基于图像清晰度无波前传感器自适应光学系统的研究

自适应光学技术能够校正大气湍流造成的光束畸变,但常规自适应光学系统需要波前传感器测量波前信息.在本文中系统不使用波前传感器,而是以图像清晰度作为优化指标,使用无模型的随机并行梯度优化算法,对大气湍流引起的波前误差进行时实补偿,结果表明此系统算法经过多次迭代后达到很好的校正效果.     

基于二次二维经验模态分解去噪的湍流退化图像复原算法

为实现大气湍流环境下的高质量成像,将自适应光学波前探测技术与数字图像处理技术相结合,并提出了一种基于二次二维经验模态分解去噪的湍流退化图像复原算法。通过在光学系统中使用哈特曼—夏克波前传感器探测波前信息,进而计算光学系统点扩散函数;然后使用改进的二次二维经验模态分解算法进行图像去噪,最后利用R-L算法实现对湍流退化图像的复原。通过搭建光学实验系统,对实际拍摄的湍流退化图像进行了复原实验。结果表明,该算法能够有效减弱噪声放大现象,得到更加稳定的高质量大气湍流退化图像复原结果。     

Assembly and evaluation of a SIL optical head for cover-layered incident NFR without disk contact with the bottom surface of a SIL

In the assembly of the solid immersion lens (SIL) optical head for cover-layered incident near-field recordings (NFRs), disk contact with the bottom surface of the SIL has previously been regarded as essential. This is because SIL optical heads are designed to interface with a cover layer. However, SILs can be contaminated and damaged by this contact. We present a new SIL optical head assembly method for cover-layered incident NFRs without disk contact with the bottom surface of the SIL. To achieve this, we added zoom optics to a Twyman–Green interferometer in the measurement beam optical path. Our assembly method eliminates SIL contamination problems and the assembly procedure becomes simple because of removing the disk contact process. In addition, it is not necessary to consider the aberrations induced by disk tilt and cover-layer thickness variation. The SIL optical head assembled by the proposed method has good optical performance satisfying the optical tolerances and the measured wavefront aberration is good agreement with simulations.     

High-speed wavefront sensor compatible with standard CMOS technology

This paper addresses the design, implementation and performance of an integrated Hartmann (–Shack) wavefront sensor suitable for real-time operation and compatible with standard CMOS technology.A wavefront sensor can be used to detect distortions in the profile of a light beam or indirectly in that of an optical component. Such a sensor can also be coupled to a deformable mirror to enable the compensation of the detected distortions in a light beam. These adaptive optical systems find more and more applications in astronomy, industry and have recently been introduced in medical setups.We use the Hartmann wavefront-sensing method, in which a light beam is sampled into a number of sub-beams, which are projected on a plane. The displacements of the light spots on this plane are used to estimate the profile of the associated arbitrary wavefront. Usually, a conventional image sensor registers the light spots and an image-processing algorithm computes their displacements from a reference grid. However, this approach restricts the operational speed of the sensor because it relies on the frame-transfer rate of the imager and on the rather slow data-reduction algorithm.The novel contribution of this work is that, to render faster operation, we introduce a Hartmann wavefront sensor that uses an addressable matrix of CMOS integrated position-sensitive detectors, namely quad cells. Each sampled light spot is associated with a quad cell such that direct information about the spot-centroid displacement is available.Each particular application has its own requirements and the developed sensor, which should be used with light sources in the visible spectrum, shall perform well for applications involving enough light (>0.5 mW beams), and there where lower-order wavefront aberrations are expected (<30 Zernike terms). However, this sensor can be modified in a variety of ways to attend to particular applications. The fabricated sensor allows operation at rates higher than 3 kHz.     

