A small-size wide-band hyperspectral imager

Abstract

The application provides a small-size wide-band hyperspectral imager, which is used to solve the technical problem that the existing wide-band spectral imager for visible near-infrared to short-wave infrared cannot meet the increasingly stringent imaging requirements. The small-size wide-band hyperspectral imager adopts an off-axis two-mirror type front optical assembly and a spectrometer assembly in the form of a free-form surface mirror, light path multiplexing and folded axis, which greatly reduces the number of lenses used, effectively compresses the length of the spectrometer, and greatly compresses the volume and weight of the spectral imager. In addition, the front surface and the rear surface of the first lens and the second lens in the spectrometer assembly are coated with a wide-band antireflection film for visible near-infrared to short-wave infrared according to the angle of light, which, combined with a wide-band cryogenic detector, can realize wide-band detection from visible near-infrared to short-wave infrared, greatly reducing the complexity and adjustment difficulty of the detector assembly and the circuit assembly.

Description

Technical Field

[0001] This invention relates to hyperspectral imagers, and more specifically to a compact, wide-band hyperspectral imager. Background Technology

[0002] Currently, wide-band spectral imagers for scenes ranging from visible and near-infrared to short-wave infrared generally come in two forms: one is a combination of two spectral imagers, where one uses a visible and near-infrared spectral imager to achieve spectral imaging in the visible and near-infrared band, and the other uses a short-wave infrared spectral imager to achieve spectral imaging in the short-wave infrared band. The other is a single front-mounted optical system plus two detectors, specifically a shared front-mounted optical system that then splits the light to two detectors to achieve wide-band imaging from visible and near-infrared to short-wave infrared. Both of these methods are no longer able to meet increasingly stringent imaging requirements in terms of spectrometer weight, size, assembly and adjustment difficulty, equipment complexity, and overall cost. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problem that existing wide-band spectral imagers for scenes, ranging from visible and near-infrared to short-wave infrared, cannot meet increasingly stringent imaging requirements, and to provide a compact wide-band hyperspectral imager.

[0004] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0005] A miniaturized broadband hyperspectral imager is characterized by including a main support plate, and front optical components, spectrometer components, detector components and circuit components mounted on the main support plate.

[0006] The front optical component includes a primary reflector and a secondary reflector; the reflecting surfaces of the primary reflector and the secondary reflector are both free-form surfaces, forming an off-axis two-reflector structure; the incident light is reflected sequentially by the primary reflector and the secondary reflector and then emitted to form the front emitted light;

[0007] The spectrometer assembly includes a slit, a first lens, a second lens, a dispersive prism, a freeform surface mirror, and a folding mirror;

[0008] The slit is positioned on the optical path of the front-emitting light and at the image plane of the front optical component; the first lens, the second lens, the dispersive prism, and the freeform surface mirror are sequentially positioned behind the slit and on the optical path of the front-emitting light; the front and rear surfaces of the slit, the first lens, and the second lens are all coated with a wide-band anti-reflection film ranging from visible near-infrared to short-wave infrared.

[0009] The outgoing light entering through the slit is transmitted sequentially through the first lens and the second lens, then refracted by the dispersive prism and enters the surface of the freeform mirror. The freeform mirror reflects the light to form reflected light. The reflected light is then refracted in the opposite direction by the dispersive prism, and then transmitted sequentially through the second lens and the first lens to form the outgoing light in the opposite direction.

[0010] The folding mirror is positioned in the optical path of the reverse-emitted light to fold the reverse-emitted light and form folded light.

[0011] The detector assembly is a cooled detector, including a detector and a cooler. The detector has a response in a wide band from visible and near-infrared to short-wave infrared, and the cooler is used to improve the signal-to-noise ratio in the wide band. The detector is placed in the optical path of the refracted light and is located at the image plane of the spectrometer assembly. It is used to receive the refracted light and perform photoelectric conversion on the refracted light to form an analog electrical signal.

[0012] The circuit assembly is electrically connected to the detector and the refrigerator, respectively, and is used to receive analog electrical signals sent by the detector and convert the analog electrical signals into digital electrical signals; at the same time, the circuit assembly is used to provide bias voltage to the detector and the refrigerator, and send control commands and cooling drive signals.

