CN116300070A - Dual-mode coaxial integrated optical system - Google Patents

Abstract

A dual-mode coaxial integrated optical system, comprising a hood (1), a primary mirror (2), a beam splitter (3), and a secondary correction imaging lens group, the optical axes of which coincide; The side is incident and the other side is output. The beam splitter (3) is located on the side of the light emitting direction of the hood (1). The secondary imaging lens group is arranged on the side; the beam splitter (3) is a semi-transparent and half-reflective lens; the main mirror (2) is a reflector, and the reflective surface of the reflector faces the outgoing light direction of the beam splitter (3); the first detector (9) for receiving the radiation light of the first waveband, it is arranged on the focal plane of the outgoing light direction of the secondary correction imaging lens group; the second detector filter and receiving lens (8) are used for receiving the radiation of the second waveband The light is arranged on the focal plane of the beam splitter (3) on the side of the transmitted light direction. The invention utilizes the beam splitter to realize large entrance pupil diameter and reduce the number of mirror groups.

Description

A dual-mode coaxial integrated optical system

technical field

The invention belongs to the technical field of optical composite guidance, and relates to a dual-mode coaxial optical integrated optical system.

Background technique

The optical system is the core component of the guidance system. With the research and development of composite new technologies, higher requirements are put forward for the miniaturization, integration and stability of the guidance structure. Although the single infrared guidance mode has the advantages of high tracking accuracy and all-weather work, it is not omnidirectional; the single laser guidance system can identify the vibration characteristics of the target object, but it is easily affected by the weather. Therefore, infrared/laser dual-mode guidance can achieve the effect of complementary advantages, and has the advantages of all-weather work, anti-electronic interference and high hit accuracy. The R-C (Ritchey-Chretien optics) catadioptric system is the most important form to meet the system requirements because the reflective film can achieve high reflectivity under wide-spectrum conditions, has the characteristics of no chromatic aberration, and compact structure. In order to obtain higher image quality and wider field of view, a secondary correction imaging lens group is often added after the reflective system.

In 2015, Yin Xiaochen and others proposed an infrared imaging/active radar common-aperture dual-mode seeker, which introduced a dichroic beamsplitter to achieve a common-aperture structure. The MTF (Modulation Transfer Function) of the infrared optical system was higher than 0.6 at 16lp/mm. In 2016, Mahmoud et al. designed a common aperture system for visible light and near-infrared. The imaging quality reached the diffraction limit, but the full field of view was only 1°. In 2019, Zhou Xiaobin simplified the secondary mirror in the Cassegrain structure into a flat mirror, which effectively reduced the lens size. The MTF of the infrared channel was 35.7lp/mm higher than 0.3. In 2020, Chen Guoqiang et al. designed an infrared/ Laser/millimeter-wave common-aperture optical system, sharing the dome and parabolic primary mirror, the secondary mirror reflects infrared and laser, and transmits millimeter-wave. In 2021, Ma Zhanpeng and others completed the design of a visible/long-wave infrared two-color optical system, using a dichroic mirror to decenter the infrared correction mirror to compensate for the influence of the dichroic mirror tilt on the optical path.

Chinese patent document CN 112068311 A provides a design method of infrared, laser, and millimeter wave three-mode common aperture, which makes the seeker system too large, which is not conducive to the miniaturization design requirements of weapon products; secondly, the three-mode common aperture technology is extremely difficult Increase, changing technical conditions, more optical lenses in the three-mode structure, low light energy utilization efficiency, small field of view design, it is difficult to increase the guidance distance, and the transmission and light splitting of each band have an impact, which greatly affects imaging quality and stability.

Contents of the invention

The invention provides a dual-mode coaxial integrated optical system to solve the technical problems of large volume and complex structure of the multi-band optical common-aperture incident optical system. The invention has the characteristics of miniaturization, light weight, large entrance pupil, large field of view and long guidance distance, and can realize precise guidance of high-precision targets.

