LP01 to LP11 mode convertor based on side-polished small-core single-mode fiber

An all-fiber LP01-LP11 mode convertor based on side-polished small-core single-mode fibers (SMFs) is numerically demonstrated. The linearly polarized incident beam in one arm experiences π shift through a fiber half waveplate, and the side-polished parts merge into an equivalent twin-core fiber (TCF) which spatially shapes the incident LP01 modes to the LP11 mode supported by the step-index few-mode fiber (FMF). Optimum conditions for the highest conversion efficiency are investigated using the beam propagation method (BPM) with an approximate efficiency as high as 96.7%. The proposed scheme can operate within a wide wavelength range from 1.3 μm to1.7 μm with overall conversion efficiency greater than 95%. The effective mode area and coupling loss are also characterized in detail by finite element method (FEM).     

基于保偏光纤模式干涉的应变传感器研究

为了进一步了解模式干涉光纤传感器的原理,并相应提高应变传感器的性能,提出一种基于保偏光纤(PMF)的模式干涉应变传感器。在两根单模光纤(SMF)之间,腰椎放大熔接一根长30mm的PMF,构成全光纤模式干涉传感器。应变的变化将会引起光纤的纤芯模与包层模相位差的变化,从而导致干涉光谱的变化。在应变范围为0～3 605με,通过光谱仪(OSA)检测宽带光源经光纤传感器后的透射光谱。采用最小二乘法对光强强度和应变进行线性拟合,发现光强减小的趋势与应变的变化有很高的线性关系,并测得应变的灵敏度可达到0.004dB/με,对应的分辨率为2.5με。本文传感器制造简单、费用较低和结构稳固,并且具有很高的分辨率,因此适用于实际测量。     

Novel dispersion compensation method for cross-coupling measurement in PM-PCF based on OCDP

For polarization maintaining photonic crystal fiber (PM-PCF), the cross-coupling measurement can be severely affected by interferogram broadening, due to the large inter-mode chromatic dispersion. In this paper, a novel dispersion compensation method is proposed to mitigate the influence, including a frequency domain algorithm and investigation of the dispersion coefficient for a phase packet in algorithm. A numerical simulation and measurement of birefringence as a function of wavelength reveal that the dispersion coefficient in PM-PCF is much larger than that in PANDA-PM fiber. After compensation, the accuracy of coupling strength measured can be restored and spatial resolution is improved. Experiments show the compensation provides high accuracy with average relative error less than 0.31% and spatial resolution improved 4.1 times.     

一种新的基于共模扼流圈传导干扰模态分离网络

测试传导性干扰的模态噪声,是设计电磁干扰(EMI)滤波器的前提条件。共模扼流圈能够抑制共模模态,而不影响差模电流的输出。根据共模扼流圈这一特点,设计一种由两个共模扼流圈为核心的共模/差模分离网络,实现共模电压和差模电压的同时输出。仿真结果表明,在150 kHz³0 MHz的测试频带,输入端口阻抗基本在50Ω,并且共模传递比(CMTR)、差模抑制比(DMRR)、差模传递比(DMTR)及共模抑制比(CMRR)四个结果显示了该分离网络的良好模态分离效果。     

一种新型的基于LP01模的双模色散补偿光纤

通过计算机模拟发现在可传输双模的三包层色散补偿光纤中如果抑制ＬＰ０２模，而仅传输ＬＰ０１模时能在一个较窄的带宽内产生大于数千ｐｓ／ｎｍ·ｋｍ的负色散，并且具有较大的模场直径、较小的弯曲损耗和偏振模色散，另外还具有较小的温度波长漂移以及同其它色散补偿光纤一样大小的损耗，是一种非常有前途的新型色散补偿光纤     

基于模态准小波的密频模态参数识别

基于Morlet小波连续变换的模态参数识别算法在故障识别和多模态参数提取中起到了重要作用,然而在密频情况下,Morlet小波连续变换尺度图上模态极值线相互混叠严重,难以有效分离模态。本文提出一种新型的模态准小波函数,运用连续小波变换理论,推导和证明了模态准小波的连续变换可以有效分离密频模态,并给出了固有频率和阻尼系数的识别公式与整体识别算法。文章针对新型的模态准小波进行了大量的仿真实验,证实了该小波在密频模态分离与参数识别方面的优越性,为密频模态参数提取提供新的思路与手段。     

