Pupil-segmentation-based adaptive optical correction of a high-numerical-aperture gradient refractive index lens for two-photon fluorescence endoscopy

The intrinsic aberrations of high-NA gradient refractive index (GRIN) lenses limit their image quality as well as field of view. Here we used a pupil-segmentation-based adaptive optical approach to correct the inherent aberrations in a two-photon fluorescence endoscope utilizing a 0.8 NA GRIN lens. By correcting the field-dependent aberrations, we recovered diffraction-limited performance across a large imaging field. The consequent improvements in imaging signal and resolution allowed us to detect fine structures that were otherwise invisible inside mouse brain slices.     

Gradient-index fiber-optic microprobes for minimally invasive in vivo low-coherence interferometry

We describe the design, construction, and application of what are believed to be the smallest fiber-optic probes used to date during imaging or diagnosis involving low-coherence interferometry (LCI). The probes use novel fiber-optic gradient-index (GRIN) lenses fabricated by a recently developed modified chemical-vapor-deposition (MCVD) process that avoids on-axis aberrations commonly marring MCVD-fabricated GRIN substrate. Fusing GRIN fiber lenses onto single-mode fiber yields automatically aligned all-fiber probes that insert into tissue through hypodermic needles as small as 31-gauge (inner diameter, 127 mum). We demonstrate the use of such probes with LCI by measuring microscopic brain motions in vivo.     

Refraction and ultra‐small‐angle scattering of X‐rays in a single‐crystal diamond compound refractive lens

In this work a double‐crystal setup is employed to study compound refractive lenses made of single‐crystal diamond. The point spread function of the lens is calculated taking into account the lens transmission, the wavefront aberrations, and the ultra‐small‐angle broadening of the X‐ray beam. It is shown that, similarly to the wavefront aberrations, the ultra‐small‐angle scattering effects can significantly reduce the intensity gain and increase the focal spot size. The suggested approach can be particularly useful for the characterization of refractive X‐ray lenses composed of many tens of unit lenses.     

Ray Model of an Incident Gaussian Beam for Analyzing a Micro-Optical Communication Device with a GRIN Lens System

For the design of reliable micro-optical devices with a high coupling efficiency, a source-modeling method necessary for ray tracing is newly proposed. This method is based on the ray-division of an incident wavefront estimated by Gaussian beam optics. The simulation result obtained using the proposed method was compared with those of the conventional methods, and its accuracy was confirmed by the experimental results. Finally, the method was used to design a micro-optical device with two GRIN lenses and a thin-film filter.     

Efficiency and alignment tolerances of LED to single-mode fibre coupling — theory and experiment

The coupling efficiency between partially coherent sources such as LEDs and single-mode fibres is calculated from near- and far-field data of the source for arbitrary coupling optics. The influence of misalignment and lens aberrations is considered. Simple formulae for coupling efficiency and alignment tolerances are derived for LEDs with a Gaussian far field. The agreement with experimental results using spherical, GRIN and taper lenses is satisfactory     

主客观相结合眼波面像差分析系统

利用Hartmann-Shack波面传感器对眼出瞳位置的波面像差进行测量,根据所测像差控制可变形镜对像差进行实时补偿.眼像差以Zernike多项式表示,通过对可变形镜的精确控制,可在光路中生成特定模式和幅值的像差.因此,被测者根据视觉的主观感觉,调节视标像差,直至获得最满意的视觉效果.该系统采用移动三棱镜和柱镜的方法对离焦和散光进行预补偿,弥补了波面传感器测量范围和可变形镜矫正范围受限制的缺点.该系统把快速、客观的测量及补偿和主观调整相结合,更加符合人眼工作的特性,可用于在人眼像差与视觉分辩的基础和临床研究.     

