Tandem lens group optical coupling system for image intensifier

Abstract

The utility model relates to the technical field of optical imaging, in particular to a series lens group optical coupling system for an image intensifier. Comprising a series lens group, and the series lens group comprises a first lens and a second lens which are sequentially arranged between a phosphorescent screen of an image intensifier and a CCD or CMOS camera in parallel from front to back; the first lens is a collimating lens and is used for converting light rays from an object into parallel light beams; and the second lens is an imaging lens and is used for focusing the parallel light beams on a camera photosensitive device to form a clear image. According to the series-connection lens group, through combination of the two lenses, effective focusing and imaging of light rays are achieved, and the series-connection lens group has a high aperture ratio, high light transmission efficiency and excellent optical resolution; compared with traditional optical fiber taper coupling, the series lens group reduces image artifacts and improves image quality. And meanwhile, maintenance and upgrading are facilitated, and a complex re-alignment process is not needed.

Description

Technical Field

[0001] This utility model relates to the field of optical imaging technology, and more specifically, to a series lens group optical coupling system for an image intensifier. Background Technology

[0002] In optical imaging systems, the output phosphor screen of an image intensifier typically needs to be effectively coupled to the camera's photosensitive element to achieve high-resolution and high-sensitivity imaging. An image intensifier is an instrument that converts ultraviolet to infrared light into electrons using a high-speed photocathode, amplifies these electrons through a microchannel plate, and then emits the amplified electrons onto a phosphor screen. In existing technologies, coupling efficiency and image quality are often limited by the lens group design.

[0003] In existing technologies, the coupling methods between the output phosphor screen of an image intensifier and the camera's photosensitive device fall into three main categories: fiber taper coupling, single-lens coupling, and tandem lens coupling. Fiber taper coupling is characterized by using optical fibers to transmit the output light from the image intensifier's phosphor screen to the sensor point-to-point, based on the principle of total internal reflection. Its disadvantages include: while theoretically the transmission efficiency can reach up to 60%, in practical applications, various loss mechanisms such as interface loss, fiber diameter, and the reduction ratio of the fiber taper make it difficult to achieve the theoretical value. Furthermore, it is prone to aliasing, shearing, and coarse artifacts, which are usually related to the fiber taper manufacturing process. Single-lens coupling images the light from the phosphor screen onto the detector using a single lens. Its disadvantages include: even with a large aperture lens, the transmission efficiency is only a single-digit percentage, far lower than the theoretical value of fiber taper coupling; in practical applications, single-lens coupling is also affected by similar loss mechanisms as fiber taper coupling. The characteristics of tandem lens group coupling are as follows: tandem lens group coupling is achieved by arranging two lenses. The first is an ultra-high efficiency coupling lens, and the second lens can be freely selected according to the size of the camera's image sensor and the pixel size to achieve optimal light transmission efficiency and optical resolution. Its advantages are: compared with conventional relay coupling lenses, the tandem lens group design provides the highest aperture size, significantly improving light transmission efficiency; the flexibility in selecting the second lens makes it easier to obtain the highest optical resolution performance.

[0004] In summary, current coupling techniques between image intensifiers and CCD or CMOS cameras, such as fiber taper coupling and single-lens coupling, suffer from low efficiency and image artifacts. While tandem lens group coupling offers advantages in efficiency and resolution, it may present challenges due to manufacturing complexity. These techniques are limited by low light energy utilization, image quality degradation, and high manufacturing difficulty. Therefore, we propose a tandem lens group optical coupling system for image intensifiers. Utility Model Content

[0005] The purpose of this invention is to provide a series lens group optical coupling system for image intensifiers to solve the problems mentioned in the background art.

[0006] To solve the aforementioned technical problems, the purpose of this utility model is to provide a tandem lens group optical coupling system for an image intensifier, comprising a tandem lens group for coupling the image output from the phosphor screen of the image intensifier to a CCD or CMOS camera; the tandem lens group includes a first lens and a second lens arranged parallel to each other from front to back between the phosphor screen of the image intensifier and the CCD or CMOS camera; wherein:

[0007] The first lens is a collimating lens, used to convert light rays from an object into parallel beams;

[0008] The second lens is an imaging lens, used to focus a parallel light beam onto the sensor, i.e., the camera's photosensitive device, to form a clear image.

[0009] As a further improvement to this technical solution, the first lens is an ultra-high efficiency coupling lens with an aperture of up to F / 0.95, used to convert light from the phosphor screen of the image intensifier into a parallel beam.

[0010] As a further improvement to this technical solution, the second lens is freely selected according to the size of the photosensitive device and the pixel size of the camera to be used, so as to optimize the light transmission efficiency and optical resolution; wherein, the size of the photosensitive device is specifically the size of the photosensitive chip target surface.