[0013] Furthermore, the front optical component also includes a first substrate, a front support frame, and a light shield;

[0014] The first substrate is mounted and fixed on the main support plate;

[0015] The front support frame is a frame structure, with its bottom fixed on the first base plate, and is provided with a primary mirror mounting position and a secondary mirror mounting position. The primary mirror and the secondary mirror are respectively installed on the primary mirror mounting position and the secondary mirror mounting position; the positions of the incident light and the front outgoing light on the front support frame are unobstructed.

[0016] The light shield is installed on the outside of the front support frame at the position corresponding to the incident light to suppress external stray light.

[0017] Furthermore, the spectrometer assembly also includes a spectrometer support frame, a first connecting cylinder, and a second connecting cylinder;

[0018] The spectrometer support frame includes a slit mounting frame, a folding mirror mounting frame, a second substrate mounted on the main support plate, and a lens mounting frame, a prism mounting frame, and a reflector mounting frame mounted on the second substrate.

[0019] The first connecting tube is a cylindrical structure that runs through the front and back, and it is mounted on a lens mounting bracket; the first lens and the second lens are sequentially mounted inside the first connecting tube;

[0020] The second connecting cylinder is a tapered cylinder, with its small end coaxially connected to the slit mounting frame and its large end coaxially connected to the front end of the first connecting cylinder via a flange;

[0021] The folding mirror mounting frame is installed on the outer wall of the second connecting cylinder;

[0022] The slit, dispersive prism, freeform surface reflector, and folding axis mirror are respectively installed on the slit mounting frame, prism mounting bracket, reflector mounting bracket, and folding axis mirror mounting frame;

[0023] A light-transmitting hole is provided on the side wall of the second connecting cylinder at the position corresponding to the folding mirror.

[0024] Furthermore, the detector assembly also includes a detector support and a third substrate;

[0025] The third substrate is mounted and fixed on the main support plate, and the detector bracket and the cooler are respectively mounted and fixed on the third substrate;

[0026] The detector is mounted on a detector bracket.

[0027] Furthermore, the primary reflector, secondary reflector, slit, and freeform surface reflector are all made of metal.

[0028] The first lens, the second lens, and the dispersive prism are all made of quartz glass.

[0029] Furthermore, the front support frame is made of the same material as the main reflector and the secondary reflector;

[0030] The reflector mounting bracket is made of the same material as the freeform surface reflector.

[0031] Furthermore, the primary reflector, secondary reflector, slit, and freeform surface reflector are all made of aluminum alloy.

[0032] Furthermore, the freeform surface shapes of the primary reflector, secondary reflector, and freeform surface reflector are all expressed using XY polynomials, and their expressions are as follows:

[0033]

[0034] in, It is the surface sagitta of the freeform surface. These are the coordinates of the freeform surface diameter. , is the curvature of the quadratic surface on the base plane. Let be the radius of curvature at the vertex. Let be the conic constant of the quadratic surface on the base plane. , is the radial and radial coordinates of a freeform surface. Let be the coefficients of each order polynomial, m be the degree of the x term in the XY polynomial, n be the degree of the y term in the XY polynomial, i = 1, 2, ..., m, j = 1, 2, ..., n.

[0035] Furthermore, the primary reflector has an aperture of 25.6 mm, a thickness of 21 mm, a radius of curvature of 60.875 mm, an eccentricity of 37 mm in the Y direction, an inclination of 36.85° in the X direction, and a spacing of 10.84 mm between the primary and secondary reflectors.

[0036] The secondary reflector has an aperture of 11.2 mm, a thickness of 8.5 mm, a radius of curvature of 36.408 mm, an eccentricity of 0 mm in the Y direction, an inclination of 36.71° in the X direction, and a distance of 48 mm between the secondary reflector and the slit.

[0037] The slit has a width of 15 μm, a length of 1 mm, and a distance of 48.2 mm between the slit and the first lens.

[0038] The first lens is a biconvex lens with an aperture of 64mm, a front surface radius of curvature of 408.7mm, a rear surface radius of curvature of 64.1mm, and a thickness of 14mm. The distance between the first lens and the second lens is 40mm.

[0039] The second lens is a concave-convex lens with the concave surface facing the object side. Its aperture is 52mm, the radius of curvature of the front surface is 50.3mm, the radius of curvature of the rear surface is 204.4mm, and the thickness is 13mm. The distance between the second lens and the dispersive prism is 27.48mm.

