CN203037936U - Ultrahigh-resolution infrared camera lens - Google Patents

Abstract

An ultrahigh-resolution infrared camera lens comprises four parts including a primary mirror 1, a secondary mirror 2, a light splitting device and photosensitive elements 5 which are placed on a main optical path in sequence. The primary mirror 1 and the secondary mirror 2 are reflecting mirrors, the light splitting device is a micro lens array and imitates the compound eye structure of the insect, small hexagonal lens arrays are respectively coated on a semi-spherical surface of a spherical lens, and micro lenses are identical in structural form and size. Light beams are split by the micro lens array, a high-definition CCD photosensitive element 5 is arranged at the back of each micro lens, a sub image is formed on each high-definition CCD photosensitive element 5. Then, feature point extraction and matching calculation are carried out on each sub image, and effective pixels in the sub images are extracted and re-spliced to finally obtain an ultrahigh-resolution image. The utility model provides a solution for the problem that an infrared instrument cannot obtain a high-resolution image as the overall resolution of an imaging system is conditioned by a CCD device.

Description

Ultra High Resolution Infrared Camera Lens

technical field

The utility model relates to an infrared lens, which utilizes a microlens array to realize the light beam splitting technology, forms an image through each microlens, and then carries out image splicing to realize super high resolution. the

Background technique

With the development of optical imaging technology, the resolution of the system will not only be limited by the diffraction limit of the optical system, but also be affected by the folding and aliasing effect caused by the insufficient sampling frequency of the detector. To solve this problem, it is necessary to improve the resolution of the system rate, the most direct solution is to reduce the pixel size of the detector. Under the premise of ensuring the clear aperture and modulation transfer function of the optical system, the smaller the pixel size, the higher the resolution. Using a detector chip with a small pixel size can make full use of the resolving power of the optical system, but its disadvantage is that it is limited by the relative aperture of the camera optics, the focal plane irradiance and the manufacturing method of the detector, and the reduction of the pixel size has a Limit value, as the pixel size of the detector decreases, the shot noise will also increase, the minimum illuminance received by the pixel will decrease, the sensitivity will decrease, and crosstalk will also occur between the pixels. Therefore, in order to balance the overall imaging performance of the detector, the photoelectric system, especially the infrared system, has certain requirements on the photosensitive area of the detector, and the size of the pixel cannot be reduced arbitrarily. the

Infrared thermal imaging technology is a passive infrared night vision technology. Its principle is that after the infrared instrument converts the power signal of the infrared radiation of the object into an electrical signal, the imaging device can simulate the spatial distribution of the surface temperature of the object one by one. After processing, a thermal image video signal is formed and transmitted to the display screen to obtain a thermal image corresponding to the thermal distribution on the surface of the object, that is, an infrared thermal image. At present, the pixels of the detectors of infrared instruments are only 4096×4096 at most, and the pixels of pictures are about 16 million pixels. The pixels of general infrared instruments are only a few million pixels, and the commonly used commercial infrared detectors are 320×240 and 640 pixels. ×480, the pixel size is 25μm~50μm, the obtained picture has low pixels and low precision. Realizing the ultra-high resolution of the imaging system is mainly a matter of improving the spatial resolution of the diffraction limit limited by the relative aperture of the optical system, and the overall resolution of most photoelectric imaging systems is mainly limited by the CCD, so it is necessary to improve the resolution of the system. There are two methods, one is to use optical methods to achieve image stitching to achieve high resolution, and the other is to improve the geometric resolution of CCD photosensitive elements. the

(1) Use the method of CCD splicing to achieve high resolution. In general, the higher the pixel of the CCD detector, the higher the quality of the formed image and the higher the definition, but the CCD detection device of the infrared instrument limits the resolution of the instrument. It is difficult to improve the quantum efficiency of infrared CCD detectors, because the energy of infrared photons is small and the quantum efficiency is low, which reduces its detection sensitivity, and it is difficult to make a large-area CCD. The aberration of the imaging system is large and the difficulty is also high. . the

