Profile-broaden ultraviolet lasing from whispering gallery mode cavity in crown-like zinc oxide

Based on the transfer matrix method,a detailed theoretical and numerical study on double-phase-shifted fiber Bragg grating(FBG)is investigated.Temporal responses of the double-phase-shifted FBG to optical pulse are analyzed and the influence of the two phase-shifts’position on the reflected output pulse is evaluated.Results demonstrate that very different temporal pulse waveforms can be achieved by adjusting the length ratio(α=L2/L1).Specifically,a transform-limited Gaussian input optical pulse can be shaped into flat-top square pulse(α=1.81)or two identical optical pulse sequences(α=1.93).     

Effect of Ce2O3 on the 1.53 μm spectroscopic properties in Er3+-doped tellurite glasses

The crown-like zinc oxide(Zn O)samples,which are composed of a hexagonal cap and a tower-like shaft,are prepared by vapor transport method.The hexagonal cap,working as a whispering gallery mode(WGM)resonant cavity,demonstrates density-dependent ultraviolet(UV)lasing emission with a broadened and squared photoluminescence(PL)profile under UV excitation at 355 nm.Theoretical analyses based on Fermi golden rule show that the broadened spectrum profile results from the special optical mode density characteristics in a WGM micro-cavity,which is in agreement with the observed results.     

A whispering gallery mode strain sensor based on microtube resonator

A novel whispering gallery mode (WGM) strain sensor based on microtube has been proposed, where perceiving strain variations are reported via the dynamical regulation of a whispering gallery mode. The WGMs in the microtube resonator were evanescently excited by a micro-nano fiber fabricated by the fusion taper technique. The structural changes of microtubes under axial strain were simulated with finite element software, and the effect of microtube wall thickness on strain sensitivity was systematically studied through experiments. The experimental results show that the strain sensitivity of thin-walled microtube is found to be 1.18 pm/με and the Q-factor in the order of 4.4×104. Due to its simple fabrication and easy manipulation as well as good sensing performance, the microtube strain sensor has potential applications in high-sensitivity optical sensing.     

波导耦合回音壁模式光学微球腔结构耦合特性分析

提出了一种耦合微球和波导系统的有效方法,并在数值和实验上进行了论证.为了研究微球腔和波导系统的耦合特性,首先通过耦合模理论研究了这个系统的2D模型.通过有限时域差分法设计了一个数值仿真系统.在快速傅里叶变换(FFT)处理样本数据后,得到了波长范围从600 nm到1 000 nm的相对强度谱曲线和传输谱曲线.在实验中,采用熔融单模光纤顶端的方法制得了石英材料微球腔.采用热拉技术制得了锥形光纤,用来作为激发微球腔中回音壁模式的波导.测试了这个微球腔-锥形光纤耦合系统,通过优化微球腔与锥形光纤的相对位置得到其品质因数高达2.3×106,耦合效率高达92.5%.这些耦合特性可以很好地用理论结果解释.这些特性表明了其在实际微腔传感和微型激光器中极具潜力.     

Calculation of radiation from a quasi-optical reflector antenna for whispering gallery mode

We propose a method to calculate the radiation characteristics of a quasi-optical reflector antenna for whispering gallery mode called Vlasov's antenna. Correction of the shape of the reflector, which was a parabolic cylinder in the original paper by Vlasov et al. (1975), is performed using wave-normal rays. The radiation field is calculated by means of an image source which is obtained with the geometrical optics. Some numerical results show that the radiated beam is gaussian-like in far zone. A scheme of high-power application (500kW, 106·4GHz, TE_12,2) to a beam transmission system is also presented     

An improved design for quasi-optical mode conversion of whispering gallery mode gyrotron radiation

Results are reported of a theoretical and experimental investigation of a quasi-optical mode converter for the transformation of whispering gallery mode gyrotron output into a linearly polarized Gaussian like beam. The mode converter consists of a helically cut waveguide launcher, similar to that originally proposed by Vlasovet al, followed by a focusing mirror. Theoretical results using aperture field methods indicate that the length of the waveguide launcher is of critical importance in providing a confined radiation pattern. Experimental results on the radiation pattern were obtained for several launcher lengths using a 0.6 MW, 149 GHz pulsed gyrotron operating in the TE_16,2 mode. Radiation pattern results for the optimum launcher length agree well with theoretical calculations using the Stratton-Chu aperture radiation theory for unperturbed waveguide modes. A mirror focusing in the azimuthal direction was designed by a geometrical optics approach to focus the radiation coming from the launcher. Good focusing with 91.4% efficiency (power in the focused beam divided by gyrotron power) was found experimentally using the combined launcher and mirror with the pulsed gyrotron. These results indicate that quasi-optical antennas are useful for transforming high order, high frequency gyrotron modes into directed beams in free space.     