[0040] The dispersive prism is a concave-convex mirror with a front surface diameter of 54 mm, a rear surface diameter of 63 mm, a front surface radius of curvature of 146.38 mm, a rear surface radius of curvature of 117.69 mm, and an inclination of 7.04° in the X direction. The distance between the dispersive prism and the freeform surface mirror is 13.15 mm.

[0041] The freeform surface mirror has a diameter of 58mm, a thickness of 8mm, a radius of curvature of 149.148mm, an eccentricity of 4.04mm in the Y direction, and a tilt of 7.04° in the X direction.

[0042] The folding mirror has an aperture of 12.2 mm and a thickness of 3 mm. Its eccentricity in the Y direction is 21.57 mm, its tilt in the X direction is 45°, the distance between the folding mirror and the first lens is 24.34 mm, and the distance between the folding mirror and the image plane of the spectrometer assembly is 21.4 mm.

[0043] Compared with the prior art, the present invention has the following beneficial technical effects:

[0044] 1. The present invention provides a compact wideband hyperspectral imager, which adopts an off-axis two-mirror front optical component and a spectrometer component in the form of a freeform surface mirror + optical path multiplexing + folded axis. This not only greatly reduces the number of lenses used, but also effectively compresses the length of the spectrometer, resulting in a significant reduction in the size and weight of the spectrometer imager. In addition, the front and rear surfaces of the first and second lenses in the spectrometer component are coated with a wideband antireflection film covering the visible and near-infrared to short-wave infrared range according to the light angle. Combined with a wideband cooled detector, a wideband detection range from the visible and near-infrared to the short-wave infrared range can be achieved through a single optical system and a set of detector components, greatly reducing the complexity and assembly difficulty of the detector and circuit components.

[0045] 2. The present invention provides a compact wideband hyperspectral imager. The front optical component adopts an off-axis two-mirror structure. It is combined with a primary mirror and a secondary mirror with a free-form surface made of all metal. Not only can the aberration be well corrected by the two mirrors and the volume be reduced, but the overall thermal stability of the system is also effectively improved.

[0046] 3. The present invention provides a miniaturized wideband hyperspectral imager, wherein the detector assembly is designed as a wideband cooled detector, which not only realizes wideband detection from visible and near-infrared to short-wave infrared, but also achieves a good signal-to-noise ratio throughout the wideband by adding a cooler. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of an embodiment of a miniaturized broadband hyperspectral imager according to the present invention;

[0048] Figure 2 This is a schematic diagram of the structure of the front optical component in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the spectrometer assembly in an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the optical path transmission of the front optical component and the spectrometer component in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the detector assembly in an embodiment of the present invention;

[0052] Figure 6 Full field-of-view dot plot of this invention embodiment;

[0053] Figure 7 The modulation transfer function curve is shown for the operating wavelength of 0.4 μm in an embodiment of the present invention.

[0054] Figure 8The optical transfer function curve is shown for an embodiment of the present invention at a working wavelength of 0.7 μm.

[0055] Figure 9 The optical transfer function curve of the embodiment of the present invention at a working wavelength of 0.9 μm is shown.

[0056] Figure 10 This is an optical transfer function curve of the embodiment of the present invention at a working wavelength of 1.6 μm;

[0057] Figure 11 The optical transfer function curve of the embodiment of the present invention at a working wavelength of 1.9 μm is shown.

[0058] Figure 12 This is an optical transfer function curve for an embodiment of the present invention at a working wavelength of 2.5 μm.

[0059] The annotations in the attached figures are explained as follows:

[0060] 1-Main support plate; 2-Front optical assembly, 21-Primary reflector, 22-Secondary reflector, 23-First substrate, 24-Front support frame, 25-Light shield; 3-Spectrometer assembly, 30-Spectrometer support frame, 301-Second substrate, 302-Lens mounting frame, 303-Prism mounting frame, 304-Reflector mounting frame, 305-Slit mounting frame, 306-Folded-axis mirror mounting frame, 31-Slit, 32-First lens, 33-Second lens, 34-Dispersion prism, 35-Freeform surface reflector, 36-Folded-axis mirror, 37-First connecting cylinder, 38-Second connecting cylinder; 4-Detector assembly, 41-Detector, 42-Refrigerator, 43-Detector bracket, 44-Third substrate; 5-Circuit assembly. Detailed Implementation

[0061] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0062] like Figure 1 As shown, a miniaturized wideband hyperspectral imager includes a main support plate 1, a front optical component 2, a spectrometer component 3, a detector component 4, and a circuit component 5; wherein the front optical component 2, the spectrometer component 3, the detector component 4, and the circuit component 5 are all mounted on the main support plate 1.