[0011] As a further improvement to this technical solution, the tandem lens group uses a large aperture, with an aperture ratio ranging from F / 1.5 to F / 0.85, to capture more light in low-light environments. Through optimized lens design and combination, this method achieves an optical transmission efficiency of up to 31.2% or higher, which is more efficient than traditional fiber taper coupling methods. The tandem lens group design reduces image artifacts, including aliasing, shearing, and coarse artifacts, improving image quality and offering significant advantages over traditional fiber taper coupling technology. The structure of the tandem lens group facilitates maintenance and upgrades, allowing for easy lens replacement without the need for complex realignment processes.

[0012] As a further improvement to this technical solution, the focal length of the first lens is between 50mm and 150mm, and the focal length of the second lens is between 30mm and 80mm, so as to achieve a suitable imaging magnification and field of view.

[0013] As a further improvement to this technical solution, the focal length and aperture of the second lens are calculated based on the determined target surface size and pixel size of the camera's photosensitive chip and the typical output resolution of the phosphor screen, so as to ensure that the output resolution is close to twice the pixel size and the image circle diameter is approximately equal to the diagonal length of the photosensitive chip target surface.

[0014] As a further improvement to this technical solution, the formula for calculating the focal length of the second lens includes:

[0015] Based on the fundamental principles and formulas of optical imaging, we have:

[0016]

[0017] in, It's the magnification factor. It is the image distance. It is the object distance; for a lens imaging system, the image distance can be calculated based on the known object distance (such as the distance from the phosphor screen of the image intensifier to the second lens) and the desired magnification.

[0018] In addition, according to the thin lens formula:

[0019]

[0020] in, It is the focal length of the lens;

[0021] The typical output size of a phosphor screen is known. and the target size of the camera sensor chip The magnification factor is ;

[0022] First, the required magnification is calculated based on the typical output size of the phosphor screen and the desired target size of the camera sensor. ;

[0023] Then, let the object distance be... (It can be roughly estimated based on the system's structure and layout, or determined based on empirical data.) Calculate the image distance ;

[0024] Finally, the calculated and Substitute into the thin lens formula The focal length of the second lens is then calculated. .

[0025] As a further improvement to this technical solution, the calculation formula for the aperture of the second lens includes:

[0026] Aperture size With luminous flux and image illuminance The relationship between them is represented as follows:

[0027]

[0028] Based on image illuminance The requirement to calculate the aperture ;

[0029] First, based on the required image plane illuminance and known luminous flux (This can be estimated based on factors such as light source intensity and system transmittance), and the formula can be applied. After deformation, we get:

[0030]

[0031] Then, the aperture is calculated. .

[0032] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0033] 1. In this tandem lens group optical coupling system for image intensifiers, the tandem lens group technology is an advanced design for improving the performance of optical systems. It achieves effective focusing and imaging of light through the combination of two lenses, featuring a high aperture ratio, high light transmission efficiency, and excellent optical resolution. Compared to traditional lenses, tandem lens groups can be designed with a larger aperture, allowing more light to pass through and improving image brightness. Through precise lens design and material selection, the light transmission efficiency of tandem lens groups is significantly improved, reducing light loss. The design of tandem lens groups can provide high-resolution imaging, which is crucial for applications requiring fine imaging.

[0034] 2. In this tandem lens group optical coupling system for image intensifiers, compared with traditional fiber taper coupling, the tandem lens group reduces image artifacts such as aliasing, shearing, and coarse artifacts, thus improving image quality. At the same time, the design of the tandem lens group allows for easy lens replacement, facilitating maintenance and upgrades without the need for a complex realignment process. The tandem lens group technology provides an efficient and high-quality solution in the field of optical imaging, and is particularly suitable for applications requiring high-resolution and high-sensitivity imaging. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the image coupling principle of an exemplary series lens group in this utility model;

[0036] In the picture:

[0037] L1, the first lens; L2, the second lens. Detailed Implementation

[0038] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model. Example 1

[0039] like Figure 1 As shown, this embodiment provides a series lens group optical coupling system for an image intensifier, including a series lens group for coupling the phosphor screen output image of the image intensifier to a CCD or CMOS camera; the series lens group includes a first lens L1 and a second lens L2 arranged parallel to each other from front to back between the phosphor screen of the image intensifier and the CCD or CMOS camera; wherein:

[0040] The first lens L1 is a collimating lens, used to convert light rays from an object into parallel beams;

[0041] The second lens L2 is an imaging lens, used to focus a parallel beam of light onto the sensor, i.e., the camera's photosensitive device, to form a clear image.