(2) The method of optical splicing to achieve high resolution is a commonly used method at present. Optical splicing is divided into two structural forms: optical path splitting and beam splitting. The beam splitting of the optical path is to pass through the beam splitting prism in front of the field diaphragm to produce several imaging planes that are mechanically separated from each other and the optical image planes are conjugate to each other, and the spatial position of each CCD photosensitive element is precisely installed and calibrated on each imaging plane. Realize the seamless splicing of the image plane. Beam splitting is the use of beam splitting to achieve optical splicing. The scene is imaged on the first spherical image plane, the light beam is split by the subsequent adapter lens array, and n CCD photosensitive elements are placed on the second image plane to cover the entire imaging field of view. The coordinate system of each CCD is calibrated, organically combined in the image reading process, and spliced by optical and mechanical methods to achieve high-resolution imaging. the

Contents of the invention

The lens in the utility model is mainly to solve the problem that the resolution of the system is limited by the photosensitive element, and provide an optical lens for realizing ultra-high resolution of an infrared instrument. the

The solution of the utility model is to adopt the method of optical splicing to realize the high resolution of the lens. The lens includes four parts: primary mirror, secondary mirror, microlens array and CCD photosensitive element. The intermediate focal plane formed by the secondary mirror is a spherical surface, and the microlens array arrayed on the hemispherical surface is a beam splitting device, which splits the target beam; in order to ensure good imaging quality, the structure of the microlens is a compound lens, which is composed of several optical elements : The optical structure and optical components of each microlens are exactly the same; the size of the microlens is determined by the minimum illumination received by the photosensitive element, and the number of microlenses is determined by the range covered by the field of view of the system and the size of the microlens . In the imaging process, each microlens in the microlens array is equipped with a CCD photosensitive element, and each photosensitive element forms a sub-image for the detection target; since the photosensitive element cannot completely cover the entire field of view, it will inevitably cause the gap between each sub-image There is a blank area between them, so it is necessary to extract and re-splicing the effective pixels in the sub-images to finally obtain a high-resolution image: after the lens is adjusted, it is sealed with silicon rubber to prevent air from entering and maintain a good airtightness of the optical instrument itself. the

Compared with the existing infrared imaging technology, the utility model has the following advantages:

1. The microlens array is used to split the light path to finally achieve ultra-high resolution, breaking through the limitation of the overall resolution of the system by the CCD photosensitive device, and significantly improving the imaging quality of the system. the

2. The intermediate focal plane is a spherical surface. On the focal plane of a general lens, the closer to the edge, the worse the imaging quality. The perfect symmetry of the spherical focal plane ensures that the imaging quality is uniform everywhere. the

3. It reduces the difficulty and cost of obtaining high-resolution images by splicing multiple images obtained multiple times. the

4. The entire optical cavity is sealed to reduce the influence of humidity and salt spray on the optical system. the

Description of drawings

Below in conjunction with accompanying drawing and embodiment the utility model is further described. the

Figure 1 is a schematic diagram of the optical path of the optical system in the super-resolution infrared camera lens. the

Figure 2 is a microlens array arranged in a hemispherical field of view. the

Figure 3 is the image stitching process. the

In the figure, 1 is the main mirror, the surface type is spherical or aspheric, 2 is the secondary mirror, the surface type is spherical or aspheric, the mirror surface is spherical, 3 is the intermediate focal plane, the focal plane type is spherical, 4 is the microlens, 5 Be photosensitive element, 6 is infrared rays. the

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. the

In the following examples, unless otherwise specified, all are conventional methods. the

