Spectral imaging system based on MEMS

Abstract

The invention discloses an MEMS-based spectral imaging system, which sequentially comprises a front unit, an MEMS, a rear unit and an image sensor from an object space to an image space, the focal plane of the front unit is positioned between the MEMS and the rear unit, the main light of the field of view of the front unit is orthogonal to the MEMS, the object plane of the rear unit is overlapped with the focal plane of the front unit, a front light path, a rear light path and a rear light path are arranged on the front light path, and the image sensor is positioned between the front light path and the rear light path. The MEMS is used for compressing an image in a field angle range, so that the image can completely pass through the MEMS; and the rear light path is used for amplifying the image passing through the MEMS to the image sensor. According to the embodiment of the invention, under the condition that the clear aperture of the MEMS is limited, the central wavelength angle deviation can be suppressed, the spectrum picture with high consistency can be obtained, and the method and the device can be widely applied to the technical field of spectrum imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of spectral imaging, and in particular to a spectral imaging system based on MEMS. Background Art

[0002] Spectral imaging is based on the principle of combining optical information with spatial information. It guides the incident light to the surface of the observed object, interacts with the object, and then uses a spectroscopic instrument to decompose the reflected or transmitted light to obtain the spectral information of the object at different wavelengths. Through appropriate optical design and detectors, an image is formed and presented in the form of a spectral cube. Hyperspectral imaging obtains high-resolution spectral information in a relatively wide wavelength range for detailed spectral feature extraction. It is widely used in scientific research, medicine, environmental monitoring and other fields, providing accurate analysis and identification of the material composition and chemical properties of objects.

[0003] The mechanism of introducing FP cavity into the optical system to achieve wavelength selection and then splitting cannot ignore the influence of optical path difference. For systems using collimated optical paths, all optical paths are near the main optical axis. The characteristics of collimated optical paths avoid the problem of optical path difference in the FP cavity. In the application scenario of spectral cameras, it is inevitable to consider the influence of off-axis optical paths, which is also the basis for realizing the application of camera perspective. Under this condition, if the FP cavity is used for wavelength selection, then for the light beam entering the FP cavity, the optical path on the main optical axis and the optical path of the off-axis field of view will obviously be inconsistent. This inconsistency increases with the increase of the field of view angle, which will have a negative impact on the final spectral imaging effect. This means that the main wavelength at the center of the frame is inconsistent with the main wavelength at the edge of the frame, and eventually the center wavelength angle-dependent drift phenomenon occurs. This negative phenomenon will weaken the usable field of view of the spectral camera and also cause errors in detection. Considering that the larger the aperture of the current MEMS (Micro-Electro-Mechanical System) chip, the more difficult it is to manufacture the system, if a telecentric optical path is used directly to correct the light beam falling on the CMOS sensor, the light aperture of the MEMS chip needs to be consistent with the diagonal of the CMOS sensor or slightly larger than the diagonal of the CMOS sensor in order to suppress the angular deviation of the central wavelength in an engineered scenario. Summary of the invention

[0004] In view of this, in order to solve one of the above problems, an embodiment of the present invention aims to provide a MEMS-based spectral imaging system, which can suppress the angular deviation of the central wavelength and obtain a spectral image with high consistency when the MEMS aperture is limited.

[0005] An embodiment of the present invention provides a spectral imaging system based on MEMS, which includes a front unit, a MEMS, a rear unit and an image sensor in order from the object side to the image side, the focal plane of the front unit is located between the MEMS and the rear unit, the field of view chief ray of the front unit is orthogonal to the MEMS, the object plane of the rear unit overlaps with the focal plane of the front unit, wherein:

[0006] The front optical path is used to compress the image within the field of view angle range so that the image can pass through the MEMS completely;

[0007] The rear optical path is used to amplify the image passing through the MEMS onto the image sensor.

