Flat field conversion system for lobster eye lens

Abstract

The invention discloses a flat field conversion system for a lobster eye lens, and belongs to the field of detection. The device comprises a light source, a lobster eye lens, a curved-surface optical fiber bundle, a relay lens group, a medium-wave infrared detector and a base. The lobster eye lens is used for receiving light projected by a detection object in a view field range. A light source is arranged at an edge field of view of a lobster eye lens, and the lobster eye lens, a curved optical fiber bundle, a relay lens group and a medium-wave infrared detector are coaxially fixed on a base in sequence from left to right. The lobster eye lens detects an object in an edge view field, medium-wave infrared light emitted by the object is converged on the front end face of the curved-surface optical fiber bundle through the lobster eye lens and performs primary imaging, and the curved-surface optical fiber bundle converts a bent image surface into a flat field and transmits the flat field to an object surface of the relay lens group. And the relay lens group transmits an image surface and performs cold diaphragm matching with the medium-wave infrared detector, so that the contradiction between a large view field and high resolution of the lobster eye lens is solved, and high-precision detection of the lobster eye system on a target at an edge view field is realized.

Description

Technical Field

[0001] The invention belongs to the field of detection and relates to a flat field conversion system for a lobster eye lens. Background Art

[0002] Bionic lobster eye lens ( Figure 1 ) consists of several microchannels forming a square plane. According to the composition of the microchannels, it is divided into two types: Schmidt type and Angle type. Different from the traditional imaging optical system with large field of view and high resolution, the bionic lobster eye lens has the characteristics of small size and low manufacturing cost, which solves the problem of large size, many lenses and high cost of traditional imaging optical system. The lobster eye optical system is more used in visible light and infrared bands. The lobster eye optical system is a reflective optical system ( Figure 2 ), there is no problem with the band characteristics of the material, and wide spectrum, common aperture, large field of view, and high-resolution target detection and imaging can be achieved. The bionic lobster eye technology has a good application prospect in seeker guidance.

[0003] However, the spherically symmetrical structure of the rectangular microchannel plate of the lobster eye lens not only widens the field of view, but also causes the curvature of its image plane. Most of the detectors currently used are planar structures. The larger the target off-axis angle, the greater the deviation between the actual detection position of the detector and the image plane position, and the more diffuse the focal spot. This limits the further expansion of the field of view of the lobster eye lens, and weakens the large field of view detection characteristics of the lobster eye lens.

[0004] With the continuous development of fiber bundle imaging, the preparation of curved fiber bundles has come into people's view. Figure 3 ) By coupling with the curved focal plane, the optical signal is transmitted independently along each fiber channel and finally becomes a flat field when it reaches the output end face. Applying the curved fiber bundle to the lobster eye imaging system can largely maintain the large field of view of the lobster eye lens, so that the curved image plane is converted into a flat field and received by the detector, and a clear image is formed at the edge of the field of view. Summary of the invention

[0005] In order to solve the problem that the target imaging diffusion spot at the edge field of view of the lobster eye lens is large and difficult to detect accurately, the purpose of the present invention is to provide a flat field conversion system for the lobster eye lens. Based on the flat field conversion system, the edge field of view of the lobster eye lens can be clearly imaged, and the small objects in the edge field of view of the lobster eye lens can be accurately positioned.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The invention discloses a flat field conversion system for a lobster eye lens, comprising a light source, a lobster eye lens, a curved optical fiber bundle, a relay lens group, a medium wave infrared detector and a base.

[0008] The curvature radius of the lobster eye lens ranges from 100 to 800 mm, the focal length is half of the curvature radius of the lobster eye lens, the curvature radius of the imaging image plane is equal to the focal length, the field of view ranges from 20° to 60°, and the lobster eye lens is used to receive light projected by the detection object within the field of view.