[0063] like Figure 2As shown, the front optical assembly 2 includes a primary reflector 21, a secondary reflector 22, a first substrate 23, a front support frame 24, and a light shield 25. Both the primary reflector 21 and the secondary reflector 22 are freeform surface reflectors, forming an off-axis two-mirror structure. Compared to traditional transmissive systems, the off-axis two-mirror structure of the front optical assembly 2 reduces the number of mirrors by at least two while maintaining image quality, and significantly reduces light energy loss.

[0064] Specifically, the first substrate 23 is mounted and fixed on the main support plate 1, and the front support frame 24 is a frame structure, with its bottom fixed on the first substrate 23. The front support frame 24 has a primary mirror mounting position and a secondary mirror mounting position, with the primary reflector 21 and the secondary reflector 22 respectively mounted on the primary mirror mounting position and the secondary mirror mounting position. The positions on the front support frame 24 corresponding to the incident light and the front-outgoing light are unobstructed, allowing the incident light and the front-outgoing light to pass through. A light shield 25 is installed on the outside of the front support frame 24 at the position corresponding to the incident light to suppress external stray light.

[0065] External incident light is incident on the reflective surface of the main reflector 21 through the light shield 25, reflected by the main reflector 21 to the reflective surface of the secondary reflector 22, and then reflected by the secondary reflector 22 before exiting to form the front-outgoing light.

[0066] Meanwhile, the primary reflector 21, secondary reflector 22, and front support frame 24 are all made of the same material, aluminum alloy, eliminating the need to consider CTE matching issues and ensuring high thermal stability. In other embodiments of the present invention, the primary reflector 21, secondary reflector 22, and front support frame 24 may also be made of other suitable metal materials, as long as the materials of the three are kept consistent, and no limitation is made here.

[0067] like Figure 3 As shown, the spectrometer assembly 3 includes a spectrometer support frame 30, a slit 31, a first lens 32, a second lens 33, a dispersive prism 34, a freeform surface mirror 35, a folded-axis mirror 36, a first connecting cylinder 37, and a second connecting cylinder 38. The slit 31 is positioned in the optical path of the front-emitting light and is located at the image plane of the front optical assembly 2. The first lens 32, the second lens 33, the dispersive prism 34, and the freeform surface mirror 35 are sequentially positioned behind the slit 31 and in the optical path of the front-emitting light. The front-emitting light incident through the slit 31 is transmitted sequentially through the first lens 32 and the second lens 33, then refracted by the dispersive prism 34 and incident on the surface of the freeform surface mirror 35, where it is reflected to form reflected light. The reflected light is then refracted in the opposite direction by the dispersive prism 34, and then transmitted sequentially through the second lens 33 and the first lens 32 to form reverse-emission light. The folding mirror 36 is placed in the optical path of the reverse-emitting light to fold the reverse-emitting light and form folded light.

[0068] Specifically, the spectrometer support frame 30 includes a slit mounting frame 305, a folding-axis mirror mounting frame 306, a second base plate 301 disposed on the main support plate 1, and a lens mounting frame 302, a prism mounting frame 303, and a mirror mounting frame 304 disposed on the second base plate 301. The first connecting cylinder 37 is a cylindrical structure that runs through the front and rear, and it is mounted on the lens mounting frame 302. The first lens 32 and the second lens 33 are sequentially mounted inside the first connecting cylinder 37. The second connecting cylinder 38 is a conical cylinder, with its small end coaxially connected to the slit mounting frame 305, and its large end coaxially connected to the front end of the first connecting cylinder 37 through a flange. The folding-axis mirror mounting frame 306 is mounted on the outer wall of the second connecting cylinder 38. The slit 31, dispersive prism 34, freeform reflector 35, and folding mirror 36 are respectively mounted on the slit mounting frame 305, prism mounting bracket 303, reflector mounting bracket 304, and folding mirror mounting frame 306. A light-transmitting hole is provided on the side wall of the second connecting cylinder 38 at the position corresponding to the folding mirror 36, so that the folding mirror 36 can receive the reflected light through the first lens 32.