[0008] Optionally, the front unit includes a first lens group, an aperture and a second lens group, the first lens group includes a first lens, a second lens, a third lens and a fourth lens, the third lens and the fourth lens constitute a first double-cemented lens group, the second lens group includes a fifth lens, a sixth lens, a seventh lens and an eighth lens, the sixth lens and the seventh lens constitute a second double-cemented lens group.

[0009] Optionally, the first lens group and the imaging system satisfy the following relationship:

[0010] -1.52 <f q / f d1 <-1.58

[0011] Among them, f q represents the combined focal length of the first lens group, f d1 Indicates the focal length of the front unit.

[0012] Optionally, the first lens, the second lens, the first doublet lens group and the first lens group satisfy the following relationship:

[0013] -11.3 <f1 / f q <-10.9

[0014] 39 <f2 / f q <45

[0015] 0.79 <f 34 / f q <0.84

[0016] Where f1 is the focal length of the first lens, f2 is the focal length of the second lens, and f 34 represents the focal length of the first doublet lens group, f q represents the combined focal length of the first lens group.

[0017] Optionally, the second lens group and the imaging system satisfy the following relationship:

[0018] 0.95 <f h / f d1 <1.15

[0019] Among them, f h represents the combined focal length of the second lens group, and f represents the focal length of the front unit.

[0020] Optionally, the fifth lens, the eighth lens, the second doublet lens group and the second lens group satisfy the following relationship:

[0021] 1.67 <f5 / f h <1.71

[0022] 2.53 <f8 / f h <2.85

[0023] 3.73 <f 67 / f h <3.92

[0024] Among them, f5 represents the focal length of the fifth lens, f8 represents the focal length of the eighth lens, and f 67 represents the focal length of the second doublet lens group, f h Indicates the combined focal length of the second lens group.

[0025] Optionally, the rear unit includes a ninth lens to a fifteenth lens, the tenth lens and the eleventh lens form a third double-cemented lens group, and the thirteenth lens and the fourteenth lens form a fourth double-cemented lens group.

[0026] Optionally, the ninth lens, the twelfth lens and the fifteenth lens satisfy the following relationship with the imaging system:

[0027] 0.58 <f9 / f d2 <0.61

[0028] 0.24 <f 12 / f d2 <0.27

[0029] -2.76 <f 15 / f d2 <-2.73

[0030] Where, f9 represents the focal length of the ninth lens, f 12 represents the focal length of the twelfth lens, f 15 represents the focal length of the fifteenth lens, f d2 Indicates the focal length of the rear unit.

[0031] Optionally, the third doublet lens group and the imaging system satisfy the following relationship:

[0032] 0.78 <f 1011 / f d2 <0.82

[0033] Among them, f 1011 represents the focal length of the triplet lens group, f d2 Indicates the focal length of the rear unit.

[0034] Optionally, the fourth doublet lens group and the imaging system satisfy the following relationship:

[0035] 0.72 <f 1314 / f d2 <0.74

[0036] Among them, f 1314 represents the focal length of the four-doublet lens group, f d2 Indicates the focal length of the rear unit.

[0037] Implementation of the embodiments of the present invention includes the following beneficial effects: the MEMS-based spectral imaging system in the embodiment includes, from the object side to the image side, a front unit, a MEMS, a rear unit and an image sensor, the focal plane of the front unit is located between the MEMS and the rear unit, the field of view main ray of the front unit is orthogonal to the MEMS, the object plane of the rear unit overlaps with the focal plane of the front unit, the front optical path is used to compress the image within the field of view angle range so that the image can pass completely through the MEMS, the rear optical path is used to amplify the image passing through the MEMS onto the image sensor, the front unit covers the field of view angle of the entire system and compresses the image within the field of view angle range to pass through the MEMS, so that the field of view main ray of the front unit is orthogonal to the MEMS, thereby achieving the suppression of the central wavelength angle deviation when the MEMS aperture is limited, and obtaining a spectral image with high consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a structural schematic diagram of a MEMS-based spectral imaging system provided by an embodiment of the present invention;

[0039] Figure 2 is a light path diagram of a front unit provided by an embodiment of the present invention;

