Segmented Planar Imaging System and Imaging Method Based on Spectrometer

Abstract

A segmented planar imaging system based on a beam splitter includes a lens array comprising lens columns. Microlenses within each lens column are paired to form baselines. These baselines are formed by the interference of light rays from two microlenses as a set of interference beams. Each microlens has two baseline formation methods. The imaging system also includes a photonic integrated circuit and an image processing module. The photonic integrated circuit includes an integrated beam splitter, an arrayed waveguide grating, waveguide transmission lines, and multiple balanced quadrature detectors. Each lens column is connected to one photonic integrated circuit. In this segmented planar imaging system, each microlens participates in forming two baselines via a beam splitter, and individual interferometer arms employ complementary baseline pairing methods. This increases the acquisition of spatial frequency information lacking in traditional systems, further improving the imaging quality of the system.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection, and more specifically to a segmented planar imaging system and imaging method based on a beam splitter. Background Technology

[0002] In recent years, with the continuous improvement of the resolution of space optical detection systems, traditional large-volume, heavy-weight, and high-power optical detection systems have become increasingly unable to meet practical needs. In 2012, Lockheed Martin proposed a novel segmented planar optical imaging system. This system combines optical synthetic aperture technology with photonic integrated circuit technology. By acquiring the spatial frequency information of the target and performing inverse Fourier transform, it reconstructs the target's light intensity distribution, thereby completing the imaging function. This system uses a microlens array instead of a traditional large-aperture lens, greatly reducing its size and weight, and providing a new approach for the development of miniaturized, lightweight, and low-power high-resolution space optical detection systems.

[0003] However, the resolution of such imaging systems is related to the baseline length of the microlens pair and the density of spectral information. In existing systems, the lens array structure limits the baseline length, resulting in a short maximum baseline and redundancy of some short baselines on the same circumference, leading to low frequency coverage and significantly impacting image quality. Therefore, how to effectively improve the acquisition and utilization of image frequency domain information is an urgent problem to be solved. Summary of the Invention

[0004] This invention proposes a segmented planar imaging system and method based on a beam splitter, which can be applied to target detection and imaging. By improving the microlens array arrangement structure and the design of the photonic integrated circuit, the density of frequency domain information is increased, and the problem of frequency domain sampling point duplication is effectively avoided, thereby improving the imaging quality of the target.

[0005] The technical solution proposed in this invention is as follows:

[0006] A segmented planar imaging system based on a beam splitter includes a lens array, wherein the lens array includes N lens columns, and each lens column includes M microlenses; M is less than or equal to N and both M and N are even numbers, and M ≥ 4;

[0007] The microlenses within the lens array are paired to form a baseline. The baseline refers to the interference of light rays from two microlenses forming a set of interference beams, and each microlens has the following two baseline formation methods:

[0008] Method 1: Microlenses symmetrically distributed on both sides of the axis of symmetry within the lens array are paired to form a baseline;

[0009] Method 2: With the central microlens of the lens array as the axis of symmetry, the microlenses symmetrically distributed on both sides are paired to form a baseline. The central microlens is paired with the outermost unpaired microlens of the array to form a baseline. The central lens is any one of the two microlenses closest to the axis of symmetry.

[0010] The imaging system also includes N photonic integrated circuits and an image processing module;

[0011] The photonic integrated circuit comprises M integrated beam splitters, 2M arrayed waveguide gratings, 2*M waveguide transmission lines, and multiple balanced quadrature detectors; each lens array is connected to one photonic integrated circuit.

[0012] The front end of the photonic integrated circuit consists of M integrated beam splitters. Each lens in the lens array is connected to an integrated beam splitter. Each beam splitter includes two output terminals. Each output terminal is connected to an arrayed waveguide grating. The output terminals of the arrayed waveguide grating are connected to multiple balanced quadrature detectors. The balanced quadrature detectors are connected to an image processing module.

[0013] The arrayed waveguide grating has at least one single-wavelength light output end. The connection relationship between the arrayed waveguide grating and the balanced quadrature detector is as follows: the same single-wavelength light output end of one of the arrayed waveguide gratings connected by two microlenses forming the same baseline is connected to the same balanced quadrature detector.

