共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
3.
Rotating mechanical systems such as gearbox are known to generate vibrations at specific frequencies. The generation of asymmetric frequency sidebands around gear meshing frequencies is typical of rotating systems, and often results in amplitude-modulated disturbances. In addition, when the angular speed of such systems exhibits small time variations, a frequency-modulation of the disturbance tones is observed. Such conditions may result in difficulties for feedforward active control systems based on short, finite impulse response control filters, as was observed by previous researchers. This is mainly due to the fact that the reference signal may not provide all the gear meshing frequencies and sidebands found in the disturbance. This work investigates adaptive notch filters in the principal component space to cancel multi-harmonic gearbox vibrations. Experimental results obtained with these adaptive notch filters show good control attenuations at targeted gearbox tones, without amplification of other closely located, unreferenced tones. 相似文献
4.
Configuration optimization of laser guide stars and wavefront correctors for multi-conjugation adaptive optics
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Multi-conjugation adaptive optics(MCAOs) have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view(FOV).The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors,such as deformable mirrors(DMs) or liquid crystal wavefront correctors(LCWCs),is a very important step in the data processing of an MCAO's controller.In this paper,a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars(LGSs) and the reasonable conjugation heights of LCWCs.Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO.Several examples are given to demonstrate our LGSs configuration optimization method.Compared with traditional methods,our method has minimum wavefront tomographic error,which will be helpful to get higher imaging resolution at large FOV in MCAO. 相似文献
5.
Thomas Weyrauch Mikhail A. Vorontsov 《Journal of Optical and Fiber Communications Reports》2004,1(4):355-379
Refractive index inhomogeneities of the turbulent air cause
wave-front distortions of optical waves propagating through the
atmosphere, leading to such effects as beam spreading, beam
wander, and intensity fluctuations (scintillations). These
distortions are responsible for severe signal fading in free-space
optical communications systems and therefore compromise link
reliability. Wave-front distortions can be mitigated, in
principle, with adaptive optics, i.e., real-time wave-front
control, reducing the likeliness of signal fading. However,
adaptive optics technology, currently primarily used in
astronomical imaging, needs to be adapted to the requirements of
free-space optical communication systems and their specific
challenges.In this chapter we discuss a non-conventional adaptive optics
approach that has certain advantages with respect to its
incorporation into free-space optical communication terminals. The
technique does not require wave-front measurements, which are
difficult under the strong scintillation conditions typical for
communication scenarios, but is based on the direct optimization
of a performance quality metric, e.g., the communication signal
strength, with a stochastic parallel gradient descent (SPGD)
algorithm.We describe an experimental adaptive optics system that consists
of a beam-steering and a higher-resolution wave-front correction
unit with a 132-actuator MEMS piston-type deformable mirror
controlled by a VLSI system implementing the SPGD algorithm. The
system optimizes the optical signal that could be coupled into a
single-mode fiber after propagating along a 2.3-km near-horizontal
atmospheric path. We investigate characteristics of the
performance metric under different atmospheric conditions and
evaluate the effect of the adaptive system. Experiments performed
under strong scintillation conditions with beam-steering only as
well as with higher-resolution wave-front control demonstrate the
mitigation of wave-front distortions and the reduction of signal
fading. 相似文献
6.
随着水下光通信、传感和激光雷达等应用的发展,研究水下光学系统成像特性具有重要意义.本文研究了海洋湍流对自适应光学成像系统特征参量(如Strehl比、Greenwood时间常数和等晕角)的影响.推导出了海洋湍流中短曝光成像Strehl比的近似解析表达式,并证明:除了在近场D_G/r_0=1附近外(D_G和r_0分别为光学系统的光瞳直径和海洋湍流中可见参数),该近似公式均可保证足够的精度.此外,还得到了海洋湍流中Greenwood时间常数和等晕角的表达式.研究表明:随着海水盐度变化引起的海洋湍流逐渐占主导地位时,这三个特征参量值均减小;随着海水湍流动能耗散率的减小或海水湍流温度方差耗散率的增大,这三个特征参量值也均减小.本文研究结果对工作于水下湍流环境中自适应光学成像系统应用具有理论参考意义. 相似文献
7.
本文讨论了自适应光学中非等晕域对补偿效果的影响,提出了一种减小非等晕性误差的新方法—位相梯度法。分析结果表明,该方法可显著增大有效校正的角范围,使非等晕性误差的影响大大减小。我们预期位相梯度法有望解决自适应光学中信标的非等晕性问题。 相似文献
8.
提出了一种抑制光束平台抖动和压电倾斜镜机械谐振的方法从而提高系统校正带宽和跟瞄精度.通过分析双二阶滤波器参数对频率特性的影响,提出了一种双二阶滤波器的设计方法,并把这种设计方法结合比例积分(PI)控制算法用于抑制光束平台抖动和压电倾斜镜机械谐振.最后,对经典PI控制算法和增加了双二阶滤波器的PI控制算法进行了实验比较,在相同的条件下,增加了双二阶滤波器的PI控制带宽比经典PI控制带宽提高了近1倍,对平台抖动控制精度提高了5倍以上.实验结果表明:增加了双二阶滤波器的PI控制算法对抑制光束平台抖动和压电倾斜镜机械谐振简单有效,可以提高系统校正带宽和跟瞄精度. 相似文献
9.
总结了国内外自适应光学技术在无线光通信系统应用中的研究进展和技术分类,同时介绍了西安理工大学在该领域的工作,包括有波前测量的自适应光学系统、无波前测量的自适应光学系统、液晶空间光调制器波前校正、偏摆镜和变形镜组合的波前校正、空间光光纤耦合自适应光学波前校正等。自适应光学技术可有效修正无线光通信系统中由大气湍流引起的畸变波前,提高耦合效率和通信性能。虽然这些方法在理论分析和工程实际中尚不完善,但不失为人们在该领域进行的有益探索。 相似文献
10.