[0040] Figure 3 is a light path diagram of a rear unit provided by an embodiment of the present invention;

[0041] Figure 4 is an optical path diagram of a MEMS-based spectral imaging system provided by an embodiment of the present invention;

[0042] Figure 5is a point diagram of a front unit provided by an embodiment of the present invention;

[0043] Figure 6 is a distortion diagram of a front unit provided by an embodiment of the present invention;

[0044] Figure 7 is an adjustment transfer function diagram of a front unit provided by an embodiment of the present invention;

[0045] Figure 8 is a distribution diagram of the main light angle under the normalized field of view of a front unit provided by an embodiment of the present invention;

[0046] Fig. 9 is a comparison diagram before and after suppression of central wavelengths of different fields of view provided by an embodiment of the present invention;

[0047] Fig.10 is a point diagram of a post-unit provided by an embodiment of the present invention;

[0048] Fig.11 is a distortion diagram of a rear unit provided by an embodiment of the present invention;

[0049] Fig.12 is an adjustment transfer function diagram of a post-unit provided by an embodiment of the present invention;

[0050] Fig.13 It is an adjustment transfer function diagram of a MEMS-based spectral imaging system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0052] Normalized field of view refers to the standardization or normalization of the field of view of an optical system.

[0053] Normalized field of Aperture is a method to standardize the parameters of an optical system. Normalized field of Aperture means dividing the aperture size of an optical system by a certain reference value of the system to obtain a relative measure.

[0054] FP cavity (Fabry-Platinum interferometer cavity): an optical cavity composed of two parallel and partially transparent mirrors. Due to the interference effect, only light of a specific wavelength can resonate in the cavity, resulting in a series of passed and suppressed spectral peaks.

[0055] The principal optical axis is an important concept in optical systems. It refers to a virtual straight line passing through the center of an optical element (such as a lens or a reflector). Light propagating along this straight line will not be deflected if it does not pass through the center point of the optical element. The principal optical axis is usually the symmetry axis of the optical system. Objects or scenes that are symmetrical along this axis will be symmetrically displayed in the image.

[0056] Aberration refers to the deviation between the ideal imaging situation and the actual imaging situation. These deviations will reduce the clarity and quality of the image. Aberration is an inevitable phenomenon in the optical system and needs to be minimized through lens design.

[0057] Distortion refers to the deviation between the geometric shape of a straight line or plane object in a scene and its actual shape when it is imaged through a lens. Distortion is a type of aberration in an optical system that does not change the clarity of the image, but causes the shape of the image to be distorted.

[0058] Chromatic Aberration: Due to the different refractive indices of light of different colors (wavelengths) in the lens, they cannot focus at the same point. There are two types of chromatic aberration: Longitudinal Chromatic Aberration, where different colors of light focus at different distances; and Lateral Chromatic Aberration, where different colors of light focus at the same distance but at different positions.

[0059] Airy Disk is a concept in optics, which refers to the specific pattern of light intensity distribution formed on the focal plane after a focused light beam passes through an optical system with a circular aperture (such as a lens or a telescope), which determines the diffraction limit of the optical system.

[0060] The spot diagram is a tool used in optical design to evaluate and compare the performance of different optical systems. It shows the focusing of the light beam passing through the optical system on the focal plane and is usually used to analyze and optimize the design of lenses or reflectors.

[0061] MTF (Modulation Transfer Function Graph) is an important tool for evaluating the imaging quality of imaging systems (such as camera lenses, telescopes, microscopes, etc.). MTF evaluates the imaging performance of the system by quantitatively describing the imaging system's ability to respond to details of different spatial frequencies.

[0062] Spatial frequency refers to the frequency with which details in an image change, and is usually measured in lines per millimeter (lp / mm) or cycles per degree.

[0063] The MTF value refers to the modulation transfer capability of an imaging system for a specific spatial frequency, usually expressed as a percentage. Ideally, a perfect imaging system would have an MTF value of 100% for all spatial frequencies.

