A modified phase diversity wavefront sensor with a diffraction grating

The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.

Active wavefront shaping for controlling and improving multimode fi ber sensor

Wavefront shaping(WFS)techniques have been used as a powerful tool to control light propagation in complex media,including multimode fibers.In this paper,we propose a new application of WFS for multimode fber-based sensors.The use of a single multimode fiber alone,without any special fabrication,as a sensor based on the light intensity variations is not an easy task.The twist effect on multimode fiber is used as an example herein.Experimental results show that light intensity through the multimode fiber shows no direct relationship with the twist angle,but the correlation coefficient(CC)of speckle patterns does.Moreover,if WFS is applied to transform the spatially seemingly random light pattern at the exit of the multimode fiber into an optical focus.The focal pattern correlation and intensity both can serve to gauge the twist angle,with doubled measurement range and allowance of using a fast point detector to provide the feedback.With further development,WFS may find potentials to facilitate the development of multimode fber-based sensors in a variety of scenarios.

Simultaneous quantification of longitudinal and transverse ocular chromatic aberrations with Hartmann-Shack wavefront sensor

A simple method to objectively and simultaneously measure eye's longitudinal and transverse chromatic aberrations was proposed.A dual-wavelength wavefront measurement system using two Hartmann-Shack wavefront sensors was developed.The wavefronts of the red(639.1 nm)and near-infrared(786.0 nm)lights were measured simultaneously for different positions in the model eye.The chromatic wavefronts were converted into Zernike polynomials.The Zernike tilt cofficient(irst term)was used to calculate the transverse chromatic aberration along the ax-direction,while the Zernike defocus coefficient(fourth term)was used to calculate the longi-tudinal chromatic aberration.The measurement and simulation data were consistent.

High signal-to-noise ratio sensing with Shack–Hartmann wavefront sensor based on auto gain control of electron multiplying CCD

High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness of the target changes in a large scale,the fixed electron multiplying（EM） gain will not be suited to the sensing limitation.Therefore an auto-gain-control method based on the brightness of light-spots array in S–H WFS is proposed in this paper.The control value is the average of the maximum signals of every light spot in an array,which has been demonstrated to be kept stable even under the influence of some noise and turbulence,and sensitive enough to the change of target brightness.A goal value is needed in the control process and it is predetermined based on the characters of EMCCD.Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust,the sensing SNR reaches the maximum for the corresponding signal level,and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band.

哈特曼-夏克波前传感器高精度球面波标定方法研究

为解决哈特曼-夏克波前传感器传统标定方法存在的测量精度低、稳定性不足等问题,提出了一种基于球面波的哈特曼-夏克波前传感器高精度绝对标定方法。通过理论推导获取了球面波的高精度标定方法,结合搭建的球面波标定实验装置,对子孔径数为128×128的哈特曼-夏克波前传感器完成高精度标定。该方法计算得到了哈特曼-夏克波前传感器结构参数f,w以及L_(0)的精确值。对标定后的哈特曼-夏克波前传感器的测量精度进行测试,实验结果表明,经本文方法标定后的哈特曼-夏克波前传感器的波前复原精度达到了PV=1.376×10^(-2)λ,RMS=4×10^(-3)λ(λ=625 nm),重复性精度为PV=3.2×10^(-3)λ,RMS=9.76×10^(-4)λ(λ=625 nm)。该方法可以为大口径的SHWFS完成高精度标定,提升测量精度。

Large dynamic range Shack-Hartmann wavefront sensor based on adaptive spot matching

The Shack-Hartmann wavefront sensor(SHWS)is widely used for high-speed,precise,and stable wavefront measurements.However,conventional SHWSs encounter a limitation in that the focused spot from each microlens is restricted to a single microlens,leading to a limited dynamic range.Herein,we propose an adaptive spot matching(ASM)-based SHWS to extend the dynamic range.This approach involves seeking an incident wavefront that best matches the detected spot distribution by employing a Hausdorff-distance-based nearest-distance matching strategy.The ASM-SHWS enables comprehensive spot matching across the entire imaging plane without requiring initial spot correspondences.Furthermore,due to its global matching capability,ASM-SHWS can maintain its capacity even if a portion of the spots are missing.Experiments showed that the ASM-SHWS could measure a high-curvature spherical wavefront with a local slope of 204.97 mrad,despite a 12.5%absence of spots.This value exceeds that of the conventional SHWS by a factor of 14.81.