[0069] like Figure 4 As shown, the incident light, after being reflected sequentially by the primary reflector 21 and the secondary reflector 22, is incident through the slit 31, then transmitted sequentially through the first lens 32 and the second lens 33, and then refracted by the dispersive prism 34 before entering the freeform surface reflector 35. The freeform surface reflector 35 reflects the light to form a reflected light, which is then refracted in the opposite direction by the dispersive prism 34 and transmitted sequentially through the second lens 33 and the first lens 32 to form a reversed outgoing light. The folding mirror 36 is located in the optical path of the reversed outgoing light and is used to fold the reversed outgoing light to form a folded light, which is used for subsequent detection and imaging.

[0070] The first lens 32, the second lens 33, and the freeform mirror 35 are used to correct aberrations, the dispersive prism 34 is used for beam splitting, and the folding mirror 36 is used to refract the reversed outgoing light to minimize the size of the imaging spectrometer. Furthermore, the front and rear surfaces of the slit 31, the first lens 32, and the second lens 33 are coated with a wide-band anti-reflection film (visible to near-infrared to short-wave infrared) according to the incident light angle, to meet the requirements of wide-band detection.

[0071] The spectrometer component 3 of the present invention not only introduces a freeform surface mirror 35, but also realizes optical path folding through optical path multiplexing + folding axis design. While ensuring wide spectrum imaging, it ensures aberration with the fewest lenses, greatly compresses the length of the spectrometer, and greatly compresses the spatial size and weight of the spectral imager.

[0072] like Figure 5As shown, detector assembly 4 is a cooled detector, including detector 41, cooler 42, detector bracket 43, and third substrate 44. The third substrate 44 is mounted and fixed on the main support plate 1. Detector bracket 43 and cooler 42 are respectively mounted and fixed on the third substrate 44, and detector 41 is mounted on detector bracket 43. Simultaneously, detector 41 is positioned in the optical path of the refracted light and at the image plane of spectrometer assembly 3, used to receive the refracted light and perform photoelectric conversion on it to form an analog electrical signal.

[0073] The optimized design of the spectrometer component 3, combined with the setting of the cooler 42 in the detector component 4, ensures that the signal-to-noise ratio in the wide band from visible and near-infrared to short-wave infrared can meet the detection requirements, thereby enabling the detector 41 to respond in the wide band from visible and near-infrared to short-wave infrared.

[0074] The circuit component 5 is electrically connected to the detector 41 and the refrigerator 42 respectively, and is used to receive the analog electrical signal sent by the detector 41 and convert the analog electrical signal into a digital electrical signal; at the same time, the circuit component 5 is used to provide bias voltage to the detector 41 and the refrigerator 42, and send control commands and cooling drive signals.

[0075] The optical system design specifications of the hyperspectral imager in this embodiment are as follows: spatial field of view 1.5°, focal length 38mm±0.5%, image-side F number 3, working wavelength 0.4μm~2.5μm, optical transfer function >0.4@33.3lp / mm, wavefront aberration <RMS0.1λ@632.8nm, optical distortion <0.5%, spectral resolution <10nm@visible and near-infrared, <20nm@shortwave infrared, lateral spectral deviation <3nm@visible and near-infrared, <6nm@shortwave infrared, and spectral distortion <0.3 pixels.

[0076] The freeform surface shapes of the primary reflector 21, secondary reflector 22, and freeform surface reflector 35 are all expressed using XY polynomials, and their expressions are as follows:

[0077]

[0078] in, It is the surface sagitta of the freeform surface. These are the coordinates of the freeform surface diameter. , is the curvature of the quadratic surface on the base plane. Let be the radius of curvature at the vertex. Let be the conic constant of the quadratic surface on the base plane. , is the radial and radial coordinates of a freeform surface. Let be the coefficients of each order polynomial, m be the degree of the x term in the XY polynomial, n be the degree of the y term in the XY polynomial, i = 1, 2, ..., m, j = 1, 2, ..., n.

[0079] The basic geometric parameters of the primary reflector 21 and the coefficients of its polynomials are shown in Table 1.

[0080] Table 1. Basic geometric parameters of the primary reflector and coefficients of polynomials of various orders.

[0081]

[0082] The basic geometric parameters and coefficients of polynomials of each order of secondary reflector 22 are shown in Table 2.

[0083] Table 2. Basic geometric parameters of the secondary reflector and coefficients of polynomials of various orders.

[0084]

[0085] The basic geometric parameters and coefficients of polynomials of various orders for the freeform surface mirror 35 are shown in Table 3.