[0064] The VIS band refers to the visible light band, which is the range of the electromagnetic spectrum that the human eye can perceive. In the spectrum, the visible light band generally covers a wavelength range from about 400 nanometers (violet light) to 700 nanometers (red light).

[0065] The near infrared (NIR) band is a region of the electromagnetic spectrum between visible light and mid-infrared. It is usually defined as the wavelength range from 700 nanometers (nm) to 2500 nanometers (nm), or in wavenumbers from 12800 cm^ -1 To 4000cm^ -1 The near-infrared band lies just outside the red part of the visible spectrum.

[0066] CRA (Chief Ray Angle) refers to the angle between the chief ray and the parallel ray in the lens.

[0067] BFL (Back Focal Length) can represent the back focal length of a lens or optical system, that is, the distance from the lens surface to its back focal point. Back focal length is an important parameter in the design and analysis of optical systems, affecting imaging performance.

[0068] Chief ray: In each field of view, the ray passing through the center of the aperture is called the chief ray.

[0069] Central wavelength angle deviation: Under the influence of the off-axis optical path, for the light beam entering the FP cavity, the optical path on the main optical axis and the optical path of the off-axis field of view will obviously be inconsistent. This inconsistency increases with the increase of the field of view, which means that the main wavelength at the center of the frame is inconsistent with the main wavelength at the edge of the frame, and finally the central wavelength angle deviation phenomenon occurs.

[0070] like Figure 1 As shown, an embodiment of the present invention provides a spectral imaging system based on MEMS, which includes a front unit, a MEMS, a rear unit and an image sensor in order from the object side to the image side, the focal plane of the front unit is located between the MEMS and the rear unit, the field of view chief ray of the front unit is orthogonal to the MEMS, and the object plane of the rear unit overlaps with the focal plane of the front unit, wherein,

[0071] The front optical path is used to compress the image within the field of view so that the image can pass through the MEMS completely;

[0072] The rear optical path is used to amplify the image passing through the MEMS onto the image sensor.

[0073] It should be noted that, in the embodiment of the present invention, the technical route of using surface exposure to obtain a spectral cube in a spectral camera is mainly to construct an FP cavity by means of MEMS, and to achieve wavelength selection by controlling two parallel plates in the MEMS to achieve changes in the FP cavity. The image sensor can be determined according to the actual application, such as a COMS sensor.

[0074] The incident light is emitted from the object side, and is compressed by the front unit, selected by the MEMS wavelength, and amplified by the rear unit, and spectrally imaged on the image sensor. The angle formed by the incident light is the field of view. The front unit, MEMS, rear unit and image sensor are coaxial.

[0075] The front unit meets the following requirements: 1. Cover the field of view angle of the entire system; 2. Compress the image within the field of view angle so that the image can pass through the MEMS completely; 3. The focal plane of the front unit is located between the MEMS and the rear unit; 4. The main light of each field of view of the front unit is perpendicular to the MEMS surface.

[0076] The rear unit meets the following requirements: 1. The object plane of the rear unit overlaps with the focal plane of the front unit, and the image of the front unit is magnified onto the image sensor; 2. The rear unit belongs to the object telecentric optical path, and there are no strict requirements for the main light of the rear unit and the surface of the CMOS sensor.

[0077] The size of the focal plane of the central wavelength angle shift is calculated by the ratio of the MEMS aperture and the image sensor; the focal length of the front unit is calculated by defining the field of view of the overall composite optical path. When the pixel size of the image sensor is determined, the spatial resolution of the front unit is obtained by inverse calculation of the magnification ratio; in this way, the three related indicators of field of view, spatial resolution, and central wavelength angle shift can be decoupled. If the spectral imaging system requires a large field of view, the front unit is modulated to have a large field of view. It is only necessary to ensure that the main light passing through the MEMS field of view is orthogonal to the MEMS, and the resolution of the front unit meets the requirements of the rear unit (image magnification optical path), so that a spectral pattern with a large field of view and suppressed central wavelength angle shift can be obtained. If the spectral imaging system needs to be equipped with an image sensor with higher resolution, when the spatial resolution of the front unit is sufficient, it is only necessary to modify the magnification ratio of the rear unit to obtain a spectral image with higher resolution and suppressed central wavelength angle shift. By adjusting the front unit or the rear unit, a spectral image with suppressed central wavelength angle shift is provided for different application scenarios.