The various units used in the examples adopt national standards uniformly. the

Embodiment 1: Composition of the optical system. the

As shown in FIG. 1 , the optical system of the camera adopts a catadioptric type, and the structure of the optical system includes a primary mirror 1 , a secondary mirror 2 , a microlens array composed of microlenses 4 , and a photosensitive element 5 . The spectroscopic device imitates the compound eye structure of insects - the spherical surface of the spherical lens is covered with many hexagonal small lens arrays, each small lens array is equipped with a CCD photosensitive device, and the system transmits the image to its respective sensor. Primary mirror 1 and secondary mirror 2 are reflective lenses, and the intermediate image plane for imaging is a spherical surface. Within the circular field of view behind the intermediate image plane, several lenses are arrayed on the spherical surface to realize beam splitting (generally, the closer the lens is to the edge, the The worse the resolution is, unlike a flat lens that loses resolution at the edge, the perfect symmetry of a spherical lens ensures that the resolution is uniform everywhere). When the infrared ray 6 emitted by the target enters the interior of the camera, it is reflected by the primary mirror 1 and reaches the secondary mirror 2, and is imaged on the intermediate focal plane 3 after being reflected again. At this time, the target has been imaged once. Then when the light passes through the spectroscopic device, it is divided into several beams by the microlens array (there are n microlens arrays, and the light is divided into n beams), and each beam of light is imaged on the photosensitive element 5 through the corresponding microlens to form a picture. Image, the resolution of this image is determined by the photosensitive element. A photosensitive element is placed behind each lens, and an image is formed on each photosensitive element. After image transmission and splicing, each high-resolution image finally forms an ultra-high-resolution image. the

(1) Primary mirror. The primary mirror is a concave mirror with a spherical or aspherical surface. The reflective surface will not introduce aberration in the imaging of the system, thereby reducing the difficulty of aberration elimination by the microlens behind. The use of aspherical lenses not only greatly simplifies the structure of optical equipment, but also greatly improves its optical performance. Taking the vertices of the surface at the origin, the equation of the surface is:

y ² =2r ₀ x-(1-e ² )x ²

Where r ₀ is the radius of curvature of the surface, and e is the eccentricity of the surface. When using Code V to optimize the optical system, the system will automatically change the curvature and eccentricity of the surface equation to improve the imaging quality.

(2) Secondary mirror. The secondary mirror is a convex mirror with a spherical or aspherical surface shape, which will not introduce aberrations in the system imaging, thereby reducing the difficulty of aberration elimination by the microlens behind. the

(3) Intermediate focal plane. The surface of the intermediate focal plane after the target is imaged by the primary mirror and the secondary mirror is a spherical surface. On the focal plane of a general lens, the closer to the edge, the worse the image quality. The perfect symmetry of the spherical focal plane ensures that the image quality is uniform everywhere. the

(4) Microlens array. The structural form and size of all the microlenses arrayed on the hemispherical surface are exactly the same as those of the central microlens, which reduces the cost of design and processing. the

(5) A hexagonal array is used for the beam splitting device. Because the array is quadrilateral or pentagonal, there will be a blank area in the middle of the microlens of the array, which has two effects on the imaging lens. One is that the beam splitting device is not fully utilized. The waste of energy is caused, and the other is to reduce the number of microlens arrays and reduce the resolution of the image obtained after the final stitching. the

(6) CCD photosensitive element. In the case of ensuring the signal-to-noise ratio and minimum illuminance, choose a CCD photosensitive element with high resolution and a photosensitive area matching the microlens as much as possible, that is, a photosensitive element with a small single pixel area, which can not only ensure the imaging quality of the microlens , and can improve the resolution of the stitched panoramic image. the

Example 2: Athermal design of the system. the

All components in the optical system will change with the change of temperature, such as the refractive index of glass material, radius of curvature, thickness, etc. will change, and then the image plane of the system will drift, causing defocus and greatly reducing the imaging quality. In order to ensure that the imaging quality of the optical system is not affected by temperature, it is necessary to carry out an athermal design for the system, so as to ensure that the focal length and image quality of the system remain unchanged or change little in a large temperature range. Common athermalization design methods include mechanical passive, electromechanical active and optical passive. (1) Mechanical passive. The mechanical passive type uses temperature-sensitive mechanical materials or memory alloys to cause axial displacement of one or a group of lenses, thereby compensating for image plane displacement caused by temperature changes. (2) Electromechanical active type. A thermal sensor and a feedback circuit are added to the system. According to the displacement relationship of the image plane when the temperature changes during the design process, when the temperature changes, the thermal sensor detects the temperature change, and the feedback circuit feeds back to the mechanical structure and moves accordingly. The lens fixed to the mechanical structure also moves to compensate for the image plane shift caused by temperature changes. This compensation method is simple in principle and easy to implement, but has low reliability, increases the volume and weight of the optical system, and is relatively costly. high. (3) Optical passive. It matches optical glasses with different temperature characteristics, corrects chromatic aberration and thermal difference, and then matches the thermal expansion of mechanical structural materials to eliminate the influence of temperature on image quality. Optical passive temperature compensation has very good performance, high reliability, light weight, low cost, and requires no power supply. the