光学波前传感技术研究进展

光学波前是光波相位面的几何表示,光学波前传感技术通过检测光波传播路径中的相位变化来分析物体的性质。该技术广泛应用于大气湍流检测、光学元件缺陷分析、生物样品研究等领域,在天文学、自适应光学、显微成像、激光系统和生物医学等方面具有重要作用。然而,常见探测器仅对光强度敏感,为了探测光学波前,通常需要在探测前端使用一系列复杂的光学元件,这导致系统体积庞大、成本高昂且结构复杂。近年来,随着微纳光学和人工智能等领域的不断进展,涌现出一系列基于新原理、新器件和新算法的集成化、小型化和高性能的光学波前传感技术。该论文系统综述了近期光学波前传感技术的研究进展,并根据其原理将其分为干涉型和非干涉型两大类,具体包括剪切干涉型、光栅干涉型、近场干涉型、算法重构型和维度关联型等技术。最后,总结了当前领域尚存的挑战,并展望了未来可能的研究方向。

扫描式眼波前像差系统的夏克–哈特曼波前传感器质心探测研究

针对扫描式眼波前像差系统难以消除所有视角方向系统噪声的问题,提出了一种在大噪声条件下准确定位光斑阵列的质心并进行波前重建的方法。首先使用中值滤波与数学形态学方法对图像进行全局处理;接着使用改进的最大间类方差方法选取每个子孔径的阈值;然后通过Suzuki轮廓跟踪算法确定需要计算的光斑窗口;最后结合所提出的中值面积法精确定位光斑质心。通过对比发现,传统方法对此类大噪声条件下的真实光斑已无法进行判别,而新提出的方法可以进行正确识别,重建波前的PV值误差小于0.015λ,RMS小于0.001λ,说明该方法的准确度与稳定性明显优于传统方法。

结合光学掩模调制的鼠眼像差精确测量

进行波前探测时,标准动物模型小鼠的眼底视网膜双层反射光会导致像差探测失效。为解决这一问题,本文提出了一种结合光学掩模调制的鼠眼像差测量方法,以期提高鼠眼波前像差测量精度。首先,根据鼠眼视网膜的关键参数,建立鼠眼波前像差探测的光学系统模型并进行光学仿真。然后,分析比较不同孔径的光学掩模对视网膜非目标层反射光束的遮拦效果,确定光学掩模参数与实验方案。最后,搭建鼠眼波前像差探测系统并开展在体鼠眼波前像差的测量实验。实验结果表明:0.5 mm孔径的光学掩模可以将鼠眼波前像差的测量均方根误差降低74.9%,与理论仿真的80%区域实现非目标层反射光遮拦效果近似。本文研究实现了对鼠眼视网膜非目标层反射光的有效遮拦,提升了鼠眼波前像差探测精度,为进一步实现鼠眼高分辨率成像奠定了基础。

微透镜阵列衍射效应对夏克一哈特曼波前探测器的影响分析

微透镜阵列的衍射效应会影响夏克—哈特曼波前探测器的探测精度。本文根据惠更斯-菲涅耳衍射理论建立二维微透镜阵列衍射模型,模拟分析使用理想平行光入射微透镜阵列时在焦平面产生的二维衍射光斑阵列。然后,通过计算衍射光斑偏移一个像素的过程中质心的误差,确定最大质心计算误差。接着,利用模式法进行波前重构,获得波前探测误差。仿真结果显示:在偏移0.21和0.79个像素,即波面偏转0.03°和0.13°时,衍射导致的波前误差最大为0.125λ。最后,实验验证了该误差计算方法的有效性。该研究结果可为夏克一哈特曼波前探测器的设计提供理论依据。

Accuracy characterization of Shack-Hartmann sensor with residual error removal in spherical wavefront calibration