[0078] Optionally, see Figure 2 The front unit includes a first lens group, an aperture and a second lens group. The first lens group includes a first lens G1, a second lens G2, a third lens G3 and a fourth lens G4. The third lens and the fourth lens form a first double-cemented lens group. The second lens group includes a fifth lens G5, a sixth lens G6, a seventh lens G7 and an eighth lens G8. The sixth lens and the seventh lens form a second double-cemented lens group. M is a MEMS device that realizes the FP cavity of the wavelength selection function; S1 is the focal plane of the front unit.

[0079] Optionally, the first lens group and the imaging system satisfy the following relationship:

[0080] -1.52 <f q / f d1 <-1.58

[0081] Among them, f q represents the combined focal length of the first lens group, f d1 Indicates the focal length of the front unit.

[0082] Optionally, the first lens, the second lens and the first doublet lens group satisfy the following relationship with the first lens group:

[0083] -11.3 <f1 / f q <-10.9

[0084] 39 <f2 / f q <45

[0085] 0.79 <f 34 / f q <0.84

[0086] Where f1 is the focal length of the first lens, f2 is the focal length of the second lens, and f 34 represents the focal length of the first doublet lens group, f q represents the combined focal length of the first lens group.

[0087] Optionally, the second lens group and the imaging system satisfy the following relationship:

[0088] 0.95 <f h / f d1 <1.15

[0089] Among them, f h represents the combined focal length of the second lens group, f d1 Indicates the focal length of the front unit.

[0090] Optionally, the fifth lens, the eighth lens, the second doublet lens group and the second lens group satisfy the following relationship:

[0091] 1.67 <f5 / f h <1.71

[0092] 2.53 <f8 / f h <2.85

[0093] 3.73 <f 67 / f h <3.92

[0094] Among them, f5 represents the focal length of the fifth lens, f8 represents the focal length of the eighth lens, and f 67 represents the focal length of the second doublet lens group, f h Indicates the combined focal length of the second lens group.

[0095] It should be noted that the focal lengths of the first lens, the second lens, the first doublet lens group, the fifth lens, the eighth lens, and the second doublet lens group are determined according to actual applications and are not specifically limited in this embodiment.

[0096] Optionally, see Figure 3 The rear unit includes a ninth lens G9, a tenth lens G10, an eleventh lens G11, a twelfth lens G12, a thirteenth lens G13, a fourteenth lens G14 and a fifteenth lens G15. The tenth lens G10 and the eleventh lens G11 form a third double-cemented lens group, and the thirteenth lens G13 and the fourteenth lens G14 form a fourth double-cemented lens group.

[0097] Optionally, the ninth lens, the twelfth lens and the fifteenth lens satisfy the following relationship with the imaging system:

[0098] 0.58 <f9 / f d2 <0.61

[0099] 0.24 <f 12 / f d2 <0.27

[0100] -2.76 <f 15 / f d2 <-2.73

[0101] Where, f9 represents the focal length of the ninth lens, f 12 represents the focal length of the twelfth lens, f 15 represents the focal length of the fifteenth lens, f d2 Indicates the focal length of the rear unit.

[0102] Optionally, the third double-cemented lens group and the imaging system satisfy the following relationship:

[0103] 0.78 <f 1011 / f<0.82

[0104] Among them, f 1011 represents the focal length of the triplet lens group, f d2 Indicates the focal length of the rear unit.

[0105] Optionally, the fourth double-cemented lens group and the imaging system satisfy the following relationship:

[0106] 0.72 <f 1314 / f d2 <0.74

[0107] Among them, f 1314 represents the focal length of the four-doublet lens group, f d2 Indicates the focal length of the rear unit.

