带有开口方环谐振腔的MIM波导的Fano谐振特性研究

本文设计了一种支持Fano谐振传输特性的金属-介质-金属(MIM)型表面等离子体光波导结构,该结构由带有枝节谐振腔的直波导和一个开口方环谐振腔组成。利用数值方法详细研究了Fano谐振传输特性对几何参数的依赖关系,并通过时域耦合模理论(CMT)对给定参数条件下的传输谱进行了拟合验证。同时,也对该结构在折射率传感器方面的应用进行了研究,通过计算介质折射率变化引起的Fano谐振峰的波长变化可以发现,传感器的灵敏度高达1500nm/RIU,品质因子超过1800。这种表面等离子体光波导结构在光子器件集成及纳米滤波器、快速光开关以及折射率传感器等领域有一定的应用前景。     

带有同心双圆环谐振腔的MIM波导的Fano谐振特性研究

本文设计了一种支持多重Fano谐振的金属-介质-金属(MIM)型表面等离子体光波导(SPW)结构,该结构由带有枝节谐振腔的直波导耦合同心双圆环谐振腔组成。利用有限元法进行数值仿真,研究了耦合距离、枝节的高度以及同心双圆环内、外环半径对Fano传输特性的影响。同时,结合磁场分布图,分析了多重Fano谐振形成的物理机理。另外,通过改变填充在同心双圆环谐振腔内介质材料的折射率研究了该结构在折射率传感器领域的应用。该波导结构具有灵敏度为1 400nm/RIU,品质因数高达1 380的传感特性。最后,本文研究了该波导结构的慢光特性,研究表明Fano峰附近的最大群折射率约为11.4,最大延迟时间约为0.076ps。这种SPW结构在纳米尺度的滤波器、折射率传感器以及慢光器件等领域有着潜在的应用前景。     

基于半圆形与矩形谐振腔耦合结构的Fano共振

设计了一种基于金属-介质-金属波导的半圆形谐振腔与矩形谐振腔的耦合结构,采用有限元方法研究了该结构的传播特性.结果表明:透射光谱中产生一个类似Fano共振线型的共振谷,该Fano共振由半圆形谐振腔的宽谱共振和矩形谐振腔的窄谱共振相互耦合所导致.变化谐振腔的结构参量,发现该Fano共振谷位置依赖于矩形谐振腔的几何参量,而对两谐振腔相对位置的微小移动不敏感;同时,改变两谐振腔的并联方式,研究了两种衍生结构的传播特性,发现这些结构均可产生明显的Fano共振.此外,通过在谐振腔中填充不同折射率的介质材料,研究了三种结构基于Fano共振效应的折射率传感特性,其折射率敏感度最高达到750 nm/RIU.研究结果可为未来芯片上基于表面等离极化激元波导的高灵敏折射率传感器的设计提供理论依据.     

基于锚形谐振腔的等离子体波导特性研究

基于表面等离子体激元在金属-介质-金属结构中优良的传输特性,设计了一种由直波导和锚形谐振腔组成的波导滤波器。仿真分析了波导滤波器传输特性和电场分布随结构参数和谐振腔内介质折射率变化规律。结果表明,该锚形谐振腔最佳结构时滤波器半峰全宽低至8 nm,品质因数高达121.9。利用共振波长与结构参数变化规律,设计了光通信波长窗口的窄带带阻滤波器。根据SPPs对谐振腔介质折射率敏感的特性,发现透射谱线随折射率变大而发生红移。本文提出的基于锚形谐振腔的等离子体MIM波导滤波器为设计特定波长的窄带带阻滤波器提供了新思路,也为基于谱线红移特性设计的介质折射率传感器提供了技术支持。     

带有T型腔的MIM波导的法诺共振特性研究

设计了一种带有枝节的金属-介质-金属(MIM)波导与T型谐振腔侧耦合的表面等离子体光波导结构。利用有限元法(FEM),数值分析了改变耦合距离、T型腔几何尺寸及其不对称性、枝节高度对法诺(Fano)共振谱线的影响。结合电磁场分布进一步揭示了Fano共振现象产生的物理机理,由此可以动态调节表面等离子体波在结构中传输时产生的Fano共振特性。另外,研究表明在T型腔内填充不同折射率的材料,利用所设计的波导结构可以实现灵敏度高达940nm/RIU的纳米尺度的折射率传感器。最后研究了结构的慢光传输特性,可以在Fano峰值附近实现约0.025ps的光学延迟。这种新型的表面等离子体光波导可能会在光子器件集成、慢光效应及纳米传感领域有着较大的应用前景。     

