CN114137735B - A Collimating Lens for IMS Spectral Imaging System with Large Aperture and Long Intercept - Google Patents

Abstract

The present invention proposes a large-aperture and long-intercept IMS spectral imaging system collimator lens, along the incident light propagation direction, the aperture stop, flat glass, first double-convex positive lens, and first meniscus negative lens are arranged coaxially in sequence. , second meniscus negative lens, first meniscus positive lens, third meniscus negative lens, second biconvex positive lens, second meniscus positive lens, third meniscus positive lens, fourth meniscus negative lens and Fourth meniscus positive lens. The F-number of the collimating lens of the present invention is 1.75, and the aperture meets the requirements for collecting the reflected light of the micro-mirror array; the front and rear intercepts meet the requirements for the assembly distance of the IMS system, and compared with the assembly scheme using relay mirrors, the optical path is greatly shortened, making The system is compact in structure; through the optimization of the initial structure and glass material, the system aberration is optimized and balanced, so that the projection position of the aperture array is close to the design value, ensuring the coupling efficiency of the aperture array and the dispersion imaging module; the selection of environmentally friendly glass materials reduces It is difficult to process and assemble, and the cost is low.

Description

A Collimating Lens for IMS Spectral Imaging System with Large Aperture and Long Intercept

technical field

The invention relates to the technical field of optical design, in particular to a large-aperture and long-intercept IMS spectral imaging system collimator lens.

Background technique

The snapshot spectral imaging system (Image Mapping Spectrometer, IMS) based on the micromirror array can obtain the three-dimensional map information (x, y, λ) of the target scene within a single exposure time. IMS technology has significant advantages in detecting time-varying targets, and is widely used in biological imaging, medical diagnosis, remote sensing detection and other fields.

The target is first imaged on the micro-mirror array by the front imaging lens of the IMS system. The micro-mirror array is composed of multiple narrow and long mirrors with different two-dimensional space pointing angles, which can divide and project the primary image to different directions. The aperture diaphragm forms an image on the rear focal plane of the collimator mirror through the front mirror and the collimator mirror, and under the modulation of the micro-reflector array, an aperture array corresponding to each spatial pointing angle is formed. After the reflected light is collimated by the collimating mirror, it enters the corresponding sub-aperture for spectroscopic dispersion, passes through the imaging mirror array for secondary imaging, and finally obtains the rearranged target map information on the detector. In the imaging process, the collimating lens needs to meet the following conditions: 1) larger aperture to collect the reflected light of the micro-mirror array; 2) longer front and rear intercepts to ensure the front-end micro-mirror array and the back-end dispersion imaging The modules have sufficient mechanical distance to facilitate system assembly; 3) Control aberration so that the projection position of the aperture array reaches the design value, so as to ensure the coupling efficiency of the aperture array and the dispersion imaging module and improve the imaging quality.

In order to ensure the coupling with the photosensitive element, the general imaging lens usually only limits the rear intercept, while the front intercept is relatively small. Therefore, it is difficult for existing imaging lenses to satisfy the conditions of large aperture, long intercept and small aberration at the same time. Solutions for IMS systems include the use of beam expanders to reduce the requirement for collimator apertures, or the use of 1:1 relay mirrors to extend the optical path to meet assembly requirements. However, the above solution introduces an additional optical lens group, which increases the difficulty of assembly and reduces the luminous flux.

Contents of the invention

In view of this, the purpose of the present invention is to provide a large-aperture and long-intercept collimator lens for an IMS spectral imaging system, which can simultaneously meet the requirements of the system for imaging quality and assembly distance.

To achieve the above object, the present invention provides the following technical solutions:

A large-aperture and long-intercept IMS spectral imaging system collimator lens is characterized in that the collimator lens is coaxially arranged in sequence along the incident light propagation direction: aperture stop, flat glass, first biconvex positive lens, second One meniscus negative lens, second meniscus negative lens, first meniscus positive lens, third meniscus negative lens, second biconvex positive lens, second meniscus positive lens, third meniscus positive lens, fourth A meniscus negative lens and a fourth meniscus positive lens; wherein, the third meniscus negative lens and the second biconvex positive lens form the first doublet lens; the third meniscus positive lens and the fourth meniscus positive lens The negative lens forms the second doublet.

Preferably, in the collimating lens of the above-mentioned large-aperture and long-intercept IMS spectral imaging system, the focal length of the collimating lens is 50 mm, and the F number is ≤ 1.77.

Preferably, in the collimating lens of the IMS spectral imaging system with a large aperture and long intercept described above, the front intercept of the collimating lens is equal to the distance between the front surface of the first biconvex positive lens and the follow-up dispersive imaging module, and the distance Not less than 15mm.

