A compact imaging spectrometer for single-exposure imaging

Abstract

The application discloses a compact imaging spectrometer for single-exposure imaging, and belongs to the technical field of imaging spectrometers.The application sequentially comprises a primary imaging objective, a field diaphragm, a beam shaping mirror, an aperture diaphragm array, a filter array, a lens group array, a focusing mirror and a detector along an optical path.The primary imaging objective is used for performing primary imaging on a target object, and the field diaphragm is inserted at a primary image surface.The aperture diaphragm array is used for dividing the aperture of the system.The application adopts the aperture diaphragm array in combination with filter light splitting in the imaging spectrometer, so that a plurality of spectral images can be captured by using only one detector in a single-exposure process, and the problems of low time resolution or complex image solving algorithm of a traditional imaging spectrometer are solved.The primary imaging objective is used, and the field diaphragm is used at the primary image surface, so that stray light is suppressed, the utilization rate of the detector is improved, and the application has the advantages of high stability, compact structure and good economy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of imaging spectrometer, and relates to a compact imaging spectrometer for single-exposure imaging. BACKGROUND

[0002] With the continuous development of science and technology, people's desire to explore the nature of matter is increasingly strong, and the internal chemical composition and molecular structure of different substances are different. Therefore, the reflected light and radiated light of the light incident on the surface of the object will exhibit different spectral characteristics. However, people not only want to obtain the spectral information of the target, but also want to obtain the spatial position information of the target. Therefore, the imaging spectrometer emerges as the times require. The imaging spectrometer refers to an instrument that combines imaging and spectral methods to obtain spatial and spectral information of an object. The imaging spectrometer has important applications in imaging medical treatment, agriculture, mineral exploration, monitoring and other fields.

[0003] At present, optical systems are constantly pursuing higher performance and lower cost, and imaging spectrometers are no exception. Since the observation target is dynamically changing, the imaging spectrometer is often required to have high temporal resolution. From the current imaging spectrometer technology, the classification of the imaging spectrometer has various ways. According to the imaging principle, the imaging spectrometer can be divided into swing-scan type imaging spectrometer, push-scan type imaging spectrometer, staring type imaging spectrometer and snapshot type imaging spectrometer. Among them, the swing-scan type and push-scan type imaging spectrometer need to move the mirror group or the target object, which requires a precise electric control system and a complex mechanical device. The traditional staring type imaging spectrometer needs a filter wheel or a modulator to change the observation wavelength of the system, which is not easy to realize real-time imaging. Although the snapshot type imaging spectrometer can overcome the shortcomings of the above three types of imaging spectrometers, the data volume is large, and subsequent image processing is required to restore the image that conforms to the visual habit of the human eye.

[0004] In 2014, Liao et al. of Beijing University of Technology proposed a portable eight-channel parallel multispectral imager in “Radiometric Calibration of an Eight-Channel Parallel Multispectral Imager”. The entire system is composed of eight channels of narrow-band filters, optical lenses, digital color CCD cameras, real-time data acquisition and storage, etc., and uses the principle of narrow-band filter imaging. However, the entire system uses eight color digital camera lenses, which greatly increases the volume, weight and cost of the system. In 2021, patent CN2019105655106 discloses a dual-channel interference type hyperspectral imaging device and method, which uses two sets of birefringent shears to obtain two different shear interference patterns in one push-scan imaging, realizing dual-channel imaging. However, it is necessary to use the relationship that the spectral pattern and the interference pattern are Fourier spectrum transform of each other, and through a complex calculation process, the spectral image that conforms to the visual habit of the human eye can be obtained. SUMMARY

[0005] The application aims to provide a compact imaging spectrometer for single-exposure imaging, which adopts an aperture diaphragm array combined with filter light splitting to capture multiple spectral images using only one detector in a single-exposure process, and solves the problems of low time resolution and complex image solving algorithm of traditional imaging spectrometers.

[0006] The application aims to achieve the above-mentioned purpose through the following technical solutions.

