F-P光纤应力传感器研制

分析了F-P光纤应力传感器工作原理,提出了F-P光纤应力传感器的数学模型,设计了F-P光纤应力传感器弹性体结构、光电转换系统.F-P光纤应力传感器光源电路设计采用APC电路.APC电路由两个运算放大器和晶体管以及外围电路组成,采用背向光反馈自动偏置控制方式,即用半导体激光器组件中的PD光电二极管监测LD背向输出的光功率.对F-P光纤应力传感器进行了静态特性标定试验,试验结果表明,该传感器具有较高的测量精度,能够满足工程测量要求.     

环形激光精密测角

目前环形激光器已发展成为角度和角速度传感器。在惯性导航和角度定位方面有重要的用途。本文介绍了环形激光器精密测量角度的试验,内容包括试验原理、四频环形激光器原理、测量结果及进一步提高测量精度的方法。本装置测量误差为±1秒左右(3σ)。不久用环形激光器将可能以优于±0.5秒的精度测量0～360度范围内的任一角度。     

基于Sagnac环形滤波器的多波长掺铥光纤激光器

为了实现2μm波段多波长激光输出,提出并设计了一种基于Sagnac环形滤波结构的多波长掺铥光纤激光器.激光器由波长793 nm的泵浦源、波分复用器、光纤耦合器、保偏光纤、掺铥光纤以及偏振控制器构成,其中Sagnac环形滤波器以及光纤环形镜作为激光器的反射端.实验中,激光器工作阈值为77.5 m W,通过调节偏振控制器,实现了稳定的单波长激光输出.波长为1 852.8 nm的单波长激光输出时,在50 min监测时间内波长最大漂移为0.1 nm,功率最大漂移为0.252 d B,激光3 d B线宽和信噪比分别为0.3 nm和35.7 d B.通过调节偏振控制器,在1 850~1 900 nm光谱范围内实现了1~4波长的激光输出.     

自调Q掺饵光纤激光器

研制出一种结构新颖的掺饵光纤激光器，该激光器利用线性光纤环形镜和半导体激光器芯片的背向反射镜组成谐振腔。采用半导体激光器芯片作为饱和吸收体，在９ｍＷ的泵浦功率下，该激光器实现了自调Ｑ脉冲输出。输出光脉冲宽度为１２μｓ，脉冲峰值功率约为２２ｍＷ，脉冲序列的重复周期约为６５μｓ。     

光纤饱和吸收体稳频窄线宽光纤激光器

结合光纤饱和吸收体与光纤光栅法布里-珀罗标准具,研制出了全光纤结构1550nm单频窄线宽掺铒光纤环形激光器.采用两个976nm激光二极管双向抽运作为抽运源,高掺杂浓度铒光纤作为增益介质,以行波腔消除空间烧孔效应,利用光纤光栅法布里-珀罗标准具窄带选模特性,以10m长低掺铒光纤饱和吸收体稳频,得到了十分稳定的窄线宽激光输出.激光器抽运阈值功率21mW,在抽运光功率为145mW时输出光功率39mW,斜率效率30%,信噪比大于50dB.采用延迟自外差方法精确测量光纤激光器线宽小于10kHz.     

激光频率分裂测波片的误差分析和实验评价

本文讨论了利用激光频率分裂技术测量波片位相延迟的主要误差因素,并对其中激光器初始位相延迟和波片非对正引入的系统误差进行补偿.误差分析表明:系统对于多级波片的测量不确定度约为1.7',对于零级波片为0.8',然后针对系统性能进行实验评价,包括:比较波片沿激光轴线对正和倾斜时对测量结果的显著影响,以及测量波片通光面内不同点的位相延迟和波片光轴与其表面的夹角.根据实测结果,系统测量重复性和复现性优于0.02°,不确定度优于2',即约λ/10~4.     

短腔的高浓度掺铒光纤激光器

本文提出采用高浓度掺铒光纤的短腔环形光纤激光器,研制出铋铝共掺和铋镓铝共掺两种石英基高浓度掺铒光纤,这两种掺铒光纤的吸收系数在1530 nm处分别达到了66.3dB/m和59.5dB/m.利用这两种石英基高浓度掺铒光纤,采用环形结构制作出了短腔的光纤激光器,光纤激光器中铒光纤长度分别仅为30 cm和90 cm.对采用这两种高浓度掺铒光纤制作的光纤激光器的输出特性进行了测试和分析.实验结果表明,采用铋镓铝共掺的掺铒光纤制作的光纤激光器具有更高的输出功率和斜率效率,在980 nm泵浦源输出功率330 mW时可以实现15 dBm的激光输出,激光器的斜率效率达到了22%.     

