Optical grating-lens array spectral imaging method

Abstract

The invention discloses a grating-lens array spectral imaging method, and particularly relates to the technical field of spectral imaging, the grating-lens array spectral imaging method comprises a focusing lens group, a mask, a micro-lens array, a grating-lens array and an image plane which are sequentially arranged along the light propagation direction, scene information is collected by the focusing lens group, focused at the mask and collimated by the micro-lens array, and the image plane is obtained. And the light is diffracted and focused on an image plane by the grating-lens array. A grating-lens array element is designed, a transmission type plane grating and a single-face micro-lens array are glued, independent spectral dispersion and imaging are carried out on parallel incident light, a diffraction element and a focusing device are integrated, and two-dimensional space information and spectral information of multi-view-field light can be obtained at the same time; the size of a spectral imaging system is reduced to 173.62 mm, the number of optical devices of an imaging spectrometer at spectral dispersion and focusing parts is greatly reduced, and integration of the optical system is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of spectral imaging technology. More specifically, the present invention relates to a grating-lens array spectral imaging method. Background Art

[0002] A spectrometer is a measuring instrument that decomposes incident composite light according to wavelength. By analyzing the decomposed light, information such as the spatial structure, light intensity, and material composition of the photographed scene can be obtained. An imaging spectrometer can simultaneously obtain two-dimensional spatial information and one-dimensional spectral information. According to the acquisition method of two-dimensional spatial information, imaging spectrometers can be divided into swing-scanning type, push-broom type, and snapshot type. Due to its advantages such as high time resolution, low cost, and simple principle, the snapshot imaging spectrometer has become the main research direction of imaging spectrometers.

[0003] Existing imaging spectrometers use gratings and prisms as dispersive elements to expand the spectrum of light, and use an additional focusing lens group to image the spectrum, resulting in a relatively large volume of the imaging spectral system, which is not conducive to calibration, integration, and movement, seriously restricting the portable development and use of imaging spectrometers. To ensure the consistency and accuracy of the dispersion effect, dispersive elements such as gratings and prisms require light to be incident at the same angle, resulting in the fact that existing imaging spectrometers can only disperse and two-dimensionally image incident light at a single incident angle, and it is difficult to simultaneously obtain the spectral and spatial information of light at multiple field angles. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention designs a grating-lens array element and provides a grating-lens array spectral imaging method.

[0005] To achieve the above object, the present invention provides the following technical solution: A grating-lens array spectral imaging method, including a focusing lens group, a mask 10, a microlens array 11, a grating-lens array 12, and an image plane 13 arranged in sequence from left to right in the light incident direction. Multi-view scene information is collected by the focusing lens group, filtered by the mask 10, and collimated by the microlens array 11. The formed parallel microbeams are diffracted by the grating-lens array 12 and focused at the image plane 13; the focusing lens group is a projection lens, and the focusing lens group includes nine lenses, namely lens 1, lens 2, lens 3, lens 4, lens 5, lens 6, lens 7, lens 8, and lens 9.

[0006] As a further improvement of the technical solution of the present invention, among the nine lenses in the focusing lens group, the refractive index nd of at least one lens is >1.8, and the Abbe number Vdl of at least one lens is <40.

[0007] The mask 10 is made by punching a light-impermeable metal copper sheet. The diameter of the sub-aperture is 50 nm, and the center-to-center spacing of the apertures is 0.7 mm. It is placed at the rear focal plane of the focusing lens group and the front focal plane of the microlens array 11 to perform field screening on the converging light, and only the light at the center position of the sub-lenses of the microlens array is retained, so as to ensure that the microlens array 11 can collimate the incident light into parallel microbeams in the same direction as the principal optical axis.

[0008] As a further improvement of the technical solution of the present invention, the microlens array 11 is arranged by 25×25 plano-convex lenses with consistent parameters. The material of the plano-convex lens is F_SILICA, the thickness is 1.2 mm, the diameter is 0.7 mm, and the radius of curvature is 1.14 mm. It is used to collimate the incident light and control the beam size, so that the light enters the grating-lens array 12 parallelly.

[0009] As a further improvement of the technical solution of the present invention, the grating-lens array 12 is formed by gluing a transmission plane grating and a single-sided microlens array. The size is 17.5×17.5×0.8 mm. The material of the transmission plane grating is K7, the grating constant is 1250 nm, the thickness is 0.3 mm. The single-sided microlens array is arranged by 25×25 sub-lenses. The material of the sub-lenses is E-FDS3, the diameter is 0.7 mm, the thickness is 0.5 mm, and the radius of curvature is 1.05 mm. It is placed behind the microlens array 11 at an inclined angle of -26°. The sub-lenses correspond to the incident parallel microbeams one by one, so that the diffracted beams are independently focused, realizing independent spectral dispersion and imaging of light rays at multiple field angles.

