A Wide-Spectrum Single-Exposure Synthetic Aperture Imaging Enhancement Device and Method

Abstract

The present application provides a wide-spectrum single-exposure synthetic aperture imaging enhancement device and method, comprising the following steps: a light source, an imaging target, a distributed aperture, a diffraction grating, and an imaging device arranged in sequence along the optical path of the light source. The light source projects onto the imaging target and forms an encoded image on the distributed aperture in a reflected manner. After the diffraction grating acquires the encoded image, it forms an enhanced image on the imaging device. The diffraction grating decomposes the encoded image into components of different wavelengths and diffracts them into the imaging device at different angles for imaging. This solution enables high-speed acquisition of images in a single exposure using an easily accessible light source and a system that does not require calibration, thereby obtaining high-quality images.

Description

Technical Field

[0001] This application relates to the field of optical space remote sensing, and particularly to a wide-spectrum single-exposure synthetic aperture imaging enhancement device and method. Background Art

[0002] With the continuous development of a series of technologies such as optics and remote sensing mapping, remote sensing technology has been widely used in astronomical exploration, remote sensing mapping, meteorological observation, and the military field. It is currently an important technical means and method for humans to obtain aerospace information through their own science and technology. Among the many remote sensors in the applied and developed astronomical and space fields, optical space remote sensors have always been the most important type of space remote sensors. People use space detectors carried on satellites to measure objects on the Earth's surface. This observation method is the fastest, has a wider field of view, and a larger coverage area. It can achieve global coverage and can monitor all-weather and continuously in terms of time.

[0003] According to the basic theory of physical optics, the angular resolution of traditional optical imaging systems is limited by wavelength and aperture. According to the Rayleigh criterion, under specific working conditions, with a certain working wavelength, only by increasing the aperture of the optical system can the resolution of the system be improved. Currently, under actual working conditions, in order to overcome problems such as the processing difficulty of large-aperture optical devices, a synthetic aperture optical system has been proposed. This system can use a certain number of small apertures to equivalently synthesize a large-aperture system, thereby breaking through the traditional single-aperture system and effectively improving the resolution of the system.

[0004] However, the current mainstream synthetic aperture optical system solutions all have certain limitations and defects. For example, in the ring synthetic aperture solution, special diffractive optical elements (DOEs) need to be custom processed. The processing cost of this device is expensive, and it needs to be pre-calibrated before use. In addition, the system robustness of the ring synthetic aperture solution is poor, and the anti-disturbance ability is weak. Moreover, each sub-aperture needs to be customized with an aberration-correcting lens and the pointing direction needs to be accurately calibrated during the phase modulation of the sub-aperture; in the double-aperture opening and closing sequence imaging (slide rail type) solution, an accurate motion control system is required and the image needs to be acquired multiple times. Not only that, this solution also requires a high storage bandwidth and can only achieve a low temporal resolution; in the wide-field time-intensity interferometry solution, the energy utilization rate of the system is extremely low, it cannot support light sources with too large a bandwidth, and it requires a certain temporal coherence.

[0005] In summary, the usage conditions of the current mainstream synthetic aperture optical systems on the market are relatively harsh, and the obtained image resolution is low, making it difficult to meet the requirements of space remote sensing. Summary of the Invention

[0006] This solution provides a wide-spectrum single-exposure synthetic aperture imaging enhancement device and method, which can acquire high-quality images by using an easily obtainable light source and a system that does not require calibration to perform high-speed acquisition of images in a single exposure manner.

[0007] In a first aspect, an embodiment of the present application provides a wide-spectrum single-exposure synthetic aperture imaging enhancement device, including:

[0008] A distributed aperture array, a multimode optical fiber, a diffraction grating, and an imaging device arranged in sequence along the optical path. Among them, the distributed aperture array couples the light reflected by the imaging target to obtain coupled light. The coupled light is incident on the multimode optical fiber and is randomly modulated to obtain modulated light. The modulated light is diffracted by the diffraction grating to obtain light field spaces of different bands. The light field spaces of different bands are recorded as enhanced images by the imaging device in the form of different intensity distributions.

