Visible-infrared dual-band diffraction optical imaging system

Abstract

The invention provides a visible-infrared dual-band diffractive optical imaging system, and relates to the technical field of photoelectricity, the system comprises a single-piece double-sided diffractive lens and a light splitting flat plate capable of reflecting visible light and transmitting long-wave infrared light, the single-piece double-sided diffractive lens and the light splitting flat plate are sequentially and coaxially arranged along a main light path, and the single-piece double-sided diffractive lens is a mixed multi-order diffractive lens. The front surface of the single-piece double-face diffraction lens is a multi-order diffraction surface, the rear surface of the single-piece double-face diffraction lens is a conventional diffraction surface, and the light splitting flat plate capable of reflecting visible light and transmitting long-wave infrared is arranged behind the single-piece double-face diffraction lens. The orthographic projection area of the single double-face diffraction lens in the main light path direction is larger than that of the light splitting flat plate capable of reflecting visible light and transmitting long-wave infrared light. The system is simple in structural style and easy to integrate, and can be applied to unmanned aerial vehicles, portable equipment and other small platforms for target monitoring.

Description

A Visible-Infrared Dual-Band Diffraction Optical Imaging System Technical Field

[0001] This invention relates to the field of optoelectronic technology, and in particular, to a visible-infrared dual-band diffraction optical imaging system. Background Technology

[0002] In the field of infrared imaging, long-wave infrared imaging technology has important application value in remote sensing, mountain disaster early warning, industrial inspection and environmental monitoring. In the face of observation tasks in complex scenes at all times, it is difficult to complete the task by relying solely on visible light cameras. However, long-wave infrared technology can also efficiently detect the passive thermal radiation of targets in environments with poor visibility such as complete darkness, smoke, and dust. Therefore, it has advantages in low visibility conditions such as night, clouds, fog, and heavy rain.

[0003] The fusion of visible-longwave infrared dual-band images combines the advantages of both bands, meeting the needs for all-weather, rapid detection and accurate identification of observation targets in complex environments. It can effectively improve the identification rate of observation targets and adaptability to different environments.

[0004] Furthermore, traditional dual-band infrared imaging systems are typically pure refractive lens systems, catadioptric-reflective lens systems, or hybrid refractive-diffractive lens systems. While these systems can achieve good chromatic aberration correction, they require multiple lens components connected in series, rely on complex rear lens group structures and precise alignment of the front and rear systems. This results in large system size, large overall dimensions, and complex structure, significantly limiting their integration into portable devices such as UAVs and other small platforms. Meanwhile, compared to the strict tolerances of refractive lenses, the tolerances of diffractive lenses are relatively relaxed.

[0005] Therefore, developing a lightweight, simple, and easily integrated visible-infrared dual-band diffraction lens is of great practical significance. Summary of the Invention

[0006] The purpose of this invention is to provide a visible-infrared dual-band diffraction optical imaging system to solve the problems of complex structure, strict tolerances and difficulty in integration of existing dual-band imaging systems.

[0007] To achieve the above objectives, the present invention provides a visible-infrared dual-band diffraction optical imaging system. This system includes a single-piece double-sided diffraction lens and a beam-splitting plate that reflects visible light and transmits long-wave infrared light, arranged coaxially along the main optical path. The single-piece double-sided diffraction lens is a hybrid multi-order diffraction lens, with its front surface being a multi-order diffraction surface and its rear surface being a conventional diffraction surface. The beam-splitting plate that reflects visible light and transmits long-wave infrared light is positioned behind the single-piece double-sided diffraction lens. The projected area of ​​the single-piece double-sided diffraction lens along the main optical path is larger than the projected area of ​​the beam-splitting plate that reflects visible light and transmits long-wave infrared light.

[0008] The beneficial effects of this invention are:

[0009] The visible-infrared dual-band diffraction optical imaging system provided by this invention achieves lightweight, simplification, and easy integration. The system uses a beam-splitting plate (such as a germanium plate) to split the light, realizing separate imaging of the visible light band and the long-wave infrared band, reducing crosstalk between the bands, and improving the imaging quality of each band. It is suitable for dual-band imaging systems, UAV airborne applications, and target monitoring tasks in complex environments.

[0010] This invention differs from traditional pure refractive optical systems and catadioptric optical systems by employing a diffractive optical system. This system is suitable for simultaneous target detection in two wavelength bands. The diffractive optical system uses a single primary mirror for both wavelength bands, further simplifying the system structure and reducing its weight.

