Dynamic space small target simulator with ultra-long pupil distance

Abstract

The present invention relates to the field of space small target simulators, and in particular to providing a dynamic space small target simulator with an ultra-long exit pupil distance, comprising a long exit pupil distance projection optical system covering the visible light and near-infrared light bands and having an exit pupil distance of 1250 mm, a polarization beam splitter prism, a double free-form surface illumination optical system with a divergence angle of ±4.3° and an unevenness of 4.7%, and a reflective silicon-based liquid crystal display. The double free-form surface illumination optical system is arranged at the incident end of the polarization beam splitter prism, the reflective silicon-based liquid crystal display is arranged at the reflecting end of the polarization beam splitter prism, the long exit pupil distance projection optical system is arranged at the exit end of the polarization beam splitter prism, and the reflective silicon-based liquid crystal display is located on the focal plane of the double free-form surface illumination optical system. The present invention ensures that the space small target simulator has good imaging quality under the condition of a long exit pupil distance, thereby realizing a long exit pupil distance, wide band, and high-precision space small target ground simulation.

Description

Technical Field

[0001] The invention belongs to the technical field of space small target simulators, and in particular relates to a dynamic space small target simulator with an ultra-long exit pupil distance. Background Art

[0002] With the rapid development of deep space exploration technology, the measurement accuracy requirements of star sensors, as the core components of spacecraft attitude control systems, are becoming increasingly higher. Therefore, the performance indicators of space small target simulators, which are ground performance calibration equipment for star sensors, are also improving accordingly.

[0003] Currently, most space small target simulators use three types of spatial light modulators as display devices: thin film field effect transistor liquid crystal display (TFT-LCD), digital micromirror device (DMD) and reflective liquid crystal on silicon (LCOS).

[0004] The exit pupil distances of space small target simulators based on TFT-LCD, DMD, and LCOS are 200mm, 60mm, and 40mm, respectively. However, the entrance pupil of a star sensor is often deep, and the outer lens hood is long. Moreover, during performance calibration, the working distance between the star sensor and the space small target simulator often exceeds 1m. The current space small target simulator has a short exit pupil distance and cannot meet the pupil connection principle, which affects the simulation accuracy of the space small target simulator.

[0005] In 2018, Xu Da's team established a star point error correction model based on wave aberration by analyzing the aberrations of the optical system. The star point position accuracy was better than 10". In 2021, Sun Gaofei's team proposed a star point position correction method based on the influence of aberrations such as distortion, coma, and field curvature. The maximum value of the corrected star point position error was reduced to 10.75". In 2024, Yun Zhikun's team proposed a starlight emission accuracy compensation method based on star point focal length traversal, which further improved the star point position accuracy. However, it has never been able to fundamentally solve the problem of pupil connection caused by too short exit pupil distance.

[0006] Furthermore, in the visible light band, star sensors are susceptible to background radiation caused by scattered sunlight, making efficient positioning and navigation difficult. Since near-infrared light is more efficient than visible light for daytime positioning and navigation, star sensors are gradually expanding their spectral range from visible light to the near-infrared band. This requires space small target simulators to expand their band from the traditional 450-780nm to 450nm-900nm to match the star sensor band. Summary of the Invention

[0007] In view of this, the present invention aims to provide a dynamic space small target simulator with an ultra-long exit pupil distance to solve the technical problem that the traditional space small target simulator has an exit pupil distance that is too short and cannot be connected with the pupil of the star sensor.

[0008] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0009] A dynamic space small target simulator with an ultra-long exit pupil distance comprises a long exit pupil distance projection optical system, a polarization beam splitter prism, a double free-form surface illumination optical system and a reflective silicon-based liquid crystal display; wherein,

[0010] The double free-form surface illumination optical system is arranged at the incident end of the polarization beam splitter prism, the reflective silicon-based liquid crystal display is arranged at the reflective end of the polarization beam splitter prism, the long exit pupil distance projection optical system is arranged at the exit end of the polarization beam splitter prism, and the reflective silicon-based liquid crystal display is located on the focal plane of the double free-form surface illumination optical system;

[0011] The illumination beam emitted by the double free-form surface illumination optical system is incident on a polarization beam splitter prism, and is polarized by the polarization beam splitter prism and split into perpendicular S-polarized light and P-polarized light. The S-polarized light is reflected by the polarization beam splitter prism to a reflective silicon-based liquid crystal display; when the reflective silicon-based liquid crystal display is in a bright state, the incident S-polarized light is modulated into P-polarized light. After being reflected by the reflective silicon-based liquid crystal display, the P-polarized light is transmitted through the polarization beam splitter prism and incident on a long-exit-pupil-distance projection optical system. The long-exit-pupil-distance projection optical system projects the target image carried by the reflective silicon-based liquid crystal display, thereby realizing the simulation of small targets in infinite space.

[0012] Furthermore, the long exit pupil distance projection optical system has an operating wavelength range of 450nm-900nm, an exit pupil distance of 1250nm, and an exit pupil diameter of 45mm;

[0013] The long pupil distance projection optical system includes seven lenses; among them,

[0014] The first lens is a positive lens made of H-FK61, with an aperture of 138 mm, a thickness of 17 mm, an Abbe number of 81.613, a distance between the first lens and the second lens of 7 mm, a radius of curvature of the first surface of the first lens of 256.23 mm, a flat second surface of the first lens, and a distance between the front vertex of the first surface of the first lens and the exit pupil of 1250 mm.

