Optical broadband phase devices using axially nonsymmetrical W-typeoptical fibers

This paper describes a numerical analysis of axially nonsymmetrical W-type optical fibers as optical-fiber-type broadband phase devices. Using these devices, phase difference between two orthogonal linear polarizations can be kept constant in a broad wavelength range. The propagation characteristics along a circular core with an elliptical cladding structure and an elliptical core with a circular cladding structure are numerically analyzed by the boundary-integral method. Using the numerical results, the performances of various broadband phase devices are theoretically compared     

Degree-of-polarization and eye-closure penalty associated with optical signals with orthogonal polarizations

We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere.     

A mutual coupling study of linear and circular polarized microstrip antennas for diversity wireless systems

In this paper, an analysis of mutual coupling is presented to examine the benefits of orthogonal polarizations and patterns for adjacent microstrip antennas. The mutual coupling between two linear polarized antennas orientated in parallel polarizations (E and H plane) is reduced using low dielectric constant materials. The mutual coupling can be reduced an additional 20-35dB at the same inter-element spacing when adjacent elements are orientated in orthogonal polarizations, O plane. Similarly, the mutual coupling between two circular polarized antennas orientated in the parallel polarization is reduced using low dielectric constant materials. However, the reduction in mutual coupling between two circular polarized antenna elements orientated in the O plane is only an additional 1-6 dB. The mutual coupling between a linear polarized sum beam (1/2/spl lambda/) and difference beam (1/spl lambda/) antenna is reduced 20-35 dB below the case when using identical antennas only in the H- and O-planes. Compact two- and four-element multielement antennas with inter-element spacings less than 0.15/spl lambda/ are fabricated and the S parameters and radiation patterns are measured.     

Coupleur de polarisation compact à guides demi-lune

Circular polarized antennas (as C-band [4–6 GHz] spatial telecommunications antennas) are generally fed by rotationally symmetrical structures radiating the two strongly decoupled orthogonal polarizations. We designed a light, compact and highly performant device to generate circular polarized waves in a circular waveguide.     

Experimental and Theoretical Study on the Symmetries of Orthogonally Polarized Optical Signals

We perform theoretical analysis and systematic measurement of the degree-of-polarization and eye-closure penalty for optical signals with orthogonal polarizations. Both the theory and experiment show that the symmetry of the DOP is maintained for the orthogonal polarizations under both first and higher-order PMD, whereas the symmetry of eye-closure penalty is broken under second-order PMD. As a result, an orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical degree-of-polarization. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare Sphere.     

A quad-polarization and frequency reconfigurable square ring slot loaded microstrip patch antenna for WLAN applications

In this paper, a novel polarization and frequency reconfigurable microstrip patch antenna which can switch between vertical and horizontal linear polarizations, left hand and right hand circular polarizations at two WLAN frequencies is presented. The orthogonal linear polarizations are achieved by a square microstrip patch antenna fed by two ports on adjacent sides. By introducing corner truncated perturbation on opposite corners of right diagonal of a square patch, orthogonal circular polarizations are achieved. By controlling the bias voltage of two PIN diodes loaded at perturbed corners, a single structure can achieve quad polarization states. Furthermore, by superimposing a square ring slot into the corner truncated square patch and incorporating four PIN diodes into the square ring slot, quad polarization are achieved at dual frequencies. Simulated and measured results indicate that the antenna can achieve quad polarization at two WLAN bands (5.15–5.35 GHz) and (5.75–5.85 GHz). The proposed antenna is simple, has low profile and can be scaled easily for other frequencies.     