Electrical characteristics of single-gate interference transistors based on various semiconductor materials

The current-voltage and high-frequency characteristics of single-gate interference T transistors based on quantum wires made of various semiconductors, specifically, Si, Ge, GaAs, InAs, GaSb, InSb, GaP, and InP, were studied theoretically. Two scattering mechanisms were taken into account in the T-transistor model in order to assess their effect on the electrical characteristics of devices. The adequacy of the suggested model was verified by comparing the results of simulation with experimental data. The calculations were performed using the QW-NANODEV subsystem for simulating the devices based on quantum wires.     

级联FPI-MZI复合干涉光纤传感器双参数特性研究

为了实现工业生产过程中温度和溶液质量分数的同时测量和传感检测, 提出了一种由法布里-珀罗干涉仪(FPI)和马赫-曾德尔干涉仪(MZI)级联干涉结构构成的双参数传感器。该传感器由融合在一起的单模光纤(SMF)和空芯光纤(HCF)组成。采用同时测量FPI反射光谱和MZI透射光谱的特征波长位移的方法, 获得了FPI和MZI对温度和折射率的灵敏度差, 建立了传感器温度-质量分数灵敏度矩阵, 实现了传感器双参数的测量。结果表明, 在40℃~150℃的温度范围内, FPI的温度敏感度为10pm/℃, 而MZI的对温度不敏感; 在质量分数0.05~0.40的范围内, FPI对折射率不敏感, 而MZI质量分数灵敏度是232.3nm/RIU; 该传感器可以实现温度与溶液质量分数的同时测量。该研究为石油、化工、电力、钢铁、机械等加工行业中双参数的动态测量提供了参考。     

Azimuthal dependence of modal interference in closely spacedsingle-mode fiber joints

We introduce a closed form expression describing modal interference in closely spaced single-mode fiber joint pairs for operation below cutoff wavelength of the intermediate fiber. The expression shows that modal interference is dependent on the cosine of the azimuthal angle between the lateral offsets of the fiber cores at the two joints. This azimuthal dependence is verified experimentally for operation both below and above the intermediate fiber cutoff wavelength. The result suggests that modal interference in field installable fiber-optic connectors incorporating short fiber stubs can be reduced or eliminated through proper tuning of the lateral offset azimuth     

Polarization analysis of LP01 and LP11intermodal interference in highly birefringent bow-tie optical fibers

A polarization analysis of bimodal highly birefringent fibers in which LP₀₁, LP₁₁, interference takes place is performed. The polarization state of the interference pattern is theoretically described in terms of recently proposed spatial Stokes parameters on the basis of coupled-mode equations and Jones matrix formalism. The general quasimonochromatic case is considered and depolarization as well as interference fading are accounted for. Special attention is paid to application of the results to fiber-optic sensors, and the basic schemes for the detection of the interference beat signal are discussed. The theoretical conclusions are supported by experiments in which the modal polarization and intermodal interferometric response to elongation of a bow-tie bimodal fiber is investigated. Measurements are carried out on both a separate fiber and on a multifiber assembly at various input conditions     

Bending characteristics of SU-8

This study characterises SU-8's material properties under large deformations in out-of-plane bending. A novel test setup is presented to deform the SU-8 to high levels, and a mathematical model presented that accurately predicts the results. This test shows that hard-baked SU-8, with a Young's modulus tested at 1.9 GPa, is capable of undergoing stresses of up to 120 MPa before failure and in some cases will undergo plastic deformation.     

点全息图的弯曲特性

与称为整体弯曲的透镜分析设计技术相类似,对点全息图的弯曲特性作了研究。     

Threshold and modal characteristics of composite-resonator vertical-cavity lasers

We report the operation of a vertical-cavity surface-emitting laser (VCSEL) with two active, coupled optical cavities. In contrast to a conventional single-cavity VCSEL, the coupling between the two electrically independent active regions produces emission into two longitudinal modes. The light output versus current characteristics are presented under various biasing conditions in each cavity. Laser operation is achieved with current injection into only one cavity, and additional current injected into the other cavity changes the effective threshold current measured. The longitudinal and transverse modes are characterized, and it is found that the modal evolution of the laser can be modified by current injection into each cavity.     