[0015] The second lens is a positive lens made of H-FK61, with an aperture of 134 mm, a thickness of 17 mm, an Abbe number of 81.613, a distance between the second lens and the third lens of 6.5 mm, a first surface of the second lens having a radius of curvature of 206.85 mm, and a second surface of the second lens being a plane;

[0016] The third lens is a negative lens made of H-LAK52, with an aperture of 134 mm, a thickness of 15 mm, an Abbe number of 54.685, a distance between the third lens and the fourth lens of 7.9 mm, a first surface curvature radius of the third lens of 4000 mm, and a second surface curvature radius of the third lens of 161.87 mm.

[0017] The fourth lens is a positive lens made of H-FK61, with an aperture of 120 mm, a thickness of 15 mm, an Abbe number of 81.613, a distance between the fourth lens and the fifth lens of 5 mm, a first surface curvature radius of the fourth lens of 190.83 mm, and a second surface curvature radius of the fourth lens of 1913.43 mm.

[0018] The fifth lens is a positive lens made of H-FK61, with an aperture of 114 mm, a thickness of 16 mm, an Abbe number of 81.613, a distance between the fifth and sixth lenses of 5.3 mm, a first surface of the fifth lens having a radius of curvature of 144.28 mm, and a second surface of the fifth lens having a radius of curvature of 812.12 mm.

[0019] The sixth lens is a negative lens made of H-LAK52, has an aperture of 108 mm, a thickness of 14 mm, an Abbe number of 54.685, a distance between the sixth lens and the seventh lens of 21.5 mm, a first surface of the sixth lens having a radius of curvature of 953.93 mm, and a second surface of the sixth lens having a radius of curvature of 111.38 mm.

[0020] The seventh lens is a positive lens made of H-FK61, has an aperture of 98 mm, a thickness of 17 mm, an Abbe number of 81.613, a distance between the seventh lens and the polarizing beam splitter prism of 21.5 mm, a first surface of the seventh lens having a radius of curvature of 953.93 mm, and a second surface of the seventh lens having a radius of curvature of 111.38 mm.

[0021] The distance between the polarization beam splitter prism and the reflective LCOS display is 15 mm.

[0022] Furthermore, the double free-form surface illumination optical system includes at least one group of LED light sources, each group of LED light sources includes two white light LEDs and two infrared light LEDs with different peak values, the two infrared light LEDs are arranged diagonally, and the two white light LEDs are arranged diagonally.

[0023] Furthermore, the double free-form surface lighting optical system also includes a beam shaping cover for shaping each group of LED light sources, the beam shaping cover includes an incident rotating refractive surface and an incident rotating total reflection surface, the incident rotating total reflection surface is located outside the incident rotating refractive surface, and the LED light source is located at the center of the incident rotating refractive surface.

[0024] Furthermore, the incident rotating refractive surface has rotational symmetry, and the incident rotating refractive surface is designed as follows:

[0025] A coordinate system is established with the position of the LED light source as the origin, the central axis as the z-axis, and the radial direction as the x-axis. After the light emitted by the LED light source passes through the incident rotating refractive surface, it is all transformed into light parallel to the z-axis;

[0026] set up and denote the unit vectors of the incident and outgoing light rays, respectively. Represents the normal vector of the refraction point, and the refractive index of the incident rotating refraction surface is , the maximum radius of the incident rotating refractive surface is , the dividing angle is ;

[0027] Will Divide into N equal parts, that is , , The point coordinates are , calculated by the following formula The normal vector ;

[0028] ;

[0029] Calculate any point on the curve of the cross section of the incident rotating refractive surface according to the following formula Coordinates , and then we get the curve of the cross section of the incident rotating refractive surface, and finally we get the incident rotating refractive surface:

[0030] ;

[0031] in, and Indicates a point The coordinates of point The incident angle is The light and the The intersection between the tangent planes of a point.

[0032] Furthermore, the incident rotating total reflection surface is designed as follows:

[0033] A coordinate system is established with the position of the LED light source as the origin, the central axis as the z-axis, and the radial direction as the x-axis. The light emitted by the LED light source is transformed into light parallel to the z-axis after being reflected by the incident rotating total reflection surface;

[0034] Assume that the refractive index of the incident rotating refractive surface is , the maximum radius of the incident rotating refractive surface is , the dividing angle is ,Will Divide into N equal parts, that is , ;

[0035] The light is totally reflected on the incident rotating total reflection surface. According to the law of reflection, the point The equation of the tangent line is:

[0036] ;

[0037] in, and Indicates a point The coordinates of the point, x and z The coordinates of any point on the tangent line;

[0038] The incident rotating total reflection surface is divided into two parts, and the The last point On this tangent line, point The incident ray equation is:

[0039] ;

[0040] in, and Indicates a point coordinates of

[0041] Point Tangent equation and point The incident light equations constitute an equation group, and by solving the equation group, the coordinates of any point on the curved surface of the incident rotational total reflection surface are obtained, and then the curved surface of the incident rotational total reflection surface is obtained, and finally the incident rotational total reflection surface is obtained.

