形腔的化学势,同时实现了单波段、双波段PIT模型的谐振波长和透射峰值的可调谐性.当石墨烯的化学势增加时,各个波段PIT窗口的谐振波长逐渐减小,发生蓝移.此外,通过动态调谐石墨烯矩形腔的谐振波长,当石墨烯矩形腔的化学势为0.41—0.44 eV时,单PIT系统的群折射率控制在79.2—28.3之间,可调谐带宽为477 nm;当石墨烯矩形腔1, 2, 3的化学势分别为0.39—0.42 eV, 0.40—0.43 eV, 0.41—0.44 eV时,双PIT系统的群折射率控制在143.2—108.6之间.并且,整个系统的尺寸小于0.5μm~2.研究结果对于超快速、超紧凑型和动态可调谐的光传感、光滤波、慢光和光存储器件的设计和制作具有一定的参考意义.     

基于六角格子光子晶体波导的高效全光二极管设计

提出了一种基于六角格子光子晶体波导微腔和Fabry-Perot(FP)腔非对称耦合的全光二极管结构, 它由一个包含非线性Kerr介质的高Q值微腔与一个光子晶体波导中的FP腔组成. 通过有限时域差分方法对其传输特性进行了仿真, 发现通过两腔的非对称耦合可以实现在特定光强度下的正向传输、反向截止的功能. 在靠近微腔方向光入射时, 特定强度的光可以激发非线性微腔的Kerr效应, 改变了Fano腔的共振频率, 从而变成透射状态. 而远离微腔方向光入射, 由于这个不对称的结构造成场局域的分布不对称, 激发微腔Kerr效应的光强还不够, 所以光不能透射. 所设计的全光二极管结构具有良好的性能参数: 最大透射率高和高透射比、光强阈值低和易于集成等.     

耦合诱导的四分之一波长超导谐振器微波传输透明

类似于利用强泵浦光调控介质光学性质实现对原共振吸收光的诱导透明,本文利用实空间量子散射理论研究了如何实现波导光子从全反射到透射的转变.结果表明,通过引入辅助四分之一波长谐振器的耦合,可实现原四分之一波长谐振器对共振微波全反射的透射.利用微纳加工工艺制备了对应上述理论模型的四分之一波长谐振器样品,在极低温条件下对该样品的微波传输特性进行了实验测试,观测到了理论预言的微波波段类电磁诱导透明的部分现象,证实了耦合谐振器的模式重整理论.     

基于表面等离子双矩形腔结构的可调微流控类EIT系统的研究

本文提出一种基于双矩形腔结构的表面等离子体类电磁诱导透明(PIT)系统,通过微流控系统来实现一种可操控的类电磁诱导透明效应。文中通过耦合模理论来对整个系统结构进行分析,并利用二维时域有限差分方法(FDTD)对该类电磁诱导透明效应系统进行数值模拟,模拟所得结果与理论分析相吻合。该系统可动态调节类电磁诱导透明效应的透射窗口中心波长及透射率、品质因子Q、慢光速度等,具有调节精确、调节范围大的优点。     

基于Kerr效应的微环谐振腔延时器件

对基于光学Kerr效应的微环谐振腔延时器件进行了研究.采用耦合模式理论计算了波导与微环谐振腔间的耦合系数,给出了所研究器件的材料及各层组分,提出不同阶数微环的情况下延时数值的控制方法.结果表明:微环谐振腔半径为300μm,波导截面尺寸为450×1 000nm2,在小于±5ps抖动的条件下,每个通道达到超过130ps的延时数值,同时延时带宽达20GHz,自由光谱范围达50GHz,工作波段在1 550nm附近,满足密集波分复用系统的要求.整个结构全光控制,且能耗不超过0.8dBm,响应速度达到ps量级,体积不超过3mm3,便于集成,满足多信道光学延时的要求,为全光通信网络中延时线的研究提供了参考.     

石墨烯超材料等离诱导透明特性和光电开关设计

基于单层图案化石墨烯超材料在太赫兹波段实现了等离子诱导透明效应，利用耦合模式理论（CMT）分析了等离子诱导透明产生的机理，得到的理论结果与时域有限差分方法计算的结果高度一致。通过调节石墨烯费米能级对等离子诱导透明特性进行了动态调控，并实现了多模同步异步开关的设计，在2.16、3.01、3.84 THz三个频率处的振幅调制度分别为95.77%、83.42%、95.58%，消光比最高可达13.73 dB。对慢光效应的研究结果表明群折射率可达180。本研究为设计光电子器件提供方案和指导。     

基于非对称微波光子晶体的电磁二极管

通过引入具有类电磁诱导透明效应的超材料,非对称光子晶体谐振腔的透射特性得到了极大的优化,包括透射峰的品质因子和谐振腔模所对应的电磁场强度.品质因子的提高与非对称场强局域的增强有利于高性能电磁二极管的实现.我们在引入非线性材料的微带波导系统中验证了该方案.实验结果显示,此二极管在1.329 GHz的工作频率下可产生高达19.7 dB的透射对比度,同时输入功率强度仅为7 dBm.此外,我们提出的方案并没有大幅增加器件体积和剧烈降低信号透过率.这些特性的亚波长尺度实现将有益于集成光学回路的小型化.     

