A field of view gating optical imaging system based on an optical fiber relay

Abstract

The application discloses a field-of-view gating optical imaging system based on a fiber image transmission bundle, which comprises a front-end telescope, a fiber image transmission bundle, a micro switch and a micro lens array and a rear-end imaging objective. The front-end telescope does not need an image-side telecentric imaging structure and has a certain field of view, and is used for imaging multiple targets in the field of view to a primary image plane; the fiber image transmission bundle is used for coupling the primary image plane and redistributing the fiber at an output end, and is used for improving the effective field of view of the system; the micro switch and the micro lens array are combined with the rear-end imaging objective to realize gating imaging of the output end image plane of the fiber image transmission bundle and to realize suppression of background light; opening multiple micro switch units can realize simultaneous detection of multiple targets. The field-of-view gating optical imaging system based on the fiber image transmission bundle can provide a higher field-of-view duty ratio and obtain a more continuous field of view compared with the prior art, and is more conducive to lightening and miniaturization of the system.

Description

Technical Field

[0001] This invention belongs to the field of all-day star sensor design and relates to a field-gated optical imaging system based on fiber optic image transmission bundle. Background Technology

[0002] All-weather star sensors enable near-Earth space platforms such as ships, aircraft, and missiles to achieve autonomous astronomical navigation without relying on satellite navigation systems, which is of significant strategic importance. Currently, the commonly used method for suppressing background sky light is to design small-field-of-view telescopes to reduce the solid angle of a single pixel on the detector. Due to the small field of view, such star sensors often only have a single star target within their field of view, making it impossible to achieve autonomous attitude determination using traditional multi-star matching methods. Instead, servo mechanisms such as two-dimensional turntables are used to track the single star within the field of view. In addition, there is a scheme that uses multiple small-field-of-view telescopes. Although this scheme does not require a two-dimensional turntable, it still requires multiple independent telescope systems, which still face problems such as large size and weight, making it difficult to meet the application requirements of airborne platforms.

[0003] The field-gated optical imaging system combines the characteristics of a large field-of-view telecentric telescope for star acquisition with the small field-of-view micro-switches and microlenses for gating imaging. It simultaneously achieves a large field-of-view imaging and strong sky background light suppression capability, and is expected to be suitable for matched star sensors in bright daytime backgrounds.

[0004] However, in existing field-gated optical imaging systems, in order for all microlens units in the microlens array to perform gated imaging of the primary image plane, the front-end telescope must be designed with an image-side telecentric optical path. The design and fabrication of an image-side telecentric optical path is more complex and costly than that of a conventional lens, and it also results in a larger size and weight. Furthermore, due to the significant vignetting phenomenon at the edge of the microlens unit's field of view, and the corresponding reduction in the effective beam aperture in this region, the Airy disk size of the image increases, leading to a decrease in the effective field of view for gated field-view imaging. This is detrimental to improving the system's detection probability for multiple stars. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the limitations of existing field-of-view gating optical imaging systems, which require a front-end image-side telecentric telescope and have a relatively small effective field of view. This invention proposes a field-of-view gating optical imaging system based on an optical fiber image bundle. This imaging system uses an optical fiber image bundle to couple the image plane of the front-end telescope, avoiding the requirement for a telecentric structure on the front-end telescope's image side. Furthermore, by rearranging the image plane at the output end of the optical fiber image bundle, the effective field of view duty cycle of the system can be improved.