[0086] Table 3. Basic geometric parameters and coefficients of polynomials for freeform surface mirrors.

[0087]

[0088] The specific parameters of each optical element in this embodiment are as follows:

[0089] The primary reflector 21 has an aperture of 25.6 mm, a thickness of 21 mm, a radius of curvature of 60.875 mm, an eccentricity of 37 mm in the Y direction, and a tilt of 36.85° in the X direction. The distance between the primary reflector 21 and the secondary reflector 22 is 10.84 mm.

[0090] The secondary reflector 22 has an aperture of 11.2 mm, a thickness of 8.5 mm, a radius of curvature of 36.408 mm, an eccentricity of 0 mm in the Y direction, an inclination of 36.71° in the X direction, and a distance of 48 mm between the secondary reflector 22 and the slit 31.

[0091] The slit 31 has a width of 15μm and a length of 1mm, and the distance between the slit 31 and the first lens 32 is 48.2mm.

[0092] The first lens 32 is a biconvex lens with an aperture of 64mm, a front surface radius of curvature of 408.7mm, a rear surface radius of curvature of 64.1mm, and a thickness of 14mm. The distance between the first lens 32 and the second lens 33 is 40mm.

[0093] The second lens 33 is a concave-convex lens with the concave surface facing the object side. Its aperture is 52mm, the radius of curvature of the front surface is 50.3mm, the radius of curvature of the rear surface is 204.4mm, and its thickness is 13mm. The distance between the second lens 33 and the dispersive prism 34 is 27.48mm.

[0094] The dispersive prism 34 is a concave-convex mirror with a front surface diameter of 54 mm and a rear surface diameter of 63 mm. The radius of curvature of the front surface is 146.38 mm and the radius of curvature of the rear surface is 117.69 mm. Its tilt in the X direction is 7.04°. The distance between the dispersive prism 34 and the freeform surface mirror 35 is 13.15 mm.

[0095] The freeform surface mirror 35 has a diameter of 58mm, a thickness of 8mm, a radius of curvature of 149.148mm, an eccentricity of 4.04mm in the Y direction, and a tilt of 7.04° in the X direction.

[0096] The folding mirror 36 has an aperture of 12.2 mm and a thickness of 3 mm. Its eccentricity in the Y direction is 21.57 mm, and its tilt in the X direction is 45°. The distance between the folding mirror 36 and the first lens 32 is 24.34 mm, and the distance between the folding mirror 36 and the image plane of the spectrometer assembly 3 is 21.4 mm.

[0097] The front optical component 2 and the spectrometer component 3 were tested using a ZYGO interferometer. The wavefront aberration of the front optical component 2 was 0.096λ@632.8nm, and the wavefront aberration of the spectrometer component 3 was 0.075λ@632.8nm, meeting the technical specifications of a wideband hyperspectral imager. Furthermore, the wideband hyperspectral imager of this embodiment has a focal length f of 38.27mm, a relative aperture D / f of 0.34, an effective field of view of 1.48° in the spatial direction, an edge field of view distortion of 0.45%, a lateral spectral deviation of 2.5nm in the visible and near-infrared range, a lateral spectral deviation of 4.7nm in the short-wave infrared range, and a spectral distortion of 0.16 pixels, fully meeting the optical system design specifications of a hyperspectral imager.

[0098] The following uses a full-field point plot and optical transfer function curves at different wavelengths to further illustrate the effect of the miniaturized wide-band hyperspectral imager of the present invention.