[0009] The curved optical fiber bundle is coupled with the image plane of the lobster eye lens, and a curved optical fiber bundle with a numerical aperture range of 0.3 to 0.7 and a front end face curvature radius equal to the curvature radius of the image plane of the lobster eye lens is selected, and the center of the front end face is placed at the focal point of the central field of view of the lobster eye lens. The curved optical fiber bundle is used to convert the curved image plane of the lobster eye lens into a flat image.

[0010] The relay lens group has an object side numerical aperture of 0.3 to 0.7 (equal to the numerical aperture of the curved optical fiber bundle), and includes one or more concave lenses or convex lenses. The relay lens group is used to adjust the light output by the curved optical fiber bundle to achieve cold stop matching of the medium-wave infrared detector, and on this basis, the image plane of the lobster eye lens is completely imaged on the medium-wave infrared detector.

[0011] The medium-wave infrared detector can detect medium-wave infrared light with a wavelength of 3 to 5 μm, and is used to receive an image output after the relay lens group proportionally magnifies the plane image output by the curved optical fiber bundle located at the object surface of the relay lens.

[0012] The light source is placed at the edge field of view of the lobster eye lens, and the lobster eye lens, the curved fiber bundle, the relay lens group and the medium-wave infrared detector are coaxially fixed on the base from left to right. The curved fiber bundle includes more than one optical fiber. The relay lens group includes more than one convex lens or more than one concave lens.

[0013] Furthermore, the lobster eye lens is a square plane composed of several micro-matrix channels. After entering the lobster eye, the light is reflected by the tiny matrix channels and converges to the focal point. Since the structure of the lobster eye lens has the characteristic of independently converging light in two vertical directions, its focusing effect is not completely concentrated, but presents a special "cross focal spot" phenomenon.

[0014] Furthermore, the aspect ratio of the lobster eye (the ratio of its length t to its channel width d) satisfies:

[0015]

[0016] where θ c is the critical grazing incidence angle. ε is a constant close to 1, and preferably, the optimal value of the constant ε is ε≈0.85.

[0017] Furthermore, when the lobster eye lens receives parallel light from the central field of view, the parallel light passes through the lobster eye lens and is reflected once, and then emerges at the focus. At this time, the angle of rotation of the light is 2θ, where θ is the axis angle of a single subchannel of the lobster eye lens. The straight line where the emergent light, the channel wall where the light is reflected by a single subchannel, and the optical axis form an isosceles triangle. When the parallel light passes through the center of the lobster eye lens and converges to the focus after one reflection, θ approaches 0, and the two waists of the isosceles triangle are approximately coincident with the base (the radius of curvature R of the lobster eye lens), so the focal length of the lobster eye lens is always equal to half of the radius of curvature R of the lobster eye lens. Within the field of view, since parallel light incident at different angles will converge on the focal plane, the image is always formed at a distance of R / 2 from the lobster eye lens, that is, the image plane is a spherical surface with a radius of R / 2.

[0018] Further, the front end face of the curved optical fiber bundle has a curvature that is the same as the curvature radius of the lobster eye image plane, and the center of the front end face of the curved optical fiber bundle is located at the focal point of the central field of view of the lobster eye lens.

[0019] Furthermore, the curved optical fiber bundle has a numerical aperture equal to the maximum numerical aperture of the image side of the lobster eye lens, thereby avoiding a large amount of energy loss caused by coupling the curved optical fiber bundle with the image plane of the lobster eye lens.

[0020] Furthermore, the magnification of the relay lens group is β, and the magnification β enables the image plane transmitted by the scaled curved light beam to be completely imaged on the medium-wave infrared detector.

[0021] The present invention discloses a working method of a flat field conversion system for a lobster eye lens, which is as follows: a light source is placed at the edge field of view of the lobster eye lens, and the lobster eye lens, the curved optical fiber bundle, the relay lens group and the medium-wave infrared detector are coaxially fixed on a base from left to right. The lobster eye lens detects objects in the edge field of view, and the medium-wave infrared light emitted by the object is converged on the front end surface of the curved optical fiber bundle through the lobster eye lens and is imaged once. The curved optical fiber bundle converts the curved image plane into a flat field and transmits it to the object plane of the relay lens group. The relay lens group transmits the image plane and performs cold stop matching with the medium-wave infrared detector, thereby solving the contradiction between the large field of view and high resolution of the lobster eye lens, and realizing the high-precision detection of targets in the edge field of view by the lobster eye system.