[0014] Preferably, the N columns of lenses in the lens array are symmetrically distributed around the center of the circle. Each column of lenses contains M lenses, including a first column consisting of M / 2 consecutively arranged large lenses and a second column consisting of M / 2 consecutively arranged small lenses. The first and second columns are located on the same straight line passing through the center of the circle and are located on opposite sides of the center of the circle, respectively. The first and second columns of adjacent lens columns are staggered and the central angles between them are equal.

[0015] Preferably, the diameter of the small lens is 0.6-0.7 times that of the large lens.

[0016] Preferably, the output end of the beam splitter is connected to an arrayed waveguide grating via a waveguide transmission line, and the arrayed waveguide grating is connected to a balanced quadrature detector via the waveguide transmission line.

[0017] The present invention also discloses a lens array comprising N lens columns, each lens column comprising M microlenses; M is less than or equal to N and both M and N are even numbers, M≥4. The lens array is characterized in that the N lens columns are symmetrically distributed around a central point, and each lens column comprises a first column consisting of M / 2 consecutively arranged large lenses and a second column consisting of M / 2 consecutively arranged small lenses. The first and second columns are located on the same straight line passing through the center of the circle and are respectively located on opposite sides of the center. The first and second columns of adjacent lens columns are staggered, and the central angles between them are equal.

[0018] Preferably, the diameter of the small lens is 0.6-0.7 times that of the large lens.

[0019] The present invention also discloses an imaging method using the aforementioned imaging system, comprising the following steps:

[0020] S1: The target light is collected by a lens array. The light from each microlens in the lens array is split into two beams by a beam splitter and the interference light signal is transmitted to the balanced quadrature detector via a waveguide transmission line.

[0021] S2: The interference light signal is detected using the balanced quadrature detector, and the in-phase signal I and the quadrature signal Q are output.

[0022] S3: The image processing module is used to process the I and Q signals to extract and store the amplitude and phase information of the target complex coherent light;

[0023] S4: The image processing module combines the amplitude and phase information of all complex coherent light to obtain the target spectrum, then performs a Fourier transform to acquire the image.

[0024] Compared with the prior art, the segmented planar imaging system of the present invention has the following advantages and beneficial effects:

[0025] 1. The present invention proposes a segmented planar imaging system based on a beam splitter. Each microlens participates in forming two baselines through the beam splitter. The individual interferometer arms adopt a complementary baseline pairing method, which can increase the acquisition of spatial frequency information that is missing in traditional systems, thereby further improving the imaging quality of the system.

[0026] 2. By using a combination of two microlenses with different diameters, the sampling coverage is more comprehensive.

[0027] 3. The imaging method described in this invention can not only improve the accuracy and robustness of dynamic target reconstruction, but also has broad application prospects and can be applied to various fields and different types of images, such as natural scenes and medical images. Attached Figure Description

[0028] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 This is a schematic diagram of a specific embodiment of the lens array described in this invention;

[0030] Figure 2 This is a schematic diagram of the lens array structure in an existing segmented planar imaging system;

[0031] Figure 3 This is a schematic diagram of a specific embodiment of the two baseline composition methods described in this invention;

[0032] Figure 4 This is a schematic diagram of a specific embodiment of the imaging system described in this invention;

[0033] Figure 5 This is a comparative diagram of the imaging method of the present invention and the imaging method of the prior art for imaging a target image.

[0034] First column, 2-Second column, 3-Microlens, 4-Axis of symmetry, 5-Center of circle. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are only for explaining this invention and are not intended to limit this invention.

[0036] The lens array described in this invention is a modified design based on the lens array of an existing segmented planar imaging system. The lens array of an existing segmented planar imaging system is as follows: Figure 2 As shown, the baseline pairing method on a single interferometer arm is singular, and the baseline pairing method of adjacent arms is the same, which limits the number of baselines and the frequency domain sampling rate. This results in redundant frequency domain information distribution on the same circumference and missing frequency domain information distribution on the same interferometer arm.