[0006] The technical solution adopted by this invention to solve its technical problem is: a field-of-view gating optical imaging system based on fiber optic image transmission bundle, characterized in that it includes: - The front-end telescope has a large field of view and is used to image multiple targets within the field of view onto the primary image plane of the system; - The fiber optic image bundle is used to couple the primary image plane and redistribute the fiber at the output end to improve the effective field of view of the system's gating imaging. - A micro-switch array is used to select the image plane at the output end of the fiber optic image bundle; - A microlens array, which corresponds one-to-one with the units in the microswitches array, wherein each microlens unit has its own optical axis, used to form multiple gated field imaging channels for the image plane at the output end of the fiber optic image bundle. - The rear imaging objective lens, together with each microlens unit, can form a magnified imaging system for magnified imaging of each gated field of view, increasing the focal length of imaging within the gated field of view, reducing the field of view angle of a single pixel of the detector, and improving the background light suppression capability. - An array detector used to receive magnified images of targets within each gated field of view.

[0007] Multiple target signal beams in strong background light are imaged onto a primary image plane by a front-end telescope; the primary image plane is coupled by an optical fiber image bundle; the output image plane of the optical fiber image bundle is rearranged to match the effective field of view of the microlens array; the output image plane of the optical fiber image bundle is then gated by a micro-switching array and a microlens array; then, the output image plane of the optical fiber image bundle within the gated field of view is magnified and imaged by a rear-end imaging objective; finally, the array detector receives the magnified target images within each gated field of view.

[0008] Furthermore, the front-end telescope is selected as a conventional telescope structure optical system, without the requirement of an image-side telecentric imaging optical system, which is beneficial for the miniaturization and weight reduction of the front-end telescope.

[0009] Furthermore, the input surface distribution of the optical fiber image bundle should match the image plane distribution of the front-end telescope, so that the principal rays of each field of view of the front-end telescope on the imaging plane are perpendicular to the corresponding optical fiber end face in the optical fiber image bundle.

[0010] Furthermore, the numerical aperture of the fiber optic image bundle input surface should be no less than half the relative aperture of the front-end telescope.

[0011] Furthermore, the fiber arrangement period of the fiber image bundle input surface should be less than the radius of the Airy disk at the imaging point of the front-end telescope, to ensure that the coupling between the fiber image bundle input end and the front-end telescope image plane satisfies the requirements of the Nyquist sampling theorem.

[0012] Furthermore, the output ends of the optical fiber image transmission bundle are arranged at intervals, and each intervally arranged optical fiber image transmission bundle output end unit corresponds to a gated field of view, and corresponds one-to-one with the micro-switching unit in the micro-switching array and the micro-lens unit in the micro-lens array. Each optical fiber image transmission bundle output end unit is located within the effective field of view of the corresponding micro-lens unit in the micro-lens array.

[0013] Furthermore, by stitching together the secondary image planes of each gated field of view received by the array detector, a primary image plane with a large effective field of view duty cycle, or even a continuous and magnified field of view, can be reconstructed.

[0014] Furthermore, by using multiple sets of fiber optic image bundles, the field of view of the front-end telescope can be divided into multiple sub-fields of view. The output ends of each set of fiber optic image bundles are distributed at a certain angle, reserving enough space to arrange the corresponding microswitches and microlens arrays, the rear imaging objective lens and the array detector, so as to realize the field of view selection imaging of each sub-field of view, thereby further increasing the effective field of view of the system.

[0015] Compared with the prior art, the present invention has the following advantages: 1. The field-view gating imaging system based on fiber optic image bundle described in this invention uses fiber optic image bundle to couple the image plane of the front-end telescope, avoiding the requirement for the telecentric structure of the front-end telescope image side, which is beneficial to the simplification, miniaturization and weight reduction of the system. 2. The field-of-view gating imaging system based on fiber optic image bundle described in this invention rearranges the image plane at the output end of the fiber optic image bundle so that the image plane at the output end of the fiber optic image bundle within each gating field of view is located within the effective field of view of the corresponding microlens unit, thereby increasing the effective field of view duty cycle of the system and improving the detection capability of the system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a field-of-view gating imaging system based on an optical fiber image bundle in Embodiment 1 of the present invention; In the figure: 1 is the front-end telescope, 2 is the fiber optic image bundle, 3 is the micro-switch array, 4 is the microlens array, 5 is the rear-end imaging objective, 6 is the array detector, 7 is the image plane of the front-end telescope, 8 is the input end of the fiber optic image bundle, and 9 is the output end of the fiber optic image bundle. Figure 2 This is a schematic diagram of the fiber bundle distribution at the output end of the fiber optic image transmission bundle in Embodiment 1 of the present invention; In the diagram: 9 is the output end of the fiber optic image bundle, and 90 is the fiber optic bundle unit.