[0007] The application discloses a compact imaging spectrometer for single-exposure imaging, which sequentially comprises a primary imaging objective, a field diaphragm, a beam shaping mirror, an aperture diaphragm array, a filter array, a lens group array, a focusing mirror and a detector along an optical path.

[0008] The primary imaging objective is used to perform primary imaging on a target object, and the field diaphragm is inserted at a primary image plane.

[0009] The field diaphragm is arranged at the image plane of the primary imaging objective, and the peripheral shape of the primary image is adjusted to be rectangular. The central part of the field diaphragm is a rectangular hole for adjusting the peripheral shape of the primary image, and the size of the central light transmission rectangular region is determined by the coordinates of the edge image points at the primary image plane. The field diaphragm is provided with a protrusion for cooperating with a lens barrel groove, and the edge of the rectangular image is parallel to the target surface of the detector through the cooperation of the lens barrel groove and the protrusion of the field diaphragm.

[0010] The beam shaping mirror is used to shape the light beam transmitted by the field diaphragm, and the light beam aperture is adjusted to a size that can leave installation space for the filter array and the lens group array.

[0011] The aperture diaphragm array is used to divide the aperture of the system. The pressing ring on the front surface of the filter array is the aperture diaphragm array of the system. The aperture diaphragm array comprises N 2 mechanical pressing rings, which divide the original aperture into N 2 sub-apertures, and N 2 mechanical pressing rings divide N 2 spectral channels. Through the introduction of the aperture diaphragm array, the imaging spectrometer can obtain information of all spectral channels using only one detector in a single-exposure process, thereby reducing the cost and improving the compactness of the imaging spectrometer.

[0012] The filter array comprises a plurality of filters. Different transmittance films are coated on the surfaces of the filters in the filter array, so that different regions on the detector obtain images containing different spectral information. Due to the adjustment of the light path by the primary imaging objective and the beam shaping mirror, the field angles corresponding to the different filters of the filter array are the same, so the spatial information contained in the images of the different regions on the detector is the same.

[0013] Preferably, when the mechanical pressure ring is four, the four mechanical pressure rings are symmetrically located around the optical axis. The filter array comprises four filters, which are distributed in four quadrants. The aperture of the compact imaging spectrometer for single-exposure imaging is divided into four parts by the aperture diaphragm array.

[0014] Preferably, when the mechanical pressure ring is nine, the nine mechanical pressure rings are arranged in a nine-square grid. The filter array comprises nine filters, which are distributed in the nine squares of the nine-square grid. The aperture of the compact imaging spectrometer for single-exposure imaging is divided into nine parts by the aperture diaphragm array.

[0015] The lens group array is used to adjust the position of the image divided by the aperture diaphragm array.

[0016] The focusing mirror adjusts the size and position of the image formed by the lens group array, so that the image formed by the lens group array can exactly fall on the target surface of the detector and fill the entire target surface.

[0017] The detector is used to receive image information.

[0018] In order to make the sub-channel images fill the detector after splicing and improve the utilization rate of the detector. The optical parameters and position parameters of the optical elements in the compact imaging spectrometer for single-exposure imaging are constrained by ray tracing, the optical elements including a primary imaging objective, a beam shaping mirror, a filter array, a lens group array, and a focusing mirror. The method for constraining the optical parameters and position parameters of the optical elements is as follows:

[0019] Step one: equivalent the primary imaging objective and the beam shaping mirror to a beam shaping system. The filter array has little effect on the light path during ray tracing; the filter array is ignored during ray tracing by using an approximation method.

[0020] Step two: set the optical parameters and position parameters of the beam shaping system, the lens group array, and the focusing mirror. Determine the image center offset Δ y by formula (1), and determine whether the set optical parameters and position parameters of the beam shaping system, the lens group array, and the focusing mirror meet the use conditions by whether the evaluation function F m in formula (2) is equal to zero. If the evaluation function F mIf not equal to zero, the optical parameters and position parameters of the beam shaping system, the lens array and the focusing mirror are reset; if the evaluation function F in formula (2) is equal to zero, step three is continued. m If not equal to zero, the optical parameters and position parameters of the beam shaping system, the lens array and the focusing mirror are reset; if the evaluation function F in formula (2) is equal to zero, step three is continued.