[0037] This invention proposes a segmented planar imaging system based on a beam splitter, comprising a lens array, wherein the lens array includes N lens columns, and each lens column includes M microlenses; M is less than or equal to N and both M and N are even numbers, and M ≥ 4; the microlenses within the lens column are paired to form a baseline, wherein the baseline is defined as the interference of light rays from two microlenses forming a set of interference beams, and each microlens has the following two baseline formation methods:

[0038] Method 1: Microlenses symmetrically distributed on both sides of the axis of symmetry within the lens array are paired to form a baseline;

[0039] Method 2: With the central microlens of the lens array as the axis of symmetry, the microlenses symmetrically distributed on both sides are paired to form a baseline. The central microlens is paired with the outermost unpaired microlens of the array to form a baseline. The central lens is any one of the two microlenses closest to the axis of symmetry.

[0040] The imaging system also includes N photonic integrated circuits and an image processing module;

[0041] The photonic integrated circuit comprises M integrated beam splitters, 2M arrayed waveguide gratings, 2*M waveguide transmission lines, and multiple balanced quadrature detectors; each lens array is connected to one photonic integrated circuit.

[0042] The front end of the photonic integrated circuit consists of M integrated beam splitters. Each lens in the lens array is connected to an integrated beam splitter. Each beam splitter includes two output terminals. Each output terminal is connected to an arrayed waveguide grating. The output terminals of the arrayed waveguide grating are connected to multiple balanced quadrature detectors. The balanced quadrature detectors are connected to an image processing module.

[0043] The arrayed waveguide grating has at least one single-wavelength light output end. The connection relationship between the arrayed waveguide grating and the balanced quadrature detector is as follows: the same single-wavelength light output end of one of the arrayed waveguide gratings connected by two microlenses forming the same baseline is connected to the same balanced quadrature detector.

[0044] One specific implementation of the lens array is as follows: Figure 1 As shown, the first column 1 and the second column 2 are located on both sides of the center 5, and are on the same straight line passing through the center of the circle. Two different sized lenses are located on both sides of the center of the circle.

[0045] The baseline refers to the interference of light from two microlenses to form a set of interference lights, and the spectral information of the interference lights is subsequently read. For example, in this invention, each set of interference lights can be detected by a balanced quadrature detector and the spectral information is output.

[0046] In the imaging system, each lens array is connected to a photonic integrated circuit. The M lenses in the lens array are connected one-to-one to M integrated beam splitters. Each beam splitter can be connected to two arrayed waveguide gratings via two waveguide transmission lines at its rear end. The arrayed waveguide gratings are connected to a balanced quadrature detector via waveguide transmission lines. The balanced quadrature detector is connected to an image processing module.

[0047] The function of the arrayed waveguide grating is to decompose the mixed light emitted by the beam splitter into multiple beams of single wavelength, with each beam connected to a balanced quadrature detector. For example, if the mixed light has K single wavelengths, the arrayed waveguide grating is connected to K balanced quadrature detectors. The arrayed waveguide grating and the balanced quadrature detectors can also be connected via waveguide transmission lines.

[0048] Each lens in the lens array participates in forming two baselines, namely: a baseline formed by pairing microlenses on both sides with the center line of the lens array as the axis of symmetry; and a baseline formed by pairing microlenses on both sides with the central microlens of the lens array as the axis of symmetry, wherein the central microlens is paired with any one of the two central microlenses in the array. Figure 3 The diagram shows the combination of microlenses in two ways of forming the baseline.

[0049] The balanced quadrature detector receives and processes single wavelength light of the same wavelength after being decomposed by two microlenses on the same baseline through an arrayed waveguide grating. The lens array of M microlenses described in this invention has a total of M-1 baseline combinations. Therefore, the number of balanced quadrature detectors required is (M-1)*K, where K is the number of single wavelength lights that need to be decomposed.

[0050] like Figure 4 As shown, a baseline combination method with M=6 is given, along with a specific connection relationship between the arrayed waveguide grating and the balanced quadrature detector. Figure 4 The dashed line above the microlens indicates the baseline combination method. Figure 4 For each arrayed waveguide grating, only one single wavelength light path is drawn. For potentially more single wavelength light paths, the connection relationships are as follows: Figure 4 Consistent.

[0051] The balanced quadrature detector receives single-wavelength optical signals transmitted by the arrayed waveguide grating. The output signals are I signals (In-phase single) and Q signals (Quadrature phase signals), from which the amplitude and phase information of the corresponding spatial frequency of a baseline combination can be extracted. After the light emitted by the arrayed waveguide grating is collected and processed into digital signals, it is transmitted to the image processing module for calculation.