[0011] The primary mirror of the technical solution provided by this invention is a single-piece double-sided diffractive lens. This primary mirror is a hybrid multi-order diffractive lens, with its front surface being a multi-order diffractive surface and its rear surface being a conventional diffractive surface. The multi-order diffractive surface on the front surface provides the main optical power, while the conventional diffractive surface on the rear surface is mainly used to correct chromatic aberration and diffraction efficiency in two wavebands. Therefore, a single-piece double-sided diffractive lens can achieve the effect of multiple traditional refractive lens groups.

[0012] This invention uses multispectral zinc sulfide (ZnS) as the primary mirror material, which covers the wavelength range from the visible light band to the long-wave infrared band, meeting the requirements for visible-infrared dual-band diffraction lens materials.

[0013] This invention uses germanium (Ge) as the beam-splitting plate material, which reflects light in the visible light band and transmits light in the long-wave infrared band to achieve the purpose of beam splitting.

[0014] The optical system in this invention has a compact structure, which is conducive to the miniaturization of the whole system and is suitable for use on UAVs for all-day observation. Attached Figure Description

[0015] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0016] Figure 1 is an optical path diagram in the visible light band provided by the present invention;

[0017] Figure 2 is a long-wave infrared band optical path diagram provided by the present invention;

[0018] Figure 3 is a schematic diagram of the visible-infrared dual-band diffraction optical system provided by the present invention.

[0019] Explanation of reference numerals in the attached figures:

[0020] 1. Single-piece double-sided diffractive lens; 2. Beam splitter plate; 3. Long-wave infrared imaging plane; 4. Visible light imaging plane. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0022] The present invention will now be described in conjunction with Figures 1, 2 and 3. Figure 1 is an optical path diagram of the visible light band provided by the present invention, Figure 2 is an optical path diagram of the long-wave infrared band provided by the present invention, and Figure 3 is a schematic diagram of the visible-infrared dual-band diffraction optical system provided by the present invention.

[0023] This invention provides a visible-infrared dual-band diffraction optical imaging system. The system includes a single double-sided diffraction lens 1 and a beam-splitting plate 2 that reflects visible light and transmits long-wave infrared light, arranged coaxially along the main optical path. The single double-sided diffraction lens 1 is a hybrid multi-order diffraction lens. The front surface of the single double-sided diffraction lens 1 is a multi-order diffraction surface, and the rear surface of the single double-sided diffraction lens 1 is a conventional diffraction surface. The beam-splitting plate 2 that reflects visible light and transmits long-wave infrared light is disposed behind the single double-sided diffraction lens 1. The projected area of ​​the single double-sided diffraction lens 1 along the main optical path is larger than the projected area of ​​the beam-splitting plate 2 that reflects visible light and transmits long-wave infrared light.

[0024] Furthermore, the visible-infrared dual-band diffraction optical imaging system provided by the present invention includes a single double-sided diffraction lens 1 arranged coaxially along the main optical path, a beam-splitting plate 2 that can reflect visible light and transmit long-wave infrared light, a visible light band image plane 4, and a long-wave infrared band image plane 3. The visible light band image plane 4 is used to place a visible light detector to receive the visible light band imaging image, and the long-wave infrared band image plane 3 is used to place a long-wave infrared detector to receive the long-wave infrared band imaging image.

[0025] The beam-splitting plate 2 is positioned behind the single-piece double-sided diffraction lens 1. The optical path behind the beam-splitting plate 2 consists of the visible light band image plane 4 and the long-wave infrared band image plane 3.

[0026] To reduce the difficulty of processing and inspecting the primary mirror in the diffractive optical system provided by this invention, this invention uses a single double-sided diffractive lens 1 and processes it using single-point diamond turning technology, which has a looser tolerance compared to traditional multi-refractive lens groups.

[0027] To reduce the weight of the system, the diffractive optical system of this invention uses a single primary mirror for its dual-band optical paths (specifically, two optical paths for the visible light band and the long-wave infrared band). Those skilled in the art should understand that the first monolithic double-sided diffractive lens 1 in the diffractive optical imaging system is the primary mirror.

[0028] In this embodiment, the material of the single-piece double-sided diffraction lens 1 is zinc sulfide (ZnS), more specifically, it can be multispectral zinc sulfide, covering the wavelength range from the visible light band to the long-wave infrared band. The refractive index of zinc sulfide material is about 2.223 at a wavelength of 8μm, and the transmittance of multispectral zinc sulfide in the infrared band is above 72% (which will be improved after coating).

[0029] In this embodiment, the material of the beam-splitting plate 2, which reflects visible light and transmits long-wave infrared light, is germanium (Ge). It has good transmittance in the infrared band but is opaque to visible light, and is therefore used as the material for the beam-splitting plate 2. The refractive index of germanium is approximately 4.005 at a wavelength of 8 μm.