The present invention proposes a dual-mode coaxial integrated optical system, including a hood, a main mirror, a beam splitter, a secondary correction imaging lens group, a first detector, and a second detector; the hood, the main mirror, the beam splitter The optical axes of the mirror and the secondary correction imaging lens group coincide;

The hood is used to transmit light, the beamsplitter is located on the side of the hood in the direction of the outgoing light, the main mirror is located on the side of the outgoing light of the beam splitter, and a secondary correction imaging lens group is set on the side of the main mirror in the direction of the outgoing light;

The beam splitter is a semi-transparent and half-reflective lens; the main mirror is a reflector, and the reflective surface of the mirror faces the direction of the reflected light of the beam splitter;

The first detector is used to receive the radiation light of the first waveband, which is arranged on the first focal plane on the side of the outgoing light direction of the secondary correction imaging lens group; the second detector is used to receive the radiation light of the second waveband, which is arranged on the beam splitter A second focal plane on the side of the transmitted light direction, the second focal plane is located between the head cover and the beam splitter.

Further, the radiated light of the first waveband and the second waveband passes through the hood and reaches the main mirror, and then is reflected to the spectroscope through the reflective surface, and the radiated light of the first waveband propagates through the secondary correction imaging lens group after being reflected by the spectroscope, and then arrives at The first detector, and the radiation light of the second waveband reaches the second detector after being transmitted by the beam splitter.

Further, the radiation light in the first band is infrared light, the radiation light in the second band is laser light, the first detector is used to receive infrared light, and the second detector is used to receive laser light.

Further, the beam splitter is a hyperboloid semi-transparent and half-reflective lens, and the surface of the beam splitter is coated with a dichroic light-splitting film, and the light-splitting film is used to realize the separation of the first wavelength reflection light path and the second wavelength transmission light path. combination.

Further, the primary mirror is a Cassegrain reflector, and the oblique section of the Cassegrain reflector is used as the reflective surface to face the outgoing light direction of the beam splitter.

Further, the head cover is a concentric spherical cover, and the material of the head cover is sapphire.

Further, the secondary correction imaging lens group includes a first aspheric mirror, a second aspheric mirror, a diffractive mirror, and a spherical mirror, and the first aspherical mirror, the diffractive mirror, a spherical mirror, and the second aspherical mirror The order of the optical centers is arranged coaxially.

Furthermore, the obscuration ratio of the primary mirror and the beam splitter is α,

The lateral magnification of the beam splitter is β ₂ ,

The primary mirror radius is r ₁ ,

The beamsplitter radius is r ₂ ,

The distance between the intersection of the primary mirror and the optical axis in the exit direction of the optical axis and the intersection of the beam splitter and the optical axis is d,

Among them, f ₁ ' is the focal length of the main mirror, f ₂ ' is the transmission focal length of the beam splitter, f' is the distance from the object side to the focal point F of the image side of the optical system, l ₂ is the distance from the main mirror focal point F1' to the intersection point of the beam splitter and the optical axis Distance, l' ₂ is the distance from the intersection of the beam splitter and the optical axis to the focus of the exit pupil of the optical system.

Further, the primary mirror is made of K9 glass, and the base material of the beam splitter is made of Chengdu Guangming H-K9L material.

Further, the material of the first aspheric mirror and/or the second aspheric mirror is IRG204 and/or IRG209 chalcogenide glass; the material of the diffractive mirror and/or spherical mirror is ZNSE and/or Germanium material.

The advantage of the present invention compared with prior art is:

(1) The present invention balances the light collection ability of the lens aperture and the optical structure, and realizes the small F number and large aperture of the system;

(2) The present invention adopts an infrared secondary correction imaging lens group to reduce the light height of the edge field of view, which is beneficial to increase the field of view and reduce stray light;

(3) The present invention utilizes the design of a high-transmittance and high-reflection beam splitter to achieve an optically larger entrance pupil aperture, reduce the number of converging mirror groups, reduce the volume, enhance the energy receiving efficiency of the optical path, and increase the guidance distance.

Description of drawings

Fig. 1 is a schematic diagram of the optical structure of the present invention;

Fig. 2 is a schematic diagram of R-C optical path tracing of the present invention;

Fig. 3 is a schematic diagram of the modulation transfer function diffraction limit under different obscuration ratios of the present invention.

Detailed ways

The present invention provides a dual-mode coaxial integrated optical system. As shown in FIG. Secondary correction imaging lens group, first detector (infrared detector) 9, second detector (laser detector) 8.

The cross section of the hood 1 is arc-shaped, and the light is emitted from the concave side of the convex surface of the hood 1, and the beam splitter 3 is located on the side of the light emitting direction of the hood 1, and the main mirror 2 is arranged on the outgoing direction side of the beam splitter 3. An infrared secondary imaging lens group is arranged on the side of the mirror 2 in the direction of the outgoing light.

