Enhanced and confined light transmission through a funnel-type aperture with a sub-wavelength outlet

Enhanced transmission through sub-wavelength hole arrays and a single sub-wavelength aperture with periodic corrugations surrounded have been investigated extensively. We report the similar phenomenon through a funnel-type aperture with a sub-wavelength outlet in a thick silver film, which was obtained numerically by using finite-difference time-domain method. Properties of the transmission spectrum can be modulated by geometric parameters of the funnel-type aperture. With periodic grooves or dielectric gratings on the output surface of the structure, beaming light emission can be obtained.     

Third- and fourth-order active dispersion compensation with a phase modulator in a terabit-per-second optical time-division multiplexed transmission

Broadening of the pulse waveforms by the higher-order dispersion of a transmission line is a critical limiting factor in achieving terabit-per-second optical time-division multiplexed (OTDM) transmission with femtosecond pulses. We show that the third- and fourth-order dispersion of a transmission line can be simultaneously compensated for by use of a phase modulator. In this method, sinusoidal phase modulation applied to the linearly chirped pulse before transmission compensates for the phase shift caused by the third- and fourth-order dispersion of the transmission line. The pulse broadening of a 380-fs pulse after a 70-km transmission in a 1.28-Tbit/s OTDM experiment was as small as 20 fs.     

Coherent propagation at high intensities on a free exciton resonance in a semiconductor: self-induced transmission

We investigate high-intensity propagation around a free exciton resonance in a semiconductor. Under certain conditions, coherent propagation can be found. We call this new effect ‘self-induced transmission on a free exciton resonance in a semiconductor’. Tuning the laser towards higher energy, thus exciting continuum states, the degree of transmission is reduced. The pulse breakup vanishes. By increasing the pulse intensity by several orders of magnitude, pulse breakup can be observed again. Using pulses with durations less than 100 fs, pulse breakup can be observed, but the behaviour under increasing pulse intensity is quite irregular. Pulse compression can occur under certain circumstances.     

Active control of the plate energy transmission in a semi-infinite ribbed plate

Active control of the plate flexural wave transmission through the beam in a semi-infinite beam-reinforced plate is analytically investigated. The ribbed plate is modeled as a continuous system, using equations of motion to describe the plate in flexure and the beam in both flexure and torsion. The maximum transmission of the plate flexural waves through the reinforcing beam is found to occur at resonance frequencies corresponding to the optimal coupling between the plate flexural waves and the flexural and torsional waves in the beam. A single control force is applied to the beam, and a cost function is developed to attenuate the far-field flexural energy transmission. It can be observed that the transmission peaks corresponding to the flexural resonances in the beam are reduced. Similarly, the transmission peaks corresponding to the torsional resonance conditions in the beam can be attenuated using a single control moment applied to the beam. Significant attenuation of all the resonance peaks in the flexural wave transmission can also be achieved with the application of a single force and a single moment collocated on the beam. In this paper, the feasibility of attenuating the flexural wave transmission due to both the flexural and torsional resonance conditions by using a single point force and point moment collocated on the beam is demonstrated.     

一种半环形表面等离子体光波导滤波器的传输特性研究

本文设计并提出一种基于金属-介质-金属结构的带有半环形共振腔的表面等离子体光波导滤波器,利用数值模拟的方法研究了其传输特性。结果表明,在该结构传输谱曲线中形成的滤波阻带位置可以通过改变半环形共振腔的半径来调整。另外由于结构固有的特性,在传输谱曲线上还可以观察到类似等离子体感应透明的传输特性,而且这一特性可以通过改变半环形共振腔与直波导之间的耦合间距和采用面对面放置的双半环结构进行调节。本文所设计的结构可以动态控制光的传输,并可以应用于紧凑型纳米光学器件集成领域。     

Theoretical Study of Millimeter Wave Harmonic Oscillator Stabilized with a Transmission Cavity

An equivalent circuit model of millimeter wave second harmonic oscillator stabilized with a transmission cavity has been proposed for constructing analytical formulations between performance parameters of the oscillator and parameters of the circuit. The model consists of an equivalent circuit of fundamental wave and that of second harmonic wave. Each of the circuits comprises circuit models of main cavity, transmission waveguide, and transmission cavity. Absorbing material placed between the transmission waveguide and the transmission cavity can suppress additional resonances originated from transmission cavity. The behavior of the second harmonic oscillator can be effectively described by the circuit model. Furthermore, based on this model, mechanical tuning characteristics have been studied at first, and then analytical formulas for quality factor and efficiency depending on circuit parameters have been derived. The circuit parameters can be conveniently extracted by electromagnetic field simulation. Hence the formulas exhibit both compact form and enough accuracy. Thereafter, general rules of performance parameters varying with circuit parameters have been deduced for the harmonic oscillators. Then some design considerations have been derived according to the corresponding analysis. The equivalent circuit model is useful for designing and adjusting millimeter wave second harmonic stabilizing oscillator with a transmission cavity.     