[0022] Beneficial effects:

[0023] 1. The present invention discloses a flat-field conversion system for a lobster-eye lens. Without changing the structure of the lobster-eye lens itself, the system is extended by using a curved optical fiber bundle. Compared with a method of directly designing an optical path for the lobster-eye lens, the system has low design and processing difficulty and low assembly difficulty, making it possible to mass-produce lobster-eye lens systems.

[0024] 2. The present invention discloses a flat-field conversion system for a lobster-eye lens. By using a curved optical fiber bundle to couple with the curved image plane of the lobster-eye lens, the problem of the image plane of the lobster-eye lens being curved when imaging at the edge of the field of view, which makes it difficult to directly couple with a flat detector, resulting in a larger diffuse spot of the received focal spot, is solved. The ability of the lobster-eye optical system to accurately detect targets at the edge of the field of view is improved.

[0025] 3. The present invention discloses a flat-field conversion system for lobster-eye lenses, which uses a relay lens group to receive the plane image output by the curved optical fiber bundle, transmits the image plane and performs cold-block matching with a medium-wave infrared detector, thereby solving the problem that the optical fiber bundle can only be coupled with a medium-wave infrared detector without a cold-block in the medium-wave infrared band, and broadens the application scope of the optical fiber bundle in the optical system of the medium-wave infrared band.

[0026] 4. The present invention discloses a flat field conversion system for lobster eye lenses, which couples the image plane of the lobster eye lens with a large field of view, high resolution and extremely large field curvature with an image transmission fiber bundle with a curved front end and the same curvature as the image plane, and uses the curved fiber bundle to transmit light and convert the curved image plane of the lobster eye lens into a flat surface. The present invention can clearly image the target at the edge of the field of view and accurately detect it. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the lobster eye lens structure.

[0028] Figure 2 This is the principle of reflective imaging of the lobster eye lens (cross section).

[0029] Figure 3 Schematic diagram of curved fiber bundle.

[0030] Figure 4 Schematic diagram of the flat-field conversion system for the lobster-eye lens.

[0031] Figure 5 Schematic diagram of imaging through a lobster eye lens.

[0032] Figure 6 It is a schematic diagram of the device of the present invention.

[0033] Figure 7 (a) is a schematic diagram of the edge field imaging of the lobster eye lens. Figure 7 (b) Schematic diagram of edge field imaging of the flat-field conversion system for the lobster-eye lens.

[0034] Among them, 1- lobster eye lens, 2- curved optical fiber bundle, 3- relay lens group, 4- medium-wave infrared detector, 5- lobster eye lens, 6- curved optical fiber bundle, 7- relay lens group, 8- medium-wave infrared detector. DETAILED DESCRIPTION

[0035] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0036] Embodiment 1:

[0037] The imaging of lobster eye lenses is different from that of other traditional transmissive compound eyes. After light enters the lobster eye, it is reflected through tiny channels and converges to a focal point (such as Figure 5 ). Since the structure of the lobster eye lens has the characteristic of independently converging light in two perpendicular directions, its focusing effect is not completely concentrated, but presents a special "cross focal spot" phenomenon. Within the field of view, the image of the lobster eye is always formed at a distance of R / 2 from the lobster eye lens, that is, the image plane is a spherical surface with O as the center and R / 2 as the radius. Therefore, the focal length of the lobster eye is defined as f=R / 2. When light passes through the lobster eye lens, it is reflected through a tiny channel to form a "cross focal spot" on the image plane. The energy is mainly concentrated in the center of the "cross focal spot", and a small part is dispersed in the cross focal arms. However, in the edge field of view, the central bright spot of the "cross focal spot" is diffused, mainly because the lobster eye image plane has a large field curvature.

