梯度折射率透镜在口腔内窥镜中的设计与应用

作为口腔内窥镜的摄像镜头，利用梯度折射率透镜质量轻、体积小、结构简单、分辨率高、成像景深大的优点，研制出一套适合医患交流及进行口腔检查与治疗的医疗装置。采用修正折射率剖面的梯度折射率透镜, 降低系统渐晕，减小畸变,获取口腔内部图像，经CCD光电转换装置转换成电信号，再将电信号经过数字信号处理以后，将该数字信息存储于计算机内部或在显示器上显示出来。口腔内窥镜是集梯度折射率透镜、光学原理、光学材料与加工、微电子、数字成像技术等为一体的新型医疗设备。特别是采用经修正的梯度折射率透镜制造的口腔内窥镜成像清晰, 在图像畸变、景深等方面优于现有产品，而且便于对患者的各种信息进行管理、查询、输出等。     

Fabrication of gradient refractive index ball lenses

The theoretical model of the Maxwell fish eye sphere lens has long been regarded as an absolute optical instrument without practical application since it was proposed. But the study on the theory of Maxwell fish eye micro-spherical lens shows that at certain condition it has fine image formation ability and coupling efficiency. Based on the Fick's diffusion equations, the distribution function of refractive index of gradient refractive index (GRIN) ball lenses is derived. Lithium-containing silicate glass is fabricated and GRIN ball lenses whose diameters are from 0.3 to 3.0 mm are made by ion exchange and the sagging method in sodium nitrate. Radial refractive index profiles of these GRIN ball lens are measured by interferometer. Results show that the distribution of the index of refraction is a parabolic curve and in concordance with the computational consequence and its Δn is 0.0002.     

梯度折射率球透镜的制备及其光线轨迹测试

自麦克斯韦鱼眼透镜理论模型提出后,长期以来学术界一直以为它只是一种绝对光学仪器,在实践中并没有应用的可能。但通过对麦克斯韦鱼眼微球透镜的理论研究表明,在一定条件下,它具有良好的成像性能和耦合效率。根据菲克定律推导出梯度折射率球透镜的折射率分布函数。并且熔制了含Li+硅酸盐玻璃和采用槽沉法以及Na+/Li+离子交换法制备直径为0.3—3.0mm的梯度折射率球透镜。通过干涉法测得了梯度折射率球透镜的折射率分布曲线,并研究了光线通过梯度折射率球透镜的轨迹。研究结果表明:在590℃,离子扩散系数为3.07×10-6mm2/s;所制备的梯度折射率球透镜的折射率分布是抛物线分布,并且和理论分析相吻合;梯度折射率球透镜的光线轨迹满足椭圆方程。     

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。     

Effect of crystalline lens surfaces and refractive index on image quality by model simulation analysis

The surfaces and refractive index of crystalline lens play an important role in the optical performance of human eye.On the basis of two eye models,which are widely applied at present,the effect of lens surfaces and its refractive index distribution on optical imaging is analyzed with the optical design software ZEMAX (Zemax Development Co.,San Diego,USA).The result shows that good image quality can be provided by the aspheric lens surfaces or (and) the gradient-index (GRIN) distribution.It has great potential in the design of intraocular lens (IOL).The eye models with an intraocular implantation are presented.     

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.     

The measurement of refractive index profile and aberration of radial gradient index lens by using imaging method

In this article, through the linear fit of objective distance and reciprocal of magnification in different imaging locations, we use imaging method to measure the central refractive index n(0) and focusing constant α of radial gradient index (GRIN) lens and obtain 10⁻³ measurement accuracy of n(0). At the same time, under distortion, the fourth-order refractive index coefficient and aberration of GRIN lens are derived.     

Graded-index time-lens implementation

The propagation of a laser pulse in a graded-index (GRIN) space lens and in an electro-optic crystal with an appropriate refractive index modulation is studied. It is shown that the crystal functions as a GRIN time lens if the propagation's second-order dispersion is included and if the phase velocity of the modulating wave equals the group velocity of the laser pulse.     

Fabrication of gradient refractive index ball lenses using the method of combination of ion exchanging and sagging

Based on the Fick’s diffusion equations, the distribution function of refractive index of a gradient refractive index ball lens (GRIN ball lens/GBL) is derived. Lithium containing silicate glass is fabricated and GRIN ball lenses (GBLs) which diameters are from 0.3 mm to 3.0 mm are made by the method of combination of Ion exchanging and sagging in sodium nitrate. Refractive index profiles of these GBLs are measured by interferometer, and the performances such as effective focal length (EFL), back focal length (BFL) and numerical aperture (NA) between GBLs and homogeneous ball lenses (HBLs) are compared. Results show that the distribution of the index of refraction is parabolic curve and its Δn is about 0.0002, the performances of the former are super to the latter.     