[0017] Figure 3 This is a schematic diagram of the distribution of microlens units in the microlens array in Embodiment 1 of the present invention; In the figure: 4 represents the microlens array, and 40 represents the microlens unit in the microlens array.

[0018] Figure 4 This is a schematic diagram of a field-of-view gating imaging system based on an optical fiber image bundle in Embodiment 2 of the present invention; In the diagram: 1 is the front-end telescope, 21 is the first group of fiber optic image transmission bundles, 22 is the second group of fiber optic image transmission bundles, 31 is the first group of micro-switches array, 32 is the second group of micro-switches array, 41 is the first group of microlens arrays, 42 is the second group of microlens arrays, 51 is the first group of rear-end imaging objectives, 52 is the second group of rear-end imaging objectives, 61 is the first group of array detectors, 62 is the second group of array detectors, 7 is the image plane of the front-end telescope, 8 is the input end of the fiber optic image transmission bundle, 91 is the output end of the first group of fiber optic image transmission bundles, and 92 is the output end of the second group of fiber optic image transmission bundles. Figure 5 This is a schematic diagram of the structure of taking two sub-fields of view, namely the first sub-field of view 71 and the second sub-field of view 72, on the image plane 7 of the front-end telescope in Embodiment 2 of the present invention. Figure 6 This is a schematic diagram of the fiber bundle distribution at the output end of the fiber optic image transmission bundle in Embodiment 2 of the present invention; In the diagram: 91 is the output end of the first group of fiber optic image transmission bundles, and 910 is the first group of fiber optic bundle units; Figure 7 This is a schematic diagram of the distribution of microlens units in the microlens array in Embodiment 2 of the present invention; In the figure, 41 represents the first group of microlens arrays, and 410 represents the microlens unit in the first group of microlens arrays. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the following embodiments, those skilled in the art can implement all the contents of the claims of the present invention.

[0020] Example 1: Embodiment 1 of the present invention is a field-gated optical imaging system based on an optical fiber image bundle with an aperture of 80mm, an operating band of short-wave infrared H-band (center wavelength of 1.65μm), a numerical aperture of 0.16 for the optical fiber image bundle, a single filament core diameter of 5μm, a system F number of 14, a shared array detector, and a total field of view of Ф5°.

[0021] like Figure 1As shown, the field-gated optical imaging system based on fiber optic image bundles of the present invention includes: a front-end telescope 1, a fiber optic image bundle 2, a micro-switching array 3, a microlens array 4, a rear-end imaging objective lens 5, and an array detector 6. The front-end telescope 1 is not limited by the structure of telecentric imaging on the image side; its field of view is Ф5°, its aperture is 80mm, its focal length is 280mm, and its relative aperture is approximately 0.286, enabling near-diffraction-limited imaging. Its Airy disk diameter on the image plane is approximately 14μm. The fiber optic image bundle 2 has a numerical aperture of 0.16, a single-filament core diameter of 5μm, and is arranged in a quadrilateral pattern, with a resolution of 150 l / mm, satisfying the sampling frequency of the telescope image plane. The fiber distribution at the input end of the fiber optic image bundle 2 matches the distribution of the telescope image plane, ensuring the coupling efficiency of each fiber to the telescope image plane. The image plane 7 of the front-end telescope 1 is located at the input end 8 of the fiber optic image bundle, and the two ends of the fiber optic image bundle 2 are the input end 8 and the output end 9 of the fiber optic image bundle, respectively.