基于微分压缩感知的图像去模糊技术研究

尽管图像去模糊是一个病态问题, 但是只要对需要恢复的图像作适当的假设就能得到唯一的稳定解。考虑了一个缺乏先验条件的图像去模糊问题, 从而将图像的恢复转换为一个盲去卷积问题。作为一个特殊的应用, 现有文献大多集中在受到大气扰动影响的短曝光图像的重建问题。大气扰动会使得光波产生随机偏离, 从而使得光学系统的PSF产生随机变化。一种处理办法是采用自适应方法, 如Shack-Hartmann干涉计。在该系统中, 光波重建的准确率与干涉计所采用的透镜数成正比, 从而使得计算非常复杂。采用微分压缩感知的方法, 可降低透镜的数目, 从而使得计算的复杂度大大降低。另一方面, 利用压缩感知理论, 降采样不会造成数据的丢失, 从而使得光波重建的准确率能够与常规方法相同。仿真表明, 采用微分压缩感知的方法能够准确地实现光波的重建, 大大提高了系统的效率。     

Dual-side see-through integral imaging 3D display system based on lens array holographic optical element

We propose a dual-side see-through integral imaging 3D display based on a lens array holographic optical element (LAHOE). The display system consists of two projectors and a LAHOE. The LAHOE is fabricated according to the theory of reflective volume holograms. An interference pattern is formed by a plane-wave beam and a spherical-wave array beam, and the interference pattern is recorded into a photopolymer material. Thus, the LAHOE is formed. When a reference beam is projected into the LAHOE, the wavefront of a convex micro-lens array is reconstructed. When a phase conjugation reference beam is projected into the LAHOE, the wavefront of a concave micro-lens array is reconstructed. So, the LAHOE possesses the optical properties of a convex micro-lens array and a concave micro-lens array. The proposed display is developed using integral imaging principle and it realizes dual-side see-through integral imaging 3D display.     

Polynomial Optics: A Construction Kit for Efficient Ray‐Tracing of Lens Systems

Simulation of light transport through lens systems plays an important role in graphics. While basic imaging properties can be conveniently derived from linear models (like ABCD matrices), these approximations fail to describe nonlinear effects and aberrations that arise in real optics. Such effects can be computed by proper ray tracing, for which, however, finding suitable sampling and filtering strategies is often not a trivial task. Inspired by aberration theory, which describes the deviation from the linear ray transfer in terms of wavefront distortions, we propose a ray‐space formulation for nonlinear effects. In particular, we approximate the analytical solution to the ray tracing problem by means of a Taylor expansion in the ray parameters. This representation enables a construction‐kit approach to complex optical systems in the spirit of matrix optics. It is also very simple to evaluate, which allows for efficient execution on CPU and GPU alike, including the computation of mixed derivatives of any order. We evaluate fidelity and performance of our polynomial model, and show applications in high‐quality offline rendering and at interactive frame rates.     

Front‐projection optical‐system design for reflective LCoS technology

Abstract— Optical designs for three‐panel LCoS projection systems are reviewed. The impact of polarization aberrations in prism‐based systems is discussed and a simple model to analyze the sensitivity of contrast to thermal gradients in prisms is presented. To eliminate stress birefringence in LCoS projection systems, we have developed a projection optical system that does not require the use of polarizing prisms. An improved off‐axis design has been designed that simplifies manufacture and reduces cost. The performance of systems based on this architecture will be discussed.     

Robot vision: An evaluation of imaging sensors

Robot vision, robotics vision, and computer vision are terms that have evolved over the past few years to include two separate but related functions that provide visual sensing for computerdriven robots. These two functions are “electro-optical imaging” and “image processing.” The purpose of electro-optical imaging is to convert optical radiation to an appropriate electronic signal for input to the robot's computer; whereas, the purpose of image processing is to extract useful information from the electronic image provided by the sensor. This article deals with the electro-optical sensing part of robot vision. It describes the operation and properties of electro-optical imaging sensors. The fundamental concepts of optical radiation, optical radiation quantities and units, and photon energies are defined. The fundamental principles for detecting optical radiation and definitions for the primary performance measures for optical detectors are given. A relatively comprehensive overview of the parameters used to describe imaging sensors is presented. Factors affecting these parameters and obtainable sensor performance are compared. Example design analyses are presented to show the interaction of various performance measures.     