The beam splitter 3 is a hyperboloid semi-transparent and semi-reflective lens. The primary mirror 2 is a Cassegrain mirror, and its oblique section faces the direction of the reflected light of the beam splitter 3 .

The optical axes of the hood 1, the main mirror 2, the beam splitter 3, and the infrared secondary correction imaging lens group are coincident.

The laser detector 8 is arranged on the focal plane of the beam splitter 3 on the side of the transmitted light direction, and the focal plane is located between the head cover 1 and the beam splitter 3 . The infrared detector 9 is arranged on the focal plane of the outgoing light direction of the infrared secondary correction imaging lens group.

The radiated light of the two bands of infrared and laser passes through the hood 1 and reaches the main mirror 2 and then reflects to the beam splitter 3. At the reflective surface on the right side of the beam splitter 3, the laser radiation is directly transmitted and then propagates to the left to reach the laser detector filter and In the receiving lens, the infrared band is directly reflected on the right surface of the beam splitter 3, propagates to the right, passes through the infrared secondary correction imaging lens group, and then reaches the infrared detector.

Among them, the base material of the beam splitter 3 element of the common aperture system is Chengdu Guangming H-K9L. Its shape is a combination of spherical and aspheric. Combination of laser (1.064um) transmission light path, a total of 26 layers of spectroscopic mask layers, a total thickness of 16.8um, an average infrared reflectance of more than 90%, and an average laser transmittance of more than 98%; the primary mirror is gold-plated to achieve a higher full-band Reflectivity, long-wave infrared is high reflection, making full use of the primary and secondary mirror space to achieve optical large entrance pupil design (infrared entrance pupil 66mm, laser entrance pupil 52mm).

Among them, the material of head cover 1 is sapphire with a thickness of 5mm, which is resistant to corrosion, impact and aerodynamic heat. In order to ensure that the optical system can adapt to various working environments, a concentric optical head cover is introduced into the structure. The 63.4mm position has enough turning space.

The material of the main reflector 2 is K9 glass, and the gold-plated film realizes the high reflectivity of laser and infrared, which is more than 99.5%, and the size is 80mm.

Preferably, the base material of the spectroscopic mirror 3 is Chengdu Guangming H-K9L, which is used in the 1.064um band receiving system. The front surface is coated with a dichroic spectroscopic film, and the front surface is aspherical. A 1.064um narrow-band filter is used at the back to cooperate with the receiving lens group. The lens diameter is 52mm, which improves the energy received by the laser entrance pupil and reduces the converging lens. There are a total of 26 layers of spectroscopic film, with a total thickness of 16.8um and an average infrared reflectivity of more than 90%. Secondary imaging is used later to reduce the increase of the entrance pupil and the suppression of stray light and ghost images caused by reducing the number of lenses.

The transmission lens group for secondary correction imaging includes lenses 4, 5, 6, and 7, wherein lens 4 and lens 7 are two aspherical surfaces, using IRG204 and IRG209 chalcogenide glass, lens 5 is a diffractive surface, and lens 6 is a spherical surface. These two lens materials use ZNSE and Germanium materials, which are beneficial to increase the field of view and reduce stray light, and avoid the formation of focal points or focal spots; the use of aspheric and diffractive surfaces reduces the probability of secondary reflections of ghost images; coating In terms of technology, ion beam-assisted technology is used to improve the uniformity of the refractive index of the film layer, supplemented by thickness error compensation technology. The material of the mechanical spacer and lens barrel is Invar, and the coefficient of thermal expansion is small, only 1.3×10 ^-6 K ^-1 . Realize the athermalization design at -40-60℃.

The invention establishes a miniaturized, integrated and stable optical structure based on the R-C model, and performs paraxial ray tracing on the infrared optical system, optical obscuration ratio, lateral magnification of the beam splitter, curvature radius of the primary mirror, curvature radius of the beam splitter and The distance between the two reflectors and the intersection of the optical axis is calculated as follows:

The obscuration ratio of primary mirror 2 and beam splitter 3 is α,

The lateral magnification of beam splitter 3 is β ₂ ,

The radius of primary mirror 2 is r ₁ ,

The radius of beam splitter 3 is r ₂ ,

The distance between the main mirror 2 and the intersection of the optical axis and the beam splitter 3 and the intersection of the optical axis in the exit direction of the optical axis is d,

