基于虚像相位阵列的光谱检测中角色散均匀性的研究

Research on Angular Dispersion Uniformity Based on the Virtual Image Phase Array Used in Spectral Detection

随着光谱学的不断发展,光谱检测作为一种快速无损的检测手段逐渐被应用于越来越多的领域中。而随着对信息精度要求的不断提高,如何得到高分辨率和低波长误差的光谱信息,是设计光谱检测系统时必须解决的问题。传统的色散元件如衍射光栅,虽然有较大的波长响应范围,但是通常只能提供nm量级的分辨率而无法满足当下的高光谱分辨率的要求。虚像相位阵列(VIPA)具有大角度色散特性,可以有效提高系统的光谱分辨率,因而近年来不断被用于精细光谱检测的研究。但其波长和色散角度对应关系存在非线性,而且同一波长易产生多个衍射级次的光斑,从而造成额外的光能损失。因此,本文主要基于VIPA的交叉色散光路就如何降低VIPA色散的非均匀性的问题进行了理论分析和实验验证。首先基于傍轴理论的色散定律展开理论分析探讨了入射光腰尺寸、入射角度等参数对于VIPA色散的非线性程度和衍射级次数量的影响。然后通过进行仿真记录了宽光谱光源在不同VIPA倾斜角度条件下各波长衍射级次的数量,以及各波长对应的光斑质心的坐标值。计算各情况下的质心坐标与拟合曲线之间的距离均差,比较了不同角度条件下线性度的好坏。最后根据理论分析和仿真实验的结果进行实验。实验中记录了VIPA的交叉色散光路在不同的VIPA倾斜条件下出现的衍射级次数量,并利用一个波长可变的激光器得到了不同波长的光源在VIPA倾斜2°的实验条件下各衍射级次光斑的质心坐标。同样通过计算不同衍射级次光斑的质心与拟合曲线之间的距离均差分析不同衍射级次的线性度好坏。实验证明通过控制入射光束参数,可以一定程度上降低VIPA色散的非均匀性。VIPA倾斜角度越大且越靠近探测器中央位置的衍射级次线性度越好。

As a fast and nondestructive detection method,spectral detection is gradually applied in more and more fields.With the continuous improvement of information accuracy requirements,obtaining spectral information with high resolution and low wavelength error is a primary challenge that researchers must face when designing spectral detection systems.Studying a new type of dispersive element becomes a feasible scheme.Traditional dispersive elements,such as diffraction gratings,have an extensive wavelength response range but usually can provide a resolution of the order of nm and cannot meet the requirements of the current hyperspectral resolution.Virtual Image Phased Array(VIPA)has the characteristics of large angular dispersion and high spectral resolution,which can effectively improve the spectral resolution of the system.Therefore,it has been continuously used in the research of fine spectral detection in recent years.However,the corresponding relationship between the wavelength and the dispersion angle is nonlinear,and the same wavelength is prone to generate multiple diffraction orders,resulting in additional light energy loss.Therefore,based on the cross-dispersion optical path of VIPA,this paper conducts theoretical analysis and experimental verification on how to reduce the dispersion nonuniformity of VIPA.Firstly,based on the dispersion law of paraxial theory,the influence of the incident waist size,incident angle and other parameters on the nonlinearity of VIPA dispersion and the number of diffraction orders is analyzed theoretically.The number of diffraction orders of each wavelength and the calibration value of the spot centroid corresponding to each wavelength of the broad spectrum light source at different VIPA tilt angles are recorded through simulation.The linearity under different angles is compared by calculating the average distance difference between the centroid coordinate and the fitting curve in each case.Finally,the experiment is carried out according to the theoretical analysis and the simulation results.The number of diffraction orders of the cross-dispersion optical path of VIPA under different VIPA tilt conditions was recorded in the experiment,and the centroid coordinates of each diffraction order spot of different wavelength light sources under the experimental condition of VIPA tilt of 2°are obtained by using a variable wavelength laser.Similarly,the linearity of different diffraction orders is analyzed by calculating the distance average between the centroid of different diffraction orders and the fitting curve.The results show that the nonuniformity of VIPA dispersion can be reduced to some extent by controlling the parameters of the incident beam.The larger the tilt angle of VIPA and the closer to the center of the detector,the better the diffraction order linearity.