[0022] Figure 2 This is a schematic diagram of the fiber bundle distribution in the output end of the fiber optic image transmission bundle. The single fiber filaments in the fiber bundle unit 90 are distributed in a checkerboard pattern. The fiber bundle unit 90 is also distributed in a checkerboard pattern at the output end 9 of the fiber optic image transmission bundle. The side length of each fiber bundle unit 90 is 2.2 mm, corresponding to a field of view of 0.45°×0.45° on the first image plane. The distribution period of the fiber bundle unit 90 is 3 mm, which corresponds one-to-one with the microlens unit 40 in the microlens array 4.

[0023] Figure 3 This diagram illustrates the distribution of microlens units 40 in the microlens array 4. Each microlens unit 40 is square, with a side length of 3mm, a focal length of 9mm, an arrangement period of 3mm, and a total of 97 units. The microswitch array 4 also has a unit aperture of 3mm and 97 units. The rear imaging objective 5 has an aperture of 35mm and a focal length of 36mm. Each microlens unit 40, together with the rear imaging objective 5, forms a magnified imaging system with a magnification of 4, used for 4x magnification imaging of the image plane at the output end of the fiber optic image bundle 2. The array detector 6 has a pixel size of 20μm and an effective pixel array number of 512×512. The diameter of the star image falling on the array detector's image plane is approximately 56μm, smaller than the size of 3×3 detector pixels, thus meeting the requirements for energy concentration and centroid extraction of the star image.

[0024] During system operation, only 1 to 4 microswitches are activated at a time for gating the field of view. Activating one microswitch results in a field of view of 0.45° / 512 = 3.16″ per pixel, providing strong background light suppression. Switching between different microswitches allows for observation of stars within different gating fields. Stitching together the image planes from different gating fields reconstructs the stellar image distribution within the complete field of view of the front-end telescope. Activating all four gating fields simultaneously provides an equivalent field of view of 6.32″ per pixel, also offering strong background light suppression. This enables simultaneous detection of multiple stars against a bright daytime background.

[0025] Example 2: Embodiment 2 of the present invention is a field-gated optical imaging system based on an optical fiber image bundle with a diameter of 70mm, an operating band of short-wave infrared H-band (center wavelength of 1.65μm), a numerical aperture of 0.11 for the optical fiber image bundle, a single filament core diameter of 8μm, a system F number of 15, two array detectors, two sub-fields of view, and a total field of view of 2×Ф3.6°.

[0026] like Figure 4As shown, the field-of-view gating optical imaging system based on fiber optic image bundles of the present invention includes: a front-end telescope 1, two sets of fiber optic image bundles 21 and 22, two sets of micro-switching arrays 31 and 32, two sets of microlens arrays 41 and 42, two sets of rear-end imaging objectives 51 and 52, and two sets of array detectors 61 and 62. The output ends of the fiber optic image transmission bundles are divided into the first group of fiber optic image transmission bundles output end 91 and the second group of fiber optic image transmission bundles output end 92. The first group of fiber optic image transmission bundles output end 91 and the second group of fiber optic image transmission bundles output end 92 correspond to the first group of fiber optic image transmission bundles 21 and the second group of fiber optic image transmission bundles 22, respectively. The first group of fiber optic image transmission bundles 21 corresponds to the first group of micro-switches array 31, and the second group of fiber optic image transmission bundles 22 corresponds to the second group of micro-switches array 32. The first group of fiber optic image transmission bundles 21 corresponds to the first group of microlens array 41, and the second group of fiber optic image transmission bundles 22 corresponds to the second group of microlens array 42. The first group of fiber optic image transmission bundles 21 corresponds to the first group of rear imaging objectives 51, and the second group of fiber optic image transmission bundles 22 corresponds to the second group of rear imaging objectives 52. The first group of fiber optic image transmission bundles 21 corresponds to the first group of array detectors 61, and the second group of fiber optic image transmission bundles 22 corresponds to the second group of array detectors 62. The front-end telescope 1 is not limited by the structure of telecentric imaging, has a field of view of Ф7.2°, an aperture of 70mm, a focal length of 350mm, and a relative aperture of approximately 0.2, enabling near-diffraction-limited imaging. Its Airy disk diameter on the image plane is approximately 20μm. The first and second sets of fiber optic image bundles 21 and 22 have a numerical aperture of 0.11, a single-filament core diameter of 8μm, and are arranged in a hexagonal pattern, achieving a resolution of 100 l / mm, which meets the sampling frequency requirements of the telescope image plane. Figure 5 As shown, two Ф3.6° sub-fields of view, namely the first sub-field of view 71 and the first sub-field of view 72, are taken on the image plane 7 of the front-end telescope. The input ends 8 of the first and second sets of fiber optic image bundles 21 and 22 are matched with the image plane distribution of the two Ф3.6° sub-fields of view, namely the first sub-field of view 71 and the first sub-field of view 72, respectively, so as to ensure the coupling efficiency of each fiber to the telescope image plane.