[0042] Furthermore, the wavelength bands of the two infrared light LEDs are both 830nm-1010nm, and the peak wavelengths are 860nm and 950nm respectively.

[0043] Furthermore, the polarization beam splitter prism is a cube with an aperture of 50.8 mm×50.8 mm×50.8 mm.

[0044] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0045] (1) The present invention designs a long-exit-pupil-distance projection optical system with an exit-pupil distance of 1250 mm and good imaging quality. When the Nyquist frequency is 61 lp / mm, the MTF value of the entire field of view is better than 0.4, the distortion is less than 0.46%, and the average energy concentration of the optical system within one pixel in the entire field of view reaches more than 82%;

[0046] (2) The present invention also designs a double free-form surface illumination optical system consisting of an incident rotating refractive surface and an incident rotating total reflection surface, which constrains the divergence angle of the illumination beam to only ±4.3°, ensuring the uniformity of the illumination beam and a non-uniformity of only 4.7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0048] Figure 1 This is a diagram of the overall architecture of the dynamic space small target simulator with an ultra-long exit pupil distance described in an embodiment of the present invention;

[0049] Figure 2 The working optical path diagram of the dynamic space small target simulator with ultra-long exit pupil distance described in the embodiment of the present invention;

[0050] Figure 3 A structural diagram of a projection optical system with a long exit pupil distance according to an embodiment of the present invention;

[0051] Figure 4 A transfer function diagram of a projection optical system with a long exit pupil distance according to an embodiment of the present invention;

[0052] Figure 5 A dot array diagram of a projection optical system with a long exit pupil distance as described in an embodiment of the present invention;

[0053] Figure 6 The figure shows the normal and distortion of the projection optical system with a long exit pupil distance according to the embodiment of the present invention;

[0054] Figure 7 A point spread function diagram of a projection optical system with a long exit pupil distance according to an embodiment of the present invention;

[0055] Figure 8 This is an energy distribution diagram of the long exit pupil distance projection optical system described in an embodiment of the present invention;

[0056] Figure 9 This is a spectrum curve diagram of the LED light source described in the embodiment of the present invention;

[0057] Figure 10 This is a diagram showing the arrangement of the LED light sources described in the embodiment of the present invention;

[0058] Figure 11 This is a schematic diagram of the design principle of the incident rotating refractive surface described in the embodiment of the present invention;

[0059] Figure 12 This is a schematic diagram of the design principle of the incident rotating total reflection surface described in the embodiment of the present invention;

[0060] Figure 13 A simulated optical path diagram of the double free-form surface illumination optical system according to an embodiment of the present invention;

[0061] Figure 14 The energy distribution diagram of the irradiated surface of the double free-form surface illumination optical system described in the embodiment of the present invention is as follows;

[0062] Figure 15 This is a light distribution curve diagram of the double free-form surface illumination optical system described in an embodiment of the present invention;

[0063] Figure 16 The present invention creates an uncorrected single-star position error heat map as described in the embodiment;

[0064] Figure 17 The corrected single-star position error heat map described in the embodiment of the present invention is created;

[0065] Figure 18 A single star position error distribution diagram of the test star map described in the embodiment of the present invention;

[0066] Figure 19 The star described in the embodiment of the present invention is created Figure 1 Hexing Figure 2 The star point position simulation accuracy diagram;

[0067] Figure 20 The star described in the embodiment of the present invention is created Figure 1 Inter-satellite angular distance error diagram;

[0068] Figure 21 The star described in the embodiment of the present invention is created Figure 2 Inter-satellite angular distance error diagram;

[0069] Figure 22 A magnitude simulation error diagram of the central field of view described in an embodiment of the present invention;

[0070] Figure 23 The star described in the embodiment of the present invention is created Figure 1 Magnitude simulation error diagram of ;

[0071] Figure 24 The star described in the embodiment of the present invention is created Figure 2 Magnitude simulation error diagram of .

[0072] Explanation of the accompanying symbols: long exit pupil distance projection optical system 1, first lens 11, second lens 12, third lens 13, fourth lens 14, fifth lens 15, sixth lens 16, seventh lens 17, polarization beam splitter prism 2, absorption cell 21, double free-form surface illumination optical system 3, first white light LED 31, second white light LED 32, first infrared light LED 33, second infrared light LED 34, incident rotating refractive surface 35, incident rotating total reflection surface 36, reflective silicon-based liquid crystal display 4, aperture 5. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0074] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0075] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0076] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0077] The following will refer to Figure 1-Figure 24 The present invention is described in detail with reference to the embodiments.

[0078] like Figure 1 As shown, an embodiment of the present invention provides a dynamic space small target simulator with an ultra-long exit pupil distance, comprising a long exit pupil distance projection optical system 1, a polarization beam splitter prism 2, a double free-form surface illumination optical system 3 and a reflective silicon-based liquid crystal display 4; wherein, the double free-form surface illumination optical system 3 is arranged at the incident end of the polarization beam splitter prism 2, the reflective silicon-based liquid crystal display 4 is arranged at the reflecting end of the polarization beam splitter prism 2, the long exit pupil distance projection optical system 1 is arranged at the exit end of the polarization beam splitter prism 2, an aperture 5 is arranged between the long exit pupil distance projection optical system 1 and the polarization beam splitter prism 2, and the reflective silicon-based liquid crystal display 4 is located on the focal plane of the double free-form surface illumination optical system 3.