[0009] In a second aspect, an embodiment of the present application provides a wide-spectrum single-exposure synthetic aperture imaging enhancement method, including irradiating an imaging target with a light source, and acquiring an enhanced image by using any one of the wide-spectrum single-exposure synthetic aperture imaging enhancement devices; and performing image reconstruction on the enhanced image by using an autocorrelation algorithm and a phase retrieval algorithm to obtain a reconstructed target.

[0010] The main contributions and innovations of the present invention are as follows:

[0011] This solution introduces a wavefront modulator - diffraction grating in the optical synthetic aperture system in the optical field. The diffraction grating is used to separate the incident wide-spectrum light into light field spaces of different bands, and the light of different bands interfere with each other, thereby enhancing the image of the target to be measured. And since this solution does not require the use of a narrow-band light source, and an easier-to-obtain white light source can be used to enhance the image to meet the requirements for the intensity distribution quality of the acquired image, the layout cost of the optical synthetic aperture device is greatly reduced, and at the same time, the application range of the optical synthetic aperture system is expanded. In addition, this solution uses an autocorrelation algorithm and a phase retrieval algorithm to reconstruct the image distribution captured by the camera. The algorithm is simple to implement and does not require calibration of the device.

[0012] Details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more concise and understandable. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0014] Figure 1It is a schematic structural diagram of a wide-spectrum single-exposure synthetic aperture imaging enhancement device according to an embodiment of the present application;

[0015] In the figure, 1 - light source, 2 - imaging target, 3 - distributed aperture, 4 - multimode optical fiber, 5 - diffraction grating, 6 - imaging device, 7 - algorithm unit.

[0016] Figure 2 It is a schematic logic diagram of a wide-spectrum single-exposure synthetic aperture imaging enhancement method according to an embodiment of the present application. Detailed implementation manners

[0017] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all the implementation manners consistent with one or more embodiments of this specification. On the contrary, they are merely examples of devices and methods consistent with some aspects of one or more embodiments of this specification as detailed in the appended claims.

[0018] It should be noted that: in other embodiments, the steps of the corresponding method are not necessarily executed in the order shown and described in this specification. In some other embodiments, the steps included in the method may be more or less than those described in this specification. In addition, a single step described in this specification may be decomposed into multiple steps for description in other embodiments; and multiple steps described in this specification may also be combined into a single step for description in other embodiments.

[0019] Embodiment 1

[0020] The embodiment of the present application provides a wide-spectrum single-exposure synthetic aperture imaging enhancement device, which can acquire high-quality images by a single exposure using an easily accessible light source and a system that does not require calibration, for imaging enhancement of the imaging target 2. Specifically, as Figure 1 shown, it includes:

[0021] A distributed aperture array 3, a multimode optical fiber, a diffraction grating 5, and an imaging device 6 arranged in sequence along the optical path. Among them, the distributed aperture array 3 couples the light reflected by the imaging target 2 to obtain coupled light, the coupled light is incident on the multimode optical fiber and is randomly modulated to obtain modulated light, the modulated light is diffracted by the diffraction grating 5 to obtain light field spaces of different bands, and the light field spaces of different bands are recorded as enhanced images by the imaging device 6 in the form of different intensity distributions.

[0022] The wide-spectrum single-exposure synthetic aperture imaging enhancement device provided by this solution has a diffraction grating 5 built-in to diffract the modulated light. Therefore, this solution can use a wide-spectrum light source 1 to irradiate the imaging target 2, without the need to select a narrow-spectrum light source.

[0023] Specifically, this solution uses a wide-spectrum light source 1 to irradiate the imaging target 2 and uses a distributed aperture array 3 to capture the light reflected by the imaging target 2. In some embodiments, the wide-spectrum light source 1 is selected as a white light source, and. The light source 1 in this solution can be any kind of white light source, such as sunlight. Compared with the traditional optical synthetic aperture system, the white light source is easier to obtain, which is convenient for the layout of the entire wide-spectrum single-exposure synthetic aperture imaging enhancement device.

[0024] The imaging target 2 in this solution can be any static object or dynamic object.

[0025] The distributed aperture array 3 of this solution is composed of multiple randomly arranged small holes. The light reflected by the imaging target 2 passes through the distributed aperture array 3 and is coupled to obtain coupled light after independent imaging through multiple small holes. The advantage of this is that high-resolution and large-field-of-view images are obtained by imaging through multiple independent small apertures and combining these imaging results.