基于石墨烯的光波导结构中的等离子体诱导透明研究

本文提出了两种新型的基于石墨烯的表面等离子体光波导(GSPW),结构由单层石墨烯直波导与侧耦合的石墨烯环形谐振腔和条形谐振腔构成,利用有限元法(finite element method,FEM)对GSPW中呈现出的等离子体诱导透明(plasmon induced transparency,PIT)现象及其慢光效应进行了研究,结果表明,传输谱中出现的PIT透明窗口峰值传输率可达到80%以上,而其两侧的传输谷值接近于0,并且PIT峰值附近的最大群折射率在112左右,具有很好的滤波特性与慢光特性。透明窗口在不改变几何结构的情况下还可通过石墨烯化学势的改变而动态调制,因此,该结构在今后基于石墨烯的高密度集成表面等离子体光波导器件的设计中具有重要的借鉴作用。     

相移光纤光栅耦合系数控制

为了通过遮挡法实现不同耦合系数π相移光纤光栅制作,分析了刻制过程中的相移形成原理,提出通过调整遮挡区长度和π相移周期次数控制π相移光纤光栅耦合系数的方法.采用传输矩阵法对刻制相移光纤光栅过程中的透射谱变化进行仿真计算,分析了不同光栅条纹可见度下遮挡区长度对相移光纤光栅透射谱的影响.基于不同遮挡区长度进行了相移光纤光栅制作实验,结果表明:通过调整遮挡区长度和π相移出现次数能够实现对相移光纤光栅耦合系数的有效控制.     

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

本文设计了一种非对称结构的类电磁诱导透明超材料结构,利用时域有限差分方法对其光学特性和类EIT效应进行了仿真分析,建立了其耦合洛伦兹模型,并对所设计超材料结构的类EIT效应进行了模拟分析.结果表明:利用两个长短不同的硅块明模和明模之间的耦合,在1555 nm附近实现了类电磁诱导透明效应;通过对该超材料的微结构参数进行优化,实现了超高Q值(Q约为8616)的类EIT效应,透射率可达96%;通过调节硅块的长度以破坏超材料结构的非对称性,实现了对类电磁诱导透明窗口的主动调控.所设计的全介质超材料结构具有低损耗、易制备、主动可调控等优点,在主动可调控的慢光器件、高灵敏的光学传感器、窄带滤波器等光学器件的设计中具有潜在的应用价值.     

Dual-band plasmon induced transparency controlled by the polarization of the incident wave

In this paper, a hybridized plasmonic waveguide system is investigated numerically. By coupling plasmonic modes with different waveguide modes, two plasmon induced transparency (PIT) windows with high transmittance and deep modulation can be realized. Through the polarization of the incident wave, the transparency windows can be dynamically controlled.     

Wideband slow light achievement in MIM plasmonic waveguide by controlling Fano resonance

In this paper, we have investigated the characteristics of an asymmetric shaped Fano line in a metal–insulator–metal (MIM) plasmonic waveguide side coupled to two resonating stub structures. The spectral properties of Fano resonance are quite distinct due to the destructive interference between a two propagating plasmon modes. Two structural parameters are carefully adjusted: physical separation between both the resonating stubs and length of resonating stubs. By tailoring the separation between both the resonating structures, coupling between both the plasmon modes is controlled, and hence asymmetric nature of Fano line can be shaped accordingly. Resonance condition of Fano line can be tuned by scaling the length of stubs. A strong red shift in resonating wavelength with varying degree of asymmetry is observed, when length of resonating structures is increased. The sharp resonant peak, due to an asymmetric shaped Fano resonance is generally accompanied by large dispersion that results in reduction of group velocity of light near Fano resonance. By controlling the coupling between resonating stub, or by scaling the length of lower resonating stub, large value of group index (n_g = 75) and delay bandwidth product (DBP = 0.2533) is obtained. The structure can be modified to suit different applications in optical buffers, optical switches and nonlinear optics devices.     

Microcavity plasmonics: strong coupling of photonic cavities and plasmons

The understanding of light‐matter interactions at the nanoscale lays the groundwork for many future technologies, applications and materials. The scope of this article is the investigation of coupled photonic‐plasmonic systems consisting of a combination of photonic microcavities and metallic nanostructures. In such systems, it is possible to observe an exceptionally strong coupling between electromagnetic light modes of a resonator and collective electron oscillations (plasmons) in the metal. Furthermore, the results have shown that coupled photonic‐plasmonic structures possess a considerably higher sensitivity to changes in their environment than conventional localized plasmon sensors due to a plasmon excitation phase shift that depends on the environment.     