Using Wavefront Tracing for the Visualization and Optimization of Progressive Lenses

Progressive addition lenses are a relatively new approach to compensate for defects of the human visual system. While traditional spectacles use rotationally symmetric lenses, progressive lenses require the specification of free-form surfaces. This poses difficult problems for the optimal design and its visual evaluation.
This paper presents two new techniques for the visualization of optical systems and the optimization of progressive lenses. Both are based on the same wavefront tracing approach to accurately evaluate the refraction properties of complex optical systems.
We use the results of wavefront tracing for continuously re-focusing the eye during rendering. Together with distribution ray tracing, this yields high-quality images that accurately simulate the visual quality of an optical system. The design of progressive lenses is difficult due to the trade-off between the desired properties of the lens and unavoidable optical errors, such as astigmatism and distortions. We use wavefront tracing to derive an accurate error functional describing the desired properties and the optical error across a lens. Minimizing this error yields optimal free-form lens surfaces.
While the basic approach is much more general, in this paper, we describe its application to the particular problem of designing and evaluating progressive lenses and demonstrate the benefits of the new approach with several example images.     

An optical target to eliminate impinging light in a light scattering simulation

Based on the Convolutional perfectly matched layers (CPML) absorbing boundary condition algorithm that is implemented at the outer boundary of a light scattering simulation, we propose a numerical target that can eliminate light impinging upon it from arbitrary directions. To model light propagation through random media to a specific position, elimination of light reaching the target position is necessary to prevent further reverberation through the simulation space and become a source of noise. Various factors that affect the performance of the optical target are analyzed, including shape of the wavefront and alignment of the impinging light. Simulation results show that incident light can be most effectively eliminated for incident wavefront normally impinging upon the optical target.     

Estimating the contribution of different parts of the atmosphere to optical wavefront aberration

Current adaptive optical telescope designs use a single deformable mirror (DM), usually conjugated to the aperture plane, to compensate for the cumulative effects of optical turbulence. The corrected field of view (FOV) of an adaptive optics system could theoretically be increased through the use of multiple DMs conjugated to a like number of corresponding planes which sample the turbulence region in altitude. Often, the atmospheric turbulence responsible for the degradation of long-exposure telescope images is concentrated in several relatively strong layers. The logical location for the planes of correction in a multiconjugate adaptive optics (MCAO) system would be the same as these “seeing layers.” Each DM would correct for the component of the total wavefront contributed by its associated turbulent layer. However, there is no known method of isolating a particular layer so that its component may be measured. Somehow, the individual components must be estimated using available measurements of the cumulative wavefront at the aperture of the telescope. This paper presents a theoretical analysis of a signal processing technique for determining these phase contributions. The method takes advantage of the spatial diversity of wavefront sensor (WFS) measurements from two or more reference sources. These separate wavefront sensor measurements are processed via minimum mean square error filtering to yield an estimate of the phase perturbation caused by a particular turbulent layer of the atmosphere. Our results indicate that multiple wavefront corrector adaptive optics systems will require much brighter reference sources than single wavefront corrector systems.     

湍流效应退化图像的数值模拟和仿真计算

大气湍流干扰空中目标的成像探测,使得观测到的目标图像是严重抖动和模糊的.为了具体分析湍流效应退化图像的特征,总结了光学成像系统的传输特性和湍流流场的统计特性,用随机相位屏对大气湍流效应进行了数值模拟,建立了湍流形成畸变波前过程的仿真模型,对点源目标发出的光波经过湍流流场后,在成像探测器焦面上形成的点源目标图像,计算了短曝光像和长曝光像的光强分布,定义了描述像点弥散和抖动的指标,并进行了定量分析和仿真计算.通过对计算结果进行分析,验证了仿真模型的合理性,并对湍流效应造成的图像退化给出了定量的描述,对进一步进行湍流效应退化图像校正算法研究具有重要意义.     

Multi‐viewer autostereoscopic display with dynamically addressable holographic backlight

Abstract— The Multi‐User 3‐D Television Display (MUTED), designed to provide three‐dimensional television (3‐D TV) by the display of autostereoscopic imagery to multiple viewers, each of whom should enjoy freedom of movement, is described. Such an autostereoscopic display system, which allows multiple viewers simultaneously by the use of head tracking, was previously demonstrated for TV applications in the ATTEST project. However, the requirement for a dynamically addressable, steerable backlight presented several problems for the illumination source. The MUTED system demonstrates significant advances in the realization of a multi‐user autostereoscopic display, partly due to the provision of a dynamic backlight employing a novel holographic laser projector. Such a technology provides significant advantages in terms of brightness, efficiency, laser speckle, and the ability to correct for optical aberrations compared to both imaging and scanned‐beam projection technologies.     