[0026] In some specific embodiments, the apertures of the small holes in the distributed aperture array 3 in this solution are the same or different. In some specific embodiments, the multiple small holes on the distributed aperture array 3 are arranged in a linear arrangement or in a two-dimensional matrix form, and this solution adjusts the aperture size according to the detection index of the system itself.

[0027] The multimode optical fiber 4 of this solution captures the coupled light after passing through the distributed aperture array 3, and the coupled light undergoes wavefront modulation and a certain degree of dispersion in the multimode optical fiber 4. In this solution, the coupled light exits the multimode optical fiber 4 to obtain modulated light, and the modulated lights interfere with each other and then enter the diffraction grating 5 to be diffracted to obtain light field spaces of different bands, thereby separating the light field spaces of different bands. The advantage of this is that the imaging device 6 can record the light field spaces of different bands as different intensity distributions.

[0028] The advantage of setting the multimode optical fiber 4 in this solution is that it can propagate multiple optical modes under a given optical frequency and polarization. Furthermore, the coupled light propagating through the distributed aperture 3 can be effectively transmitted to the diffraction grating 5 through the multimode optical fiber 4 after being modulated, minimizing the loss of image information.

[0029] Specifically, the point spread function PSF of the multimode optical fiber 4 of this solution is:

[0030]

[0031] Among them, L(x1, y1) represents the arrangement function of the distributed aperture array. It represents the wavefront modulation of the multimode fiber, and this wavefront modulation is a random function. h(x, y; x1, y1; z) represents the optical field transmission function of the multimode fiber, z represents the optical path of the fiber, and a is the side length of the object plane.

[0032] In this solution, the diffraction grating 5 is a wavefront modulator in the optical field. It diffracts the incident modulated light into multiple beams of different wavelengths at different angles, and the beams of different wavelengths at different positions on the diffraction grating 5 interfere with each other optically, so as to obtain an interference image that is more enhanced than diffraction and is recorded by the imaging device 6.

[0033] Specifically, due to the diffraction characteristics of the diffraction grating 5 itself, the encoded light is decomposed into components of different wavelengths in the diffraction grating and diffracted into the imaging device 6 at different angles for imaging to obtain an enhanced image. That is to say, in this solution, the encoded light constructed by broadband white light is diffracted by the diffraction grating 5, and optical interference is achieved between the diffraction optical paths at different positions, so that an interference image that is more enhanced than ordinary diffraction is recorded.

[0034] Specifically, the transmittance function of the diffraction grating 5 in this solution is:

[0035]

[0036] Among them, φ is the phase factor, f0 = 1 / grating period, representing the number of grating lines per unit length.

[0037] The optical transfer function of the diffraction grating 5 is:

[0038]

[0039] Among them, the optical transfer function OTF can also be expressed as Among them, M(x, y) is the modulation function, which reflects the reduction multiple of the modulation degree of the cosine component of the spatial frequency. is the phase transfer function.

[0040] In this solution, the imaging device 6 performs high-speed acquisition on the optical field space of different bands output by the diffraction grating 5 in a single-exposure manner, and acquires the different light intensity distributions corresponding to the optical field space of different bands to obtain an enhanced image.

[0041] In some specific embodiments, the imaging device 6 is a camera. Among them, the light intensity distribution of the enhanced image acquired by the imaging device 6 is expressed as:

[0042] I(x, y, λ) = O(x0, y0, λ) * PSF · G(x, y, λ)

[0043] Among them, PSF is the point spread function of the multimode optical fiber 4, G(x, y, λ) is the grating function, and O(x0, y0, λ) is the target reflection function of the imaging target 2 under the light source 1.

[0044] In other words, the imaging device 6 acquires different light intensity distributions of the imaging target 2 under the illumination of the light source 1, where the light intensity distribution is expressed as the product of the point spread function of the multimode optical fiber, the grating function of the diffraction grating, and the target reflectivity function of the imaging target 2.

[0045] Specifically, since this solution uses a broadband light source to illuminate the imaging target 2 and the diffraction grating 5 separates the light fields of different bands, the intensity distribution is recorded by different regions of the imaging device 6 to obtain an enhanced image. Since the setting on the diffraction grating enables image enhancement by using the interference of light rays of different bands, there is no need to calibrate the device or establish a dataset of the point spread function.