角膜手术后眼模型的构建和人工晶状体设计

根据角膜屈光手术前的角膜地形图、眼内各组分的轴向间距和波前像差,运用ZEMAX光学设计软件,构建了术前的个性化眼模型.结合角膜屈光手术后实际测量的波前像差,建立了术后个性化眼模型.运用该模型,为角膜屈光手术眼设计了双球面人工晶状体.研究表明:对于角膜屈光手术后人眼,用术后个性化眼模型计算的人工晶状体度数可靠.该模型还能够为术后眼设计矫正像散和其他高阶像差的人工晶状体,同时可以用来评估角膜手术联合白内障术后人眼的光学性能,以及手术中各类偏差对视觉质量的影响.     

Preparations on Several GRIN Lenses

Gradient index materials have been developed from glass melting process to GRIN lenses. Two kinds of GRIN lenses have been fabricated by ion-exchange and glass fusion/diffusion. The main applications to GRIN lenses are demonstrated.     

Experimental generation and characterization of Devil’s vortex-lenses

We propose the first experimental approach for both generation and characterization of high quality Devil’s vortex-lenses. These new type of lenses, able to produce a sequence of optical vortices, are addressed onto a programmable spatial light modulator (SLM) operating in phase-only modulation. The static aberrations arising by the lack of flatness of the SLM display are characterized and mostly compensated by using a Shack–Hartmann wavefront sensor. The analysis of the residual aberrations and their effect on the vortex-lens performance are studied.     

用于复色哈特曼人眼波像差测量的折/衍混合调焦系统

设计了一个折/衍混合多色调焦系统,可用于哈特曼波前传感器测量不同波长下人眼的波像差.系统由两片折射透镜和一个二元衍射面构成,焦距调整范围为－200～200 mm.系统性能达到衍射受限,在0.488～0.655 μm波长范围内,焦点色位移小于3 μm.整个系统结构简单、紧凑,同哈特曼波前传感器相匹配,可用于普通人群眼波像差的测量.     

Full-field measurement of surface reflectivity using a microscopy for refractive index profiling of GRIN lenses

This paper outlines an improved technique for profiling the refractive index of Graded-index (GRIN) lenses based on the measurements obtained from a reflectivity image. Reflective cross-sectional image of the GRIN lens were compared with a reflectance reference target under illumination at small incidence angles to obtain the full-field refractive index distribution of the GRIN lens quickly and easily.     

Evaluating Optical Quality of a Bifocal Soft Contact Lens in Near Vision Using a Shack–Hartmann Wavefront Aberrometer

To assess optical characteristics of bifocal soft contact lenses (BCLs) in use, we measured wavefront aberrations of human eyes, of eyes with a monofocal soft contact lens (MCL), and of eyes with a BCL. Modulation transfer functions (MTFs), Strehl ratios, and simulated images for far and near vision were produced with the measured aberrations. High order aberrations of subject 1 were significantly smaller than those of subject 2 (t-test, P = 0.001). We found that wearing the BCL improved the optical quality of an eye in subject 1, expressed as the horizontal MTF from 2 to 48 cycles per degree (cpd) for near vision and the Strehl ratio (t-test, P = 0.009 for Strehl ratio). But we did not find the same effect in subject 2. This difference may be due to the difference in the aberrations of the eyes of the two subjects.     

Limitations of the Shack–Hartmann sensor for testing optical aspherics

Aspheric lenses and surfaces are increasingly used in modern high-quality optics. Therefore, new measuring methods for an accurate quantification of these aspheres are also necessary. The current approach to quantify aspheres is to apply null systems such as computer-generated holograms as a part of a null lens in a interferometer. An alternative to this method is the Shack–Hartmann wavefront sensor. The dynamic range of this sensor can be adjusted by the optical parameters of the applied microlens array. Hence, large wavefront aberrations can be measured directly without a null lens. However, there are basic limitations in the dynamic range of a Shack–Hartmann sensor (SHS) depending on the curvature of the incident wavefront. In this paper, an analytical expression to determine the strongest wavefront curvature which can be measured with a defined microlens array of an SHS is derived. It allows to calculate the microlens parameters required to measure the wavefront of a test lens. Particularly, the influence of rotational symmetric aspherical wavefront shapes to the dynamic range of an SHS has been studied. A comparison between interferometry and the SHS has been accomplished. Numerical solutions using scalar diffraction theory illustrate the analytical predictions.     