[0079] Currently, target displays primarily include TFT-LCD, DMD, and LCOS. TFT-LCDs have a low aperture ratio and insufficient light energy utilization, making it difficult to achieve wide dynamic range modulation of target energy. DMDs have large individual micromirrors and large spacing between adjacent micromirrors, which limits their ability to simulate targets with high precision. LCOS, however, features small individual pixel size, close pixel spacing, high aperture utilization, and high light energy utilization. Therefore, the present invention selects LCOS (i.e., a reflective liquid crystal on silicon display 4) as the target display device for the dynamic spatial small target simulator. However, LCOS can only modulate light beams in the S-polarization state and requires a dual free-form surface illumination optical system 3 and a polarization beam splitter prism 2 for illumination. Therefore, the present invention constructs an ultra-long exit pupil distance dynamic spatial small target simulator whose overall architecture comprises a long exit pupil distance projection optical system 1, a polarization beam splitter prism 2, a dual free-form surface illumination optical system 3, and a reflective liquid crystal on silicon display 4.

[0080] The polarization beam splitter prism 2 is formed by gluing a pair of high-precision right-angle prisms together, and a polarization beam splitting medium film is plated on the gluing surface.

[0081] like Figure 2 As shown in the figure, the working principle of the ultra-long pupil distance dynamic space small target simulator is:

[0082] The illumination beam emitted by the double free-form surface illumination optical system 3 is a non-polarized beam, which is incident on the polarization splitting medium film of the polarization splitting prism 2 at the Brewster angle, and is polarized by the polarization splitting prism 2 into vertical S-polarized light and P-polarized light. The P-polarized light is transmitted through the polarization splitting prism 2 and absorbed by the absorption cell 21, and the S-polarized light is reflected by the polarization splitting prism 2 to the reflective silicon-based liquid crystal display 4; when the reflective silicon-based liquid crystal display 4 is in the bright state, the incident S-polarized light is modulated into P-polarized light, and the P-polarized light is reflected by the reflective silicon-based liquid crystal display 4 and then transmitted through the polarization splitting prism 2 to the long exit pupil distance projection optical system 1, and the long exit pupil distance projection optical system 1 projects the target image carried by the reflective silicon-based liquid crystal display 4, thereby realizing the simulation of a small target in infinite space.

[0083] It should be noted that the polarization efficiency of the polarization beam splitter prism 2 is related to the numerical aperture angle of the illumination light beam emitted by the double free-form surface illumination optical system 3. The larger the numerical aperture angle of the illumination light beam, the more P-polarized light is mixed into the S-polarized light. In order to avoid this problem, the illumination light beam emitted by the double free-form surface illumination optical system 3 should be incident on the polarization beam splitter prism 2 with a small numerical aperture angle.

[0084] The ultra-long-exit-pupil-distance dynamic space small target simulator operates in the 450nm-900nm wavelength range. The star sensor it interfaces with has a field of view of 4° and an entrance pupil diameter of 45mm. To ensure pupil convergence, the exit pupil diameter of the long-exit-pupil-distance projection optical system 1 is also set to 45mm. Furthermore, to prevent mechanical interference between the ultra-long-exit-pupil-distance dynamic space small target simulator and the star sensor, the exit pupil of the long-exit-pupil-distance projection optical system 1 is set to 1250mm. The performance parameters of the long-exit-pupil-distance projection optical system 1 are shown in Table 1.

[0085] Table 1 Index parameters of long pupil distance projection optical system 1

[0086]

[0087] The present invention uses the SXGA-R5 model of Kopin Corporation as the reflective silicon-based liquid crystal display 4, with a resolution of 2048×1536, a pixel size of 8.3 μm, and an effective luminous size h of 10.63 mm. At this time, the focal length of the long exit pupil distance projection optical system 1 is calculated according to formula (1):

[0088] (1);

[0089] It can be concluded that the focal length of the long exit pupil distance projection optical system 1 is 304.41 mm.

[0090] The long-exit-pupil-distance projection optical system 1 of the present invention adopts a reverse design, that is, a 45 mm diameter is used as the entrance pupil, a light beam is emitted at the field of view angle of the star sensor, enters the long-exit-pupil-distance projection optical system 1, and is finally imaged on the reflective silicon-based liquid crystal display 4 at the focal plane of the long-exit-pupil-distance projection optical system 1.

