高精度成像角膜曲率计光学系统设计

张雪莹, 王劲松, 黄国林, 等. 高精度成像角膜曲率计光学系统设计[J]. 光电工程, 2019, 46(1): 180392. doi: 10.12086/oee.2019.180392
引用本文: 张雪莹, 王劲松, 黄国林, 等. 高精度成像角膜曲率计光学系统设计[J]. 光电工程, 2019, 46(1): 180392. doi: 10.12086/oee.2019.180392
Zhang Xueying, Wang Jinsong, Huang Guolin, et al. Design of optical system for high accuracy imaging keratometry[J]. Opto-Electronic Engineering, 2019, 46(1): 180392. doi: 10.12086/oee.2019.180392
Citation: Zhang Xueying, Wang Jinsong, Huang Guolin, et al. Design of optical system for high accuracy imaging keratometry[J]. Opto-Electronic Engineering, 2019, 46(1): 180392. doi: 10.12086/oee.2019.180392

高精度成像角膜曲率计光学系统设计

  • 基金项目:
    吉林省重点科技研发项目(20180201025GX)
详细信息
    作者简介:
    通讯作者: 王劲松(1973-),男,博士,副教授,博士生导师,主要从事精密仪器设计方面的研究。E-mail:soldier_1973@163.com
  • 中图分类号: TH745

Design of optical system for high accuracy imaging keratometry

  • Fund Project: Supported by Jilin Province Key Technology R & D Project Fund (20180201025GX)
More Information
  • 为减小成像角膜曲率计沿光轴方向的对准误差,提高角膜屈光度测量精度,设计一种高精度成像角膜曲率计光学系统。光学系统包括成像系统和低相干干涉测量系统。成像系统由成像物镜、角膜和测量靶环构成,其中成像物镜采用双远心光路设计;低相干干涉测量系统采用光栅尺实现扫描反射镜的位移测量,再通过低相干干涉信号对角膜顶点和测量靶环进行定位,实现了对角膜顶点和测量靶环距离间的精确测量。成像物镜在最大空间频率为70 lp/mm处的调制传递函数大于0.4,畸变小于0.05%。设计结果表明,该系统结构紧凑,成像质量好,操作简单,满足成像角膜曲率计对角膜屈光度的高精度测量需求。

  • Overview: In order to reduce the alignment deviation of the imaging keratometer along the optical axis and improve the measurement accuracy of corneal diopter, a high precision imaging keratometer optical system was designed. The optical system includes imaging system and low coherence interferometry system. The imaging system consists of imaging objective, cornea, and measurement target ring. Imaging objective lens consists of double telocentric light path, which has large depth of field, low distortion and constant magnification in a certain object distance range. The magnification of the image stays the same with any object distance changes within a certain object distance range. The change of image distance does not affect the size of the image as well. It also has advantages of being insensitive to the object distance and the image distance change contribute to the image obtained by different human eyes and the magnification stability when the human eye moves slightly because of the relatively large depth of field. It is convenient and quick to align in the direction of the optical axis during measurement. The low-coherence interferometry system uses the grating scale to measure the displacement of the scanning mirror, and then locates the vertices of the cornea and the measuring target ring by low-coherence interference signals, achieving accurate measurement between the apex of the cornea and the distance of the measuring target ring. The use of low coherence interferometry solves the problem of using the double telocentric lens in the imaging keratometer which is hardly determining the distance from the apex of the cornea to the measuring target ring accurately, and improves the measurement accuracy of this distance. The design completed system has the following parameters, the total length of the imaging objective system is 85 mm, the object height is 14 mm, the image height is 6.2 mm, the magnification is -0.4, the depth of field is 8 mm, the spectral range is 900 nm~980 nm, and the maximum spatial frequency is 70 lp/mm. The modulation transfer function at mm is greater than 0.4, and the distortion is less than 0.05%. The parameters meet the design requirements of corneal index. The low-coherence interferometry system uses a broadband light source with a center wavelength of 850 nm, a 2×2 fiber coupler with a split ratio of 99:1, and a linear delay line with a scan speed of 120 mm/s to achieve precise positioning of the cornea. The system has compact structure, good imaging quality and simple operation, and meets the high-precision measurement requirements of imaging keratometer for corneal diopter. In summary, the system has practical significance for realizing high-precision corneal curvature measurement.

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  • 图 1  高精度成像角膜曲率计光学系统原理图

    Figure 1.  High-precision imaging keratometer optical system schematic

    图 2  双远心镜头成像原理图

    Figure 2.  Double telecentric lens imaging schematic

    图 3  初始结构图

    Figure 3.  Initial structure diagram

    图 4  双远心成像物镜结构图

    Figure 4.  Double telecentric imaging objective lens structure diagram

    图 5  MTF曲线图

    Figure 5.  MTF graph

    图 6  点列图

    Figure 6.  Plot diagram

    图 7  场曲畸变图

    Figure 7.  Field curvature and distortion

    图 8  点扩散函数图

    Figure 8.  PSF graph

    图 9  低相干干涉测量系统

    Figure 9.  Low coherence interferometry system

    图 10  干涉信号仿真图

    Figure 10.  Interference signal simulation diagram

    表 1  成像物镜设计参数

    Table 1.  Imaging objective design parameters

    Parameter Value
    Working distance/mm 75
    Object height/mm 13~15
    Image height/mm ≥6
    β -0.4
    Depth of field/mm ≥6
    Spectral range/nm 940±40
    Max frequency/(lp·mm-1) 70
    下载: 导出CSV

    表 2  光学系统优化设计参数

    Table 2.  Optical system optimization design parameters

    Surf OBJ 1 2 3 4 5 6 STO
    Radius - 43.55 127.014 -704.7 16.377 8.47 17.75 -
    Thickness 75 2.594 2.299 15.5594 3.2259 8.048 11.235 2.04
    Glass N-LAF21 N-BAF52 SF4 N-BAF10
    Surf 8 9 10 11 12 13 IMA
    Radius -6.668 9.855 -7.564 22.44 13.677 -80.72 -
    Thickness 2.29 3.508 12.801 2.04 2.884 16.704 -
    Glass SF4 N-SK16 N-SK16 SF4
    下载: 导出CSV

    表 3  设计结果参数

    Table 3.  Design result parameters

    Parameter Value
    Source/nm 850
    Scanning delay line length/mm 100
    Scanning delay line speed/(mm×s-1) 120
    Fiber optic coupler split ratio 99:1
    下载: 导出CSV

    表 4  不同物距放大率的变化率

    Table 4.  The rate of change of the magnification of different object distances

    Object distance/mm β Rate of change
    72 -0.40028 0.0007
    73 -0.40019 0.000475
    74 -0.40011 0.000275
    75 -0.40000 0
    76 -0.39990 -0.00025
    77 -0.39982 -0.00045
    78 -0.39974 -0.00065
    下载: 导出CSV

    表 5  角膜曲率测量误差理论值

    Table 5.  Corneal curvature measurement error theoretical value

    Object distance/mm β Δd/mm Δr/mm
    72 -0.40028 80 0.003
    73 -0.40019 80 0.005
    74 -0.40011 80 0.007
    75 -0.40000 80 0.009
    76 -0.39990 80 0.011
    77 -0.39982 80 0.012
    78 -0.39974 80 0.014
    下载: 导出CSV
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出版历程
收稿日期:  2018-07-23
修回日期:  2018-09-13
刊出日期:  2019-01-01

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