[0108] It should be noted that the focal lengths of the ninth lens, the third doublet lens group, the twelfth lens, the fourth doublet lens group, and the fifteenth lens are determined according to actual applications and are not specifically limited in this embodiment.

[0109] In a specific embodiment, see Figure 4 , the spectral imaging system includes a front unit, MEMS, a rear unit and a CMOS image sensor. The system parameters of the optical system are as follows: the CMOS image height is 3.6mm, the pixel size of CMOS is 3.3um, the field of view of the system is 39.5°, and the aperture of MEMS is 2mm. The optical path parameters of the front unit are as follows: Fnumber = 2.5, the focal length is 2.2mm, the working wavelength range is 690nm~920nm, the image height of the focal plane is 1.6mm, and the optical system is designed with a standard spherical mirror. The maximum viewing angle of the system is about 20°, and the spherical mirror system controls the CRA of the light beam after passing through the last lens to be parallel to the normal direction of the FP cavity parallel plate (MEMS). The optical characteristic parameters of each lens and optical device in the objective system are shown in Table 1.

[0110] Table 1

[0111]

[0112] Wherein, the focal length of the first lens group is f q The ratio of the focal length f of the system is -1.556, the focal length f1 of the first lens and the combined focal length f of the first lens group q The ratio is -11.2, the focal length f2 of the second lens and the combined focal length f of the first lens group q The ratio is 42, and the focal length of the first double cemented lens G34 is f 34 Combined focal length f with the first lens group q The ratio is 0.82, and the combined focal length of the second lens group is f hThe ratio of the focal length f of the system is 1.054, and the focal length f5 of the fifth lens and the combined focal length f of the second lens group are h The ratio is 1.691, and the focal length of the second doublet lens G67 is f 67 Combined focal length f with the second lens group h The ratio of the focal length f8 of the eighth lens G8 to the combined focal length fh of the second lens group is 3.889, and the ratio of the focal length f8 of the eighth lens G8 to the combined focal length fh of the second lens group is 2.686.

[0113] A spot diagram is a tool used in optical design to evaluate and compare the performance of different optical systems. It shows how well a beam of light passing through the optical system is focused on the focal plane. Figure 5 In this embodiment, the spot diagram shows the area formed by the Airy disk radius; the imaging quality of the optical lens is excellent, and all working wavelengths converge within the Airy disk radius.

[0114] Distortion refers to the deviation between the geometric shape of a straight line or plane object in a scene and its actual shape when it is imaged through a lens. Distortion is a type of aberration in an optical system that does not change the clarity of the image, but causes the shape of the image to be distorted. Figure 6 The imaging system involved in this example is used in a photographic system, and the optical TV distortion is less than 2%. The TV distortion of the distortion lens of this imaging system is less than 1%.

[0115] MTF (Modulation Transfer Function Graph) is an important tool for evaluating the imaging quality of imaging systems (such as camera lenses, telescopes, microscopes, etc.). MTF evaluates the imaging performance of the system by quantitatively describing the imaging system's ability to respond to details of different spatial frequencies. Figure 7 , Figure 7 The horizontal axis in represents the spatial frequency; spatial frequency refers to the frequency of changes in details in the image, usually measured in lines per millimeter (lp / mm) or cycles per degree. Figure 7 The vertical axis in is the MTF value; the MTF value refers to the modulation transfer capability of the imaging system for a specific spatial frequency, usually expressed as a percentage. Ideally, a perfect imaging system has an MTF value of 100% for all spatial frequencies. The MTF graph of the lens is distributed over the entire field of view close to the diffraction limit. Figure 7It can be seen that the MTF characteristic of the front unit is close to the diffraction limit; according to the calculation of the Nyquist frequency, if the overall system is to have sufficient imaging capability when the pixel is 3.3um, the resolution capability of the front-end amplifier optical path needs to be able to have clear imaging at an equivalent of 1.65um; reverse calculation shows that the Nyquist frequency of the system is about 303lp / mm; according to the MTF diagram, it can be seen that the MTF value of the system is >0.2 at the Nyquist frequency of the front optical path; the system has good imaging capability.