Two-dimensional modal analysis based on maximum likelihood

The authors present a method for estimating the parameters of 2-D damped harmonic (modal) signals in additive Gaussian noise. This method applies in the cases of single or multiexperiment data and incoherent or coherent signals. Both synthesis and analysis models for the data are developed. Central to these models are the signal and orthogonal subspaces. Under the assumption of distinct modes in one of the two dimensions, there exists an invertible function between the parameters of these two subspaces. This function can be used to express the optimization problem given by maximum likelihood in terms of the orthogonal subspace. The resulting problem can be solved by any of several methods, including total least squares and iterative quadratic maximum likelihood (IQML)     

Studies on a few-mode fiber-optic strain sensor based on LP01-LP02 mode interference

We studied a fiber-optic strain sensor based on interference between LP₀₁-LP₀₂ modes of a circularly symmetric few-mode fiber (FMF). A simple theoretical analysis for predicting the performance characteristics of such a sensor is developed. Fiber elongations producing differential phase shift of 2π (δl_2π) between the two modes are measured, which is found to be independent of sensing length of the fiber as predicted by theory. A good agreement between the experimental and theoretical values of δl_2π is observed. Theoretical calculations predict that the sensitivity of such a sensor is maximum for fibers with V=4.82 and increases with the increase in the core cladding index difference Δn     

基于LP3913的便携设备电源管理系统

介绍了多功能电源管理单元器件LP3913的基本结构和工作原理,并以S3C2440A处理器为控制核心设计了基于LP3913的电源管理系统.该系统设计采用USB外接电源和锂离子电池供电,整个电路结构紧凑,功能完善.     

Analysis of modal characteristics and thermal effects on photonic crystal fiber laser

In this paper, thermo-optics effects on fiber lasers based on index-guiding photonic crystal fibers (PCFs) are studied. The modal characteristics of the PCF lasers are discussed in terms of the thermal effects. Modal analysis of PCF has been done with help of plane wave expansion and supercell lattice methods. The thermal analysis is performed by obtaining the effective index of fundamental mode and core confinement factor (CCF) when the fiber laser was pumped. The results show that PCF laser structure has negligible modal sensitivity to thermal load in comparison to conventional fiber laser. Analyzing the mode performance of the fiber laser under thermal load shows that the assumed PCF laser at 80 W/m pump power show ∼500° rise in temperature and 0.34% propagation constant variation in fundamental mode index and 0.04% CCF variation in fundamental mode.     

Temperature measurement based on photonic crystal modal interferometer

Based on the interferences between core modes and cladding modes in photonic crystal fiber (PCF),a novel temperature sensor is presented and experimentally demonstrated.The peak wavelength of the interference spectrum linearly increased with an increase in temperature.A measurement sensitivity of 10.38 pm/℃ was experimentally achieved for temperatures ranging from 30℃ to 100℃.Experimental results also indicate that the curvature and transverse load do not have a distinguishable influence on the transmission spectrum of the proposed fiber sensor,which ensures its applicability for practical applications.     

基于微机械薄膜变形镜的闭环实时模式复原

为了求解基于微机械薄膜变形镜自适应光学系统的最优模式控制电压,以使系统的入射畸变波前像差降到最小,采用了一种基于改进的奇异值分解闭环实时模式复原算法,可通过调整控制参量g1,gθ和W来优化波前复原的复原精度和收敛速度;采用一人眼出射畸变波前像差作为自适应光学系统的原始波前,与现有的几种实时模式复原算法相对比,其在收敛速度和复原精度上都有所改善。结果表明,基于改进的奇异值分解闭环实时模式复原算法,在一定程度上解决了微机械薄膜变形镜由于薄膜面型宽交连值、驱动电极单调但非线性的控制电压求解问题,算法可调整空间大、适用范围也较广。