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.     

Enhancement of nonlinear optical phenomena from crown-like nanostructure zinc oxide based on whispering gallery mode

Whispering gallery mode （WGM）-enhanced nonlinear optical phenomena from crown-like nanostructure zinc oxide （ZnO） samples are observed. The samples are synthesized by vapor-phase transport method. The morphology and crystal struc- ture are examined and characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD） and high-resolution transmission electron microscopy （HRTEM）, and they are excited by femtosecond laser pulses with cen- tral wavelengths of 355 nm, 800 nm and 1150 nm, respectively. The typical stimulated emission presents a red shift com- pared with spontaneous emission, which is observed under the excitation of 355 nm with a relatively low threshold. The ultraviolet （UV） frequency up-conversion emission is obtained when the excitation pulse wavelengths are selected as 800 nm and 1150 nm, respectively. The peak position and the relationship between the emission intensity and excitation inten- sity demonstrate that the UV up-conversion photoluminescence （PL） is induced by two- and three-photon absorptions. The PL characteristics and their WGM-enhanced mechanism are investigated.     

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.     

Thermally induced whispering gallery mode laser in MEH-PPV solutions

We report on thermally activated whispering gallery laser modes of a solution of MEH-PPV conjugated polymer supported by a silica optical fiber. The viscosity of the polymer solution gives place to a thin shell of the gain solution around the fiber driven by capillary action. Whispering gallery modes (WGMs) are thermally induced by a decrease in the refractive index of the polymer solution under intense optical pumping. The laser emission is produced because the evanescent waves of the WGMs couple the surrounding gain medium. These results support the use of conjugated polymers in optofluidic laser systems and highlight the importance of physicochemical properties, such as viscosity and optically induced heating, on the performance of the devices.     

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     

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.     

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.     

Laser-tuned whispering gallery modes in silica microbubble resonator integrated with iron oxide particles

A 473-nm-laser-tuned whispering gallery mode(WGM) silica microbubble resonator integrated with iron oxide particles is demonstrated in this paper. Owing to the photo-induced thermal effect, the WGM resonance wavelength could be tuned by adjusting laser power density of the illuminating light absorbed by the iron oxide particles. A wavelength tuning sensitivity of 0.03 nm/(mW·mm^-2) and a tuning range of 0.18 nm are experimentally achieved. Moreover, the influence of ambient temperature on the WGM spectral characteristics is experimentally studied, and a silica-microbubble-based reference scheme is demonstrated to compensate for the temperature-caused resonance wavelength variation. The proposed laser-tuned microresonator has great potential in optical modulation and high-precision optical filtering applications.     

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.     

Travelling-wave whispering gallery resonance sensor in millimetre-wave range

A high sensitivity sensor with a simple structure is presented for analysis of (bio)chemicals in liquid or solution form. The proposed technique is based on the travelling-wave whispering gallery resonance perturbation method in the millimetre-wave range. The resonance modes are launched inside a dielectric disk through coupling into a dielectric image waveguide. The top surface of the disk is used as the sensing area where the resonancemode interacts with the sample. Theoretical analysis and experimental results for the proposed sensor are discussed.     

Study of whispering gallery modes in anisotropic single-crystaldielectric resonators

The Rayleigh-Ritz method and the finite element method nongenerating spurious solutions are employed for analysis of whispering gallery modes (WGMs) in cylindrical single-crystal anisotropic dielectric resonators. These methods allow accurate computation of the resonant frequencies, the Q-factors (depending on the dielectric and on the conductor losses), and the electromagnetic field distributions for all WGMs in the presence of additional elements like metal shields, MIC substrate, or supports. Different families of modes are studied both theoretically and experimentally. The mode coupling phenomenon is investigated. A WGM single-crystal quartz resonator is presented having an unloaded Q-factor greater than 30000 at about 100 GHz, including radiation and dielectric losses     

Study of whispering gallery modes in double disk sapphireresonators

A mode matching method for determining the resonant frequencies of the whispering gallery modes in a double cylindrical disk dielectric resonator is presented. The method has an improved accuracy in the calculation of the transverse magnetic modes with high axial numbers in a single uniaxial-anisotropic disk resonator. In this paper, frequency tuning and detuning due to the interaction between various whispering gallery modes will also be discussed     

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).     

Slot line excitation of whispering gallery oscillations in shielded dielectric resonators

Electrodynamic characteristics of a half-disc shielded dielectric resonator operating in the 8-mm wavelength range have been investigated experimentally. A slot line was proposed for the excitation of whispering gallery modes in such resonator. It has been found out that the proposed excitation technique is effective and allows the high-Q oscillations of higher orders to be excited in a shielded dielectric resonator without additional energy losses. The partial shielding of the resonator in question was proposed for its spectrum rarefaction.     

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   

基于岛状多晶氧化锌薄膜的电泵浦紫外随机激光

光电子集成是当前光电技术和信息工程领域的新趋势和研究热点，其中光源集成化和工艺相容性已成为制约其进一步发展和应用的关键问题。报道了一种设计简单的、可直接集成在硅衬底上面的激子型激光二极管器件和工艺。基于岛状多晶氧化锌薄膜构建了一个金属/绝缘体/半导体（Au/MgO/ZnO MIS）异质结器件。利用Si衬底与ZnO外延层之间天然的大晶格失配，诱导ZnO薄膜表面形成了高度无序的多晶岛状纳米结构，从而在异质结激活层（ZnO/MgO界面区域）形成了高度无序的折射率随空间变化的散射介质。这极大增强了光学散射，有利于获得低阈值的随机激射。文中这种简单的光源器件结构设计和制备工艺提供了一种自下而上的实现氧化锌基集成光电子器件的新思路。     

Al掺杂ZnO紫外探测器的快速响应技术

通过交变电场下的紫外光响应测试,观察到ZnO基薄膜在254 nm紫外光激发下的慢响应现象,并测量了响应时间常数。为提高ZnO基薄膜紫外探测器的性能,采用磁控溅射法,制备了纯ZnO薄膜和掺Al浓度为10 at.%(原子比例)的ZnO薄膜紫外探测器,测量了样品的频率特性曲线。结果表明,Al掺杂能有效地抑制ZnO薄膜的慢响应,实现探测器对紫外光的响应时间常数τ<25μs的快速响应。     

On a self-consistent calculation of the self-modulation instability in gyrotrons operating in whispering gallery modes

A self—consistent calculation of the self—modulation instability in gyrotrons operating in whispering gallery modes is carried out in the cold cavity approximation for satellite modes. The approach is illustrated numerically in the case of the planned operation of the KfK gyrotron in the TE_10,4 mode.     

Analysis of curvature losses of whispering gallery modes in anoptical dielectric disk by the finite-element method

The finite-element method is applied to the analysis of curvature losses of whispering gallery modes in an optical dielectric disk. Numerical examples on the dielectric disks with various side shapes are given. We also demonstrate that when the curvature radius of the disk is large enough, the difference between the propagation constants obtained by considering and by ignoring the curvature loss is very small