Research on micro-optical lenses fabrication technology

We present a detail investigation on the development of a series of gradient index (GRIN) optical glass microlens and polymer microlens and microlens arrays in our laboratory in recent years. The special glass material GRIN lenses have been fabricated mainly by using ion-exchange technology, which are applied to construct micro-optic devices and other applications. On one hand, we demonstrated the light propagation and imaging properties of GRIN lenses and the results analyzed. On the other hand, we have explored a drop-on-demand ink-jet printing method to produce microlens array using nano-scale polymer droplets involved with a uniform ultraviolet light and heat solidifying process. The experimental setup for manufacturing polymer microlens array and the performance of refractive microlens elements are also given in this paper.     

梯度透镜折射率分布高次项系数的数值计算

本文从光线方程出发,给出了一系列利用径向梯度透镜球象差进行数值计算求解折射率分布高次项系数的公式及测量计算结果。     

Simple equivalent systems for GRIN lenses in inhomogeneous medium

Simple single-lens equivalent systems for graded-index （GRIN） lenses in inhomogeneous medium obtained using matrix optics are proposed in this letter. Due to its simplicity, the equivalent optical system enables quick analysis of the imaging properties of GRIN lens rod immersed in inhomogeneous medium. This facilitates the optical analysis of complicated optoelectronics systems in inhomogeneous medium utilizing GRIN lens rods.     

无线光通信系统中的光接收机设计

介绍了无线光通信的特点，比较了光电检测器、光纤接收模块、自聚焦透镜和多模光纤接收机耦合三种设计方案，提出了自聚焦透镜和多模光纤之间的耦合设计是最优方案。详细讨论了自聚焦透镜和多模光纤之间的耦合设计和电信号处理过程。试验证明，采用该方案后系统输出信号的信噪比显著提高，完全可以满足通信系统的要求。     

模拟合成孔径雷达数据片波差的测量和胶片、波差的容限

本文介绍一种用马赫-陈德干涉系统测量模拟合成孔径雷达数据片波差的方法.该法能把两种原因产生的波差区分开来,即把通过胶片变形的波面与平面参考波面比较,求出胶片厚度不平产生的波差;把合成孔径雷达数据片的一级衍射波面与两个半径不等的参考球面波比较,分别求出由模拟装置产生的方位维和斜距维波差.本文给出一些实验结果和分析.这种方法还可以用于测量真实合成孔径雷达数据片的波差.由胶片厚度变化产生的波差可以用液体门补偿.但是,在实际中使用液体门是很繁复的,有时也没有必要.因此,我们认瑞利准则出发导出合成孔径雷达数据片胶片厚度变化产生的波差的容限,以此作为判断是否要用液体门的依据.     

The study of wavelength-dependent wavefront aberrations based on individual eye model

Theoretical calculations of the wavelength dependence of the ocular wavefront aberrations are performed with individual eye model. Individual eye model, based on the traditional Gullstrand-Le Grand eye model, has been established with measured individual cornea data, eyeball depth and wavefront aberrations. We analyze the wavelength-dependent wavefront aberrations at 12 different visible wavelengths (between 400 and 750 nm) for eight eyes. The change of defocus with wavelength (longitudinal chromatic aberration, LCA) is noticeable, and in good agreement with the results from references. In most cases, the primary spherical aberration changes significantly with wavelength. In comparison with the primary spherical aberration, the other higher-order wavefront aberrations have a smaller change with wavelength. These results have potential applications in those situations where defocus or higher-order wavefront aberrations information in arbitrary wavelength is required.