The widely used Shack-Hartmann wavefront sensor(SHWFS)is a wavefront measurement system.Its measurement accuracy is limited by the reference wavefront used for calibration and also by various residual errors of the sensor itself.In this study,based on the principle of spherical wavefront calibration,a pinhole with a diameter of 1μm was used to generate spherical wavefronts with extremely small wavefront errors,with residual aberrations of 1.0×10^(−4)λRMS,providing a high-accuracy reference wavefront.In the first step of SHWFS calibration,we demonstrated a modified method to solve for three important parameters(f,the focal length of the microlens array(MLA),p,the sub-aperture size of the MLA,and s,the pixel size of the photodetector)to scale the measured SHWFS results.With only three iterations in the calculation,these parameters can be determined as exact values,with convergence to an acceptable accuracy.For a simple SHWFS with an MLA of 128×128 sub-apertures in a square configuration and a focal length of 2.8 mm,a measurement accuracy of 5.0×10^(−3)λRMS was achieved across the full pupil diameter of 13.8 mm with the proposed spherical wavefront calibration.The accuracy was dependent on the residual errors induced in manufacturing and assembly of the SHWFS.After removing these residual errors in the measured wavefront results,the accuracy of the SHWFS increased to 1.0×10^(−3)λRMS,with measured wavefronts in the range ofλ/4.Mid-term stability of wavefront measurements was confirmed,with residual deviations of 8.04×10^(−5)λPV and 7.94×10^(−5)λRMS.This study demonstrates that the modified calibration method for a high-accuracy spherical wavefront generated from a micrometer-scale pinhole can effectively improve the accuracy of an SHWFS.Further accuracy improvement was verified with correction of residual errors,making the method suitable for challenging wavefront measurements such as in lithography lenses,astronomical telescope systems,and adaptive optics.

基于Transformer结构的高精度湍流波前重构

动态变化的大气湍流和观测目标的亮度的降低严重影响了夏克-哈特曼波前传感器(SHWFS)探测波前的精度。针对这两种复杂的观测条件,本文提出了一种以Transformer结构为基础的神经网络模型,它具有很好的全局建模能力,可以高精度地从SHWFS光斑阵列图像中重建波前。通过在动态变化的典型大气湍流相干长度r_(0)下进行仿真模拟,所提出的网络模型的残余波前RMS误差值稳定在0.010~0.024μm之间。与已有的方法相比,本文方法能够更准确地重构波前像差。此外,本文方法的重构精度受导星或观测目标的亮度变化影响很小。因此,本文方法的重构精度对两种观测条件变化均具有较强的稳定性,为大口径天文光学望远镜的高分辨率成像提供了一种有前景的方法。

Wavefront detection performance analysis of plenoptic sensor

A numerical simulation model of plenoptic sensor aberration wavefront detection is established to simulate and analyze the detection performance of plenoptic sensor aberration wavefront for different turbulence intensities.The results show that the plenoptic sensor can achieve better distortion wavefront detection,and its wavefront detection accuracy improves with turbulence intensity.The unique optical structure design of the plenoptic sensor makes it more suitable for aberration wavefront detection in strong turbulent conditions.The wavefront detection performance of the plenoptic sensor is not only related to its wavefront reconstruction algorithm but also closely related to its structural parameter settings.The influence of structural parameters on the wavefront detection accuracy of plenoptic sensors under different turbulence intensities is simulated and analyzed.The variation law of wavefront detection accuracy and structural parameters under different turbulence intensities is summarized to provide a reference for the structural design and parameter optimization of plenoptic sensors.