[0091] Considering that the long exit pupil distance projection optical system 1 has the characteristics of a long exit pupil distance, the Elfer eyepiece optical system with small distortion, large field of view and external exit pupil is selected as the initial structure. The polarization beam splitter prism 2 will produce certain aberrations for the light beam, which needs to be taken into consideration during the design process. During the design, the thickness and material of the polarization beam splitter prism 2 are set according to the actual aperture. In the present invention, the aperture of the polarization beam splitter prism 2 is 50.8mm×50.8mm, and the material is K9. By optimizing the long exit pupil distance projection optical system 1, the aberration of the polarization beam splitter prism 2 is compensated to achieve higher imaging quality. The optimized long exit pupil distance projection optical system 1 is as shown in FIG. Figure 3 As shown, the long exit pupil distance projection optical system 1 includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16 and a seventh lens 17. The optical parameters of the seven lenses are shown in Table 2:

[0092] Table 2 Optical parameters of long pupil distance projection optical system 1

[0093]

[0094] The long pupil distance projection optical system 1 adopts the reverse design principle. The first lens 11 and the second lens 12 are positive lenses, which are mainly used to reduce the large incident angle of light after passing through the lens and converge parallel light beams.

[0095] The third lens 13 is a negative lens, which is mainly used to compensate for the spherical aberration caused by the positive lens.

[0096] The fourth lens 14 , the fifth lens 15 and the sixth lens 16 are used to further converge the light beam without generating excessive aberration.

[0097] The seventh lens 17 serves as a compensating lens to compensate for the aberrations of the first lens 11 to the sixth lens 16 and the polarization beam splitter prism 2 , thereby achieving higher imaging quality.

[0098] Since the optical path is reversible, the long exit pupil distance projection optical system 1 designed according to the above method can refract the light beam emitted by the reflective silicon-based liquid crystal display 4 into a parallel light beam after being refracted by the long exit pupil distance projection optical system 1, thereby simulating an infinitely distant target and providing a test image.

[0099] The imaging quality of the optimized long pupil distance projection optical system 1 is as follows: Figure 4-Figure 8 As shown, Figure 4is the transfer function of the long exit pupil distance projection optical system 1. When the Nyquist frequency is 61 lp / mm, the MTF value of the full field of view is better than 0.4, and the imaging quality of the long exit pupil distance projection optical system 1 is good; Figure 5 This is the spot diagram of the long exit pupil distance projection optical system 1. The diffuse spot radius of each field of view is smaller than the size of one pixel, indicating that the image point spread size of the long exit pupil distance projection optical system 1 is controlled within a small range, meeting the design requirements of the long exit pupil distance projection optical system 1. Figure 6 The field curvature and distortion of the projection optical system 1 with a long exit pupil distance are as follows: the maximum field curvature is 0.13 mm, and the maximum distortion is 0.46%, which meets the design requirement of less than 1%; Figure 7 is the point spread function of the full field of view at the image plane of the projection optical system 1 with a long exit pupil distance. The energy center and the center of mass of the imaging point are basically consistent, and the imaging quality is good. Figure 8 This is the energy distribution diagram of the long exit pupil distance projection optical system 1. Under the full field of view, the average energy concentration of the long exit pupil distance projection optical system 1 within one pixel reaches more than 82%, which is close to the diffraction limit, indicating that the energy entering the long exit pupil distance projection optical system 1 is fully utilized.

[0100] The dual-freeform surface illumination optical system 3 provides a uniform, low-NA illumination beam covering a wavelength of 450 nm to 900 nm for a reflective liquid crystal on silicon display 4. The design of the dual-freeform surface illumination optical system 3 will be described from three perspectives: light source selection and arrangement, initial structural design principles, and optimization and simulation.

[0101] The first aspect: light source selection and arrangement

[0102] In order to ensure that the light source can meet the 450nm-900nm, the light source uses two white light LEDs with a wavelength range of 400nm-780nm, a narrow-band infrared LED with a peak wavelength of 860nm and a wavelength range of 830nm-1010nm, and a narrow-band infrared LED with a peak wavelength of 950nm and a wavelength range of 830nm-1010nm. The spectral curves of the three LEDs are as follows: Figure 9 shown.

[0103] The LED light source is arranged in the form of Figure 10 As shown, a first white light LED 31 and a second white light LED 32 are placed on one diagonal line, and a first infrared light LED 33 and a second infrared light LED 34 with peak wavelengths of 860 nm and 950 nm are placed on the other diagonal line. The present invention uses the first white light LED 31, the second white light LED 32, the first infrared light LED 33, and the second infrared light LED 34 as a group of LED light sources, and uses at least one group of LED light sources to illuminate the reflective silicon-based liquid crystal display 4.

[0104] Second aspect: initial structural design principles

[0105] In order to constrain the beam angle of the double free-form surface illumination optical system 3 and control the uniformity, the present invention designs a beam shaping cover for shaping the LED light source. Each group of LEDs is provided with a beam shaping cover, and the beam shaping cover includes an incident rotating refractive surface 35 and an incident rotating total reflection surface 36.

[0106] (1) Design of incident rotating refractive surface 35

[0107] The design principle of the incident rotating refractive surface 35 is as follows Figure 11 As shown, incident rotating refractive surface 35 is located near the center of the LED light source. Therefore, a coordinate system is established with the LED light source's location as the origin, with the system's central axis as the z-axis and the radial axis as the x-axis. Light from the LED light source is completely transformed into light parallel to the z-axis after passing through incident rotating refractive surface 35. Furthermore, since incident rotating refractive surface 35 is rotationally symmetric, its shape can be determined by simply calculating the curve on its cross-section.