[0116] See also Figure 8 , the distribution of the angle between the chief ray of each field of view and the direction of the normal of the FP cavity parallel to the plane; according to the angle of the chief ray of each field of view, it can be known that after constraining the CRA, the maximum angle of the chief ray is about 0.5.

[0117] See also Fig. 9 , Fig. 9 This is the change of the central wavelength before and after suppression when the field of view changes; after correction by the front unit, the drift of the central wavelength is greatly alleviated; Fig. 9 The curve shows the drift of the central wavelength when the central wavelength is 800nm ​​with the change of the field of view. Before suppression, the maximum wavelength drift makes the central wavelength drift to 750nm. After calibration of the front unit, the maximum central wavelength drift is still around 800nm, which solves the problem of central wavelength drift from the root.

[0118] The optical path parameters of the rear unit are as follows: F number = 6.2, focal length is 20mm, the working wavelength range is 690nm~920nm, the image height of the focal plane is 3.6mm, the optical system is designed with a standard spherical mirror, and the system is essentially a conjugate magnification system with a maximum object height of 0.9mm. The light beam is controlled by the spherical mirror system to finally fall on the CMOS.

[0119] The optical characteristic parameters of each lens and optical device in the rear unit are shown in Table 2.

[0120] Table 2

[0121]

[0122] The ratio of the focal length f9 of the ninth lens to the focal length f of the system is in the range of 0.58 to 0.6, and the focal length f of the third doublet lens G1011 is 1011 The ratio of the focal length f of the system is in the range of 0.78 to 0.82. The focal length f of the twelfth lens 12 The ratio of the focal length f of the system is in the range of 0.24 to 0.265. The focal length f of the fourth doublet lens G1314 is 1314The ratio of the focal length f of the system is in the range of 0.72 to 0.74. The focal length f of the fifteenth lens is 15 The ratio to the system focal length f ranges from -2.76 to -2.73.

[0123] See also Fig.10 The spot diagram shows the area formed by the Airy disk radius; the imaging quality of the optical lens is excellent, and all working wavelengths converge within the Airy disk radius.

[0124] See also Fig.11 The imaging system involved in this example is used in a photographic system, and the optical TV distortion is less than 2%. The TV distortion of the distortion lens of this imaging system is less than 1%.

[0125] See also Fig.12 Since the Fnumber of the rear unit is 6.2, the Airy disk diameter is about 10.6um to 14um in the response wavelength range of 700 to 930nm; its Nyquist frequency is calculated to be about 48lp / mm; according to the MTF graph, the phase correction of the system is close to the theoretical limit; the phase difference of each field of view is handled very well. The rear lens is an amplification system that does not bring additional aberrations.

[0126] During the system assembly process, the focal plane of the front unit is located at the object plane of the rear unit, and the system can be directly spliced; see Fig.13 , Fig.13 The MTF diagram of the overall composite optical path is shown in Figure 2. Since the pixel size of the system's CMOS image sensor is 3.3um, according to the calculation of the Nyquist frequency, the system's Nyquist frequency is about 151lp / mm, and the actual MTF performance of the composite optical path is close to the theoretical limit, which means that the composite optical path has a high spatial resolution under the premise of having the characteristics of low central wavelength angle deviation, and this method can well achieve the decoupling of the three related indicators of field of view angle, spatial resolution, and central wavelength angle deviation.

[0127] Implementation of the embodiments of the present invention includes the following beneficial effects: the MEMS-based spectral imaging system in the embodiment includes, from the object side to the image side, a front unit, a MEMS, a rear unit and an image sensor, the focal plane of the front unit is located between the MEMS and the rear unit, the field of view main ray of the front unit is orthogonal to the MEMS, the object plane of the rear unit overlaps with the focal plane of the front unit, the front optical path is used to compress the image within the field of view angle range so that the image can pass completely through the MEMS, the rear optical path is used to amplify the image passing through the MEMS onto the image sensor, the front unit covers the field of view angle of the entire system and compresses the image within the field of view angle range to pass through the MEMS, so that the field of view main ray of the front unit is orthogonal to the MEMS, thereby achieving the suppression of the central wavelength angle deviation when the MEMS aperture is limited, and obtaining a spectral image with high consistency.