Polarization determination utilizing two arbitrarily polarizedantennas

Microwave polarimeter systems typically consist of two orthogonally polarized receiving antennas. Formulas for extracting the unknown polarization antennas with known polarization states are presented. Numerical results are generated showing the size of the errors made by assuming perfect orthogonal polarizations (either circular or linear)     

GaAs (110)量子阱的电子自旋弛豫

采用固态源分子束外延的方法在GaAs(110)取向衬底上生长了GaAs/AlGaAs多量子阱结构.对样品进行了低温光致发光谱和时间分辨光致发光谱的测量,结果表明激发功率和激发波长对室温下量子阱内电子的自旋弛豫时间有强烈的影响.对于常见的GaAs(100)量子阱起支配作用的D'yakonov-Perel' (DP)自旋弛豫机制,在GaAs (110)量子阱材料里被充分地抑制了.对于缺失了DP相互作用的GaAs (110)多量子阱,电子-空穴相互作用对自旋弛豫时间随激发功率变化有重要的影响.     

GaAs (110)量子阱的电子自旋弛豫

采用固态源分子束外延的方法在GaAs(110)取向衬底上生长了GaAs/AlGaAs多量子阱结构.对样品进行了低温光致发光谱和时间分辨光致发光谱的测量,结果表明激发功率和激发波长对室温下量子阱内电子的自旋弛豫时间有强烈的影响.对于常见的GaAs(100)量子阱起支配作用的D'yakonov-Perel' (DP)自旋弛豫机制,在GaAs (110)量子阱材料里被充分地抑制了.对于缺失了DP相互作用的GaAs (110)多量子阱,电子-空穴相互作用对自旋弛豫时间随激发功率变化有重要的影响.     

高双折射单模光纤温度传感器

1 引言 偏振干涉型光纤温度计的灵敏度介于干涉型和强度型之间。典型的干涉型光纤温度传感器是以光纤耦合器为核心,构成Mach-Zehnder的一类干涉仪,它是以两根光纤分别作为干涉仪的测量臂和参考臂。虽然灵敏度高,但由于外界环境因素对参考臂的干扰极为敏感,以致在一般条件下,难以正常工作。文献[2]则以一根高双折射光纤中正交偏振模HE_(11)对外界因素有不同相移,使这两个模式的光发生干涉,从而能有效地克服外界因素的干扰。本文利用时间相     

TE-TM mode conversion of an optical beam wave in thin-film opticalwaveguides

The TE-TM mode conversion efficiency when a Gaussian beam wave propagates in thin-film optical waveguides is discussed. For film thicknesses at which strong coupling between the TE and TM modes is obtained, two hybrid modes have oppositely rotating circular polarizations, or linear polarizations perpendicular to each other with equal magnitude of TE-wave and TM-wave components. In the former (i.e. circular polarization), complete TE-TM mode conversion is impossible. In the latter (i.e. linear polarization) complete TE-TM mode conversion is available. These claims are based on the fact that the direction of power flow of the hybrid modes depends on the polarization     

Dual-Frequency Operation in a Short-Cavity Ytterbium-Doped Fiber Laser

A dual-frequency 2-cm silica fiber laser with a wavelength spacing of 0.3 nm has been demonstrated using a polarization-maintaining (PM) fiber-Bragg-grating (FBG) reflector. The birefringence of the PM FBG was used to generate the two single-mode (SM) lasing frequencies of orthogonal polarizations. The SM operation in each wavelength has been verified. The output power reaches 43 mW with the optical signal-to-noise ratio of greater than 60 dB. The fiber laser shows stable dual-frequency output under pump variations     

Single-Fed Microstrip Patch Antenna With Switchable Polarization

A single-fed reconfigurable microstrip antenna that can provide various polarization diversities is presented in this paper. The antenna is excited by a microstrip feed line through aperture coupling. When two PIN diodes are used to respectively reconfigure the coupling slot and the open stub of the feed line, the polarization of the microstrip antenna can be switched between vertical and horizontal polarizations. For the reconfigurable antenna with the linear polarization diversity, it can be converted to a circularly-polarized antenna with switchable polarization sense by introducing a perturbation segment. Moreover, an antenna with the quadri-polarization diversity, including dual orthogonal linear polarizations and two circular polarizations, is also developed from the structure of the switchable circular polarization microstrip antenna, and only three diodes are required. Details of the antenna design are shown, and the measured results for the constructed prototype are also exhibited and discussed.     