[0108] set up and denote the unit vectors of the incident and outgoing light rays, respectively. Represents the normal vector of the refraction point, and the refractive index of the incident rotating refractive surface 35 is , the maximum radius of the incident rotating refractive surface 35 is , the dividing angle is .Will Divide into N equal parts, that is , .point The coordinates are , The unit vector of the outgoing light is represented by the direction of the light emitted from the origin after passing through the incident rotating refractive surface 35. The vector is represented by , since it is emitted along the z axis, so x=0, the size of z is the maximum value of A The distance between the projection point on the Z axis and the origin can be calculated by Snell's law. The normal vector :

[0109] (2);

[0110] In formula (2), the N on the left side of the equal sign corresponds to N(x, z), and the content under the square root includes O and I, but the dot product is a scalar, so the left side of the equal sign is a scalar Vector N; the right side of the equal sign is ultimately in vector form. By comparing the left and right sides of the equal sign, we can find the size of N0 corresponding to x0 and z0, and we can get .

[0111] The incident angle is The light and the Intersection between tangent planes of a point:

[0112] (3);

[0113] From (2) and (3), we can get According to the above method, the coordinates of any point on the curve of the cross section of the incident rotating refractive surface 35 can be calculated according to the following formula: Coordinates :

[0114] (4).

[0115] (2) Design of incident rotating total reflection surface 36

[0116] The design principle of the incident rotating total reflection surface 36 is as follows Figure 12 As shown, the incident rotating total reflection surface 36 is located outside the LED light source, that is, outside the incident rotating refractive surface 35. It is also required that the light emitted by the LED light source is transformed into light parallel to the z-axis after being reflected by the incident rotating total reflection surface 36.

[0117] The light is totally reflected on the incident rotating total reflection surface 36. According to the law of reflection, the point The equation of the tangent line is:

[0118] (5);

[0119] in, and Indicates a point The coordinates of the point, x and z The coordinates of any point on the tangent line.

[0120] When the curved surface of the incident rotating total reflection surface 36 is fine enough, it can be considered that the point The last point Also on this tangent line. Point The incident ray equation is:

[0121] (6);

[0122] Point on the curve of the incident rotating total reflection surface 36 The coordinates of are located at the intersection of the two lines determined by equations (5) and (6), and can be obtained by solving the equations. The above method is used to calculate the shape of any point on the curve of the incident rotating total reflection surface 36, ultimately obtaining the surface shape of the incident rotating total reflection surface 36.

[0123] The third aspect: optimization and simulation

[0124] The LED light source divergence angle selected in the present invention is ±60°. Under the conditions that the irradiance uniformity of the double free-form surface illumination optical system is better than 95% and the beam divergence angle is better than ±5°, according to the initial structure of the double free-form surface illumination optical system 3 obtained above, and the double free-form surface illumination optical system 3 is optimized by Lighttools software, the simulated optical path, irradiation surface energy distribution and light distribution curve of the double free-form surface illumination optical system 3 are obtained, as shown in FIG. Figure 13-15 shown.

[0125] Depend on Figure 14 It can be obtained that the uniformity of the double free-form surface illumination optical system 3 on the irradiation surface is:

[0126] (7);

[0127] in, is the maximum light intensity, is the minimum light intensity. Figure 15 It can be seen that the divergence angle of the LED light source after passing through the incident rotating refractive surface 35 and the incident rotating total reflection surface 36 is ±4.3°.

[0128] It can be seen from this that the double free-form surface illumination optical system 3 designed in the present invention with a beam shaping cover (composed of an incident rotating refractive surface 35 and an incident rotating total reflection surface 36) constrains the divergence angle and ensures uniformity, achieving a divergence angle of ±4.3° and a non-uniformity of 4.7%.

[0129] Since the performance of the long-exit-pupil-distance dynamic space small target simulator obtained through actual processing deviates from the theoretical design results, it is necessary to first perform precision correction and calibration before conducting performance verification experiments. An experimental platform is built using a theodolite, an illuminometer, and a long-exit-pupil-distance dynamic space small target simulator.

[0130] The accuracy correction calibration process is as follows:

[0131] The reflective silicon liquid crystal display 4 is divided into equidistant 10×10 grids, and the pixels at the intersection of the grids are lit as sampling points for the field of view test of the dynamic space small target simulator with a long pupil distance; the azimuth of the sampling points is tested using a theodolite. and pitch angle and the azimuth of the center point of the field of view and pitch angle , then the single star position of the sampling point can be expressed as:

[0132] (8);

[0133] By comparing with the theoretical single star position of the sampling point, the single star position error heat map of the sampling point without precision correction is obtained, such as Figure 16 On this basis, the least squares fitting method is applied to complete the correction of the dynamic space small target simulator with long pupil distance. The single star position error heat map of the corrected sampling point is shown as follows: Figure 17 shown.