[0038] like Figure 4 As shown, the present embodiment discloses a flat-field conversion system for a lobster-eye lens, comprising a lobster-eye lens 1, a curved optical fiber bundle 2, a relay lens group 3 and a medium-wave infrared detector 4.

[0039] The curvature radius of the lobster eye lens 1 is 100 mm, the focal length is 50 mm, the curvature radius of the curved image plane is 50 mm, and the field of view of the lobster eye lens 1 is 20°.

[0040] In order to couple with the image plane of the lobster eye lens 1 , the curved optical fiber bundle 2 is selected to have a front end face curvature radius of 50 mm and a numerical aperture of 0.5, and the center of the front end face is placed at the focus of the lobster eye lens 1 .

[0041] The relay lens group 3 is an infrared relay lens with a zoom ratio of 1:1, which images the image transmitted by the curved optical fiber bundle 2 on the medium-wave infrared detector 4 in a 1:1 ratio.

[0042] The medium-wave infrared detector 4 is an antimonide medium-wave infrared detector, and the distance between the window of the medium-wave infrared detector 4 and the detector chip is 30 mm.

[0043] Functions of each component:

[0044] The lobster eye lens 1 is used to receive light projected by a detection object within the field of view.

[0045] The curved optical fiber bundle 2 is used to transform the curved image surface of the lobster eye lens into a flat image.

[0046] The relay lens group 3 is used to adjust the light so that it matches the cold stop of the medium-wave infrared detector 4 .

[0047] The relay lens group 3 is used to enlarge the image plane of the curved light beam so that it can be completely imaged on the medium-wave infrared detector 4.

[0048] The medium-wave infrared detector 4 is used to receive the image of the system.

[0049] The working method of a flat field conversion system for a lobster eye lens disclosed in this embodiment is as follows:

[0050] like Figure 6 As shown, the lobster eye lens 1, the curved optical fiber bundle 2, the relay lens group 3 and the medium-wave infrared detector 4 are coaxially fixed on the base from left to right, and the light source is placed at the edge field of view of the lobster eye lens 1. The lobster eye lens 1 detects objects in the edge field of view, and the medium-wave infrared light emitted by the object is converged on the front end surface of the curved optical fiber bundle 2 through the lobster eye lens and imaged once. The curved optical fiber bundle 2 converts the curved image plane into a flat field and transmits it to the object plane of the relay lens group 3. The relay lens group 3 transmits the image plane 1:1 and performs cold stop matching with the medium-wave infrared detector 4, thereby solving the contradiction between the large field of view and high resolution of the lobster eye lens, and realizing the accurate detection of targets at the edge field of view by the lobster eye system.

[0051] like Figure 7 (a) shows the schematic diagram of the imaging of the edge field of view of the lobster eye lens. The "cross focal spot" on the image plane is diffuse and the energy is not concentrated. Figure 7 (b) is the edge field imaging of the flat-field conversion system for the lobster-eye lens. The "cross focal spot" diffusion is reduced, and obvious "cross focal arms" appear. The position of the object can be detected through the clear "cross focal arms".