用夏克-哈特曼探测器测量人眼波前像差

为了精确测量人眼的高低阶像差,设计并搭建了一套人眼波前像差精确测量光学系统。该系统采用夏克-哈特曼波前探测器进行波前探测,可以在不同瞳孔、不同视场和不同调焦状态下精确测量人眼的波前像差。用ZEMAX软件对系统进行模拟分析,验证了该系统的探测精度,讨论了系统的调焦性能。用该系统实验分析了人眼各阶像差的分布情况、瞳孔大小和调焦状态对人眼波前像差的影响,以及人眼波前像差的时间和空间变化特性(变化频率约3 Hz,等晕角约为1.5°)。结果表明,该系统精度高(PV<1/20λ),操作方便,是人眼波像差的研究和个性化角膜手术的有力工具。

哈特曼波前传感器的应用

夏克—哈特曼（S－H）波前传感器可以用很高的采样频率同时测量出光场的相位分布和强度分布。它不仅作为波前传感器广泛地应用于自适应光学系统之中，而且还用于光学元件和光学系统的检测、激光光束质量诊断和大气扰动测量之中。我们研制了一系列S－H波前传感器。本文总结了这些传感器在不同领域的测量结果。

哈特曼传感器测量人眼波像差的特性研究

准确测量人眼波像差,对提高正常眼睛的视力和人眼屈光矫正手术具有重要的实验和临床 价值。对哈特曼传感器测量人眼波像差的精确性和重复性进行了研究,测量人眼离焦的精度为0.2D,波像差的平均偏差为0.065mm。

Shack-Hartmann波前传感器图像自适应阈值的选取

Shack-Hartmann(S-H)波前传感器光斑图像阈值的选取对质心探测精度有较大的影响。本文分析了S-H波前传感器光斑图像的特点,研究了光斑图像阈值对质心探测精度的影响,在此基础上提出了一种基于灰度直方图原理的多峰自适应阈值选取方法。实验结果表明,对于信噪比>4的S-H波前传感器光斑图像,本方法能够比较有效地自动选取每帧图像的阈值;但对于信噪比<4的图像,分割效果不是很理想。将使用本阈值算法的S-H波前传感器应用到自适应光学系统中进行闭环校正实验,结果显示,校正后的系统波前误差从10.41λ(PV值,λ=632.8nm)降低到0.12λ,基本达到了衍射极限水平,表明本方法可以满足S-H波前传感器的实用要求。

高级像差对人眼成像质量和视觉的影响

定量地研究高级像差对人眼成像质量和视觉的影响对人眼像差矫正具有重要的实验和临床意义。利用Hartmann-Shack波前传感器人眼像差仪测量了正常人眼6mm瞳孔的波前像差,由波前像差计算出人眼光学系统的光学调制传递函数MTF和Strehl比率,并由MTF和视网膜空间像调制度AIM曲线计算出人眼视锐度和对比敏感度函数CSF。根据MTF和Strehl比率分析了高级像差对人眼成像质量的影响,根据视锐度和对比敏感度函数CSF分析了高级波像差对视觉的影响。研究表明Zernik前6级像差对人眼成像质量和视觉的影响是不可忽略的,更高级的像差对人眼成像质量和视觉的影响较小,甚至可以忽略。对Zernik前6级像差进行矫正,可以得到相当好的视觉。

云南天文台1．2m望远镜61单元自适应光学系统

云南天文台1．2 m望远镜61单元自适应光学系统已经完成升级改造并投入使用。该自适应光学系统主要由倾斜跟踪控制回路、高阶校正回路以及高分辨力成像系统组成。为了提高系统的跟踪精度,倾斜跟踪控制回路由两级倾斜校正回路串联而成,用于校正望远镜的跟踪误差和大气湍流引起的倾斜跟踪误差。高阶校正回路主要由一套哈特曼波前传感器、一块61单元变形反射镜以及一套高速数字波前处理机组成。系统中哈特曼波前传感器的工作波段为400-700 nm,系统成像波段为700-900 nm。在介绍61单元自适应光学系统各组成部分的基础上,对该系统的性能进行了分析,并给出了实际天文恒星目标的高分辨力自适应光学成像观测结果。

一种Hartmann-Shack波前传感器图像的自适应阈值选取方法

在Hartmann-Shack波前传感器中,图像阈值的选取对质心探测精度有较大的影响。根据 模式识别理论,提出一种适用于Hartmann-Shack波前传感器图像阈值选取的新方法棗基于类别方差的自适应门限方法。实验结果表明,本方法在Hartmann-Shack波前传感器图像信噪比大于3时,能够比较有效地自动选取每帧图像的阈值。