基于Fano共振的金属-绝缘体-金属-石墨烯纳米管混合结构动态可调折射率传感器

为了解决传统金属-绝缘体-金属(metal-insulator-metal,MIM)波导结构传感器不可动态调控的问题,本文将石墨烯纳米管引入MIM波导耦合圆环谐振腔结构,设计了一种动态可调的MIM-石墨烯纳米管混合结构折射率传感器.采用有限元法对系统的传输特性、电场分布和磁场分布进行数值研究,并通过多模干涉耦合模理论进行分析验证.结果表明,Fano共振源自于TM₁₀腔共振模式和石墨烯等离子体电共振模式之间的相干耦合.通过改变石墨烯的化学势可以在较大波长范围内动态调谐Fano共振的谐振波长和线宽,从而实现折射率传感器的动态调控.在最佳结构参数下,传感器灵敏度可达1250 nm/RIU.与传统的MIM波导结构相比,该器件具有结构简单、动态可调、易于加工且工作波段范围大等诸多优点,对设计可动态调控的高性能纳米光子集成器件具有一定的指导意义.     

基于耦合开口方环共振空腔的可控法诺共振研究

基于表面等离子激元理论与金属-介质-金属波导结构提出一个由开口方环共振空腔、挡板及MIM波导组成的波导结构,并使用有限元方法系统地研究了该结构的透射特性.仿真计算结果表明:该结构可以产生法诺共振现象,其共振波长可以通过改变开口方环空腔的长度及开口大小进行调节,该结构敏感度可达1 600nm/RIU,品质因数为1.31×10~5.此外,通过调整方环共振空腔上开口的位置,在波导中产生了双重法诺共振现象,其敏感度可达1 700nm/RIU,品质因数为8.3×10~4.该结构有望在光学集成回路,尤其是纳米生物传感器方面得到比较广泛的应用.     

含金属双缝的金属-电介质-金属波导耦合环形腔Fano共振慢光特性研究

基于表面等离子亚波长结构的传输特性,提出一种含金属双缝的金属-电介质-金属波导耦合环形腔结构。由金属双缝波导谐振腔形成的较宽的连续态波与由环形谐振腔形成的较窄的孤立态波耦合干涉相消,形成Fano共振。结合耦合波理论,分析了该结构形成Fano共振的传输及相位特性。采用有限元分析法对该结构进行模拟仿真,定量分析了结构参数对结构慢光特性的影响,实现结构参数优化。结果表明,优化后的结构群折射率可达205。该结构能为集成等离子慢光器件的设计提供有效的理论参考。     

基于眼型谐振腔的Fano谐振曲线尖锐度的分析

为了获得较大的尖锐度,提升微环传感器的灵敏度,提出利用眼型谐振腔结构在下路端输出的非对称Fano谐振光谱,眼型谐振腔由一个外环和内环构成,外环与总线波导耦合,内环与外环耦合.利用传输矩阵法对下路端输出光谱进行了数值计算,在不同剩余电场比例系数下,发现非对称Fano谐振峰的尖锐度随电场剩余比例系数的增大而增大;改变外环与总线波导间的场强耦合系数和内环与外环之间的场强耦合系数,其尖锐度的最大值随外环和内环场强耦合系数变化缓慢增大,尖锐度最大值处谐振点传输系数值在不同电场剩余比例系数和内外环场强耦合系数下稳定在-6dB附近.因此利用眼型谐振腔结构下路端的Fano谐振峰,可获得对耦合系数不敏感的尖锐度和谐振点传输系数,降低器件对耦合区加工准确度的要求.     

基于十字连通形环形谐振腔金属-介质-金属波导的折射率传感器和滤波器

提出了由十字连通形环形谐振腔耦合两个金属-介质-金属(metal-insulator-metal, MIM)波导的结构,并用有限元法数值研究了表面等离极化激元在结构中的传输特性.通过对透射谱的研究,系统地分析了MIM结构的传感特性.结果表明,在透射光谱中有三个共振峰,即存在三种共振模式,其中透射峰与材料的折射率呈线性关系.通过对结构参数的优化,得到了折射率灵敏度(S)高达1500 nm/RIU的理论值,相应的传感分辨率为1.33×10~(-4)RIU.更重要的是,灵敏度不受结构参数变化的影响,这意味着传感器的灵敏度不受制造偏差的影响.此外,谐振波长与环形腔中心半径成线性关系,该器件在较大波长范围内实现可调谐带通滤波.透射强度随着波导与环形腔间距的增大而减小,透射带宽同时减小,因此,可以通过控制环形腔与波导的耦合距离来调谐透射强度及透射带宽.研究结果对高灵敏度纳米级折射率传感器和带通滤波器的设计以及在生物传感器方面的应用都具有一定的指导意义.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.