正交线偏振激光器及其在精密测量中的新应用

介绍了正交线偏振激光器及其在精密测量中的新应用,包括:1)正交偏振双频激光器,2)纳米激光测尺(基于频率分裂的激光器两偏振光竞争位移传感器)测量原理,3)直接利用波片形成频率分裂的波片位相延迟测量原理,4)激光回馈波片位相延迟测量原理.这些新应用的原理,结构简单,可溯源到光波长.如,纳米激光测尺已在应用中,测量范围12mm,分辨力79nm,线性度小于5×10-5,基于频率分裂的波片位相延迟测量系统重复性达到0.3',而激光回馈波片位相延迟测量系统具有在线检测的优点.     

磁电系,电磁系,电动系仪表的误差调整

在电工仪表计量中,磁电系、电磁系、电动系(C、T、D)仪表在精密仪表中占绝大多数,本文将分别介绍这些仪表误差的机械调整法,以供电表计量人员参考。一、D型仪表误差的机械调整 1.由于作用力矩在起始位置强,在后部位置弱,使仪表产生前正后负的误差。此时用增大α角减少β角的方法调整,即顺时针方向扳动指针,顺时针方向移动测量机构底座;刻度盘左移(见图1)。当作用力矩在起始位置弱,在后部位置强时,使仪表产生前负后正的误差。此时用减小α增大β角的方法调整,即逆时针方向扳动指针;逆时针方向移动测量机     

一种新型全光纤弹速测量系统的研制

研制了一种新型的利用激光光束反射原理的全光纤弹速测量系统。该系统采用了全光纤结构和光纤耦合器等无源器件,以输出光功率1mW, 工作波长1300nm的半导体激光器作为测试系统的光源,用光纤耦合器进行分光,实现了在一根光纤中同时传输光源和接受目标反射的信号光,避免了复杂的调节和准直过程。该系统结构简单、可靠性高,利用它,成功地测量了霍普金森杆发射的子弹速度,结果表明其速度测量相对不确定度小于1%。     

Optical Characterization of All-Magnetic NOT Gate Operation in Vortex Rings

We have demonstrated deterministic operation of inverters (NOT gates) using vortex magnetization states in pairs of linked 5 $mu$m diameter permalloy rings with a small region of overlap. The input ring is clipped so that the state can be controlled by global fields, and is designed to switch at lower fields than the unclipped output ring, which then inverts the logical state of the input. Optical coatings over half of each ring provide distinct magnetooptic Kerr effect (MOKE) signatures for saturation, clockwise, and counterclockwise states in our focused beam system. We demonstrate that excessive overlap between the rings leads to overall shape anisotropy dominating the behavior of the structure.      

Numerical modeling of short-pulse excimer lasers with negative branch unstable cavities

A one-dimensional code for the numerical simulation of negative branch unstable resonators with an intracavity aperture that are applied to high-gain, short-pulse XeCl lasers is described. The model predicts near- and far-field performance of the output laser beams. The intracavity aperture size is shown as an important parameter for control of the output beam energy and divergence. A comparison with experimental measurements is presented.     

Optical axis perturbation in folded planar ring resonators

A mathematical model of a four-sided folded planar ring resonator is established. The model can be modified into a triangular ring resonator, a square ring resonator, and a four-sided folded ring resonator, all of which are widely used for ring laser gyroscopes by changing certain design parameters such as incident angle Ai and side ratio H. By use of the extended matrix formulation, the optical axis perturbation, including optical axis decentration and optical axis tilt, in those planar ring resonators is analyzed in detail resulting in some novel findings. It has been determined that the longer the mirror radius, the larger the mode volume, the higher the sensitivity of optical axis decentration and the lower the sensitivity of optical axis tilt. The same mirror misalignment value, mostly the misalignment induced by optical axis decentration in the x and y components, has the conventional ratio of 1:[cos(Ai)](2) for the symmetrical points of the resonator. Details of the effect of Ai and H on the optical axis tilt have also been determined. The difference in optical axis tilt between different kinds of ring resonator is disclosed. The sensitivity of optical axis tilt was found to undergo singular rapid change along with the right edge of the second stable area. This singular behavior is useful for those resonators that have a small incident angle, such as Ai=15 degrees , because those resonators have a second stable region. These interesting findings are important for cavity design, cavity improvement, and alignment of planar ring resonators.     