[0128] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A spectral imaging system based on MEMS, characterized in that: The front unit, MEMS, rear unit and image sensor are included in sequence from the object side to the image side. The focal plane of the front unit is located between the MEMS and the rear unit. The main ray of the field of view of the front unit is orthogonal to the MEMS. The object plane of the rear unit overlaps with the focal plane of the front unit. The front optical path is used to compress the image within the field of view angle range so that the image can pass through the MEMS completely; The rear optical path is used to amplify the image passing through the MEMS onto the image sensor.

2. The spectral imaging system according to claim 1, characterized in that: The front unit includes a first lens group, an aperture and a second lens group, the first lens group includes a first lens, a second lens, a third lens and a fourth lens, the third lens and the fourth lens form a first double-cemented lens group, the second lens group includes a fifth lens, a sixth lens, a seventh lens and an eighth lens, the sixth lens and the seventh lens form a second double-cemented lens group.

3. The spectral imaging system according to claim 2, characterized in that: The first lens group and the imaging system satisfy the following relationship: -1.52<f q / f d1 <-1.58 Among them, f q represents the combined focal length of the first lens group, f d1 Indicates the focal length of the front unit.

4. The spectral imaging system according to claim 3, characterized in that: The first lens, the second lens and the first doublet lens group satisfy the following relationship with the first lens group: -11.3<f1 / f q <-10.9 39<f2 / f q <45 0.79<f 34 / f q <0.84 Where f1 is the focal length of the first lens, f2 is the focal length of the second lens, and f 34 represents the focal length of the first doublet lens group, f q represents the combined focal length of the first lens group.

5. The spectral imaging system according to claim 2, characterized in that: The second lens group and the imaging system satisfy the following relationship: 0.95<f h / f d1 <1.15 Among them, f h represents the combined focal length of the second lens group, f d1 Indicates the focal length of the front unit.

6. The spectral imaging system according to claim 5, characterized in that: The fifth lens, the eighth lens, the second doublet lens group and the second lens group satisfy the following relationship: 1.67<f5 / f h <1.71 2.53<f8 / f h <2.85 3.73<f 67 / f h <3.92 Among them, f5 represents the focal length of the fifth lens, f8 represents the focal length of the eighth lens, and f 67 represents the focal length of the second doublet lens group, f h Indicates the combined focal length of the second lens group.

7. The spectral imaging system according to claim 1, characterized in that: The rear unit includes a ninth lens to a fifteenth lens, the tenth lens and the eleventh lens form a third double-cemented lens group, and the thirteenth lens and the fourteenth lens form a fourth double-cemented lens group.

8. The spectral imaging system according to claim 7, characterized in that: The ninth lens, the twelfth lens and the fifteenth lens satisfy the following relationship with the imaging system: 0.58<f9 / f d2 <0.61 0.24<f 12 / f d2 <0.27 -2.76<f 15 / f d2 <-2.73 Where, f9 represents the focal length of the ninth lens, f 12 represents the focal length of the twelfth lens, f 15 represents the focal length of the fifteenth lens, f d2 Indicates the focal length of the rear unit.

9. The spectral imaging system according to claim 7, characterized in that: The third doublet lens group and the imaging system satisfy the following relationship: 0.78<f 1011 / f d2 <0.82 Among them, f 1011 represents the focal length of the triplet lens group, f d2 Indicates the focal length of the rear unit.

10. The spectral imaging system according to claim 7, characterized in that: The fourth double-cemented lens group and the imaging system satisfy the following relationship: 0.72<f 1314 / f d2 <0.74 Among them, f 1314 represents the focal length of the four-doublet lens group, f d2 Indicates the focal length of the rear unit.

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