Experimental study of a high efficiency quasi-optical mode converter for whispering gallery mode gyrotrons

A mode converter for whispering gallery mode gyrotrons has been designed and experimentally demonstrated. Experiments were performed on a megawatt power level, 3μs pulsed gyrotron operating in the TE_16,2,1 whispering gallery mode at 146 GHz. The gyrotron cavity employs a non-linear uptaper to minimize radial mode conversion. About 99% of the output power is in the TE_16,2 mode. The quasi-optical converter consists of a helically cut Vlasov-type waveguide launcher and a reflector. The doubly curved reflector, designed using geometric optics and vector diffraction theory, was built to focus the full radiation pattern to a small, gaussian-like focal spot. Of the power incident in the TE_16,2 mode, 96% is directed by the launcher and reflector to a gaussian-like focal spot in the far field. Small fractions of other modes were found to form distinct focal spots in the far field. Analysis of the power in the other focal spots allows for a good quantitative measurement of gyrotron output mode content, potentially on a single shot basis.     

Modelization of the whispering gallery mode in microgear resonators using the Floquet-Bloch formalism

In this paper, a two-dimensional (2-D) method describing the whispering gallery mode in a microgear resonator is presented. The microgear is a microdisk surrounded by a circular grating. The method, which is based on the Floquet-Bloch formalism, analytically describes the field within the disk and outside the grating. On the other hand, the field within the grating is calculated using a finite-difference scheme in polar coordinates. Matching the boundary conditions, it is possible to work in a forced oscillation regime or in a free oscillation regime (laser mode). The resonant wavelength and quality factor can then be deduced. Compared to the coupled mode theory and to 2-D finite-difference time-domain computations, the method is faster and more accurate. Moreover, a polarization effect of the microgear is demonstrated. The TE polarization experiences a Q-factor improvement contrary to TM polarization. Finally, microgear structures prove to be more efficient than micro flowers.     

基于回音壁微腔的可见光波段光频梳研究进展（特邀）

基于光学微腔的光频梳具有阈值低、光谱宽及结构紧凑等特点,在精密测量与传感等领域具有重要的应用前景,因此近年来微腔光频梳成为国际研究热点。目前相关的研究都聚焦于红外波段锁模光频梳的产生原理和应用探索,虽然可见光波段的光频梳在精密光谱、原子钟及生物医学等领域有特殊应用价值,但是可见光频梳的实现极具挑战性。文中在简要阐述光频梳产生原理的基础上,介绍了在可见光波段实现光频梳的主要挑战,以及目前三种实现方案的研究进展,包括利用材料的二阶与三阶非线性效应、调节微腔的几何色散和模式强耦合效应调控色散来产生可见光频梳。     

Diffraction of a TM whispering gallery mode by the edge of a nonperfectly conducting spherically curved sheet

Electromagnetic scattering is a function of the scatterer's material properties as well as its geometry. Therefore, it is necessary to examine the effect of the physical properties of a body on diffraction phenomena besides the geometrical properties. The aim here is to give a rigorous asymptotic solution for the diffraction of high-frequency electromagnetic fields by an edge on a spherically curved sheet having a particular impedance property. The solution is interpreted with the terminology of the geometrical theory of diffraction (GTD).     

Cellular nonlinear network based on semiconductor tunneling nanostructure

We propose and analyze a cellular nonlinear network (CNN) based on a semiconductor nanostructure consisting of multiple layers of two semiconductors along with an incorporated quantum dot layer. An elementary logic cell of the proposed CNN consists of two resonant tunneling diodes connected in series through a quantum dot. The cell may be realized with multiple layers of two semiconductor materials with an embedded dot layer in between. The local interconnections of nanocells are achieved via tunneling between the neighboring quantum dots. Cells may be biased by the common column contacts, and only edge cells have individual I/O ports. Using approximate tunneling characteristics, we simulated network dynamics and found procedures leading to useful logic functionality. In order to illustrate network capabilities for image processing, we present examples of filtering, erosion, dilation, and edge detection carried out on a test image on a 400/spl times/269 cell template. The realization of a number of logic functions in one module is possible due to the incorporation of nonlinear (tunneling) elements for cell interconnections. The proposed CNN architecture for nanostructures demonstrates powerful computing potential that will be beneficial for many practical applications.     