Analysis on the polarization property of the eigenmodes in a nonplanar ring resonator

Based on the theory of the Abeles matrix, the reflections from the multilayer dielectric mirrors in a nonplanar ring resonator are discussed in detail considering the imperfect layer thickness and the incident angle errors. The polarization of Gaussian beams in nonplanar ring resonators are analyzed by using a statistical method and the way to analyze the stability of a nonplanar ring resonator in the perspective of polarization is also presented. The results show that a nonlanar ring resonator with a finite mode size may not have the reasonable polarization performances sometimes; the eigenmodes might be right- and left-handed elliptically polarized instead of circularly polarized, and they also have different ellipticity and round trip losses, which are critical for a nonplanar ring resonator. These interesting findings are important to the cavity designs of ring resonators with a nonplanar structure.     

Triangular laser resonators with astigmatic compensation

The magnitudes and locations of the beam waists in both the sagittal and the tangential planes have been found by means of the ABCD matrix method for a triangular resonator. Equilateral and isosceles resonators are discussed, and curves are given from which resonators with astigmatism-free beams can be designed. A frequency-doubled triangular Nd ring laser has been constructed after this design, and it is demonstrated that this laser emits a single longitudinal mode with a circular TEM(00) Gaussian beam.     

Pinning characteristics of domain wall in giant magnetoresistance spin valve stripe, consisting of a nano-wire and a circular ring

We investigated a technique for proving the pinning behaviors of a domain wall (DW) in spin-valve stripes with artificial configurations, which consist of a nano-wire, a large pad and sharp tip at the ends of the wire, and a circular ring at the center. It was found from the GMR measurement at various positions that a DW was pinned at a ring during DW's propagation from the side of pad to the side of tip. Micromagnetic simulation revealed that the initial onion magnetic states of the ring changes continuously to final reverse onion state via counterclockwise vortex state when a counterclockwise tail-to-tail DW pass through the ring. In addition, the simulation results indicated that the magnetic states at a circular ring were determined by the type and chirality of DW. We also studied the characteristics of domain wall motion in the same configuration, when the nano-ring was replaced with square and diamond structures.     

Switching of ± 360° domain wall states in a nanoring by an azimuthal Oersted field

We demonstrate magnetic switching between two 360° domain wall vortex states in cobalt nanorings, which are candidate magnetic states for robust and low power magnetoresistive random access memory (MRAM) devices. These 360° domain wall (DW) or 'twisted onion' states can have clockwise or counterclockwise circulation, the two states for data storage. Reliable switching between the states is necessary for any realistic device. We accomplish this switching by applying a circular Oersted field created by passing current through a metal atomic force microscope tip placed at the center of the ring. After initializing in an onion state, we rotate the DWs to one side of the ring by passing a current through the center, and can switch between the two twisted states by reversing the current, causing the DWs to split and meet again on the opposite side of the ring. A larger current will annihilate the DWs and create a perfect vortex state in the rings.     

Modeling of a short-term stability measuring system of quartz crystal resonators

A new numerical model of a short-term stability measuring system of quartz crystal resonators is presented. It is based on the phase bridge method using a pair of resonators driven by a low-noise source. The output signal, obtained with a phase detector, is proportional to the phase difference introduced by the resonators. The numerical transfer function of each bridge path is given by the model. The output spectral density of the phase fluctuations is computed from these transfer functions and the numerical approximation of the low-noise source. The model was applied to third overtone, SC-cut, 10 MHz BVA quartz crystal resonators. It enables the rejection of the source noise versus the resonant frequency of quartz crystal resonators to be quantified.     

Flux-Closure Magnetic States in Triangular Cobalt Ring Elements

Ferromagnetic ring elements on the micrometer and submicrometer scale exhibit flux-closure magnetic vortex states in an intermediate step of their magnetization reversal. These clockwise or counterclockwise flux-closure states are of interest for applications that encode binary information in magnetic elements. Here, we study the magnetization reversal process of triangular cobalt rings made by e-beam lithography and lift-off. We demonstrate that full control over the direction of flux-closure magnetic states can be achieved solely by homogeneous external magnetic fields applied in particular directions. We have extracted statistical experimental data pertaining to the range of critical field values that trigger magnetization reversal from magnetic force microscopy images, and we explain the results on the basis of micromagnetic simulations     

Special features of the distributed feedback lasers based on gyrotropic cubic crystals

The oscillation conditions were determined for the distributed feedback lasers based on gyrotropic cubic crystals. The frequencies of clockwise (counterclockwise) polarized longitudinal eigenmodes decrease (increase) by ω_ρ=ρc/n (ρ is the specific optical rotation of the crystal, n is the index of refraction, c is the speed of light in vacuum) relative to the Bragg frequency ω₀=πc/Λn (Λ is the phase grating period). The gain threshold is higher for the clockwise than for the counterclockwise polarized waves.