[0027] Figure 6This is a schematic diagram of the fiber bundle distribution in the output end 91 of the first group of fiber optic image transmission bundles. The distribution of the second group of fiber bundle units in the output end 92 of the second group of fiber optic image transmission bundles is the same as that of the first group. The output end 91 of the first group of fiber optic image transmission bundles corresponds to a sub-field of view, namely the first sub-field of view 71. The single-filament fibers in the first group of fiber bundle units 910 in the output end 91 of the first group of fiber optic image transmission bundles are distributed in a cluster. The first group of fiber bundle units 910 are distributed in a checkerboard pattern in the output end 91 of the first group of fiber optic image transmission bundles. The diameter of each cluster of fiber bundle units is 2.44 mm, corresponding to a field of view size of Ф0.4° on the first image plane. The distribution period of the first group of fiber bundle units 910 is 4 mm, which corresponds one-to-one with the first group of microlens units 410 in the first group of microlens array 41. Figure 7 This is a schematic diagram showing the distribution of the first group of microlens units 410 in the first group of microlens array 41. The distribution of the second group of microlens units in the second group of microlens array 42 is the same as that of the first group. The first group of microlens array 41 is a circular microlens array with microlens units having a diameter of 4mm, a focal length of 15mm, an arrangement period of 4mm, and a total of 57 array units. The first group of microswitches array 41 also has a unit aperture of 4mm and 57 units. The first and second group of rear imaging objectives 51 and 52 both have an aperture of 38mm and a focal length of 45mm. Each microlens unit, together with the rear imaging objective, constitutes a magnified imaging system with an imaging magnification of 3, used for 3x magnification imaging of the image plane at the output end of the fiber optic image bundle. The first and second array detectors 61 and 62 both have a pixel size of 20 μm, with an effective pixel array number of 512 × 512. The diameter of the star image falling on the detector image plane is approximately 60 μm, which can be distributed within 3 × 3 detector pixels, meeting the requirements for energy concentration and centroid extraction of the star image. The output end 92 of the second set of fiber optic image bundles corresponds to another sub-field of view, namely the second sub-field of view 72. The distribution of the second set of fiber optic bundle units, the second set of micro-switches array 32, and the second set of microlens array 42 is the same as that of the first set. The distribution of the second set of fiber optic bundle units in the output end 92 of the second set of fiber optic image bundles is the same as that of the first set; the distribution of the second set of microlens units in the second set of microlens array 42 is the same as that of the first set. The two sub-fields of view have a total of 114 gated field of view imaging channels.