As shown in Figure 2, where f ₁ ' is the focal length of the main mirror 2, F ₁ ' is the focal length of the main mirror 2, f ₂ ' is the transmission focal length of the beam splitter 3, F ₂ ' is the transmission focus of the beam splitter 3, and f' is the object square to the focal point F of the image side (exit pupil) of the optical system, l ₂ is the distance from the focal point F ₁ ' of the main mirror 2 to the intersection point of the beam splitter and the optical axis, and l' ₂ is the distance from the intersection point of the beam splitter 3 and the optical axis to the optical system image The distance from the focal point F of the square. In Fig. 2, h ₁ is the height of the object space, h ₂ is the height of the image space transmitted by the beam splitter, Δ is the distance between F ₁ ' and F ₂ ', b is the intersection point of the main mirror 2 and the optical axis to the image space of the optical system ( Exit pupil) the distance of the focal point F, d is the distance from the intersection of the main mirror 2 and the optical axis to the intersection of the beam splitter 3 and the optical axis, d=l ₂ '-b, x ₂ ' is the distance from F ₂ ' to F, D ₂ is the distance from the object space to the primary mirror 2.

The number of detector pixels selected by the long-wave infrared optical system is 384×288, the pixel size is 12 μm, and the diagonal diameter of the image is 2y'=5.76mm. The field angle is taken as 4.16°×3.12°, and the field angle calculated according to the diagonal is 2ω=±2.6°. According to the half-field angle and half-image height calculation, the focal length of the long-wave infrared optical system is:

Retain the common light path part of the infrared optical system, namely the hood, primary mirror and spectroscopic mirror surface parameters, set the left side of the spectroscopic mirror as a transmissive material, the laser part and the primary mirror of the long-wave infrared part have the same aperture, and the laser receiving lens Optimization concentrates the light of each field of view on the photosensitive surface of the APD, focusing on the optimization of the edge field of view.

The design of the optical structure needs to comprehensively consider the optical performance and spatial arrangement. An important factor affecting the optical performance of the catadioptric structure is the obscuration ratio, which can also be defined as the ratio of the aperture of the secondary mirror to the aperture of the beam entering the primary mirror. For infrared systems with reflectors, small F-numbers and large fields of view also affect the system's blocking ratio. The larger the aperture of the secondary mirror, the larger the blocking ratio, which will reduce the energy of the system, and at the same time cause the optical diffraction limit to drop at low and medium frequencies. By taking different obscuration ratio coefficients, observe the variation trend of the diffraction limit at different frequencies. The F number is set at 0.96, the center wavelength is 10um, and the obscuration ratios are respectively 0, 0.15, 0.333, 0.4 and 0.6. MTF (Modulation Transfer Function) The change of the diffraction limit to the spatial frequency. In the case of no obscuration, the MTF diffraction limit at 50lp/mm can reach 0.47. As the obscuration ratio increases, the diffraction limit will show a significant decrease in the middle and low frequencies. When the obscuration ratio is reduced to 0.6, the MTF diffraction limit at 50lp/mm can only reach 0.22. As shown in Figure 3. In the case of no obscuration, the MTF diffraction limit at 50lp/mm can reach 0.47. As the obscuration ratio increases, the diffraction limit will show a significant decrease in the middle and low frequencies.

The secondary correction imaging transmission lens group uses multiple transmission lenses to realize the compensation of the residual aberration of the primary and secondary mirrors. The traditional structure only eliminates spherical aberration and coma. Since the infrared guided imaging structure belongs to a large field of view and small F number system, it is necessary to introduce a transmissive compensation lens to correct aberrations such as astigmatism and field curvature. The transmissive lens can be used in sulfur Choose from materials such as glass, Germanium, ZnSe, and AMTIR-I. In the joint optimization process of the refractive system and the reflective system, it is necessary to ensure that the system blocking ratio is small enough to meet the sufficient pupil area, and the aperture of the lens should be smaller than the diameter of the mirror, so as to avoid blocking the light caused by the mechanical aperture of the lens and facilitate transmission The installation of the type lens barrel and the integral reflector. In addition, in order to avoid the excessive light angle of the edge field of view of the small F-number system from affecting the edge thickness of the lens, a secondary imaging structure is introduced to help keep the light in the transmission lens group smooth and reduce the difficulty of processing the lens. The influence of stray light can be reduced by setting an extinction diaphragm at the primary image plane.