Preferably, in the IMS spectral imaging system collimating lens of a kind of large-aperture long-intercept above-mentioned, the rear intercept of described collimating lens is equal to the distance of the rear surface of the 4th meniscus positive lens and the micromirror array, and this distance Not less than 35mm.

It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

(1) The focal length of the collimating lens of a kind of large-aperture and long-intercept IMS spectral imaging system provided by the present invention is 50 mm, and the F-number is 1.75, and the aperture meets the requirement of collecting the reflected light of the micromirror array.

(2) The front intercept of the collimating lens provided by the present invention is 17.5mm, the rear intercept is 39.36mm, and the total optical length is 121.24mm, which meets the requirements of the assembly distance of the IMS system. Compared with the assembly scheme using relay mirrors, The optical path is greatly shortened, making the system compact.

(3) The collimating lens provided by the present invention optimizes and balances the system aberration by optimizing the initial structure and glass material. The full field of view of the collimating lens is 12.6°, and the distortion of the maximum field of view does not exceed 0.8%, so that the projection position of the aperture array is close to the design value, ensuring the coupling efficiency of the aperture array and the dispersion imaging module.

(4) The collimating lens provided by the present invention adopts 10 spherical lenses and selects environmentally friendly glass materials, which reduces the difficulty of processing and assembly, and has low cost.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 accompanying drawing is the IMS spectral imaging system aperture array projection schematic diagram of the present invention;

Accompanying drawing of Fig. 2 is a structural diagram of the present invention;

Fig. 3 accompanying drawing is the modulation transfer function (MTF) curve figure of the present invention;

Fig. 4 accompanying drawing is field curvature and distortion figure of the present invention;

Fig. 5 accompanying drawing is the chromatic focus shift curve of the present invention;

Fig. 6 is the projection distribution of the aperture array of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to accompanying drawings 1-6, which is a large-aperture long-intercept IMS spectral imaging system collimator lens disclosed by the present invention, specifically including: aperture stop STOP, flat glass 0, first biconvex positive lens 1, second First meniscus negative lens 2, second meniscus negative lens 3, first meniscus positive lens 4, third meniscus negative lens 5, second biconvex positive lens 6, second meniscus positive lens 7, third meniscus Moon positive lens 8, the fourth meniscus negative lens 9 and the fourth meniscus positive lens 10; wherein, the third meniscus negative lens and the second biconvex positive lens form the first doublet; the third A meniscus positive lens and a fourth meniscus negative lens form a second doublet.

In order to further optimize the above technical solution, the focal length of the collimating lens is 50mm, and the F number is ≤1.77.

In order to further optimize the above technical solution, the front intercept of the collimator lens is equal to the distance between the front surface of the first biconvex positive lens 1 and the subsequent dispersive imaging module, and the distance is not less than 15 mm.

In order to further optimize the above technical solution, the back intercept of the collimating lens is equal to the distance between the back surface of the fourth meniscus positive lens 10 and the micromirror array, and the distance is not less than 35 mm.

In order to facilitate the understanding of the present invention, the specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

二者满足以下关系：First, determine the aperture parameters of the collimating mirror according to the IMS system parameters. Figure 1(a) is the equivalent optical path diagram of the aperture array projection. As shown in the figure, the aperture stop is imaged on the rear focal plane of the collimator after passing through the front mirror and the collimator mirror, forming a sub-aperture. The two-dimensional spatial pointing angle of each mirror surface of the micromirror array is (α _m,n ,β _m,n ), and the corresponding spatial pointing angle of the reflected light is

The two satisfy the following relationship:

Among them, θ is the overall deflection angle of the micromirror array.

和准直镜焦距f₂，可以确定每个子孔径的中心位置坐标(x_m,y_m)，见下式：According to the spatial pointing angle of the reflected light

and the focal length of the collimator f ₂ , the coordinates (x _m , y _m ) of the center position of each sub-aperture can be determined, see the following formula:

The arrangement of the aperture array on the exit pupil surface of the collimator is shown in Figure 1(b). According to the coordinates (x _m , y _m ) of the center position of the sub-apertures, the horizontal and vertical distances between adjacent sub-apertures can be obtained as d _x , d _y . According to the object-image relationship, the sub-aperture diameter d _sub has the following relationship with the aperture stop diameter D _ape :

Among them, f ₁ is the focal length of the front mirror.

The number of sub-apertures arranged in the horizontal direction and vertical direction of the aperture array are N _x and N _y respectively, and the exit pupil diameter D _L2 of the collimator should meet the following conditions:

In this embodiment, the focal length _f2 of the collimating mirror is 50 mm. According to the above calculation method, in the imaging design stage, the entrance pupil diameter of the collimating mirror is at least 28.16 mm, that is, F≤1.77.