[0134] according to Figure 16 and Figure 17 It can be seen that the maximum error of the single star position error after accuracy correction is -3.83". However, since the distribution of small space targets only has a certain probability of coinciding with the test sampling points, it is ideal to evaluate the correction accuracy only by the accuracy of the sampling points. Therefore, a pixel point is randomly selected in each area of the 10×10 grid, and a test star map of 100 star points is constructed to evaluate the accuracy of the dynamic space small target simulator with long pupil distance. The test results are shown in the figure below. Figure 18 As shown. Figure 18 It can be seen that the distribution of single star position errors of the 100 test star points is relatively close to the normal distribution, with the maximum value being 4.46″ and the minimum value being -3.94″. It does not show a distribution relationship that is strongly correlated with the field of view size. This shows that the position of the star point has little effect on the single star position error, and the simulation accuracy of the long pupil distance dynamic space small target simulator has been well corrected.

[0135] The performance verification experiment process is as follows:

[0136] To avoid the particularities of single-image performance verification, the performance verification experiment for the long-exit-pupil-distance dynamic space small target simulator uses two star images with known star positions and magnitudes to verify the accuracy of the simulator's geometric and radiometric simulations. The star positions and magnitudes for the two images are shown in Table 3.

[0137] Table 3 Star positions and magnitudes of star charts

[0138]

[0139] (1) Geometric feature simulation accuracy

[0140] Use theodolite to measure the stars Figure 1 Hexing Figure 2 The center point of the star and the azimuth and elevation angles of each star point can be obtained according to formula (7): Figure 1 Hexing Figure 2 The star point position simulation accuracy is as follows: Figure 19 shown.

[0141] according to Figure 19 It can be concluded that the star Figure 1The star point position error is distributed between -3.94″ and 0.94″. Figure 2 The star point position error is distributed between -3.52″ and 3.43″. At this time, according to formula (7), the inter-satellite angular distance error heat map of the two star maps can be obtained, as follows: Figure 20 and Figure 21 shown.

[0142] according to Figure 20 and Figure 21 As can be seen, the star Figure 1 The inter-satellite angular distance error is distributed between -6.41″ and 2.80″. Figure 2 The inter-satellite angular distance error is distributed between -7.69″ and 7.16″.

[0143] (2) Geometric feature simulation accuracy

[0144] According to Table 3, Figure 1 The magnitudes of the 10 stars range from 4.9 to 5.6. Figure 2 The magnitudes of the 10 stars are between 5.2 and 6. At the same time, when multiple stars are lit in the star map, energy superposition will occur, making it impossible to evaluate the accuracy of the radiation characteristic simulation. Therefore, the present invention first selects a central star point, controls the magnitude of the central star point to be 3 to 6, and uses a 0.5-magnitude interval to measure the radiation characteristic simulation accuracy of the dynamic space small target simulator with a long pupil distance. The results are as follows Figure 22 On this basis, the Figure 1 Hexing Figure 2 The magnitude simulation errors of the star points are measured one by one, and the measurement results are as follows Figure 23 and Figure 24 shown.

[0145] from Figure 22-24 It can be seen that the dynamic space small target simulator with long exit pupil distance has the ability to simulate the radiation characteristics of stars from magnitude 3 to 6, with a simulation accuracy between -0.049 and 0.085. It can realize the superimposed simulation of radiation characteristics on the basis of the geometric feature simulation accuracy, thereby verifying the geometric feature simulation accuracy and radiation feature simulation accuracy of the dynamic space small target simulator with long exit pupil distance.

[0146] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0147] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A dynamic space small target simulator with an ultra-long pupil distance, characterized in that: It includes a long pupil distance projection optical system, a polarization beam splitter prism, a double free-form surface illumination optical system and a reflective silicon-based liquid crystal display; among which, The double free-form surface illumination optical system is arranged at the incident end of the polarization beam splitter prism, the reflective silicon-based liquid crystal display is arranged at the reflective end of the polarization beam splitter prism, the long exit pupil distance projection optical system is arranged at the exit end of the polarization beam splitter prism, and the reflective silicon-based liquid crystal display is located on the focal plane of the double free-form surface illumination optical system; The illumination beam emitted by the dual free-form surface illumination optical system is incident on a polarization beam splitter prism, where it is polarized and split into perpendicular S-polarized light and P-polarized light. The S-polarized light is reflected by the polarization beam splitter prism onto a reflective silicon-based liquid crystal display. When the reflective silicon-based liquid crystal display is in a bright state, the incident S-polarized light is modulated into P-polarized light. After being reflected by the reflective silicon-based liquid crystal display, the P-polarized light is transmitted through the polarization beam splitter prism and incident on a long-exit-pupil-distance projection optical system. The long-exit-pupil-distance projection optical system projects the target image carried by the reflective silicon-based liquid crystal display, thereby simulating a small target in infinite space. The double free-form surface illumination optical system includes at least one set of LED light sources, each set of LED light sources includes two white light LEDs and two infrared light LEDs with different peak values, the two infrared light LEDs are arranged diagonally, and the two white light LEDs are arranged diagonally; The double free-form surface illumination optical system further includes a beam shaping cover for shaping each group of LED light sources. The beam shaping cover includes an incident rotating refractive surface and an incident rotating total reflection surface. The incident rotating total reflection surface is located outside the incident rotating refractive surface, and the LED light source is located at the center of the incident rotating refractive surface. The incident rotating refractive surface has rotational symmetry, and the design of the incident rotating refractive surface is as follows: A coordinate system is established with the position of the LED light source as the origin, the central axis as the z-axis, and the radial direction as the x-axis. After the light emitted by the LED light source passes through the incident rotating refractive surface, it is all transformed into light parallel to the z-axis; set up and denote the unit vectors of the incident and outgoing light rays, respectively. Represents the normal vector of the refraction point, and the refractive index of the incident rotating refraction surface is , the maximum radius of the incident rotating refractive surface is , the dividing angle is ; Will Divide into N equal parts, that is , , The point coordinates are , calculated by the following formula The normal vector ; ； Calculate any point on the curve of the cross section of the incident rotating refractive surface according to the following formula Coordinates , and then we get the curve of the cross section of the incident rotating refractive surface, and finally we get the incident rotating refractive surface: ； in, and Indicates a point The coordinates of point The incident angle is The light and the The intersection between the tangent planes of a point.