[0030] In the visible-infrared dual-band diffraction optical imaging system provided by this invention, the focal length of the visible light imaging system is smaller than that of the long-wave infrared imaging system.

[0031] The visible light band is transmitted through a single double-sided diffractive lens 1 and then reflected by a beam splitter 2 to form the optical path of the visible light imaging system. The operating wavelength of the visible light imaging system is 400nm~700nm, the center wavelength of the visible light imaging system is 588nm, the entrance pupil diameter of the visible light imaging system is 50mm, and the focal length of the visible light imaging system is 115mm.

[0032] The long-wave infrared band is transmitted through a single double-sided diffractive lens 1 and then through a beam splitter plate 2 to form the optical path of the long-wave infrared imaging system. The operating wavelength of the long-wave infrared imaging system is 8000~11000nm, the center wavelength of the long-wave infrared imaging system is 10.16μm, the entrance pupil diameter of the long-wave infrared imaging system is 50mm, and the focal length of the long-wave infrared imaging system is 156mm.

[0033] The visible-infrared dual-band diffraction optical imaging system provided by this invention has a primary mirror aperture of 50mm. The visible light band imaging system has a focal length of 115mm and an aperture number (F-number) of 2.3. The long-wave infrared band imaging system has a focal length of 156mm and an aperture number (F-number) of 3.12.

[0034] In this embodiment, in order to ensure that the optical system has a suitable optical power and effectively corrects chromatic aberration while using a single-piece double-sided diffractive lens 1, the choice of surface type is carefully considered. The single-piece double-sided diffractive lens 1 in this invention adopts a structure in which both sides are diffractive surfaces, and the single-piece double-sided diffractive lens 1 in this invention is a hybrid multi-order diffractive lens.

[0035] The front surface of the monolithic double-sided diffractive lens 1 is used to provide optical power, and the rear surface of the monolithic double-sided diffractive lens 1 is used to correct the chromatic aberration between the visible light band and the long-wave infrared band.

[0036] In this embodiment, the front surface of the monolithic double-sided diffraction lens 1 is a multi-order diffraction surface, exhibiting better dispersion properties. Therefore, the optical power is provided by the front surface. For the selection of the surface shape of the front surface, a custom annular surface shape is adopted. The annular surface shape sagitta of the front surface of the monolithic double-sided diffraction lens 1 is as follows:

[0037] ;

[0038] in, The annular surface profile sagitta of the front surface of the monolithic double-sided diffractive lens 1. Let be the radial coordinates of the front surface of the monolithic double-sided diffractive lens 1. , , Let be the rectangular coordinates of the front surface of the monolithic double-sided diffractive lens 1 in a rectangular coordinate system. The front surface of a single-piece double-sided diffractive lens 1 The quadratic coefficients of each aspherical ring, The front surface of a single-piece double-sided diffractive lens 1 The coefficients of the quartic term of an aspherical ring zone, The front surface of a single-piece double-sided diffractive lens 1 The axial offset of each aspherical ring is determined by the diffraction order of the front surface of the single double-sided diffractive lens 1. The front surface of a single-piece double-sided diffractive lens 1 The maximum radial radius of an aspherical ring. The front surface of a single-piece double-sided diffractive lens 1 The maximum radial radius of an aspherical ring.

[0039] In this embodiment, the rear surface of the monolithic double-sided diffractive lens 1 is a conventional diffractive surface, which hardly bears any optical power. Therefore, the rear surface is used to correct the chromatic aberration between the visible light band and the long-wave infrared band. The rear surface of the monolithic double-sided diffractive lens 1 has a binary 2 surface type, and the phase of the rear surface of the monolithic double-sided diffractive lens 1 is as follows:

[0040] ;

[0041] in, The phase of the rear surface of the monolithic double-sided diffractive lens 1 is shown. The diffraction order is the rear surface of the monolithic double-sided diffraction lens 1. For example, the diffraction order could be 1, 1, or 2. Let be the phase coefficient of the rear surface of the monolithic double-sided diffractive lens 1. Let be the normalized radius of the rear surface of the monolithic double-sided diffraction lens 1. ,in, Let be the radius of each annular zone on the rear surface of the monolithic double-sided diffractive lens 1. The maximum radius of the diffractive optical element. For the number of phases, For preset values, for Second phase of Second phase coefficient. Wherein, For example, it can take values ​​like 2, 4, etc. For instance, when i=1, for The second phase coefficient of (second phase).