[0010] The beneficial effects of the present invention: 1. Realize the light miniaturization of the imaging spectrometer. The present invention designs a grating-lens array element, glues a transmission plane grating and a single-sided microlens array, performs independent diffraction and focusing on the incident parallel microbeams, realizes light dispersion and spectral imaging at the same time, cancels the spectral imaging module in the traditional imaging spectrometer, reduces the size of the imaging spectrometer to 173.62 mm, simplifies the optical path complexity, and is easy to integrate with detectors such as CCD or CMOS. 2. Realize multi-field-angle imaging of the imaging spectrometer. The present invention uses a focusing lens group to focus incident light at multiple field angles to the focal plane with low field curvature characteristics, selectively transmits and collimates specific field-angle light through the mask and the microlens array, obtains multiple microbeams parallel to the principal optical axis, and the grating-lens array element performs independent diffraction and imaging on the parallel microbeams to obtain multi-spectral images with a field angle of 26.6°. Description of the Drawings

[0012] Figure 1 It is the overall simulation diagram of the optical structure of the present invention.

[0013] Among them, 1 is the first lens; 2 is the second lens, 3 is the third lens; 4 is the fourth lens; 5 is the fifth lens; 6 is the sixth lens; 7 is the seventh lens; 8 is the eighth lens; 9 is the ninth lens; 10 is the mask; 11 is the microlens array; 12 is the grating-lens array; 13 is the image plane.

[0014] Figure 2 It is the optical path diagram of the mask, microlens array and grating-lens array. Specific embodiments

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] As shown in the attached Figure 1 The grating-lens array spectral imaging method shown includes a focusing lens group, a mask 10, a first microlens array 11, a grating-lens array 12, and an image plane 13 arranged in sequence from left to right in the light incident direction. Scene information is collected by the focusing lens group, filtered by the mask 10, and collimated by the microlens array 11. The formed parallel microbeams are diffracted by the grating-lens array 12 and focused on the image plane 13; the focusing lens group is a projection lens, and the focusing lens group includes nine lenses, which are lens 1, lens 2, lens 3, lens 4, lens 5, lens 6, lens 7, lens 8, and lens 9 in sequence. Preferably, among the nine lenses in the focusing lens group, at least one lens has a refractive index nd > 1.8 and at least one lens has an Abbe number Vdl < 40. The specific parameters of each lens are shown in the following table.

[0017] Surface R value (mm) Thickness (mm) Nd Vd S1 55.72 9.05 1.81 40.61 S2 24.51 9.05 S3 -55.18 2.00 1.69 49.23 S4 38.36 10.97 1.73 28.23 S5 -75.43 32.85 S6 44.41 5.26 1.72 29.51 S7 17.80 7.32 1.71 53.87 S8 -104.22 0.21 S9 35.90 2.55 1.52 64.21 S10 42.26 24.36 S11 -18.09 2.11 1.72 29.51 S12 91.93 2.59 S13 -50.33 4.70 1.71 53.87 S14 -27.91 0.96 S15 108.18 10.15 1.56 47.09 S16 -32.05 0.20 S17 34.62 5.72 1.69 54.86 S18 69.34 5.22 S19 Infinity 21.73 1.52 64.21 S20 Infinity 6.47 Among them, the R value refers to the radius of curvature of the surface, and the thickness refers to the on-axis distance from the current surface to the next surface. For example, the thickness of surface S1 is the distance from S1 to S2, which may be the on-axis thickness of the medium or the lens, or the on-axis air gap between them. Nd and Vd are the refractive index and Abbe number of the material respectively.

[0018] As the image segmentation and collimation module, the specific parameters of the mask 10 and the microlens array 11 are shown in the following table. The mask 10 is placed at the back focal length of the focusing lens group to segment the focused incident light, allow appropriate field-of-view light to pass through, and collimate it into parallel microbeams parallel to the principal optical axis by the microlens array 11.

[0019] Surface R value (mm) Thickness (mm) Material S1 Infinity 0.10 MIRROR S2 Infinity 1.50 S3 Infinity 1.20 F_SILICA S4 -1.14 6.00 Among them, S1 and S2 are the mask 10, S3 and S4 are the surfaces of the microlens array 11. The R value represents the curvature radius of a single sub-lens of the lens array. The microlens array 11 is arranged by 25×25 plano-convex sub-lenses with consistent parameters, and the diameter of the sub-lens is 0.7 mm. The mask is made by punching a light-impermeable copper sheet, and its sub-aperture diameter is 50 nm, and the center distance between the apertures is 0.7 mm. During the installation process, the apertures of the mask 10 correspond one by one to the centers of the sub-units of the first microlens array 11.

