Multi-frequency switch and excellent slow light based on tunable triple plasmon-induced transparency in bilayer graphene metamaterial∗

We propose a novel bilayer graphene terahertz metamaterial composed of double graphene ribbons and double graphene rings to excite a dynamically adjustable triple plasma-induced transparency (PIT) effect. The coupled mode theory (CMT) is used to explain the PIT phenomenon, and the results of the CMT and the finite-difference time-domain simulation show high matching degree. By adjusting the Fermi levels of graphene, we have realized a penta-frequency asynchronous optical switch. The performance of this switch, which is mainly manifested in the maximum modulation depth (MD = 99.97%) and the minimum insertion loss (IL = 0.33 dB), is excellent. In addition, we have studied the slow-light effect of this triple-PIT and found that when the Fermi level of graphene reaches 1.2 eV, the time delay can reach 0.848 ps. Therefore, this metamaterial provides a foundation for the research of multi-frequency optical switches and excellent slow-light devices in the terahertz band.     

Dynamically tunable multiband plasmon-induced transparency effect based on graphene nanoribbon waveguide coupled with rectangle cavities system

A dynamically tunable multiband plasmon-induced transparency (PIT) effect in a series of rectangle cavities coupled with a graphene nanoribbon waveguide system is investigated theoretically and numerically by tuning the Fermi level of the graphene rectangle cavity. A single-PIT effect is realized using two different methods: one is the direct destructive interference between bright and dark modes, and the other is the indirect coupling through a graphene nanoribbon waveguide. Moreover, dual-PIT effect is obtained by three rectangle cavities side-coupled with a graphene nanoribbon waveguide. Results show that the magnitude of the dual-PIT window can be controlled between 0.21 and 0.74, and the corresponding group index is controlled between 143.2 and 108.6. Furthermore, the triple-PIT effect is achieved by the combination of bright-dark mode coupling and the cavities side-coupled with waveguide mechanism. Thus, sharp PIT windows can be formed, a high transmission is maintained between 0.51 and 0.74, and the corresponding group index is controlled between 161.4 and 115.8. Compared with previously proposed graphene-based PIT effects, the size of the introduced structure is less than 0.5 μm². Particularly, the slow light effect is crucial in the current research. Therefore, a novel approach is introduced toward the realization of optical sensors, optical filters, and slow light and light storage devices with ultra-compact, multiband, and dynamic tunable.     

Liquid refractive index sensor based on slow light in slotted photonic crystal waveguide

A high sensitive and compact refractive index sensor based on slotted photonic crystal waveguide (S-PhCW) is demonstrated. This design is worked on a Mach–Zehnder interferometer (MZI) configuration with S-PhCW as the measuring arm, which can be used to detect any changes in refractive index that correspond to different concentration of the measuring liquid. Combining the slow light enhancement in photonic crystal waveguide (PhCW) with the advantage of excellent optical confinement in slot waveguide, the sensitivity of this simple scheme can reach to 2.3 × 10⁹ nm/RIU with the active region of only 1 mm long.     

Temperature-induced effect on refractive index of graphene based on coated in-fiber Mach-Zehnder interferometer

The temperature-induced complex refractive index(CRI) effect of graphene is demonstrated theoretically and experimentally based on a graphene coated in-fiber MZI(Mach-Zehnder interferometer). The relationships between real and imaginary parts of the graphene CRI and temperature are obtained through investigating the dip wavelength and intensity of the MZI interference spectrum changing with temperature, respectively. The temperature effect of CRI of the graphene is also analyzed theoretically. Both experimental and theoretical studies show that the real part and imaginary part of the CRI nonlinearly decrease and increase with temperature increasing, respectively. This graphene-coated in-fiber MZI structure also possesses the advantages of easy fabrication, miniaturization, low cost and robustness. It has potential applications in nanomaterial-based optic devices for communication and sensing.     

Optical control of light propagation in photonic crystal based on electromagnetically induced transparency

A kind of photonic crystal structure with modulation of the refractive index is investigated both experimentally and theoretically for exploiting electromagnetically induced transparency(EIT).The combination of EIT with periodically modulated refractive index medium gives rise to high efficiency reflection as well as forbidden transmission in a threelevel atomic system coupled by standing wave.We show an accurate theoretical simulation via transfer-matrix theory,automatically accounting for multilayer reflections,thus fully demonstrate the existence of photonic crystal structure in atomic vapor.     