Size effect of semiconductor quantum wells in excitonic spin generation under drift

The excitonic spin polarization in dependence of the size of semiconductor quantum well (QW) was investigated by observing the two different circular polarizations of photoluminescence (PL). From the measurements of PL in QWs, it was found that there is a difference between the two different polarization conditions, which is caused by spin-dependent phase-space filling. The PL spin polarization was estimated from the signals of the left and right circularly polarized PL and was found to depend on the size of the wells as well as on the strength of the bias field. The effects of the size of the well and applied electric field on the excitonic PL spin polarization were studied.     

Polarization-dependent nonlinear gain in semiconductor lasers

We have numerically studied the nonlinear gain coefficients in terms of spectral hole burning for the optical fields in parallel and orthogonal polarizations in semiconductor lasers by solving the equation of motion for the density matrix in perturbation series. The electronic band structures and the transition matrix elements used in the calculations are obtained by diagonalizing Luttinger's Hamiltonian. In the present analysis for InGaAsP lasers, the cross-saturation coefficient for the parallel polarizations is twice as large as the self-saturation. Also, the cross-saturation coefficient for the orthogonal polarizations, which affects the polarization switching and polarization bistable operations of the laser, rests between the two. The relative magnitude of self-saturation coefficients and cross-saturation coefficients for orthogonal polarizations satisfies the condition for polarization bistable operations. We also discuss the effect of carrier heating on gain saturation coefficients     

Generation and radiation of high-power ultrawideband nanosecond pulses

The results of investigation of the generation and radiation of high-power ultrawideband electromagnetic pulses are presented. The possibility of obtaining wave beams of radiation with orthogonal polarizations of the electric field is shown. The radiating system is a 16-element antenna array that can be separated into two subarrays operating in orthogonal polarizations and excited by pulses separated in time. Two design versions of orthogonal subarrays are studied.     

通过圆偏振光提高飞秒激光诱导击穿光谱的发射强度

激光诱导击穿光谱(LIBS)是一种快速、实时的元素成分分析技术。为了提高LIBS的灵敏度,人们已经提出多种方法来提高LIBS的光谱强度。本文采用飞秒脉冲激光烧蚀黄铜产生LIBS,对比了圆偏振和线偏振下LIBS光谱的强度,结果发现圆偏振下的光谱强度比线偏振下的强,光谱强度大约提高了15%。采用飞秒激光照射金属时,金属内部的自由电子吸收光子的能量。在线偏振飞秒激光场中,电子在脉冲的每个光学周期中经历交替的加速和减速;而圆偏振飞秒激光可以连续加速电子,因此电子可以获得更高的能量,这使得圆偏振飞秒激光产生的光谱强度不同于线偏振飞秒激光产生的光谱强度,圆偏振激光有助于改善飞秒LIBS信号的强度。     

Probability distribution of rain-induced cross-polarization

The cross-polarization discrimination of a radiorelay link using two orthogonal polarizations has been calculated from the statistical distribution of the rain intensity, and the size, deformation and canting angle of raindrops. At frequencies of 18.8 GHz and 28.8 GHz and for a path length of 20 km the results are plotted as a function of the path-averaged rain rate. Furthermore, the distributions of the cross-polarization discrimination in the worst case for a path perpendicular to the main wind direction are obtained from the statistical distribution of the path-averaged rain rate for linear and circular polarizations.     

一种H型缝隙和L型探针耦合双极化微带天线的设计

设计了一种宽带、低交叉极化、高隔离度的双极化微带天线结构,采用L型探针耦合和H型缝隙耦合两种方式相结合,结构简单.天线设计频率为2.4 GHz,两端口-10 dB阻抗带宽达到26.7%和30%,隔离度在整个带宽内低于-32 dB、交叉极化电平在60°方位角内低于-24 dB、在主瓣内低于-32 dB,理论仿真和实验测试结果吻合较好.