Functional organic single crystals for solid‐state laser applications

Because of long‐range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid‐state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state‐of‐the‐art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light‐emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.     

谐振式集成光学陀螺解调特性分析

基于激光器频率谱检测技术,沿着光的传输方向分析了光波在谐振式集成光学陀螺系统中的传播,结合输入信号特征,建立频域内的数学模型,通过数值仿真和实验得到了调频检测系统下的解调曲线。按照光的传输方向：激光器、声光晶体移频器、光波导环形谐振器、探测器,利用贝塞尔函数展开和光场耦合模理论分析了谐振式集成光学陀螺解调特性,及其调频调制检测系统解调输出信号与谐振频率偏差之间的关系。通过数值计算,分析了解调曲线的变化规律,得到了施加在激光器压电陶瓷驱动器上调制波形的最佳调制系数。在实验上搭建了激光器频率调制解调技术系统,得到了解调曲线。数值仿真和实验结果表明,当调制系数M=2时,线性工作区间斜率最大,解调曲线最好。实测形状与理论分析结果相符,从解调信号得到±2×10³ rad/s的陀螺动态范围。     

A novel low-loss four-bit bandpass filter using RF MEMS switches

This paper details the design and simulation of a novel low-loss four-bit reconfigurable bandpass filter that integrates microelectromechanical system(MEMS)switches and comb resonators.A T-shaped reconfigurable resonator is reconfigured in a'one resonator,multiple MEMS switches'configuration and used to gate the load capacitances of comb resonators so that a multiple-frequency filtering function is realized within the 7-16 GHz frequency range.In addition,the insertion loss of the filter is less than 1.99 dB,the out-of-band rejection is more than 18.30 dB,and the group delay is less than 0.25 ns.On the other hand,the size of this novel filter is only 4.4 mm×2.5 mm×0.4 mm.Our results indicate that this MEMS reconfigurable filter,which can switch 16 central frequency bands through eight switches,achieves a low insertion loss compared to those of traditional MEMS filters.In addition,the advantages of small size are obtained while achieving high integration.     

New designed helical resonator to improve measurement accuracy of magic radio frequency

Based upon the new designed helical resonator, the resonant radio frequency (RF) for trapping ions can be consecutively adjusted in a large range (about 12 MHz to 29 MHz) with high Q-factors (above 300). We analyze the helical resonator with a lumped element circuit model and find that the theoretical results fit well with the experimental data. With our resonator system, the resonant frequency near magic RF frequency (where the scalar Stark shift and the second-order Doppler shift due to excess micromotion cancel each other) can be continuously changed at kHz level. For ⁸⁸Sr⁺ ion, compared to earlier results, the measurement accuracy of magic RF frequency can be improved by an order of magnitude upon rough calculation, and therefore the net micromotion frequency shifts can be further reduced. Also, the differential static scalar polarizability Δα₀ of clock transition can be experimentally measured more accurately.     

Robust supergain beamforming for circular array via second-order cone programming

The phenomenon of supergain for a circular array and its robust beamforming are presented. The coplanar superdirective array gain of the circular array, although it is not so extreme as an endfire line array, outperforms a lot over that of a conventional delay-and-sum beamformer in isotropic noise fields when the inter-element spacings are much smaller than one-half wavelength. However, optimum beamforming algorithms can be extremely sensitive to slight errors in array characteristics. The performance are known to degrade significantly if some of underlying assumptions on the sensor array is violated. Therefore, white noise gain constraint is used to improve the robustness of the supergain beamformer against random errors. We show that the design of the weight vector of robust supergain beamformer can be reformulated as a form of second-order cone programming and resolved efficiently via the well-established interior point method. Results of computer simulation for a 24-element circular array confirm satisfactory performance of the approach proposed in this paper.     

Influence of nonlinear absorption effects on optical bistability in semiconductor ring resonators

We present a theoretical investigation of optical bistability in a nonlinear semiconductor ring resonator, by taking into account the two-photon absorption and the free-carrier absorption. By solving the intensity equation within the ring resonator, a parametric formulation is obtained for describing the bistability relation between the input and the output intensities. Numerical results show that the nonlinear absorption effects can affect the critical points and domain of the optical bistability.     

Crosstalk and bandwidth of lossy microring add/drop multiplexers

Performance characteristics and the design for optimum crosstalk suppression and extended bandwidth are described for lossy microring add/drop multiplexers. Restrictions constraining the single-ring architecture are contrasted with the increased flexibility of the series-coupled double-ring design. Expressions to compute the bandwidth of the lossy filter maintaining a minimum crosstalk are provided.     

In‐line monitoring of UV photopolymerization with a quartz crystal resonator

An in‐line monitoring device using a quartz crystal resonator for thin film polymerization was proposed, and its performance has been evaluated by implementing in the UV polymerization of 2‐hydroxyethyl methacrylate with a photoinitiator of 1‐chloroanthraquinone. Because the variation of resonant resistance of the resonator is proportional to the square root of viscosity change that is closely related to the polymerization degree, the resistance can be used as a measure of the polymerization degree. The resistance measurements were compared with the outcome of instrumental analyses of polymerization degree using an FTIR spectrometer and a gel permeation chromatograph. The experimental results showed that the resistance measurements were consistent with the experimental outcome of the instrumental analyses, and this indicates the effectiveness of the proposed device. Owing to the simplicity and availability of the resonator system, its wide utilization in the monitoring of a variety of film polymerization processes, including photoresistor application, is expected. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2428–2439, 2006     

Extension of the range of resonator scanning spectrometer into submillimeter band and some perspectives of its further developments

Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′_{ka′, kc′}-J_{ka, kc} = 5_1,5-4_2,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 3_1,3-2_2,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given.     

高分子梯度溶液吸声机理的研究

制备了高分子均匀溶液和梯度溶液,并在声管中测试其声衰减性能.实验结果表明,高分子梯度溶液的声衰减效果明显优于(即大于)相应的均匀溶液的声衰减.根据连续分层介质中声波传播理论建立了计算高分子梯度溶液声衰减的数学模型.计算结果与实验结果一致.由实验和理论分析结果得出了高分子梯度溶液的梯度吸声机理,即多次反射、多次吸收,最终将声能转化为热能.