[0021]

[0022] Wherein, Δ is the eccentricity of the lens array, l'3 is the distance between the focusing mirror and the detector, f1, f2 and f3 are the focal lengths of the beam shaping system, the lens array and the focusing mirror respectively, d 12 is the distance between the beam shaping system and the lens array.

[0023] The evaluation function F is defined as m The expression is as follows:

[0024]

[0025] Wherein, the meaning of the symbol || is to take the absolute value, x is the length of the detector target surface, F m is the comprehensive reaction of the detector utilization rate of the imaging spectrometer. F m The smaller the value of F is, the higher the detector utilization rate of the imaging spectrometer is.

[0026] Step three, the optical parameters and position parameters of the beam shaping system, the lens array and the focusing mirror set in step two are brought into formula (3). Through formula (3), the focal length f of the imaging spectrometer at this time is determined. If the focal length of the imaging spectrometer at this time meets the design requirements, the set optical parameters and position parameters of the beam shaping system, the lens array and the focusing mirror are output as the structure parameters of the imaging spectrometer; if the focal length of the imaging spectrometer at this time does not meet the preset requirements, step two is repeated, and the optical parameters and position parameters of the beam shaping system, the lens array and the focusing mirror are reset.

[0027]

[0028] Wherein, d 23 is the distance between the lens array and the focusing mirror.

[0029] The working method of the compact imaging spectrometer for single-exposure imaging disclosed by the application is as follows:

[0030] The light emitted by the target object passes through the primary imaging objective lens in sequence, and the peripheral shape of the primary image is adjusted to be rectangular through the field diaphragm. The primary image adjusted to be rectangular is emitted by the beam shaping mirror as a square beam, and the square beam is divided into N 2The block contains light with the same information. The light containing the same spatial information passes through the filter array located in each sub-channel, and the light containing the same spatial information and different spectral information after the filter array continues to propagate backward based on the spectral channel construction of the incident light by the filter array. The propagation direction is adjusted by the lens array and the focusing mirror, so that the sub-channel image surface splicing completely covers the entire detector target surface. The image obtained by the detector is directly exported to the computer, that is, an image with the same spatial information and different spectral information of the target object is obtained, and multiple spectral images are captured by single exposure.

[0031] Advantages:

[0032] 1. The compact imaging spectrometer for single exposure imaging disclosed by the application forms multiple spectral channels by the aperture diaphragm array combined with the filter array, realizes the information of all spectral channels by single exposure, directly obtains multiple images containing the same spatial information in line with the visual habits of human eyes, realizes the simultaneous imaging of multiple spectral channels by using only one detector, and reduces the volume, weight and cost of the system.

[0033] 2. The compact imaging spectrometer for single exposure imaging disclosed by the application realizes the suppression of stray light by setting the structural form of the one-time imaging objective, the field diaphragm, the beam shaping mirror and the aperture diaphragm array, and significantly improves the target recognition probability of the monitoring and tracking system.

[0034] 3. According to the ideal optical system imaging theory, the compact imaging spectrometer for single exposure imaging disclosed by the application uses the ray tracing method to establish a determination method for the structural parameters of the imaging spectrometer, actively balances the image surface center offset of the imaging spectrometer and the design requirements by using the focal length and position of each optical structure, and realizes the determination of the structural parameters of the imaging spectrometer.