[0052] The two baselines of a single lens array adopt a complementary pairing method. In method 1, the M microlenses of the lens array are paired with the microlenses symmetrically distributed on both sides of the center line of the array to form baselines, thereby forming baseline lengths of 1, 3, 5...M-1 times the microlens diameter. In method 2, the M microlenses of the lens array are paired with the central lens of the array to form baselines, with the lenses symmetrically distributed on both sides of the array to form baselines. The central microlens is paired with the outermost unpaired microlens of the array to form a baseline. The central lens is any one of the two central microlenses, thereby forming baseline lengths of 2, 4, 6...M-2 times the microlens diameter. The combined baseline length distribution is 1, 2, 3...M-1 times the microlens diameter, forming a continuous distribution over the first M-1 baseline lengths.

[0053] Assuming the diameters (apertures) of the small and large lenses are d and D respectively, and the spectral information of the interferometer arms with the same diameter but in different quadrants is conjugate, the baseline length of the interferometer arms formed by the large lens is D, 2D, 3D…(M-1)D, and the baseline length of the interferometer arms formed by the small lens is d, 2d, 3d…(M-1)d. In the same diametrical direction, the spectral information of the large and small lens interferometer arms is conjugate, and the resulting baseline length can be expressed as d, 2d, 3d…(M-1)d, D, 2D, 3D…(M-1)D. By using lenses with unequal diameters, the frequency sampling density on the same diameter is increased, thereby improving the image reconstruction effect.

[0054] Interferometric imaging systems use microlenses to interfere with light emitted from incoherent target sources, and then extract the amplitude and phase information of the complex coherence factor from the interference fringes. The baseline vector is the position vector between two microlenses within the exit pupil plane, and the baseline length is the length of the baseline vector. The segmented planar imaging system provided by this invention can acquire spectral information with continuously distributed baseline lengths of 1, 2, 3…M-1 without increasing the area of ​​the imaging system. Existing segmented planar imaging systems can only acquire spectral information with baseline lengths of 1, 3, 5… Therefore, the segmented planar imaging system provided by this invention can acquire more spectral information.

[0055] Based on the above-mentioned microlens array, the present invention can employ a segmented planar imaging system based on a beam splitter, comprising at least one microlens array, as well as N photonic integrated circuits and one image processing module.

[0056] The photonic integrated circuit includes M beam splitters, 2M waveguide transmission lines, 2M arrayed waveguide gratings, and multiple balanced quadrature detectors. M lenses are connected one-to-one to the beam splitters, and the rear ends of the M beam splitters are connected to the 2M waveguide transmission lines; that is, one lens connects two waveguide transmission lines through a beam splitter. The waveguide transmission lines are connected to the arrayed waveguide gratings. The arrayed waveguide gratings are connected to the multiple balanced quadrature detectors. The balanced quadrature detectors are connected to an image processing module.

[0057] The specific embodiments of the present invention provide a method for acquiring high-density image spectral information, while having a small system size and weight, and can be widely used in aviation, aerospace and other high-precision image acquisition fields.

[0058] In one specific embodiment, the lens array of the interferometer arm comprises 60 microlenses. All interferometer arm lenses are in close contact. The microlenses used include two specifications: large lenses and small lenses. The small lens array and the large lens array are aligned in the same diametrical direction and distributed on both sides of the center. Preferably, the diameter (aperture d) of the small lens is 4 mm, and the aperture (D) of the large lens is 7 mm. The microlenses are arranged closely together. In this embodiment, the number of interferometer arms, N, is 36, and each interferometer arm is uniformly distributed in a radial pattern around the single lens at the center of the microlens array. The two lens arrays of a single interferometer arm can form a baseline with lengths of 1, 2, 3...59, a total of 59 lens diameters.

[0059] The effects of this invention can be further illustrated by simulation. Table 1 shows the simulation parameters of the segmented planar imaging system of this invention.

[0060] Table 1

[0061]

[0062] Based on the simulation results of different lens diameter ratios, as shown in Table 2, when the lens ratio is 0.6-0.7, the peak signal-to-noise ratio (PSNR) is the highest and the structural similarity index (SSIM) can also maintain a high level.