[0028] During system operation, each sub-field of view activates only 1 to 2 microswitches at a time for gating the field of view. Activating one microswitch results in a field of view angle of 0.4° / 512 = 2.81″ per pixel, providing strong background light suppression. Switching between different microswitches allows for observation of stars within different gating fields. Stitching together the imaging planes of different gating fields reconstructs the stellar image distribution within the complete field of view of the front-end telescope. If two gating fields are activated in each sub-field of view, the equivalent field of view angle per pixel is 3.97″, still providing strong background light suppression. With a total of four gating fields across the two sub-fields, simultaneous detection of multiple stars against a bright daytime background is possible.

[0029] The parts of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A field-of-view gating optical imaging system based on fiber optic image bundles, characterized in that, The system includes: - The front-end telescope (1) has a large field of view and is used to image multiple targets within the field of view onto the primary image plane of the system; - Fiber image bundle (2) is used to couple the primary image plane and redistribute the fiber at the output end to improve the effective field of view of the system's gating imaging; - Micro-switch array (3) is used to select the image plane at the output end of the fiber optic image bundle (2); - A microlens array (4) corresponds one-to-one with the units in the micro-switching array (3), wherein each microlens unit (40) has its own optical axis, which is used to form multiple gated field imaging channels for the image plane at the output end of the fiber optic image bundle (2). - The rear imaging objective (5) and each microlens unit (40) can form a magnified imaging system for magnified imaging of each gated field of view, increasing the focal length of the imaging within the gated field of view, reducing the field of view angle of a single pixel of the detector, and improving the background light suppression capability. - Array detector (6), used to receive magnified target images within each gated field of view; Multiple target signal lights in strong background light are imaged onto a primary image plane by the front-end telescope (1); the primary image plane is coupled by the fiber optic image bundle (2); the output image plane of the fiber optic image bundle (2) is rearranged to match the effective field of view of the microlens array (4); the output image plane of the fiber optic image bundle (2) is then gated by the micro-switching array (3) and the microlens array (4); then, the output image plane of the fiber optic image bundle (2) within the gated field of view is magnified and imaged by the rear imaging objective (5); finally, the magnified target image within each gated field of view is received by the array detector (6). The input surface distribution of the fiber optic image bundle (2) should match the image surface distribution of the front-end telescope (1) so that the principal rays of each field of view of the front-end telescope (1) on the imaging surface are perpendicular to the corresponding fiber end face in the fiber optic image bundle (2). The output ends of the fiber optic image bundle (2) are arranged at intervals. Each interval arrangement of the fiber optic image bundle (2) output end unit corresponds to a gated field of view and corresponds one-to-one with the micro-switching unit (3) in the micro-switching array and the micro-lens unit in the micro-lens array (4). Each fiber optic image bundle (2) output end unit is located within the effective field of view of the corresponding micro-lens unit in the micro-lens array (4).

2. The system according to claim 1, characterized in that: The front-end telescope (1) is selected as a conventional telescope structure optical system.

3. The system according to claim 1, characterized in that: The numerical aperture of the fiber optic image bundle (2) at the input surface is not less than half the relative aperture of the front-end telescope (1).

4. The system according to claim 1, characterized in that: The fiber arrangement period of the fiber image bundle (2) input surface should be less than the radius of the Airy disk of the imaging point of the front-end telescope (1) to ensure that the coupling of the fiber image bundle (2) input end to the image plane of the front-end telescope (1) satisfies the requirements of the Nyquist sampling theorem.

5. The system according to claim 1, characterized in that: The secondary image planes of each gated field of view received by the array detector (6) are stitched together to reconstruct the primary image plane.

6. The system according to claim 1, characterized in that: The field of view of the front-end telescope (1) is divided into multiple sub-fields of view by using multiple sets of fiber optic image bundles (2). The output ends of each set of fiber optic image bundles (2) are distributed at a certain angle, and sufficient space is reserved to arrange the corresponding micro-switch array (3) and microlens array (4), the rear imaging objective (5) and the array detector (6), so as to realize the field-view gating imaging of each sub-field of view.

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