The utility model uses an optical passive method to carry out an athermal design for the instrument, and uses mutual compensation between glass materials to eliminate the influence of temperature changes on the imaging quality of the instrument to ensure that the instrument works normally within the range of -10°C to 40°C. the

Embodiment 3, the acquisition of the image of ultra-high resolution

In the imaging process, each microlens in the microlens array is equipped with a photosensitive element. Since the photosensitive element cannot completely cover the entire field of view, there will inevitably be a blank area between each sub-image, so the sub-image needs to be extracted and re-stitched. effective pixels. The image acquisition method adopted by the utility model is as follows: first obtain several sub-images from the photosensitive element behind the microlens array, then perform feature point extraction and matching calculation on each sub-image, and determine the overlapping areas and Repeat the position, merge several images, complete the stitching of panoramic images, and finally get a super high-resolution image. the

Embodiment 4, airtightness of system

The entire optical cavity is sealed to reduce the impact of moisture and salt spray on the optical system. Each optical component is sealed with silicon rubber after installation and adjustment to prevent air from entering and maintain good sealing of the optical instrument itself. In order to prevent fog, window glass is added to the front of the optical lens, and three anti-hydrophobic films are coated on the outer surface of the window glass. The metal parts in the cavity of the optical lens are treated with anti-acid oxidation, and the moving parts are coated with aviation grease. All exposed metal parts are cadmium-plated or stainless steel with good corrosion resistance is used to improve their corrosion resistance. In order to avoid the impact of vibration on the imaging quality of the system, it is necessary to obtain the motion information of the carrier through the attitude sensing component, use the tracking algorithm to perform motion compensation, and adjust the working attitude of the lens in real time, so as to obtain stable and reliable data output. the

In addition, the infrared camera lens in this utility model can achieve ultra-high resolution, and any equivalent change or modification on the shape, structure and features made by using the design spirit of the camera lens in this utility model can achieve ultra-high resolution, All are considered to fall within the protection scope of the present utility model. the

Claims (5)

1. A super-high-resolution infrared camera lens, wherein the optical system of the camera adopts a catadioptric type, and the lens includes four primary mirrors (1), secondary mirrors (2), light splitters and photosensitive elements (5) The part is characterized in that: the intermediate focal plane (3) formed by the primary mirror (1) and the secondary mirror (2) is a spherical surface, and the microlens array arrayed on the hemispherical surface is a beam splitting device, which splits the target light beam; the microlens ( 4) The structural form is a compound lens, which is composed of several optical elements. the 2. The ultra-high resolution infrared camera lens according to claim 1, characterized in that: the size of the microlens (4) is determined by the minimum illuminance received by the photosensitive element, and the number of the microlens (4) is determined by the system The coverage of the field of view and the size of the microlens are determined. the 3. The ultra-high-resolution infrared camera lens according to claim 1 or 2, characterized in that: the optical components and optical structures of each microlens (4) in the microlens array are identical. the 4. The ultra-high resolution infrared camera lens according to claim 3, characterized in that: each microlens (4) in the microlens array is equipped with a CCD photosensitive element, and each photosensitive element forms an image of the detection target. sub image. the 5. The ultra-high resolution infrared camera lens according to claim 4, characterized in that: the lens is sealed with silicon rubber after being adjusted. the

Images