Optical switch effect of metal–dielectric–metal plasmonic waveguide coupled with stub structure

The transmission line theory (TLT) and the finite difference time domain (FDTD) method are applied to investigate the optical transmission characteristics of the metal–dielectric–metal (MDM) plasmonic waveguide coupled with a stub structure. The transmission rate of the FDTD simulation results demonstrates periodically variation from less than 1% to more than 92% as a function of the length of the stub, which fits well with the results of TLT. Furthermore, the transmission also performs a periodically switch distribution with the change of the refractive index of the stub from 1.0 to 2.0 gradually. Both methods are adopted for modulating the superposition phase of the interference between the reflected surface plasmon polaritons (SPPs) wave from the end of the stub and the passing SPPs wave in the waveguide, which can be interpreted as the principle mechanism for the optical switch effect of the MDM waveguide with a stub structure.     

Triple optomechanical induced transparency in a two-cavity system

We theoretically investigate the optomechanical induced transparency(OMIT) phenomenon in a two-cavity system which is composed of two optomechanical cavities. Both of the cavities consist of a fixed mirror and a high-Q mechanical resonator, and they couple to each other via a common waveguide. We show that in the presence of a strong pump field applied to one cavity and a weak probe field applied to the other, a triple-OMIT can be observed in the output field at the probe frequency. The two mechanical resonators in the two cavities are identical, but they lead to different quantum interference pathways. The transparency windows are induced by the coupling of the two cavities and the optical pressure radiated to the mechanical resonators, which can be controlled via the power of the pump field and the coupling strength of the two cavities.     

Band-pass plasmonic filter based on periodic cascade resonant cavities

A band-pass plasmonic filter based on periodic cascade resonant cavities is theoretically designed and analyzed. The transmission modes of surface plasmon polariton are well studied by the finite-difference time-domain method. The structure indicates the band-pass selection capability with several types of modes in the transmission spectra. The results show that the number of the transmission modes depends on the number of the cascade cavities period. These modes exhibit a shift with varying incident intensity involving Kerr medium in cascade cavities. The structure provides flexibility in design for pass-bands filter.     

非线性克尔效应对飞秒激光偏振的超快调制

研究了近红外飞秒激光的偏振在太赫兹频率的超快调制.利用抽运-探测光谱技术,通过改变两个脉冲之间的延迟时间可以控制光脉冲的旋转角.在Li：NaTb（WO₄）₂磁光晶体中观察到探测光的偏振随延迟时间变化的高速振荡,振荡信号的中心频率为0.19 THz.这种超快偏振调制现象可以解释为,抽运-探测实验构置中,前向传播的抽运光诱导的光学克尔非线性引起被晶体远端表面所反射的背向传播的探测光脉冲偏振面的额外旋转.通过改变抽运光的圆偏振旋性可以控制探测光调制信号的相位和振幅.实验结果表明,非线性光学克尔效应可以作为一种全新的手段,在磁光晶体中实现近红外飞秒激光以太赫兹频率的超快偏振调控.这将在超快磁光调制器等全光器件中得以应用.实验结果将有助于偏振依赖的超快动力学过程的研究.     

Saturable and reverse saturable absorption of a linear polymer in dimethylformamide

An all-optical tunable narrow-band filter with an ultrafast response time of 10 ps is realized in a two-dimensional nonlinear polystyrene photonic crystal. The pump and probe scheme is adopted to measure tunability based on the picosecond optical Kerr effect. The passband of the photonic crystal filter shifts about 4 nm under excitation of 14.7 GW/cm² pump intensity, which is in agreement with the theoretical prediction. PACS 42.70.Qs; 61.46.+w; 81.15.-z     

CS_2飞秒超快非线性特性的实验研究

采用中心波长800 nm、脉宽30 fs的超短激光脉冲,通过飞秒光开关技术对CS_2的飞秒超快非线性特性进行了实验研究.在探测光强与抽运光强比为1∶10时,得到了较理想的光克尔时间分辨曲线.通过实验测定的光克尔信号强度与激发光和探测光偏振方向夹角的依赖关系表明:30 fs的超短激光脉冲激发CS_2的克尔信号主要是源于光诱导双折射效应,而非用200 fs的超短激光脉冲时来自瞬态栅的自衍射效应.     

Plasmonic waveguiding in a hexagonally ordered metal wire array

We propose the inclusion of a structured pattern of nanoscale metal wires in a silica fiber to form a symmetric plasmonic waveguide. The surface plasmon polariton modes within the waveguide are studied by varying the wire diameter and spacing. Simulation results show that hybridization of the single-wire mode and the gap plasmon mode can yield a hybrid mode with optimum propagation lengths comparable to those reported for other structures but with better light confinement. The fiber can be easily doped with a gain material to offset the loss so that the resultant waveguide will be useful for integration with electronic circuits at nanometer dimensions.