[0042] Figure 1 In this process, the image output from the phosphor screen is emitted from the image intensifier. The light rays are divergent and are converted into parallel rays by the first lens L1, which acts as a collimating lens (this process utilizes the principle of lens refraction; the special curvature design of the lens changes the direction of light propagation, thus achieving collimation). The parallel rays are then focused by the second lens L2, which acts as an imaging lens (this process is also based on the principle of lens refraction; by adjusting the position and focal length of the lens, the light rays converge to a single point on the sensor, thus achieving imaging). Finally, a clear image is formed on the camera's sCMOS sensor. The sCMOS (scientific-grade complementary metal-oxide-semiconductor) sensor is a high-sensitivity, low-noise image sensor commonly used in scientific research, industrial inspection, and other fields with high image quality requirements. It converts received light signals into electrical signals, which are then processed and stored by subsequent electronic equipment.

[0043] In the picture, and These are the focal lengths of the first lens L1 and the second lens L2, respectively. Focal length is an important parameter of a lens, which determines the lens's ability to refract light and its imaging characteristics.

[0044] The collimating lens determines the ability of a collimating lens to convert diverging rays into parallel rays. A suitable lens can ensure that the light rays can be effectively collimated, providing a good foundation for the subsequent imaging process.

[0045] The imaging lens determines the ability of the imaging lens to focus parallel light rays into an image; this is achieved by adjusting the distance between the second lens L2 and the sCMOS sensor, making it close to and eventually equal to... Clear images can be obtained on the sensor.

[0046] In this embodiment, the first lens L1 is an ultra-high efficiency coupling lens with an aperture of up to F / 0.95, used to convert the light from the phosphor screen of the image intensifier into a parallel beam. The first lens L1 is preferably designed with an ultra-large aperture of 50mm focal length and 0.95 aperture to ensure that the image circle diameter of the output image is less than 25mm, meeting the minimum usage requirement of 6mm, so as to achieve effective collimation of the light output from the phosphor screen.

[0047] Furthermore, the second lens L2 is freely selected according to the size of the photosensitive device and the pixel size of the camera to be used, so as to optimize the light transmission efficiency and optical resolution; wherein, the size of the photosensitive device is specifically the size of the photosensitive chip target surface.

[0048] In this embodiment, the tandem lens group uses a large aperture with an aperture ratio in the range of F / 1.5 to F / 0.85 to capture more light in low-light environments.

[0049] Furthermore, in the tandem lens group, the focal length of the first lens L1 is between 50mm and 150mm, and the focal length of the second lens L2 is between 30mm and 80mm, to achieve suitable imaging magnification and field of view. Through optimized lens design and combination, this method achieves an optical transmission efficiency of 31.2% or higher, which is more efficient than traditional fiber taper coupling methods. The tandem lens group design reduces image artifacts, including aliasing, shearing, and coarse artifacts, improving image quality and offering significant advantages over traditional fiber taper coupling technology. The structure of the tandem lens group is easy to maintain and upgrade, allowing for easy lens replacement without a complex realignment process. Compared to conventional relay coupling lens methods, this tandem lens group design provides the largest aperture size, significantly improving light transmission efficiency; furthermore, the selection of the second lens is very flexible, making it easier to achieve the highest optical resolution performance.

[0050] In a series of lenses, the focal length of the lens determines the magnification and field of view of the image; for example, if the focal length of the first lens L1 is 100mm, then the focal length of the second lens L2 can preferably be 53mm.

[0051] Specifically, in the imaging process, light emitted from the phosphor screen of the image intensifier first passes through the first lens L1 and is converted into a parallel beam or a beam of a specific form. Then, it is focused onto the camera's photosensitive device by the second lens L2 to form a clear image. This process follows the basic principles of optical imaging and achieves efficient and high-resolution imaging through specific lens parameter design.

[0052] In this embodiment, the selection method for the second lens L2 includes: first, determining the target surface size and pixel size of the camera's photosensitive chip; then, calculating the required focal length and aperture of the second lens L2 based on the typical output resolution of the phosphor screen, to ensure that the output resolution is close to twice the pixel size and the image circle diameter is approximately equal to the diagonal length of the photosensitive chip target surface, thereby ensuring that the output resolution and image circle diameter meet the technical requirements. In an optical imaging system, the image circle refers to the circular image area projected by the lens; when light passes through the lens, it forms a circular spot on the imaging plane (e.g., the plane where the camera's photosensitive element is located), and the range of this circular spot is the image circle.

[0053] Furthermore, the method for calculating the required focal length of the second lens L2 includes:

[0054] Based on the fundamental principles and formulas of optical imaging, we have:

[0055]

[0056] in, It's the magnification factor. It is the image distance. It is the object distance; for a lens imaging system, the image distance can be calculated based on the known object distance (such as the distance from the phosphor screen of the image intensifier to the second lens L2) and the desired magnification.