According to the assembly requirements of the IMS system, the micromirror array and the dispersion imaging module are respectively located on the front and rear focal planes of the collimator, and the front and rear intercepts of the collimator need to ensure sufficient assembly distance. In this embodiment, the front intercept of the collimating lens is ≥15 mm, and the rear intercept is ≥35 mm.

In the optical design software, set the object field of view, entrance pupil diameter and wavelength range according to the design requirements. Input the initial structure of the collimating lens, set the focal length of the collimating lens, the front and rear intercepts, and the modulation transfer function as the constraint targets, set the curvature radius, thickness, and material of each mirror surface as variables, and run the software repeatedly until better imaging is obtained result.

The structural diagram of a large-aperture and long-intercept IMS system collimator lens provided in this embodiment is shown in FIG. 2 . The collimating lens is designed according to the reverse optical path. When designing, the exit pupil of the collimating lens becomes the entrance pupil, and the light rays of each field of view enter the entrance pupil in the form of parallel light. The front imaging mirror of the IMS spectral imaging system is an image-space telecentric structure. In order to realize the pupil connection, the optical structure of the collimator lens is an image-space telecentric structure. Along the propagating direction of the incident light, set coaxially in sequence: aperture stop STOP, flat glass 0, biconvex positive lens 1, meniscus negative lens 2, meniscus negative lens 3, meniscus positive lens 4, meniscus negative lens 5, Biconvex positive lens 6 , meniscus positive lens 7 , meniscus positive lens 8 , meniscus negative lens 9 and meniscus positive lens 10 . The meniscus negative lens 5 and the biconvex positive lens 6 form the first doublet lens, and the meniscus positive lens 8 and the meniscus negative lens 9 form the second doublet lens.

The optical performance indicators realized in this embodiment are as follows:

The collimator lens has a focal length of 50mm, an entrance pupil diameter of 28.5mm, an F-number of 1.75, a full field of view of 12.6°, a wavelength range of 450-650nm, a front intercept of 17.5mm, and a rear intercept of 39.36mm. The F-number of the collimator lens in this embodiment meets the requirements for collecting reflected light from the micromirror array, and the front and rear intercepts meet the requirements for the assembly distance of the IMS system, without introducing additional optical components, making the system compact and without loss of luminous flux.

Specific lens parameters are shown in the table below:

FIG. 3 is a diagram of the modulation transfer function of the collimator lens in this embodiment. At the Nyquist frequency of 22 lp/mm, the modulation transfer functions of each field of view are higher than 0.6, and the imaging quality is relatively high. FIG. 4 is a field curvature and distortion diagram of the collimating lens in this embodiment, and it can be seen that the distortion value is less than 0.8% at the maximum field of view. FIG. 5 is the chromatic focus shift curve of the collimating lens in this embodiment, it can be seen that this embodiment has corrected the primary chromatic aberration. Applying this embodiment to an IMS spectral imaging system, Fig. 6 is a distribution diagram of the central coordinates of each sub-aperture of the aperture array formed by the projection of the aperture stop. It can be seen that after modulation by the collimating lens proposed in this embodiment, the projection positions of the sub-apertures are close to The design value, the maximum deviation value is only 0.38mm, and the collimated beams of each sub-aperture and the subsequent dispersive imaging module can be well coupled.

The above-mentioned embodiments are only preferred embodiments of the present invention, but not all embodiments. The optical design software used in the present invention can be any optical design software such as ZEMAX and CODEV. The method for calculating the design parameters of the collimating lens provided by the invention can be applied to IMS spectral imaging systems with other parameters.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other. As for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and for the related information, please refer to the description of the method part.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (1)

1. A collimating lens for an IMS spectral imaging system with a large aperture and long intercept, characterized in that the collimating lens is arranged coaxially along the direction of incident light propagation: aperture stop, flat glass, first biconvex positive lens , the first meniscus negative lens, the second meniscus negative lens, the first meniscus positive lens, the third meniscus negative lens, the second biconvex positive lens, the second meniscus positive lens, the third meniscus positive lens, The fourth meniscus negative lens and the fourth meniscus positive lens; wherein, the third meniscus negative lens and the second biconvex positive lens form the first doublet lens; the third meniscus positive lens and the fourth The meniscus negative lens forms the second doublet; The focal length of the collimating lens is 50mm, and the F number is ≤1.77; The front intercept of the collimating lens is equal to the distance between the front surface of the first biconvex positive lens and the subsequent dispersion imaging module, and the front intercept of the collimating lens is not less than 15mm; The back intercept of the collimating lens is equal to the distance between the rear surface of the fourth meniscus positive lens and the micromirror array, and the back intercept of the collimating lens is not less than 35 mm.

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