[0099] Figure 6 The full-field dot plot of this embodiment shows that the diameter of the geometrically diffused spot across the entire field of view and the entire spectrum is smaller than the diameter of the Airy disk, thus achieving the diffraction limit. Figures 7-12 The figures show optical transfer function curves at different wavelengths according to embodiments of the present invention. Figure 7 This is a modulation transfer function curve at an operating wavelength of 0.4 μm according to an embodiment of the present invention. Figure 8 This is an optical transfer function curve at an operating wavelength of 0.7 μm, according to an embodiment of the present invention. Figure 9 This is an optical transfer function curve at a working wavelength of 0.9 μm according to an embodiment of the present invention. Figure 10This is an optical transfer function curve at an operating wavelength of 1.6 μm, according to an embodiment of the present invention. Figure 11 This is an optical transfer function curve at an operating wavelength of 1.9 μm, according to an embodiment of the present invention. Figure 12 The figure shows the optical transfer function curve of the embodiment of the present invention at a working wavelength of 2.5 μm; it can be seen that its optical transfer function reaches the diffraction limit across the entire field of view and the entire wavelength band.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A compact, wide-band hyperspectral imager, characterized in that: It includes a main support plate (1), and a front optical assembly (2), a spectrometer assembly (3), a detector assembly (4) and a circuit assembly (5) disposed on the main support plate (1); The front optical component (2) includes a primary reflector (21) and a secondary reflector (22); the reflecting surfaces of the primary reflector (21) and the secondary reflector (22) are both free-form surfaces, and the two constitute an off-axis two-reflector structure; the incident light is reflected by the primary reflector (21) and the secondary reflector (22) in sequence and then emitted to form the front emitted light; The spectrometer assembly (3) includes a slit (31), a first lens (32), a second lens (33), a dispersive prism (34), a freeform mirror (35), and a folding mirror (36). The slit (31) is disposed on the optical path of the front-emitting light and is located at the image plane of the front optical component (2); the first lens (32), the second lens (33), the dispersive prism (34), and the freeform mirror (35) are disposed in sequence behind the slit (31) and are located on the optical path of the front-emitting light; the front and rear surfaces of the slit (31), the first lens (32), and the second lens (33) are all coated with a wide-band anti-reflection film from visible near-infrared to short-wave infrared. The outgoing light incident through the slit (31) is transmitted through the first lens (32) and the second lens (33) in sequence, and then refracted by the dispersive prism (34) before being incident on the surface of the freeform mirror (35). The freeform mirror (35) reflects the light to form a reflected light. The reflected light is refracted in the opposite direction by the dispersive prism (34), and then transmitted through the second lens (33) and the first lens (32) in sequence to form a reverse outgoing light. The folding mirror (36) is placed in the optical path of the reverse-emitted light to fold the reverse-emitted light and form folded light; The detector assembly (4) is a cooled detector, including a detector (41) and a cooler (42). The detector (41) has a response in a wide band from visible near-infrared to short-wave infrared. The cooler (42) is used to improve the signal-to-noise ratio in the wide band. The detector (41) is placed on the optical path of the refracted light and is located at the image plane of the spectrometer assembly (3). It is used to receive the refracted light and perform photoelectric conversion on the refracted light to form an analog electrical signal. The circuit component (5) is electrically connected to the detector (41) and the refrigerator (42) respectively, and is used to receive the analog electrical signal sent by the detector (41) and convert the analog electrical signal into a digital electrical signal; at the same time, the circuit component (5) is used to provide bias voltage to the detector (41) and the refrigerator (42) and send control commands and cooling drive signals.

2. The compact broadband hyperspectral imager according to claim 1, characterized in that: The front optical component (2) also includes a first substrate (23), a front support frame (24), and a light shield (25); The first substrate (23) is mounted and fixed on the main support plate (1); The front support frame (24) is a frame structure, and its bottom is fixed on the first base plate (23). It is provided with a primary mirror mounting position and a secondary mirror mounting position. The primary mirror (21) and the secondary mirror (22) are respectively installed on the primary mirror mounting position and the secondary mirror mounting position. The positions of the incident light and the front outgoing light on the front support frame (24) are unobstructed. The light shield (25) is installed on the outside of the front support frame (24) at the position corresponding to the incident light, in order to suppress external stray light.

3. The compact broadband hyperspectral imager according to claim 2, characterized in that: The spectrometer assembly (3) also includes a spectrometer support frame (30), a first connecting cylinder (37) and a second connecting cylinder (38); The spectrometer support frame (30) includes a slit mounting frame (305), a folding mirror mounting frame (306), a second substrate (301) disposed on the main support plate (1), and a lens mounting frame (302), a prism mounting frame (303), and a mirror mounting frame (304) disposed on the second substrate (301). The first connecting tube (37) is a cylindrical structure that runs through the front and back, and it is mounted on the lens mounting bracket (302); the first lens (32) and the second lens (33) are installed in the first connecting tube (37) in sequence; The second connecting cylinder (38) is a tapered cylinder, with its small end coaxially connected to the slit mounting frame (305) and its large end coaxially connected to the front end of the first connecting cylinder (37) through a flange; The folding mirror mounting frame (306) is mounted on the outer wall of the second connecting cylinder (38); The slit (31), dispersive prism (34), freeform surface mirror (35), and folded-axis mirror (36) are respectively installed on the slit mounting frame (305), prism mounting bracket (303), mirror mounting bracket (304), and folded-axis mirror mounting frame (306); A light-transmitting hole is provided on the side wall of the second connecting cylinder (38) at the position corresponding to the folding mirror (36).