[0020] The grating-lens array 12 is the core of the present invention and undertakes the functions of diffraction and focusing. The specific parameters are shown in the following table. The present invention designs a new type of optical element, gluing a transmissive planar rectangular grating and a single-sided microlens array. The single-sided microlens array has the same number of sub-lenses as the microlens array 11, the same diameter of the sub-lenses, and they correspond one by one. Any microbeam parallelly emitted from the microlens array 11 is diffracted by the grating-lens array 12 and independently focused by the corresponding sub-lens, forming strip-shaped rainbow diffraction fringes on the image plane 13. The grating-lens array 12 simultaneously completes the functions of diffraction and focusing, realizes independent spectral dispersion and imaging of light rays at multiple field angles, cancels the spectral focusing module in the traditional imaging spectrometer, greatly reduces the size of the imaging spectrometer, lightens the weight of the spectrometer, and achieves the purpose of light and miniaturized design of the imaging spectrometer.

[0021] Surface R value (mm) Thickness (mm) Material S1 Infinity 0.30 K7 S2 Infinity 0.50 E-FDS3 S3 -1.05 1.00 S4 Infinity Among them, S1, S2, and S3 are the surfaces of the grating-lens array 12. The R value represents the curvature radius of a single sub-lens of the lens array, and it is placed at an inclination of -26° around the X-axis. The grating constant of the grating-lens array 12 used in the present invention is 1250 nm, and the microlens array is a 25×25 two-dimensional lens array, and the diameter of its sub-lens is 0.7 mm; S4 is the image plane 13.

[0022] As attached Figure 2 As shown, the spectrometer provided by the present invention adopts a new type of diffractive and focusing optical element. By using the grating-lens array 12, the spectral focusing module in the traditional imaging spectrometer can be cancelled, realizing a light and miniaturized design, which is convenient for integration. The overall length of the spectrometer is 173.62 mm, and the length of the diffraction and focusing part is 1.8 mm.

[0023] Working principle: The present invention provides a novel dispersion element integrating diffraction and focusing, namely, a grating-lens array. This element is formed by gluing a transmissive diffraction grating and a single-sided microlens array. With the help of a projection lens, multi-field incident light is focused onto the mask 10 plane. By using the combination of the mask 10 and the microlens array 11, appropriate field-of-view light is selected and collimated into multiple parallel microbeams emerging in the same direction. The grating-lens array 12 element performs independent diffraction on these microbeams and focuses them onto the image plane 13, realizing the dispersion of multi-field light. Since the grating-lens array 12 element is small in size and the spectral focusing module in the imaging spectrometer can be omitted, it can be integrated with sensors such as CCD and CMOS, significantly reducing the size of the imaging spectrometer and completing the lightweight and miniaturized design of the imaging spectrometer.

[0024] In summary, the spectral imaging system of the grating-lens array proposed by the present invention adopts a novel diffraction and focusing optical element, can eliminate the spectral focusing module in the traditional imaging spectrometer, realizes spectral imaging of multi-field light and lightweight and miniaturized design, and is convenient for integration.

[0025] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A grating-lens array spectral imaging method, characterized in that: The invention comprises a focusing lens group, a mask 10, a microlens array 11, a grating-lens array 12 and an image plane 13 which are arranged in sequence from left to right in the direction of incident light. Multi-view scene information is collected by the focusing lens group, filtered by the mask 10, and collimated by the microlens array 11. The formed parallel micro-light beams are diffracted by the grating-lens array 12 and focused on the image plane 13. The focusing lens group is a projection lens, and the focusing lens group comprises nine lenses, namely, lens 1, lens 2, lens 3, lens 4, lens 5, lens 6, lens 7, lens 8 and lens 9.

2. The grating-lens array spectral imaging method according to claim 1, characterized in that: Among the nine lenses in the focusing lens group, the refractive index nd of at least one lens is greater than 1.8, and the Abbe number Vdl of at least one lens is less than 40.

3. The grating-lens array spectral imaging method according to claim 1, characterized in that: The mask 10 is made of a light-proof metal copper sheet with holes, the sub-aperture diameter is 50nm, the aperture center spacing is 0.7mm, and is placed at the rear focal plane of the focusing lens group and the front focal plane of the microlens array 11 to perform field screening on the converged light and only retain the light at the center position of the sub-lens of the microlens array to ensure that the microlens array 11 can collimate the incident light into a parallel micro-beam in the same direction as the main optical axis.

4. The grating-lens array spectral imaging method according to claim 1, characterized in that: The microlens array 11 is composed of 25*25 plano-convex lenses with consistent parameters. The plano-convex lenses are made of F_SILICA, have a thickness of 1.2 mm, a diameter of 0.7 mm, and a curvature radius of 1.14 mm. They are used to collimate incident light and control the beam size so that the light enters the grating-lens array 12 in parallel.

5. The grating-lens array spectral imaging method according to claim 1, characterized in that: The grating-lens array 12 is formed by gluing a transmission plane grating and a single-sided microlens array, with a size of 17.5*17.5*0.8mm, wherein the transmission plane grating is made of K7, the grating constant is 1250nm, and the thickness is 0.3mm; the single-sided microlens array is composed of 25*25 sub-lenses arranged, the sub-lenses are made of E-FDS3, the diameter is 0.7mm, the thickness is 0.5mm, the radius of curvature is 1.05mm, and it is placed behind the microlens array 11 at an inclination angle of -26°.

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