[0057] In addition, according to the thin lens formula:

[0058]

[0059] in, It is the focal length of the lens;

[0060] Assuming the typical output size of the phosphor screen is known. and the target size of the camera sensor chip The magnification factor is ;

[0061] First, the required magnification is calculated based on the typical output size of the phosphor screen and the desired target size of the camera sensor. ;

[0062] Then, assuming the object distance has been determined (It can be roughly estimated based on the system's structure and layout, or determined based on empirical data.) Calculate the image distance ;

[0063] Finally, the calculated and Substitute into the thin lens formula Solve for the focal length of the second lens. .

[0064] The algorithm for calculating the magnification factor based on the resolution of the phosphor screen (e.g., assuming a typical output resolution of 35 lp / mm) is as follows:

[0065] First, based on the resolution of the phosphor screen (Assuming the number of pixels in the horizontal and vertical directions, for example) (and the resolution of the camera sensor target surface) Calculate the magnification in the horizontal and vertical directions. and :

[0066]

[0067]

[0068] Typically, the average value can be taken as the overall magnification, i.e. .

[0069] Furthermore, the calculation method for the required aperture of the second lens L2 includes:

[0070] Aperture size With luminous flux and image illuminance The relationship between them is expressed as follows:

[0071]

[0072] To ensure sufficient light capture in low-light environments, it is necessary to consider the image plane illuminance. The requirement to calculate the aperture ;

[0073] First, based on the required image plane illuminance and known luminous flux (This can be estimated based on factors such as light source intensity and system transmittance), and the formula can be applied. After deformation, we get:

[0074]

[0075] Then, the aperture is calculated. .

[0076] Among them, luminous flux Image plane illuminance The requirements are:

[0077] Luminous flux It can be estimated based on the intensity of the light source, the transmittance of the system, and the characteristics of the phosphor screen; the luminous intensity of the light source can be considered. The system's transmittance and the area of ​​the phosphor screen Then the luminous flux .

[0078] Image illuminance The requirements can be determined based on the performance of the camera's image sensor and the desired image quality. Different cameras have different sensitivities, and the image illuminance can be determined based on the required exposure level. .

[0079] In addition, the Rayleigh criterion can be introduced to optimize system performance during the calculation of the required aperture of the second lens L2, specifically:

[0080] In practical applications, to improve the performance of optical imaging systems, such as ensuring that the output resolution is close to twice the pixel size, optimization can be performed based on the Rayleigh criterion; the Rayleigh criterion formula is:

[0081]

[0082] in, It is the smallest distinguishable distance. It is the wavelength of light. It's the focal length. It is the aperture diameter;

[0083] Based on the wavelength range of the light in the system (assuming it is the visible light range), (between 400nm and 700nm), and the focal length calculated earlier. The required aperture diameter can be calculated by working backward from the desired resolution (which is related to the pixel size). And then according to Adjust the aperture size to ensure optimal system performance.

[0084] In summary, the tandem lens group optical coupling system of this technical solution achieves efficient coupling between the image intensifier and the camera sensor through precise design of the collimating lens and imaging lens, thereby improving imaging quality and overall system performance.

[0085] Those skilled in the art will understand that the process of implementing all or part of the steps of the above embodiments can be carried out by hardware or by a program instructing the relevant hardware.

[0086] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed utility model. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. A tandem lens group optical coupling system for an image intensifier, characterized in that: The image intensifier includes a series lens assembly for coupling the output image from the phosphor screen to a CCD or CMOS camera. The series lens assembly comprises a first lens (L1) and a second lens (L2) arranged parallel to each other from front to back between the phosphor screen and the CCD or CMOS camera. The first lens (L1) is a collimating lens used to convert light rays from an object into parallel beams; The second lens (L2) is an imaging lens used to focus a parallel beam of light onto the camera's image sensor to form a clear image.

2. The tandem lens group optical coupling system for an image intensifier according to claim 1, characterized in that: The first lens (L1) is an ultra-high efficiency coupling lens with an aperture of up to F / 0.95, used to convert light from the phosphor screen of the image intensifier into a parallel beam.

3. The tandem lens group optical coupling system for an image intensifier according to claim 1, characterized in that: The second lens (L2) is selected according to the size of the photosensitive device and the pixel size of the camera to be used; wherein, the size of the photosensitive device is the size of the photosensitive chip target surface.

4. The tandem lens group optical coupling system for an image intensifier according to claim 1, characterized in that: The tandem lens group uses a large aperture with an aperture ratio ranging from F / 1.5 to F / 0.85 to capture more light in low-light environments.

5. The tandem lens group optical coupling system for an image intensifier according to claim 1, characterized in that: The focal length of the first lens (L1) in the tandem lens group is between 50mm and 150mm, and the focal length of the second lens (L2) is between 30mm and 80mm.

6. The tandem lens group optical coupling system for an image intensifier according to claim 1, characterized in that, The focal length and aperture of the second lens (L2) are calculated based on the determined target size and pixel size of the camera's image sensor and the typical output resolution of the phosphor screen.

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