2. The dynamic space small target simulator with an ultra-long exit pupil distance according to claim 1, characterized in that: The working band of the long pupil distance projection optical system is 450nm-900nm, the pupil distance is 1250nm, and the exit aperture is 45mm; The long pupil distance projection optical system includes seven lenses; among them, The first lens is a positive lens made of H-FK61, with an aperture of 138 mm, a thickness of 17 mm, an Abbe number of 81.613, a distance between the first lens and the second lens of 7 mm, a radius of curvature of the first surface of the first lens of 256.23 mm, a flat second surface of the first lens, and a distance between the front vertex of the first surface of the first lens and the exit pupil of 1250 mm. The second lens is a positive lens made of H-FK61, with an aperture of 134 mm, a thickness of 17 mm, an Abbe number of 81.613, a distance between the second lens and the third lens of 6.5 mm, a first surface of the second lens having a radius of curvature of 206.85 mm, and a second surface of the second lens being a plane; The third lens is a negative lens made of H-LAK52, with an aperture of 134 mm, a thickness of 15 mm, an Abbe number of 54.685, a distance between the third lens and the fourth lens of 7.9 mm, a first surface curvature radius of the third lens of 4000 mm, and a second surface curvature radius of the third lens of 161.87 mm. The fourth lens is a positive lens made of H-FK61, with an aperture of 120 mm, a thickness of 15 mm, an Abbe number of 81.613, a distance between the fourth lens and the fifth lens of 5 mm, a first surface curvature radius of the fourth lens of 190.83 mm, and a second surface curvature radius of the fourth lens of 1913.43 mm. The fifth lens is a positive lens made of H-FK61, with an aperture of 114 mm, a thickness of 16 mm, an Abbe number of 81.613, a distance between the fifth and sixth lenses of 5.3 mm, a first surface of the fifth lens having a radius of curvature of 144.28 mm, and a second surface of the fifth lens having a radius of curvature of 812.12 mm. The sixth lens is a negative lens made of H-LAK52, has an aperture of 108 mm, a thickness of 14 mm, an Abbe number of 54.685, a distance between the sixth lens and the seventh lens of 21.5 mm, a first surface of the sixth lens having a radius of curvature of 953.93 mm, and a second surface of the sixth lens having a radius of curvature of 111.38 mm. The seventh lens is a positive lens made of H-FK61, has an aperture of 98 mm, a thickness of 17 mm, an Abbe number of 81.613, a distance between the seventh lens and the polarizing beam splitter prism of 21.5 mm, a first surface of the seventh lens having a radius of curvature of 953.93 mm, and a second surface of the seventh lens having a radius of curvature of 111.38 mm. The distance between the polarization beam splitter prism and the reflective LCOS display is 15 mm.

3. The dynamic space small target simulator with an ultra-long exit pupil distance according to claim 1, characterized in that: The design of the incident rotating total reflection surface is as follows: A coordinate system is established with the position of the LED light source as the origin, the central axis as the z-axis, and the radial direction as the x-axis. The light emitted by the LED light source is transformed into light parallel to the z-axis after being reflected by the incident rotating total reflection surface; Assume that the refractive index of the incident rotating refractive surface is , the maximum radius of the incident rotating refractive surface is , the dividing angle is ,Will Divide into N equal parts, that is , ; The light is totally reflected on the incident rotating total reflection surface. According to the law of reflection, the point The equation of the tangent line is: ； in, and Indicates a point The coordinates of the point, x and z The coordinates of any point on the tangent line; The incident rotating total reflection surface is divided into two parts, and the The last point On this tangent line, point The incident ray equation is: ； in, and Indicates a point coordinates of Point Tangent equation and point The incident light equations constitute an equation group, and by solving the equation group, the coordinates of any point on the curved surface of the incident rotational total reflection surface are obtained, and then the curved surface of the incident rotational total reflection surface is obtained, and finally the incident rotational total reflection surface is obtained.

4. The dynamic space small target simulator with an ultra-long exit pupil distance according to any one of claims 1 to 3, characterized in that: The wavelengths of the two infrared LEDs are both 830nm-1010nm, with peak wavelengths of 860nm and 950nm respectively.

5. The dynamic space small target simulator with an ultra-long exit pupil distance according to claim 1, characterized in that: The polarizing beam splitter prism is a cube with an aperture of 50.8mm×50.8mm×50.8mm.

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