具有镜像对称结构的一维光子晶体的透射谱

计算了具有镜像对称性结构的一维光子晶体的透射谱.在光子晶体的禁带中得到了多个完全透射峰.用数学归纳法得到了简单的迭代关系式用以计算多个完全透射峰的频率.只要结构具有镜像对称性，中心透射峰总是存在，而其他透射峰则依赖于缺陷的位置和折射率.适当选择对称结构，可以得到一个近完全透射带. 关键词： 光子晶体 缺陷模 透射谱     

High-optical-throughput individual nanoscale aperture in a multilayered metallic film

The optical transmission of an individual subwavelength aperture in a multilayered metal film is shown to be enhanced compared with that of a homogeneous metal film. The enhancement effect is due to the light coupling to surface plasmon excitation facilitated by a film periodicity. The sensitivity of the transmission to the dielectric filling of the aperture is also shown. The latter effect can be used to switch and control the transmittance. Devices based on enhanced transmission through nanosized apertures can find applications in high-density optical and magneto-optical data storage, high-resolution microscopy, and photolithography, where nanoscale light sources with high-optical-power throughput are required, as well as in sensor applications.     

Optical control over surface-plasmon-polariton-assisted THz transmission through a slit aperture

We demonstrate optical control over the transmission of terahertz (THz) radiation through a single subwavelength slit in an otherwise opaque silicon wafer. The addition of periodic corrugation on each side of the wafer allows coupling to surface plasmon polaritons, so that light not impinging directly on the slit can contribute to the transmission. A significant enhancement of the THz transmission can be achieved through control of the surface wave propagation length by excitation at optical wavelengths. The observed transmission increase is in distinct contrast to the reduction reported for photoexcitation of arrays of holes in semiconductors.     

Tuning the extraordinary optical transmission through subwavelength hole array by applying a magnetic field

The transmission of light through a thin Ag film with a periodic subwavelength hole array can be influenced by the presence of the externally applied magnetic field H. Using a three-dimensional finite element method, we show that the spectral locations of the transmission peak resonances can be shifted by varying the magnitude and direction of the H. The transmission peaks have blueshift, and the higher the magnitude of H the larger the blueshift. The shift is due to the change of cavity resonance condition as a result of the magneto-induced anisotropy in the optical properties of the Ag film. Hence, high transmittance for any desired wavelength can be achieved by applying an appropriate H to the metallic film of optimized material and hole parameters.     

Light transmission through metallic slit with a bar

The transmission characteristics of a metallic slit with a bar are investigated by using the two-dimensional finite difference time-domain method. It is found that the introduction of a bar enriches the transmission spectrum. As the bar locates at the center of the electric (magnetic) field antinodes, the transmission peaks have longer (shorter) wavelengths in comparison with the corresponding resonant peaks of the single slit. It is true for both the fundamental mode and second order mode. The proposed mode in a previous paper [Y. Wang, Y. Wang, Y. Zhang, S. Liu, Opt. Express 17 (2009) 5014] can well explain the above phenomenon. The increase in ability to accumulate charge or decrease in the length of current flow dominates when the bar lies at different positions, which results in a redshift or blueshift of transmission peaks. Moreover, it is also found that the transmission spectrum of the studied structure can be tuned by adjusting the length and width of the bar. It is expected that our results may be utilized to control the electromagnetic wave in subwavelength optics.     

Fiber Sagnac Loop Filter with a Symmetrical Piecewise Uniform FBG

We propose a novel comb filter by using a symmetrical piecewise uniform fiber Bragg grating (S-PUFBG) in a Sagnac interferometer. The filter has wide bandwidth, equal passband spacing, and low insertion loss. The total transmission bandwidth is determined by the number and the parameters of the grating segments, while the transmission spectrum can be cosine modulated to realize comb-like filtering, and the modulating frequency can be controlled by adjusting the fiber length difference in the Sagnac loop.     

Perfect optical nonreciprocity in a double-cavity optomechanical system

Nonreciprocal devices are indispensable for building quantum networks and ubiquitous in modern communication technology. Here, we propose to take advantage of the interference between optomechanical interaction and linearly-coupled interaction to realize optical nonreciprocal transmission in a double-cavity optomechanical system. Particularly, we have derived essential conditions for perfect optical nonreciprocity and analysed properties of the optical nonreciprocal transmission. These results can be used to control optical transmission in quantum information processing.     

Controllable electromagnetic transmission based on metallic nanoslit with a microcavity

In this paper, we explore the electromagnetic transmission through a vertical metallic nanoslit with a horizontal microcavity. The introduction of microcavity gives rise to the changes of slit transmission spectrum in the number and amplitude of transmission peak and dip, owing to the electromagnetic coupling between slit and microcavity. The transmission through the slit with microcavity strongly depends on whether the isolated slit is in resonance or not, and the microcavity resonance is an additional factor that influences the transmission. The transmission spectrum can be adjusted by changing the opening position of slit, and the slit depth, the width and depth of microcavity. Our results are analysed and discussed from the view of Fano resonance. These results may be of value in tuning electromagnetic wave in subwavelength optics and designing plasmonic devices based on composite metallic nanoslit structures.     