It should be noted that the above is only a schematic illustration and illustration of the present invention, and those skilled in the art should understand that any modification and replacement of the present invention falls within the protection scope of the present invention. The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims (10)

1. A dual-mode coaxial integrated optical system is characterized in that it comprises a hood (1), a primary mirror (2), a beam splitter (3), a secondary correction imaging lens group, and a first detector (9) , the second detector (8); the optical axes of the hood (1), the main mirror (2), the beam splitter (3), and the secondary correction imaging lens group coincide; The hood (1) is used to transmit light, the beam splitter (3) is located on the side of the light exit direction of the hood (1), and the main mirror (2) is located on the side of the light exit direction of the beam splitter (3). The secondary correction imaging lens group is set on the side of the light emitting direction; The beam splitter (3) is a semi-transparent and half-reflective lens; the main mirror (2) is a reflector, and the reflective surface of the reflector faces the reflected light direction of the beam splitter (3); The first detector (9) is used to receive the radiant light of the first wave band, and it is arranged on the first focal plane of the outgoing light direction side of the secondary correction imaging lens group; the second detector (8) is used to receive the light of the second wave band The radiation light is arranged on the second focal plane on the side of the light transmission direction of the beam splitter (3), and the second focal plane is located between the head cover (1) and the beam splitter (3). 2. The dual-mode coaxial integrated optical system according to claim 1, characterized in that the radiated light of the first waveband and the second waveband passes through the hood (1) and reaches the primary mirror (2) through the reflective surface Reflected to the beam splitter (3), the radiation light of the first band is reflected by the beam splitter (3), propagates through the secondary correction imaging lens group, and then reaches the first detector (9), and the radiation light of the second band passes through the beam splitter (3) After transmission, it reaches the second detector (8). 3. The dual-mode coaxial integrated optical system according to claim 1, wherein the radiation light in the first band is infrared light, the radiation light in the second band is laser light, and the first detector (9) It is used for receiving infrared light, and the second detector (8) is used for receiving laser light. 4. The dual-mode coaxial integrated optical system according to claim 3, characterized in that, the beam splitter (3) is a hyperboloid semi-transparent and half-reflective lens, and the surface of the beam splitter (3) is coated with a dichroic A light-splitting film of a color system, the light-splitting film is used to realize the combination of the first wavelength reflection light path and the second wavelength transmission light path. 5. The dual-mode coaxial integrated optical system according to claim 1, characterized in that, the primary mirror (2) is a Cassegrain reflector, and the oblique section of the Cassegrain reflector is used as the The reflective surface faces the outgoing light direction of the beam splitter (3). 6. The dual-mode coaxial integrated optical system according to claim 1, characterized in that, the head cover (1) is a concentric spherical cover, and the material of the head cover is sapphire. 7. The dual-mode coaxial integrated optical system according to claim 1, wherein the secondary correction imaging lens group comprises a first aspheric mirror (4) and a second aspheric mirror (7), a diffractive mirror (5), spherical mirror (6), according to the light incident to the outgoing direction, the order of the first aspheric mirror (4), the diffractive mirror (5), the spherical mirror (6), and the second aspheric mirror (7) are sequentially coaxial with the optical center arrangement. 8. The dual-mode coaxial integrated optical system according to claim 1, characterized in that, The blocking ratio of the primary mirror (2) and the beam splitter (3) is α,

The lateral magnification of the beam splitter (3) is β ₂ ,

The radius of the primary mirror (2) is r ₁ ,

The radius of the beam splitter (3) is r ₂ ,

The distance between the main mirror (2) and the intersection of the optical axis and the beam splitter (3) and the intersection of the optical axis in the exit direction of the optical axis is d,

Among them, f ₁ ' is the focal length of the main mirror (2), f ₂ ' is the transmission focal length of the beam splitter (3), f' is the distance from the object side to the focal point F of the image side of the optical system, l ₂ is the focal point F1 of the main mirror (2) ' to the distance from the intersection of the beam splitter and the optical axis, l' ₂ is the distance from the intersection of the beam splitter (3) and the optical axis to the focal point of the exit pupil of the optical system. 9. The dual-mode coaxial integrated optical system according to claim 1, characterized in that the primary mirror (2) is made of K9 glass, and the base material of the beam splitter (3) is made of Chengdu Guangming H-K9L material. 10. The dual-mode coaxial integrated optical system according to claim 1, characterized in that, the material of the first aspheric mirror (4) and/or the second aspheric mirror (7) is IRG204 and/or IRG209 chalcogenide Glass; the material of the diffraction mirror (5) and/or the spherical mirror (6) adopts ZNSE and/or Germanium material.

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