[0035] 4. The compact imaging spectrometer for single exposure imaging disclosed by the application sets the center of the field diaphragm as a rectangular hole, realizes the maximum reduction of pixel waste between spectral channels without aliasing. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is an optical structure schematic diagram of the compact imaging spectrometer for single exposure imaging disclosed by the application;

[0037] Figure 2 It is a ray tracing optical path schematic diagram of the compact imaging spectrometer for single exposure imaging provided by the application;

[0038] Figure 3 It is a structural parameter selection flowchart of the compact imaging spectrometer for single exposure imaging provided by the application;

[0039] Figure 4 A filter distribution diagram of a compact imaging spectrometer for single-exposure imaging provided by the present application is shown in the figure;

[0040] Figure 5 An imaging effect diagram of a compact imaging spectrometer for single-exposure imaging provided by the present application is shown in the figure;

[0041] In the figure: 1-target object, 2.1-first imaging objective, 2.2-beam shaping mirror, 2-beam shaping system, 3-field stop, 4-aperture stop array, 5-filter array, 6-lens group array, 7-focusing mirror, 8-detector. DETAILED DESCRIPTION

[0042] In order to better illustrate the purposes and advantages of the present application, the present application is described in detail below in combination with the accompanying drawings and examples.

[0043] As shown in the accompanying Figure 1 A compact imaging spectrometer for single-exposure imaging disclosed by the present application includes a first imaging objective 2.1, a field stop 3, a beam shaping mirror 2.2, an aperture stop array 4, a filter array 5, a lens group array 6, a focusing mirror 7, and a detector 8.

[0044] The first imaging objective 2.1 is used to image the target object 1 once, and is used to insert the field stop;

[0045] The field stop 3 is placed at the image plane of the first imaging objective 2.1, so that the image of each channel is rectangular, and after splicing, it covers the entire detector target surface, improving the utilization rate of the detector. At the same time, the introduction of the field stop 3 effectively suppresses the stray light of the system, improving the imaging effect of the system;

[0046] The beam shaping mirror 2.2 is used to perform beam shaping on the light transmitted by the field stop 3. The first imaging objective 1 and the beam shaping mirror 2.2 jointly adjust the aperture of the incident light beam, providing sufficient space for mechanical installation of the filter array 5 and the lens group array 6;

[0047] The filter array 5 includes four different filters, which are distributed in four quadrants, as shown in the accompanying Figure 4 The four filters have four different wavelength selection characteristics, which are used to select the spectral range of different channels, generating different spectral channels;

[0048] The lens group array 6 includes four lens groups, which are located immediately behind the four filters in the filter array 5. It is used to adjust the image position after the filter array 5 is divided;

[0049] The focusing lens 7 is used to adjust the size of the image formed by the lens array 6 to match the size of the target surface of the detector 8.

[0050] The detector 8 is used to receive the two-dimensional spectral image information, and the imaging effect is shown in Fig. 4. Figure 5 Since the detector used is an infrared detector, the picture seen is black and white, but the spectral information contained in each channel is different.

[0051] The parameters determined according to the constraint method of the optical parameters and the position parameters of the optical elements in the imaging spectrometer disclosed in the embodiment are as follows:

[0052] The focal length f1 of the beam shaping system 2, the focal length f2 of the lens array 6, the focal length f3 of the focusing lens 7, the eccentricity Δ of the lens array 6, the distance l'3 between the focusing lens 7 and the detector 8, the distance d 12 between the beam shaping system 2 and the lens array 6, and the distance d 23 between the lens array 6 and the focusing lens 7, and the length x of the target surface of the detector selected are shown in Table 1. The focal length f1 of the beam shaping system 2, the focal length f2 of the lens array 6, the focal length f3 of the focusing lens 7, the eccentricity Δ of the lens array 6, the distance l'3 between the focusing lens 7 and the detector 8, the distance d 12 between the beam shaping system 2 and the lens array 6, and the distance d 23 between the lens array 6 and the focusing lens 7, and the length x of the target surface of the detector selected are not limited to those shown in Table 1, and can be adjusted according to actual needs by those skilled in the art.