Performance evaluation of GRIN lenses by ray tracing method

Plastic gradient-index lenses produce clear images with negligible aberration and distortion. One of the methods for fabricating these lenses involves pulling up the core fiber vertically from a polymer solution whose refractive index has been adjusted to the desired value. Since the molecules from the solution diffuse into the inner layer, the monomer components are distributed in the radial direction. The monomer distribution is fixed in the photopolymerization process, and this forming process is repeated several times with adjusting the composition of the solution; hence, a specific refractive index distribution is obtained. We considered a numerical model of the interdiffusion process and analyzed refractive index distribution that could well reproduce the experimental results. Moreover, we employed the ray tracing method to calculate the modulation transfer function and used the transfer function to evaluate the GRIN lens performance. Simulation results showed that our evaluation method well duplicates the experimental results. We thus developed an integrated simulation method for the fabrication and performance evaluation of GRIN lenses.     

Three‐dimensional Luneburg lens at optical frequencies

A Luneburg lens is a fascinating gradient refractive index (GRIN) lens that can focus parallel light on a perfect point without aberration in geometrical optics. Constructing a three‐dimensional (3D) Luneburg lens at optical frequencies is a challenging task due to the difficulty of fabricating the desired GRIN materials. Here, we present the practical implementation of a 3D Luneburg lens at optical frequencies. Such a 3D Luneburg lens is designed with GRIN 3D simple cubic metamaterial structures, and fabricated with dielectric metamaterials by femtosecond laser direct writing in the commercial negative‐photoresist IP‐L. Simulated and experimental results exhibit an interesting 3D ideal focus for the infrared light. The protocol for developing the 3D Luneburg lens with ideal focus would prompt the potential applications in integrated light‐coupled devices and lab‐on‐chip integrated biological sensors based on infrared light.

     

层状GRIN板折射率分布的自动测量

采用溶液 凝胶扩散共聚法成功地合成了二元体系的甲基烯酸苄酯 甲基烯酸甲酯 (BZMA MMA)层状梯度折射率板 ,折射率分布是其主要性能指标。给出了一种测量该制品折射率分布的简便实验装置和自动实现方法。该测量方法基于激光干涉的原理 ,由计算机自动跟踪干涉条纹的移动来计算梯度折射率材料的折射率分布。实验表明 ,该方法简单易行 ,具有较高的折射率测量精度 ,为科学评价自研制梯度折射率材料的性能提供了保证     

含Li+的径向梯度折射率棒透镜的研究

研究发现在硼硅酸盐系统玻璃中,利用Li⁺/Na⁺离子交换来制取径向梯度折射率(GRIN)棒透镜时,基质玻璃中重要的成分Li₂O含量对径向GRIN棒透镜的象差和数值孔径值有着明显的影响,并着重分析和讨论了实验中Li₂O含量对径向GRIN棒透镜中折射率分布、数值孔径及象差影响机制.进一步指出实验中Li₂O含量存在一个最佳值,既能够满足径向GRIN棒透镜获得较大的数值孔径又满足其具有较小的象差.     

Design,fabrication and evaluation of a photographic objective that uses a radial GRIN lens

Some technical issues in the design, fabrication and evaluation process of the photographic objective lens are treated. In the design process, a unique design technique called the quasi-equivalent glass method is applied. Also, a convenient method is described for the determination of tolerances of the refractive index profile. Performance evaluation showed that the GRIN material made by sol-gel method is usable for photographic lenses.     

自聚焦透镜的三维相干成像特性分析

运用傅里叶光学方法，分析并推导了自聚焦透镜的三维相干成像公式。研究表明，虽然自聚焦透镜中介质折射率是径向渐变折射率分布，不同于薄透镜中的均匀分布，但是由于它的三维相干成像性质却类似于薄透镜，从而使自聚焦透镜可以在成像和光学信息处理系统中有效地代替薄透镜，实现光学系统的微型化。     

方形自聚焦透镜5×5阵列的成像特性

采用离子交换工艺和精密加工技术制作了方形自聚焦透镜5×5阵列,并对其成像特性进行研究。结果表明：方形自聚焦透镜阵列相对于圆形孔径阵列而言,能有效增大填充系数,提高受光面积,其多重像和综合像的像质均匀,成像质量好。分析了导致多重像偏离和综合像变形的原因,并给出解决这一问题的关键技术。     

Effect of laser beam induced nonlinearity on the performance of crystalline lens

This paper presents the performance of the human crystalline lens having gradient index (GRIN) structure in the presence of a moderate power laser pulse. Nonlinear dynamical equations have been set-up governing the laser pulse propagation in the lens by taking into account the nonlinearity introduced by the laser pulse. Semi-analytical results have been obtained by using the paraxial ray approximation when GRIN and nonlinearity effects are simultaneously present. Performance of the lens has been analyzed in two explicit cases. In the first case, only the GRIN structure is considered while in the second case the nonlinearity and the GRIN both are considered. A moderate power laser pulse can be used for self-focusing in the crystalline lens when GRIN effects alone are not sufficient to focus the laser pulse in the crystalline lens.     

低色差GRIN棒透镜制备工艺的研究

熔制了含Li+硅酸盐玻璃,玻璃的棒料在NaNO3熔盐中进行离子交换后得到了梯度折射率(GRIN)棒。采用干涉法测得了GRIN棒的折射率分布曲线。实验结果表明:通过所述的工艺,可以获得直径达5mm的GRIN棒,其折射率分布曲线与双曲正割曲线接近。分析表明GRIN棒的轴向色差评价函数值约为0 6～0 7%。