[0042] To reduce the lateral size of the system, the visible-infrared dual-band diffraction optical imaging system provided by this invention uses a beam-splitting plate 2. This beam-splitting plate 2 is at a 45° angle to the primary mirror, reflecting visible light in a direction perpendicular to the primary mirror. This invention uses the beam-splitting plate 2 to separate the visible light band and the long-wave infrared band for independent imaging. In other words, a single double-sided diffractive lens 1 is at a 45° angle to the beam-splitting plate 2, which reflects visible light and transmits long-wave infrared light.

[0043] In practical applications, the image restoration of thin and light optical imaging systems similar to the visible-infrared dual-band diffraction optical imaging system in this invention is often handled by a back-end image restoration network.

[0044] This invention can be applied to target monitoring on drones, portable devices, and other small platforms.

[0045] The diffractive optical imaging system provided by this invention achieves the goals of lightweight design, simple structure, and easy integration. It realizes dual-band imaging in the visible light and long-wave infrared bands using a single double-sided diffractive lens, and also exhibits different degrees of aberration correction in each field of view. This provides new ideas for the design of high-performance, compact, and multifunctional intelligent optical systems in the future.

[0046] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0047] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0048] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A visible-infrared dual-band diffraction optical imaging system, characterized in that, The system includes a single double-sided diffractive lens and a beam-splitting plate that reflects visible light and transmits long-wave infrared light, arranged coaxially along the main optical path. The single double-sided diffractive lens is a hybrid multi-order diffractive lens, with its front surface being a multi-order diffraction surface and its rear surface being a conventional diffraction surface. The beam-splitting plate that reflects visible light and transmits long-wave infrared light is positioned behind the single double-sided diffractive lens. The projected area of ​​the single double-sided diffractive lens along the main optical path is larger than the projected area of ​​the beam-splitting plate that reflects visible light and transmits long-wave infrared light.

2. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The visible light band is transmitted through the single double-sided diffractive lens and then reflected by the beam splitter to form the optical path of the visible light imaging system. The operating wavelength of the visible light imaging system is 400~700nm, and the focal length of the visible light imaging system is 115mm.

3. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The long-wave infrared band is transmitted through the single-piece double-sided diffraction lens and then through the beam splitter to form the optical path of the long-wave infrared imaging system. The operating wavelength of the long-wave infrared imaging system is 8000~11000nm, and the focal length of the long-wave infrared imaging system is 156mm.

4. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The front surface of the monolithic double-sided diffractive lens is used to provide optical power, and the rear surface of the monolithic double-sided diffractive lens is used to correct chromatic aberration in the visible light band and the long-wave infrared band.

5. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The annular surface profile of the front surface of the monolithic double-sided diffractive lens is as follows: ;in, The annular surface profile sagitta of the front surface of the monolithic double-sided diffractive lens. The radial coordinates of the front surface of the monolithic double-sided diffractive lens are given. The front surface of a single-piece double-sided diffractive lens The quadratic coefficients of an aspherical ring zone, The front surface of a single-piece double-sided diffractive lens The coefficients of the quartic term of an aspherical ring zone, The front surface of the monolithic double-sided diffractive lens is the first Axial offset of an aspherical ring The front surface of the monolithic double-sided diffractive lens is the first The maximum radial radius of an aspherical ring. The front surface of the monolithic double-sided diffractive lens is the first The maximum radial radius of an aspherical ring.

6. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The rear surface of the monolithic double-sided diffractive lens is a two-dimensional (two-faceted) type, and the phase of the rear surface of the monolithic double-sided diffractive lens is as follows: ;in, The phase of the rear surface of the monolithic double-sided diffractive lens. The diffraction order is the rear surface of the monolithic double-sided diffractive lens. The phase coefficient of the rear surface of the monolithic double-sided diffractive lens is given. The normalized radius of the rear surface of the monolithic double-sided diffractive lens is given by [reference to radius]. ,in, Let be the radius of each annular band on the rear surface of the monolithic double-sided diffractive lens. The maximum radius of the single-piece double-sided diffractive lens is given. For the number of phases, For preset values, for Second phase of Secondary phase coefficients.

7. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The single-piece double-sided diffractive lens forms a 45° angle with the beam-splitting plate that reflects visible light and transmits long-wave infrared light.

8. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The system includes a single double-sided diffractive lens arranged coaxially along the main optical path, a beam-splitting plate that reflects visible light and transmits long-wave infrared light, a visible light band image plane, and a long-wave infrared band image plane. The visible light band image plane is used to place a visible light detector to receive visible light band imaging images, and the long-wave infrared band image plane is used to place a long-wave infrared detector to receive long-wave infrared band imaging images.

9. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The material of the single-piece double-sided diffraction lens is zinc sulfide.

10. The visible-infrared dual-band diffraction optical imaging system according to claim 1, characterized in that, The material of the beam-splitting plate that can reflect visible light and transmit long-wave infrared light is germanium.

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