Resonant optical transmission through a one-dimensional photonic crystal adjacent to a thin metal film

We theoretically and experimentally reveal that the large resonant optical transmission (ROT) can be realized through a one-dimensional photonic crystal adjacent to a thin metal film, at a frequency in the original band-gap of the photonic crystal (PC). The influence of periodic number of PC and the thickness of the adjacent metal on the transmission frequency and intensity is studied in detail. An optimum design is given to reach the maximum transmission efficiency, meanwhile a mechanism underlining the ROT phenomenon is proposed. An effective admittance-matching theory is proposed to understand this effect and quantitatively determine the operating frequency, which matches very well with the simulated and measured results. The effects might be very useful to realize some optical filters and sensor devices since the structure is easy for mass production and is matured technically to be prepared in industry.     

缓变回旋管谐振腔研究

在高次模回旋管中, 模式竞争是亟待解决的问题. 本文基于广义传输线理论, 得到能准确描述缓变结构谐振腔模式耦合的一阶传输线方程组; 通过分析耦合系数, 优化得到了一种新型光滑渐变(缓变)谐振腔. 与直线连接的(折变)谐振腔相比, 该腔体有更强的模式抑制能力, 腔中非工作模式归一化幅值可达-100 dB, 输出行波段非工作模式归一化幅值可达-88.6 dB.     

Quantum key distribution experiment through a PLC matrix switch

Quantum key distribution (QKD) is being studied as a way to provide unconditionally secure communications. Several experiments have shown its feasibility. However, most experiments have used a point-to-point occupied optical link. In order to use QKD for secure communications on a real network, it is preferable to be able to change parties on demand and to have quantum transmission and ordinary optical transmission share the optical network. In this work, QKD through a silica-based planar lightwave circuit (PLC) 8 × 8 non-blocking matrix switch was investigated. We found that an interferometer type switch can work even for a single-photon-level light and that a multi-user QKD network can be constructed using a silica-based PLC 8 × 8 non-blocking matrix switch. In addition, single-photon-level transmission and ordinary optical transmission can share the same 8 × 8 non-blocking matrix switch, so which shows the possibility of sending quantum signals through current optical networks.     

基于少模光纤的模分复用系统多输入多输出均衡与解调

针对光纤模分复用传输系统中模式耦合串扰问题, 设计并制备了一种新型少模光纤, 其较高的模式差分群延时保证各模式信道独立传输.在此基础上, 提出一种级联多输入多输出(MIMO)延时均衡算法, 进一步减少源于模式复用器和解复用器的模式串扰, 提高基于少模光纤的模分复用传输系统的传输距离和传输容量.与传统MIMO均衡算法相比, 级联MIMO延时均衡算法在没有显著增加计算复杂度的条件下, 能够应用于模式差分群延时很大的模分复用传输系统.对单信道传输速率为 40 Gbps的四相相移键控两模复用传输系统进行仿真, 经40 km少模光纤传输后, 采用级联MIMO均衡算法较普通MIMO均衡算法有1.7 dB的质量因子的提升. 仿真结果证明, 使用少模光纤和级联MIMO延时均衡算法能够有效地消除模分复用信号间的串扰, 有望在下一代大容量光纤传输系统中获得 推广应用. 关键词： 模分复用 少模光纤 模式差分群延时 多输入多输出均衡     

Quantum transmission across a low-dimensional nanoscale diffuse junction

The transmission across a nano-scale diffuse junction between two metals is studied numerically for 1D wires and 2D ribbons within a tight-binding model. In such a situation, a junction electric potential must appear to equilibrate the electrochemical potential on each side of the junction. We compute the transmission under two very different potential distributions and we find that the typical transmission does not depend on the details of this distribution. The transmission is found to follow a scaling law. The variations of the 1D transmission are explained in a semi-classical way by considering the multiple reflections caused by the barriers due to the on-site energy mismatch between the two metals. Both the 1D and 2D results can also be partly interpreted in the frame of the Anderson theory of localisation.     

Spatially-temporal dynamics of a passively Q-switched Raman-active solid-state oscillator

The spatially-temporal model of an all-solid-state passively Q-switched oscillator with an active medium providing the stimulated Raman scattering is presented. The model does not presume a Gaussian shape of the cylindrically symmetric modes at both fundamental and Stokes wavelengths. It is found, that the highly-nontrivial spatially-temporal dynamics can be regularized by an optimal choice of oscillator parameters, viz. initial transmission of a saturable absorber, curvature of a spherical mirror, and output mirror transmission at the fundamental and Stokes wavelengths. As a result, the pulse can be substantially temporally squeezed and spatially broadened at both fundamental and Stokes wavelengths.