[0053] Table 1 Optical parameters and position parameters of optical elements of the imaging spectrometer

[0054] Parameter f1 f2 f3 Δ [l'3] d 12 ]]> d 23 ]]> x value -210 75 50 5.5 27.27 10 15 16

[0055] The specific working method of the imaging spectrometer disclosed in the embodiment is as follows:

[0056] A target object 1 is set, and the light emitted by the target object 1 passes through the first imaging objective lens 2.1, the field diaphragm 3 and the beam shaping lens 2.2 in sequence, becomes a square light beam, and hits the aperture diaphragm array 4, and is divided into four pieces of light containing the same information. After passing through the filter array 5, the light waves are wavelength-screened. Then, after adjustment by the lens array 6 and the focusing lens 7, the entire target surface of the detector can be completely covered. The image obtained by the detector is directly exported to a computer, and an image having the same spatial information and different spectral information of the target object 1 is obtained, and multiple spectral images are captured in a single exposure.

[0057] The above detailed description of the specific description, the purpose, technical scheme and beneficial effects of the application are further described in detail, it should be understood that the above description is only a specific embodiment of the application, and is not used to limit the protection scope of the application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A compact imaging spectrometer for single-exposure imaging, characterized by: The optical path sequentially comprises a primary imaging objective lens (2.1), a field diaphragm (3), a beam shaping mirror (2.2), an aperture diaphragm array (4), a filter array (5), a lens group array (6), a focusing mirror (7), and a detector (8); The primary imaging objective lens (2.1) is used for imaging a target object (1) and inserting a field diaphragm at a primary image plane; The field diaphragm (3) is arranged at the image plane of the primary imaging objective lens (2.1) and adjusts the peripheral shape of the primary image to a rectangle; the middle part of the field diaphragm (3) is a rectangular hole for adjusting the peripheral shape of the primary image, and the size of the central light transmission rectangular region is determined by the coordinates of the edge image points at the primary image plane; the field diaphragm (3) is provided with a protrusion for cooperating with a lens barrel groove, and the protrusion of the field diaphragm (3) and the lens barrel groove make the edges of the rectangular image parallel to the target surface of the detector; The beam shaping mirror (2.2) is used for shaping the light beam from the field diaphragm (3) and adjusting the light beam aperture to a size capable of leaving installation space for the filter array (5) and the lens group array (6); The aperture diaphragm array (4) is used for segmenting the aperture of the system; the pressing ring in front of the filter array (5) is the aperture diaphragm array (4) of the system; the aperture diaphragm array (4) comprises N 2 mechanical pressing rings, and the original aperture is split into N 2 sub-apertures; N 2 spectrum channels are segmented by the N 2 mechanical pressing rings; by introducing the aperture diaphragm array (4), the imaging spectrometer can obtain information of all spectrum channels by using only one detector in a single exposure process, so that the cost is reduced and the compactness of the imaging spectrometer is improved. The filter array (5) comprises a plurality of filters; different transmittance films are coated on the surfaces of the filters in the filter array (5) to make different regions on the detector obtain images containing different spectral information; due to the adjustment of the light ray direction by the primary imaging objective lens (2.1) and the beam shaping mirror (2.2), the field angles corresponding to different filters in the filter array (5) are the same, so the spatial information contained in the images of different regions on the detector is the same; The lens group array (6) is used for adjusting the image position of the image divided by the aperture diaphragm array (5); The focusing mirror (7) adjusts the size and position of the image formed by the lens group array (6) so that the image formed by the lens group array (6) can exactly fall on the target surface of the detector (8) and fill the entire target surface; The detector (8) is used for receiving image information.