[0063] Table 2 Simulation results for different lens diameter ratios

[0064]

[0065] The simulation parameters of the existing segmented planar imaging system and the present invention are shown in Table 1. The simulation results for the target are as follows: Figure 5 As shown, Figure 5 The left side of the image is a schematic diagram of the prior art, and the right side is a schematic diagram of the image obtained using the present invention. Figure 5 Comparing the left and right images, the outline of the imaged object is clearer and the details are more obvious; the comparison of imaging quality is shown in Table 3.

[0066] Table 3

[0067]

[0068] In summary, it can be seen that, due to the ability of this invention to acquire frequencies corresponding to more baseline lengths and the increased spectral information density, the peak signal-to-noise ratio (PSNR) and structural similarity index (SSIM) are significantly improved compared to existing segmented planar imaging systems, resulting in better image reconstruction.

[0069] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A segmented planar imaging system based on a beam splitter, comprising a lens array, wherein the lens array comprises N lens columns, and each lens column comprises M microlenses; M is less than or equal to N and both M and N are even numbers, and M ≥ 4; Its features are, The microlenses within the lens array are paired to form a baseline. The baseline refers to the interference of light rays from two microlenses forming a set of interference beams, and each microlens has the following two baseline formation methods: Method 1: Microlenses symmetrically distributed on both sides of the axis of symmetry within the lens array are paired to form a baseline; Method 2: With the central microlens of the lens array as the axis of symmetry, the microlenses symmetrically distributed on both sides are paired to form a baseline. The central microlens is paired with the outermost unpaired microlens of the array to form a baseline. The central microlens is any one of the two microlenses closest to the axis of symmetry. The imaging system also includes N photonic integrated circuits and an image processing module; The photonic integrated circuit comprises M integrated beam splitters, 2M arrayed waveguide gratings, 2*M waveguide transmission lines, and multiple balanced quadrature detectors; each lens array is connected to one photonic integrated circuit. The front end of the photonic integrated circuit consists of M integrated beam splitters. Each lens in the lens array is connected to an integrated beam splitter. Each beam splitter includes two output terminals. Each output terminal is connected to an arrayed waveguide grating. The output terminals of the arrayed waveguide grating are connected to multiple balanced quadrature detectors. The balanced quadrature detectors are connected to an image processing module. The arrayed waveguide grating has at least one single-wavelength light output end. The connection relationship between the arrayed waveguide grating and the balanced quadrature detector is as follows: the same single-wavelength light output end of one of the arrayed waveguide gratings connected by two microlenses forming the same baseline is connected to the same balanced quadrature detector.

2. The segmented planar imaging system based on a beam splitter according to claim 1, characterized in that, The lens array consists of N columns of lenses symmetrically distributed around the center of the circle. Each column contains M lenses, including a first column consisting of M / 2 consecutively arranged large lenses and a second column consisting of M / 2 consecutively arranged small lenses. The first and second columns are located on the same straight line passing through the center of the circle and are located on opposite sides of the center. The first and second columns of adjacent lens columns are staggered and the central angles between them are equal.

3. The segmented planar imaging system based on a beam splitter according to claim 2, characterized in that, The diameter of the small lens is 0.6-0.7 times that of the large lens.

4. The segmented planar imaging system based on a beam splitter according to claim 1, characterized in that, The output of the beam splitter is connected to an arrayed waveguide grating via a waveguide transmission line, and the arrayed waveguide grating is connected to a balanced quadrature detector via the waveguide transmission line.

5. An imaging method, employing the imaging system according to any one of claims 1-4, comprising the following steps: S1: The target light is collected by a lens array. The light from each microlens in the lens array is split into two beams by a beam splitter and the interference light signal is transmitted to the balanced quadrature detector via a waveguide transmission line. S2: The interference light signal is detected using the balanced quadrature detector, and the in-phase signal I and the quadrature signal Q are output. S3: The image processing module is used to process the I and Q signals to extract and store the amplitude and phase information of the target complex coherent light; S4: The image processing module combines the amplitude and phase information of all complex coherent light to obtain the target spectrum and then performs a Fourier transform to acquire the image.

Images