Modal prediction for closed-loop adaptive optics 总被引:1,自引:0,他引:1
The correction efficiency of adaptive optics is limited mainly by measurement noise and time delay. To overcome this problem, we describe a new modal linear predictive controller whose parameters are optimized by means of a recursive least-squares algorithm to minimize the residual optical phase variance. The method copes with the recursivity of the closed-loop operation. We demonstrate that the optimal rejection transfer function for adaptive optics is proportional to the frequency signal-to-noise ratio. Finally, we present what we believe to be the first experimental results obtained with a predictor used to control the tip-tilt mirror of an adaptive-optics system. 相似文献
11.
Mohammad Moradi 《Optical Review》2008,15(2):125-129
The goal of this study was to analyse anisoplanatism of adaptive optics under an inhomogeneous turbulent atmosphere over a
pupil of finite size. By means of a numerical model with layers of turbulence software was proposed by which point spread
function (PSF), optical transfer function (OTF) as well as system isoplanatic angle can be calculated. Atmospheric turbulence
was simulated with the aid of a set of moving random phase screens with arbitrary statistics. Both reference and target are
assumed to be the point light sources. To simulate atmospheric turbulence we applied the concept of a number of moving random
phase screens with Kolmogorov spectrum. In my investigation I used the model of the Shack-Hartmann wave front sensor and the
ideal model of a wave front adaptive mirror that is assumed to reproduce a given number of Zernike polynomials without time
delays. The designed software allows calculation of instantaneous and average values of phase correction errors at different
angles between a reference beacon and target source. Simulations can be made with a broad range of parameters of an adaptive
system and atmospheric turbulence. The system of the model allows changing of the control algorithm of phase correction. Both
common phase conjugation and weighted phase conjugation algorithm have been tested. This program is capable of calculating
the effects of beam diffraction during propagation in the atmosphere. 相似文献
12.
掌握湍流基本规律及其廓线结构分布,是大气光学理论与应用研究中的关键问题之一。利用随机并行梯度下降算法对大气湍流廓线统计模式拟合进行了研究。在已获合肥地区整层大气折射率结构常数C2N平均廓线的前提下,以广义Hufnagel-Valley湍流模型为基础,拟合获得了该地区不同时间与不同季节的湍流模式廓线。研究发现,该方法获得的该地区湍流模式廓线在整层大气高度上均能很好地同实测平均廓线相符合,且两者所表征的整层湍流特征参量也能保持非常好的一致性。对寻求基于Hufnagel-Valley模型的通用湍流廓线模式拟合方法进行了有益的探索。 相似文献
13.
A. M. Vorontsov P. V. Paramonov M. T. Valley M. A. Vorontsov 《Waves in Random and Complex Media》2008,18(1):91-108
Numerical modeling of optical wave propagation in atmospheric turbulence is traditionally performed by using the so-called 'split'-operator method, where the influence of the propagation medium's refractive index inhomogeneities is accounted for only within a set of infinitely narrow phase distorting layers (phase screens). These phase screens are generated on a numerical grid of finite size, which corresponds to a rather narrow slice (spatial area) of atmospheric turbulence. In several important applications including laser target tracking, remote sensing, adaptive optics, and atmospheric imaging, optical system performance depends on atmospheric turbulence within an extended area that significantly exceeds the area associated with the numerical grid.
In this paper we discuss methods that allow the generation of a family of long (including infinitely long) phase screens representing an extended (in one direction) area of atmospheric turbulence-induced phase distortions. This technique also allows the generation of long phase screens with spatially inhomogeneous statistical characteristics. 相似文献
In this paper we discuss methods that allow the generation of a family of long (including infinitely long) phase screens representing an extended (in one direction) area of atmospheric turbulence-induced phase distortions. This technique also allows the generation of long phase screens with spatially inhomogeneous statistical characteristics. 相似文献
14.
15.
《Optik》2014,125(21):6413-6417
Free space optics (FSO) is one of the sprouting technologies in optical communication systems domain. It can be employed as an alternative for the conventional radio frequency (RF) links to work out the current limitations in communication systems. But, the major drawback in FSO communication is the effect of random environment conditions on its performance. In this paper, we analyze the bit error rate (BER) and outage performance of single-input single-output (SISO) and multiple-input multiple-output (MIMO) FSO systems in strong atmospheric turbulence using binary phase shift keying subcarrier intensity modulation (BPSK-SIM) signaling technique. The closed-form expressions are derived and the results are realized in terms of 2D and 3D plots. 相似文献
16.
自适应光学实时大气湍流补偿实验 总被引:18,自引:9,他引:9
本文报道了用自适应光学系统实时探测和校正距地面约15m高的340m水平传输通道上的大气湍流效应的实验.实验结果表明,用自适应光学校正后,对点目标和一定扩展度的扩展目标都可提高成像质量. 相似文献
17.
自适应光学对大气扰动波前的补偿效果研究 I.水平大气传输时的结果分析 总被引:1,自引:0,他引:1
讨论了光波在水平大气湍流中传输时的情况。计算结果表明自适应光学系统的补偿效果与光波传播路径上的横向风有很大的关系。大气湍流的强度越大,自适应光学系统的截止频率越高,横向风的影响也越大。计算结果还表明在相同的r0或者相同的大气湍流强度下,球面波所受大气扰动的自适应光学补偿效果受横向风的影响要比平面波的厉害。本文还将理论分析的结果和数值模拟的结果进行了比较,表明数值模拟结果受横向风的影响比理论分析结果受横向风的影响大。最后,文中分析了以上现象并对此作出了合理的解释 相似文献
18.
19.