Performance of liquid‐crystal displays for fire‐service thermal‐imaging cameras

Abstract— As use of handheld thermal‐imaging cameras (TICs) becomes more prevalent in the first‐responder community, it is important that standard test metrics be available to characterize imaging performance. A key performance consideration is the quality of the image presented on the TIC display. This paper focuses on TICs that use liquid‐crystal displays to render an image for the user. Current research on TIC performance for first‐responder applications makes use of trained observers and/or composite‐video‐output‐signal measurements. Trained observer tests are subjective and composite video output tests do not evaluate the performance of the complete imaging system. A non‐destructive objective method was developed that tests the performance of the entire thermal‐imaging system, from the infrared sensor to the display. A thermal target was used to correlate the measured thermal imager composite video output signal with the luminance of the display. A well‐characterized charge‐coupled‐device (CCD) camera and digital recording device were used to measure the display luminance. An electro‐optical transfer function was determined that directly relates the composite video output signal to the luminance of the display, providing a realistic characterization of system performance.     

Enhancement of PZT embedded swing arm actuator using integrated read/write performance and actuation

The current technological challenges associated with the rotary-type seesaw arm actuator for small-form-factor (SFF) disk drives are the small skew focusing, which causes off-axis aberrations and reduces optical quality. This article develops a novel design for a seesaw arm actuator and suspension assembly that is based on a micro-PZT actuator to position pickup head. Dual-stage actuation relaxes the dynamic requirement on the focusing stroke. The proposed actuator with a tilt-compensation mechanism uses a PZT bender to drive pickup head focusing. This combined system, optical module and dual stage actuator, is effectively self-aligned the optical axis for read/write performance in both experiment and simulation result. Finite element modeling and dynamic measurements reveal significant improvements in the actuator bandwidth with and without micro-PZT actuator compensation.     

Predecessor/successor approach for high-performance run-time wavefront scheduling

Most scientific applications rely on parallel multiprocessor computing to enhance performance. However, the irregular loops within these applications obstruct the parallelism analysis at compile-time. Rauchwerger et al. presented a run-time method to extract the hidden parallelism in a program using dependence chains. The relative overhead degrades this approach’s performance due to the mass storage requirement and huge array reference processing. In this study, a new predecessor/successor approach is developed in which high-level predecessor/successor information is recorded and processed efficiently. A predecessor/successor table is constructed first in the inspector phase so that only the successor iterations in the current wavefront need to be examined, instead of the entire loop iterations during wavefront scheduling. Usually, the performance of dependence chain approach degrades dramatically for a hot-spot access pattern, but our scheme works very efficiently in this case. The experimental results using synthetic code and real programs are presented to prove the superiority of the proposed approach.     

Shape and topology optimization of acoustic lens system using phase field method

A layout optimization method for a two-dimensional acoustic lens system used in underwater imaging is presented. To this end, a shape and topology optimization is formulated for the design problem of a lens system for the first time. The layout of a lens system to be optimized includes the number of lenses, shape of lens surfaces, distances between lenses, and lens materials. A phase field function is employed to implicitly parameterize the boundaries of the lenses, which move according to design sensitivities during optimization. Multiple lenses with different materials are optimized using a single phase field function. Because the ratio of the acoustic wavelength with respect to lens dimensions is large, diffraction effects should be taken into account. Accordingly, the performance of a lens system should be analyzed using wave acoustics and not the ray tracing method. The optimization problem is formulated to remove the aberrations of coma and field curvature. The validity of the proposed optimization method is demonstrated by solving benchmark design problems including a lens system with a large field of view.     

Production of identical pyramid wavefront sensors for multi-conjugate adaptive optic systems using the LIGA process

Pyramid wavefront sensors are the key components of new multiconjugate adaptive optics systems used for wavefront correction of terrestrial telescopes. The sensor consists of a very flat four faces pyramid made in a transparent material that requires an accurate control of the quality of its turned edges, its surfaces and the size of its pyramid tip. Moreover identical copies of these optical elements are needed to fulfil the requirements of the multiconjugate adaptive optics systems. This paper presents the fabrication method of Pyramid wavefront sensors using the LIGA process. Results are described and discussed.