基于单端探测温度和折射率的MZI光纤传感器

提出并演示了一种基于单端探测的光纤传感器,可同时测量温度和折射率。微结构光纤探头由两个玻璃光纤微球拼接在一起,并在该探头的末端利用真空电子束蒸镀一层铝膜以增加反射,从而形成微球结构的马赫-曾德尔型光纤传感头。实验结果表明,该器件的温度灵敏度和折射率可分别达到50.77 pm/℃和-21.94 nm/RIU。这项工作提出了一种低成本、高分辨率的基于光纤方法实现的多功能传感应用。单端探测的马赫曾德尔型光纤传感器小尺寸的优势可应用到小体积气体的测量,而它的全二氧化硅设计提供了高温或化学严酷环境的兼容性。     

带多孔硅表面缺陷腔的半无限光子晶体Tamm态及其折射率传感机理

结合表面缺陷半无限光子晶体Tamm态与多孔硅光学传感机理,在光子晶体表面缺陷腔中引入多孔硅,并利用其高效的承载机制,提出基于多孔硅表面缺陷光子晶体Tamm态的折射率传感结构.在半无限光子晶体中缺陷腔与原来的周期性分层介质结构的界面上存在Tamm态,通过入射角度调制使其在缺陷腔中实现多次全反射,并在缺陷腔中加入吸收介质,使谐振波长在缺陷腔中完成衰荡,从而在反射谱中得到缺陷峰;调整光子晶体参数,使缺陷峰的半高全宽得到优化,提高其品质因数(Q值);在此基础上,根据Goos-H?nchen相位移与谐振波长的关系,建立由待测样本折射率改变所导致的多孔硅表面吸附层有效折射率变化与缺陷峰值波长漂移之间的关系模型,并分析其折射率传感特性.结果表明,此生物传感结构Q值为1429,灵敏度为546.67 nm/RIU,证明了该传感结构的有效性,可为高Q值和高灵敏度折射率传感器的设计提供一定的理论参考.     

Whispering gallery mode microlasers and refractive index sensing based on single polymer fiber

The realization of whispering gallery mode (WGM) lasing in polymer fibers is hindered by an appropriate method to dissolve the polymer and the gain material. In this work, microfibers fabricated by directly drawing from a dye doped polymer solution are exhibited as high quality microlasers and microsensors. Multi‐mode and even single‐mode lasing is observed from the fiber under optical pumping at room temperature. The linewidth of lasing mode is narrower than 0.09 nm. The lasing mechanism is unambiguously verified by comprehensive spectroscopic analysis and ascribed to WGMs. Diameter‐ and polarization‐dependent lasing characteristics are systematically investigated, showing good agreement with the theoretical calculation. Particularly, application of the fiber laser for refractive index sensing based on resonant shift of lasing mode is demonstrated and the sensitivity up to about 300 nm/RIU is achieved. The promising potential of high quality polymer microfibers as optical sensors and multi‐function components for flexible photonic integrated systems is highly expected.     

基于光纤气泡和纤芯失配的Mach-Zehnder干涉液体折射率传感器

介绍了一种基于光纤气泡和纤芯失配的Mach-Zehnder干涉液体折射率传感器. 将两根纤芯经过腐蚀的普通单模光纤熔接在一起, 在熔接点处形成一个气泡, 在距气泡20 mm处级联一段20 mm的细芯光纤, 再接入一段单模光纤, 形成单模光纤-气泡-单模光纤-细芯光纤-单模光纤结构的传感器. 气泡与光纤芯径失配处的两个节点起到光纤耦合器的作用, 从而形成光纤Mach-Zehnder干涉仪. 环境液体折射率的变化,将使得传感器透射谱能量发生变化, 通过测量干涉谱波峰峰值能量从而实现对折射率的测量. 并对所制作传感器的折射率响应特性进行了实验研究, 实验结果表明干涉谱波峰峰值能量与环境液体折射率之间存在良好的线性关系, 当环境液体折射率变化范围在1.351–1.402时, 响应灵敏度为143.537 dB/RIU, 线性度0.996. 该传感器在生物化学领域有较好的应用前景. 关键词： 光纤气泡 纤芯失配 Mach-Zehnder干涉仪 折射率传感     