4. The compact broadband hyperspectral imager according to claim 3, characterized in that: The detector assembly (4) also includes a detector support (43) and a third substrate (44). The third substrate (44) is mounted and fixed on the main support plate (1), and the detector bracket (43) and the refrigerator (42) are respectively mounted and fixed on the third substrate (44); The detector (41) is mounted on the detector bracket (43).

5. The compact broadband hyperspectral imager according to claim 4, characterized in that: The primary reflector (21), secondary reflector (22), slit (31), and freeform reflector (35) are all made of metal. The first lens (32), the second lens (33), and the dispersive prism (34) are all made of quartz glass.

6. The compact broadband hyperspectral imager according to claim 5, characterized in that: The front support frame (24) is made of the same material as the main reflector (21) and the secondary reflector (22); The reflector mounting bracket (304) is made of the same material as the freeform surface reflector (35).

7. A compact broadband hyperspectral imager according to claim 6, characterized in that: The primary reflector (21), secondary reflector (22), slit (31), and freeform reflector (35) are all made of aluminum alloy.

8. The compact broadband hyperspectral imager according to claim 7, characterized in that: The freeform surface shapes of the primary reflector (21), secondary reflector (22), and freeform surface reflector (35) are all expressed using XY polynomials, and their expressions are as follows: ; in, It is the surface sagitta of the freeform surface. These are the coordinates of the freeform surface diameter. , is the curvature of the quadratic surface on the base plane. Let be the radius of curvature at the vertex. Let be the conic constant of the quadratic surface on the base plane. , is the radial and radial coordinates of a freeform surface. Let be the coefficients of each order polynomial, m be the degree of the x term in the XY polynomial, n be the degree of the y term in the XY polynomial, i = 1, 2, ..., m, j = 1, 2, ..., n.

9. A compact broadband hyperspectral imager according to claim 8, characterized in that: The primary reflector (21) has an aperture of 25.6 mm, a thickness of 21 mm, a radius of curvature of 60.875 mm, an eccentricity of 37 mm in the Y direction, an inclination of 36.85° in the X direction, and a spacing of 10.84 mm between the primary reflector (21) and the secondary reflector (22). The secondary reflector (22) has an aperture of 11.2 mm, a thickness of 8.5 mm, a radius of curvature of 36.408 mm, an eccentricity of 0 mm in the Y direction, an inclination of 36.71° in the X direction, and a distance of 48 mm between the secondary reflector (22) and the slit (31). The slit (31) has a width of 15 μm and a length of 1 mm, and the slit (31) is spaced 48.2 mm from the first lens (32). The first lens (32) is a biconvex lens with an aperture of 64 mm, a front surface curvature radius of 408.7 mm, a rear surface curvature radius of 64.1 mm, and a thickness of 14 mm. The distance between the first lens (32) and the second lens (33) is 40 mm. The second lens (33) is a concave-convex lens with the concave surface facing the object side. Its aperture is 52mm, the radius of curvature of the front surface is 50.3mm, the radius of curvature of the rear surface is 204.4mm, and the thickness is 13mm. The distance between the second lens (33) and the dispersive prism (34) is 27.48mm. The dispersive prism (34) is a concave-convex mirror with a front surface diameter of 54 mm, a rear surface diameter of 63 mm, a front surface radius of curvature of 146.38 mm, a rear surface radius of curvature of 117.69 mm, and an inclination of 7.04° in the X direction. The distance between the dispersive prism (34) and the freeform surface mirror (35) is 13.15 mm. The freeform surface reflector (35) has a diameter of 58 mm, a thickness of 8 mm, a radius of curvature of 149.148 mm, an eccentricity of 4.04 mm in the Y direction, and a tilt of 7.04° in the X direction. The folding mirror (36) has an aperture of 12.2 mm and a thickness of 3 mm. Its eccentricity in the Y direction is 21.57 mm and its tilt in the X direction is 45°. The distance between the folding mirror (36) and the first lens (32) is 24.34 mm, and the distance between the folding mirror (36) and the image plane of the spectrometer assembly (3) is 21.4 mm.

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