[0046] This device can be applied to accurately measure buildings and terrain on the ground surface in space remote sensing technology.

[0047] Embodiment 2

[0048] This solution provides a broadband single-exposure synthetic aperture imaging enhancement method, including:

[0049] Using the light source 1 to illuminate the imaging target 2, and using the broadband single-exposure synthetic aperture imaging enhancement device described in Embodiment 1 to acquire the enhanced image;

[0050] Performing image reconstruction on the enhanced image using the autocorrelation algorithm and the phase retrieval algorithm to obtain the reconstructed target.

[0051] In this solution, since the image obtained by the imaging device is the image after passing through the diffraction grating, and the function of the grating is to suppress the sidelobes of the OTF, enhance the contrast of the speckle, and improve the coherence degree, the image quality can be significantly improved by processing the enhanced image using the autocorrelation algorithm and the phase retrieval algorithm.

[0052] In this solution, the enhanced image obtained by the imaging device 6 of a broadband single-exposure synthetic aperture imaging enhancement device is transmitted to the algorithm unit 7, and the autocorrelation algorithm and the phase retrieval algorithm are used to reconstruct the enhanced image. Specifically, due to the randomness of the point spread function PSF of the multimode optical fiber, the autocorrelation result of the light intensity signal recorded by the camera is equal to the autocorrelation of the target reflectivity function. Therefore, in this solution, the autocorrelation result of the light intensity signal recorded by the imaging device 6 is first calculated according to the autocorrelation of the reflectivity function of the imaging target 2, and then the phase retrieval algorithm is used to reconstruct the enhanced image.

[0053] Specifically, the phase retrieval algorithm is a signal processing algorithm commonly used in digital communication, and its main purpose is to retrieve the phase information of the original signal from the received signal so as to reconstruct the enhanced image.

[0054] Those skilled in the art should understand that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0055] The above embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A wide-spectrum single-exposure synthetic aperture imaging enhancement device for enhancing the imaging of an imaging target, characterized in that, Comprising: A distributed aperture array, a multimode optical fiber, a diffraction grating, and an imaging device arranged in sequence along the optical path. The distributed aperture array couples the light reflected by the imaging target to obtain coupled light. The distributed aperture array is composed of multiple randomly arranged small holes. The light reflected by the imaging target passes through the distributed aperture array and is independently imaged through multiple small holes and then coupled to obtain coupled light. The coupled light is incident on the multimode optical fiber and is randomly modulated to obtain modulated light. The modulated light is diffracted by the diffraction grating to obtain a light field space of different wavelength bands. The light field spaces of different wavelength bands are recorded as enhanced images by the imaging device in the form of different intensity distributions. The point spread function PSF of the multimode optical fiber is: ； Among them, represents the arrangement function of the distributed aperture array, represents the wavefront modulation of the multimode fiber, represents the optical field transmission function of the multimode fiber, z represents the optical path of the fiber, and a is the side length of the object plane.

2. The wide-spectrum single-exposure synthetic aperture imaging enhancement device according to claim 1, characterized in that, Illuminating the imaging target with a wide-spectrum light source and using a distributed aperture array to capture the light reflected by the imaging target.

3. The wide-spectrum single-exposure synthetic aperture imaging enhancement device according to claim 2, wherein The light source is sunlight.

4. The wide-spectrum single-exposure synthetic aperture imaging enhancement device according to claim 1, wherein The transmittance function of the diffraction grating is: Where φ is the phase factor, f0 = 1 / grating period, representing the number of grating lines per unit length.

5. The wide-spectrum single-exposure synthetic aperture imaging enhancement device according to claim 1, characterized in that, The imaging device acquires the different light intensity distributions of the imaging target under the illumination of the light source, where the light intensity distribution is expressed as the product of the point spread function of the multimode optical fiber, the grating function of the diffraction grating, and the target reflectivity function of the imaging target.

6. A wide-spectrum single-exposure synthetic aperture imaging enhancement method, comprising: Illuminating the imaging target with a light source and using the wide-spectrum single-exposure synthetic aperture imaging enhancement device according to any one of claims 1 to 5 to acquire an enhanced image; Performing image reconstruction on the enhanced image using the autocorrelation algorithm and the phase retrieval algorithm to obtain a reconstructed target.

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