基于高介电常数基板和金属结构负折射材料的设计,仿真与验证

通过将单回路镜像对称开口金属环结构印制在高介电常数基板上,实现了一种金属含量比传统负折射材料更少,"双负"通带比全介质负折射材料更宽的负折射材料.分析了高介电常数基板产生负介电常数以及"双负"通带形成的机理,通过仿真实验分析了影响"双负"通带的因素.通过制作样品验证了这一机理实现"双负"的可行性,理论分析与实验结果都表明这种方法可实现较宽频段内的"双负"通带. 关键词： 负折射材料 负介电常数 负磁导率 介质谐振器原理     

基于D型双芯PCF的近红外宽检测范围SPR折射率传感器

现有报道的PCF-SPR折射率传感器的检测范围普遍较窄,不能实现低折射率的检测,且工作波段多数集中在可见光或通信波段,这限制了传感器的应用范围.鉴于此,提出了一种基于D型双芯PCF结构的SPR传感器,使用氧化铟锡作为等离子体材料沉积在D型PCF抛光表面,并对该传感器的理论模型进行了分析,包括金属参数对传感性能的影响,P...     

High-sensitivity refractive index sensors based on Fano resonance in a metal-insulator-metal based arc-shaped resonator coupled with a rectangular stub

A metal-insulator-metal (MIM)-based arc-shaped resonator coupled with a rectangular stub (MARS) structure is proposed. This structure can generate two tunable Fano resonances originating from two different mechanisms. The structure has the advantage of being sensitive to the refractive index, and this feature makes it favorable for application in various microsensors. The relationship between the structural parameters and Fano resonance is researched using the finite element method (FEM) based on the software COMSOL Multiphysics 5.4. The simulation reveals that the sensitivity reaches 1900 nm/refractive index unit (RIU), and the figure of merit (FOM) is 23.75.     

湍流折射率谱型对大气闪烁和相位起伏功率谱的影响

基于Taylor湍流冻结假设理论,在不同湍流折射率谱型条件下,推导得出了光波闪烁和相位起伏频谱的表达式;数值计算了湍流谱型中折射率标度指数、内尺度以及外尺度变化时对光波频谱的影响。结果表明:随着折射率起伏标度指数的增大,闪烁频谱的低频段不再仅为常数,高频段下降的幂率逐渐增大,同时相位频谱在整个起伏频率段下降的幂率越来越大;湍流内尺度的增加将引起光波频谱的高频段下降的幂率越来越大;而随外尺度的减小,闪烁频谱低频段的振幅减小,这种影响在大口径接收时较为明显,相位谱的低频段幂率减小。     

湍流折射率谱型对大气闪烁和相位起伏功率谱的影响

基于Taylor湍流冻结假设理论,在不同湍流折射率谱型条件下,推导得出了光波闪烁和相位起伏频谱的表达式;数值计算了湍流谱型中折射率标度指数、内尺度以及外尺度变化时对光波频谱的影响。结果表明：随着折射率起伏标度指数的增大,闪烁频谱的低频段不再仅为常数,高频段下降的幂率逐渐增大,同时相位频谱在整个起伏频率段下降的幂率越来越大;湍流内尺度的增加将引起光波频谱的高频段下降的幂率越来越大;而随外尺度的减小,闪烁频谱低频段的振幅减小,这种影响在大口径接收时较为明显,相位谱的低频段幂率减小。     

Nonlinearity of refractive index in glasses based on heavy metal oxides with different lead and tellurium contents

We have studied the nonlinearity of the refractive index at a wavelength of 1.08 μm for optical lead silicate and lead phosphate tellurite glasses of different compositions. We have shown that the nonlinear refractive index n₂ increases as the lead content increases in lead silicate glasses and as the tellurium content increases in lead phosphate tellurite glasses, where the latter are typically have higher values of n₂, as high as 24·10⁻¹³ cgs units (47·10⁻¹⁶ cm²/W), and lower Rayleigh losses. We have established a correlation between the nonlinear refractive index and the microstructure of the studied glasses. The highly nonlinear glasses are distinguished by extensive fluctuations in the heavy metal oxide concentration which are “frozen” during cooling of the glass melt. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 780–784, November–December, 2007.     

基础实验中光速和介质折射率测量方法的研究

采用一种新型光速测定仪测量光速和介质折射率,对测量方法进行了研究和改进,分析了测量误差的来源.在此基础上,采用精密数字相位计代替示波器测量相位,设计了新的测量方案,并采用最小二乘法进行线性拟合,从而提高了测量精度,其精度达到±0.1%.