2. A compact imaging spectrometer for single-shot imaging according to claim 1, characterized in that: The light emitted by the target object (1) passes through the primary imaging objective (2.1) in turn, the peripheral shape of the primary image is adjusted to be rectangular by the field diaphragm (3), and the peripheral shape of the primary image is adjusted to be rectangular. The rectangular primary image exits the square light beam through the beam shaping mirror (2.2), the square light beam hits the aperture diaphragm array (4), and the light beam is divided into N 2 The block contains the same information; the light containing the same spatial information passes through the filter array (5) located in each sub-channel, the spectral channel is constructed based on the incident light of the filter array (5), and the light containing the same spatial information and different spectral information continues to propagate after passing through the filter array (5); the transmission direction is adjusted through the lens array (6) and the focusing mirror (7), so that the sub-channel image surface is completely paved after splicing the entire detector target surface; the image obtained by the detector is directly exported to the computer, that is, the image with the same spatial information and different spectral information of the target object (1) is obtained, and a plurality of spectral images are captured by single exposure.

3. A compact imaging spectrometer for single-shot imaging according to claim 2, wherein: When the mechanical pressure ring is four, the four mechanical pressure rings are symmetrically located around the optical axis; the filter array (5) comprises four filters distributed in four quadrants; and the aperture diaphragm array (4) divides the aperture of the compact imaging spectrometer for single exposure imaging into four parts.

4. A compact imaging spectrometer for single-shot imaging according to claim 2, wherein: When the mechanical pressure ring is nine, the nine mechanical pressure rings are arranged in a nine-grid form; the filter array (5) comprises nine filters distributed in the nine grids of the nine-grid form; and the aperture diaphragm array (4) divides the aperture of the compact imaging spectrometer for single exposure imaging into nine parts.

5. A compact imaging spectrometer for single-shot imaging according to claim 2, 3 or 4, characterised in that: The optical parameters and position parameters of the optical elements in the compact imaging spectrometer for single exposure imaging are constrained by the ray tracing method, the optical elements comprising the primary imaging objective lens (2.1), the beam shaping mirror (2.2), the filter array (5), the lens group array (6), and the focusing mirror (7); and the method for constraining the optical parameters and position parameters of the optical elements is as follows: Step one, equivalent the primary imaging objective (2.1) and the beam shaping mirror (2.2) to the beam shaping system (2); the filter array (5) has little effect on the light path in the ray tracing process; in the ray tracing process, the filter array (5) is ignored by using the approximation method; Step 2: Set the optical and positional parameters of the beam shaping system (2), lens array (6), and focusing lens (7); determine the image plane center offset Δ using formula (1). y ; and through the evaluation function F in formula (2) m Whether it equals zero, determine whether the optical parameters and position parameters of the set beam shaping system (2), lens array (6) and focusing lens (7) meet the usage conditions; If the evaluation function F in formula (2) m If the value is not zero, then reset the optical and positional parameters of the beam shaping system (2), lens array (6), and focusing lens (7); If the evaluation function F in formula (2) m If the result is zero, proceed to step three. where Δ is the eccentricity of the lens array (6), l'3 is the distance between the focusing lens (7) and the detector (8), f1, f2, f3 are the focal lengths of the beam shaping system (2), the lens array (6) and the focusing lens (7) respectively, d 12 is the distance between the beam shaping system (2) and the lens array (6); Defining the evaluation function F m The expression is as follows: Wherein, the meaning of || symbol is to take absolute value, x is the length of the detector target surface, F m is the comprehensive reaction of the utilization rate of the imaging spectrometer detector (8) ; F m The smaller the value of F, the higher the utilization rate of the imaging spectrometer detector (8). Step three, bring the optical parameters and position parameters of the beam shaping system (2), the lens group array (6) and the focusing mirror (7) set in step two into formula (3); through formula (3), the focal length f of the imaging spectrometer at this time is determined; if the focal length of the imaging spectrometer at this time meets the design requirements, the optical parameters and position parameters of the set beam shaping system (2), the lens group array (6) and the focusing mirror (7) are output as the structure parameters of the imaging spectrometer; if the focal length of the imaging spectrometer at this time does not meet the preset requirements, repeat step two to reset the optical parameters and position parameters of the beam shaping system (2), the lens group array (6) and the focusing mirror (7); where d 23 is the distance between the lens array (6) and the focusing mirror (7).

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