Frequency stability of Ti/sup 3+/-doped whispering gallery mode sapphire resonator oscillator at 34 K

The operation of a 12.7 GHz cryogenic oscillator based on a whispering gallery mode resonator doped with Ti/sup 3+/ ions is presented. The resonator operates at 34 K and exhibits a frequency stability order 2/spl times/10/sup -13/ for 8 s相似文献   

Fiber-optic add-drop device based on a silicamicrosphere-whispering gallery mode system

An all-optical passive four-port system including a fused silica microsphere and two tapered fibers is proposed and demonstrated for the application as a channel adding-dropping device. It is shown that channels can be selectively exchanged between two fibers by coupling to a whispering gallery mode resonance in the microsphere. Finesse in excess of 11150 is measured for the loaded whispering gallery modes     

Composite materials based on nanostructured zinc oxide

Composites formed from ZnO nanorods in combination with CuO or Ag nanoparticles are produced by the deposition of CuO or Ag nanoparticles onto ZnO nanorod arrays grown by the hydrothermal technique. The CuO nanoparticles are synthesized by the vacuum thermal deposition of a Cu layer followed by vacuum annealing at a temperature of 350°C for 1 h. CuO particles covered with a layer of nanoneedles are obtained. The current-voltage characteristics of the ZnO/CuO layers are indicative of the formation of a p-n junction. The ZnO/Ag composites are produced by the electrical deposition of Ag nanoparticles synthesized in an aqueous solution of silver nitrate and sodium citrate. The surface morphology and the optical and electrical properties of the samples are studied.     

The performance limit of coherent OTDR enhanced with optical fiberamplifiers due to optical nonlinear phenomena

This paper theoretically and experimentally clarifies the limit of incident optical pulse power in coherent optical time-domain reflectometry (C-OTDR) enhanced with optical fiber amplifiers. The critical pulse power, at which the performance of C-OTDR is degraded by the effect of optical nonlinear phenomena in a single-mode optical fiber, depends on the amplified optical pulse waveform and the pulse width. For a pulse width of 1 μs or longer, the incident pulse power is limited by the effect of self-phase modulation (SPM). When an optical pulse having a power gradient within the pulse width is incident to a single-mode optical fiber, the optical frequency of the backscattered signal is shifted by SPM, and the center frequency of the signal moves outside the receiver band, so the sensitivity of C-OTDR is degraded. For a pulse width of 100 ns, the incident optical pulse power is limited by four-wave mixing (FWM) which transfers the energy from the incident optical pulse to Stokes and anti-Stokes light as a result of the interaction between the incident optical pulse and amplified spontaneous emission. This paper also demonstrates the high performance of C-OTDR enhanced with EDF A's with 48, 44, 39, and 29 dB single-way dynamic ranges for pulse widths of 10 μs, 4 μs, 1 μs, and 100 ns, respectively, limited by the effect of SPM or FWM. These results are believed to be the best performance of C-OTDR with EDFA's     

共振混频过程的超快弛豫现象研究

本文报导利用共振混频过程,可在不利用超短脉冲激光情况下对皮秒甚至飞秒量级的超快弛豫进行测量。采用密度矩阵方法对该混频过程的二能级系统的非线性极化率XR进行了计算,结果表明过程的频率特性与样品的纵向弛豫时间T1和横向弛豫时间T2有关。实验测量得到孔雀绿水溶液的T1和T2分别为1.20ps和0.09ps。     

Integrated optical SPR sensor based on mode conversion efficiency

A novel type of integrated optical surface plasmon resonance (SPR) sensor is proposed, for which the operational principle is based on the launching efficiency of eigenmodes in the sensor head. The sensor comprises an inverted-rib-type dielectric waveguide, a portion of which is covered with a thin gold layer. Eigenmodes in the sensor head are coupled modes of a surface plasmon polariton and a dielectric guided wave. The excitation efficiency of the coupled modes varies significantly depending on the refractive index of the analyte medium on the sensor head. Following this principle, the transmission coefficient of light through the sensor head can be used as a sensitive measure of the variation in the refractive index of the analyte medium.     

基于光纤非线性效应的全光再生器研究

本文对光纤非线性效应的物理机理做了理论分析,并在此基础上,利用optisystem仿真平台和matlab编程软件联合仿真实现了基于光纤非线性效应的几种全光再生方案,仿真结果与理论分析吻合。     

All-optical discrimination based on nonlinear transmittance of MQWsemiconductor optical gates

This paper proposes an all-optical regenerator utilizing a novel all-optical discriminator. The impacts of nonlinearity of optical gates on discrimination performance are estimated. The evaluation of discrimination performance shows that amplified spontaneous emission noise and wave form distortion in optical signals can be effectively suppressed. We experimentally demonstrate the suppression using a low-temperature-grown optical switch up to 10 Gb/s