[0052] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flat field conversion system for lobster eye lenses, characterized by: It includes a light source, a lobster eye lens, a curved optical fiber bundle, a relay lens group, a medium-wave infrared detector and a base; The curvature radius of the lobster eye lens ranges from 100 to 800 mm, the field of view ranges from 20° to 60°, the focal length is half of the curvature radius of the lobster eye lens, the curvature radius of the imaging image plane is equal to the focal length, and the lobster eye lens is used to receive light projected by the detection object within the field of view; The curved optical fiber bundle is coupled with the image plane of the lobster eye lens, and a curved optical fiber bundle with a numerical aperture range of 0.3 to 0.7 and a front end face curvature radius equal to the curvature radius of the image plane of the lobster eye lens is selected, and the center of the front end face is placed at the focal point of the central field of view of the lobster eye lens; the curved optical fiber bundle is used to convert the curved image plane of the lobster eye lens into a flat image; The relay lens group has an object-side numerical aperture of 0.3 to 0.7 and includes one or more concave lenses or convex lenses. The relay lens group is used to adjust the light output by the curved optical fiber bundle to achieve cold stop matching of the medium-wave infrared detector, and on this basis, the image plane of the lobster eye lens is completely imaged on the medium-wave infrared detector; The medium-wave infrared detector detects medium-wave infrared light with a wavelength of 3 to 5 μm, and is used to receive an image output after the relay lens group proportionally magnifies the plane image output by the curved optical fiber bundle located at the object surface of the relay lens; The light source is placed at the edge of the lobster eye lens. The lobster eye lens, curved optical fiber bundle, relay lens group and medium-wave infrared detector are coaxially fixed on the base from left to right.

2. A flat field conversion system for a lobster eye lens as claimed in claim 1, characterized in that: The curved optical fiber bundle includes more than one optical fiber; the relay lens group includes more than one convex lens or more than one concave lens.

3. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: The lobster eye lens is a square plane composed of several tiny matrix channels. After entering the lobster eye, the light is reflected by the tiny matrix channels and converges to a focal point. Since the structure of the lobster eye lens has the characteristic of independently converging light in two vertical directions, its focusing effect is not completely concentrated, but presents a "cross focal spot".

4. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: When the lobster eye lens receives parallel light from the central field of view, the parallel light passes through the lobster eye lens and is reflected once, and then emitted to the focus. At this time, the angle of rotation of the light is 2θ, where θ is the axis angle of a single sub-channel of the lobster eye lens. The straight line where the emitted light, the channel wall where the light is reflected by a single sub-channel, and the optical axis form an isosceles triangle. When the parallel light passes through the center of the lobster eye lens and converges to the focus after one reflection, θ approaches 0, and the two waists and base of the isosceles triangle approximately coincide with each other, so the focal length of the lobster eye lens is always equal to half of the radius of curvature R of the lobster eye lens. Within the field of view, since parallel light incident at different angles will converge on the focal plane to form an image, the image is always formed at a distance of R / 2 from the lobster eye lens, that is, the image plane is a spherical surface with a radius of R / 2.

5. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: The aspect ratio of lobster eyes satisfies: where θ c is the critical grazing incidence angle; ε is a constant close to 1.

6. A flat field conversion system for a lobster eye lens as claimed in claim 5, characterized in that: The optimal value of the constant ε is ε≈0.

85.

7. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: The front end face of the curved optical fiber bundle has a curvature that is the same as the curvature radius of the lobster eye image plane, and the center of the front end face of the curved optical fiber bundle is located at the focal point of the central field of view of the lobster eye lens.

8. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: The curved optical fiber bundle has a numerical aperture equal to the maximum numerical aperture of the image side of the lobster eye lens, thereby avoiding a large amount of energy loss caused by coupling the curved optical fiber bundle with the image plane of the lobster eye lens.

9. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: The magnification of the relay lens group is β, and the magnification β enables the image plane transmitted by the curved light beam to be completely imaged on the medium-wave infrared detector.

10. A flat field conversion system for a lobster eye lens as claimed in claim 1 or 2, characterized in that: The light source is placed at the edge field of view of the lobster-eye lens. The lobster-eye lens, curved fiber bundle, relay lens group and medium-wave infrared detector are coaxially fixed on the base from left to right. The lobster-eye lens detects objects in the edge field of view. The infrared radiation energy emitted by the object converges on the front end surface of the curved fiber bundle and forms an image. The curved fiber bundle converts the curved image plane into a flat field and transmits it to the object plane of the relay lens group. The relay lens group transmits the image plane and performs cold-stop matching with the medium-wave infrared detector, thereby realizing high-precision detection of targets at the edge field of view by the lobster-eye system.

Images