CN113777777A - Photoelectric imaging system with laser defense function - Google Patents
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Abstract
The invention provides a photoelectric imaging system with a laser defense function, which is a photoelectric imaging system combining wavefront coding and light field imaging, and comprises a wavefront coding imaging lens, a micro-lens array, an area array detector, an image processing device and an output display device, wherein incident laser is modulated by the wavefront coding imaging lens to generate a diffraction-free Airy beam, the beam is subjected to angle discrete sampling by the micro-lens array near a focal plane and finally received by the area array detector, and the area array detector sends a fuzzy intermediate image after the received angle discrete sampling to a signal processor for refocusing and decoding processing to form a clear digital image which is output and displayed by the output display device. The invention can ensure the imaging quality and has the laser defense function.
Description
Technical Field
The invention relates to a photoelectric imaging system, in particular to a photoelectric imaging system with a laser defense function.
Background
The photoelectric imaging system represented by a digital camera is widely applied, and mainly comprises an optical imaging device, a photoelectric detection device, an image processing device and an output display device, wherein the photoelectric detection device is generally placed near a focal plane of the optical imaging device and is vertical to an optical axis of the optical imaging device, and a target object is imaged on the plane of the detector through focusing during work so as to obtain clear image output. When incident laser irradiates the photoelectric imaging system, the incident laser is focused into a light spot with a small area on the surface of the detector due to the convergence effect of an optical imaging device (objective lens) on the laser, and the light spot can become a secondary light-emitting source, so that a part of the incident laser returns through the objective lens according to an original incident light path again to generate a strong backward reflection laser echo, and the photoelectric imaging system can be detected and positioned by the incident laser, and the phenomenon is called a cat eye effect. Meanwhile, the converged light spots form extremely high power density on the surface of the detector, and when the incident laser power is high, the photoelectric detector is easily interfered by laser to cause blindness. Therefore, besides good imaging capability, the optoelectronic imaging system should also have the capability of anti-laser detection and positioning and the capability of preventing interference from blinding. Various laser defense schemes of the photoelectric imaging system have been proposed, but the corresponding photoelectric imaging system is difficult to meet the application requirements because of the reasons of obviously influencing the imaging performance of the system or requiring the prior knowledge for defense, and the like.
The photoelectric imaging system defocuses, and moves an imaging surface of the area array detector, which is away from the vicinity of the focal plane, to the objective lens for a certain distance, namely certain defocusing is performed, and when the distance of the detector, which is away from the imaging surface, reaches ten times of the theoretical focal depth of the imaging objective lens, the photoelectric imaging system with the defocusing structure can obviously reduce the cat eye effect of the photoelectric system and reduce the laser power of the laser reaching the surface of the detector. The conventional out-of-focus solution of the photoelectric imaging system has the disadvantage of contradiction between the improvement of laser defense capability and the maintenance of imaging quality. However, studies show that the larger the defocus range is better for improving the laser defense capability, and when the defocus exceeds λ/4, the imaging quality of the system is significantly reduced and cannot be recovered by image processing techniques such as inverse filtering.
The light field imaging system can simultaneously record four-dimensional light field information including light intensity distribution and light direction, if the micro lens array is arranged on the image surface of the main lens, and the photoelectric detector is arranged on the focal plane of the micro lens array, then light spots arriving on the photoelectric detector contain dispersed light spots of the direction information, so that cat eye laser echo can be reduced, the laser blinding threshold value can be improved, the image processor reconstructs the four-dimensional light field data obtained by the photoelectric detector by using a corresponding refocusing algorithm, a clear image with high image quality can be recovered, and the system structure is shown in figure 1. Compared with a conventional imaging system without defocusing, the peak light intensity of a far-field echo of the light field imaging system and the receiving power of an echo detector are respectively reduced by three magnitude levels and more than two magnitude levels, the peak light intensity and the maximum single-pixel incident power on the surface of a photoelectric detector are also reduced by nearly two magnitude levels, and the system has better anti-laser reconnaissance and anti-laser blinding effects. However, when the scheme is adopted, if the micro-lens array is in a negative defocusing state (far away from the main lens), the imaging quality of the system is reduced, the cat eye echo is obviously enhanced, and the aim of laser light interception of the photoelectric imaging system cannot be achieved.
A typical wavefront coding photoelectric imaging system is configured as shown in fig. 2, a phase plate is inserted into an aperture stop of an imaging objective lens to form a wavefront coding imaging lens, the phase plate modulates an incident light field to form a blurred intermediate image on an area array detector near a focal plane of the imaging lens, the area array detector converts the image into an electrical signal, and an image processor performs digital reconstruction on the blurred intermediate image output by the detector to recover a clear output image. The phase plate is specially designed, so that the optical transfer function of the wavefront coding imaging lens has obvious defocus invariance, and even under the condition that the defocus amount of the area array detector is large, the wavefront coding photoelectric imaging system can still keep high imaging quality. Compared with a conventional imaging system without defocusing, the defocusing wavefront coding system can reduce the peak light intensity of far-field echo and the receiving power of an echo detector by more than two orders of magnitude, so that a better anti-laser reconnaissance effect is achieved, but the defocusing wavefront coding imaging system can only reduce the peak light intensity of the detector and the maximum single-pixel incident power by more than one order of magnitude, so that the anti-laser blinding effect is general. For the wave-front coding system, the incident Gaussian beam forms an L-shaped diffraction-free Airy light field near the focal plane of the system after being modulated by the cubic phase, and the size and the light intensity distribution of the L-shaped diffraction-free Airy light field can be kept stable in a larger defocusing range, so that the field depth extension characteristic is better, but the energy of a central main lobe of the light field is concentrated, and the further improvement of the anti-laser blinding performance of the wave-front coding system is also limited.
Disclosure of Invention
The invention aims to provide a photoelectric imaging system which can ensure imaging quality and has a laser defense function.
The technical solution for realizing the purpose of the invention is as follows: the photoelectric imaging system with the laser defense function is characterized by being a photoelectric imaging system combining wavefront coding and light field imaging, and comprising a wavefront coding imaging lens, a micro-lens array, an area array detector, an image processing device and an output display device, wherein incident laser is modulated by the wavefront coding imaging lens to generate diffraction-free Airy beams, the beams are subjected to angle discrete sampling by the micro-lens array near a focal plane and finally received by the area array detector, and the received blurred intermediate images after the angle discrete sampling are sent to a signal processor by the area array detector to be subjected to refocusing and decoding processing to form clear digital images which are output and displayed by the output display device.
Furthermore, the intermediate image received by the signal processor, namely the original light field image, contains five-dimensional light field image information including the space of the object to be shot, the five-dimensional light field image needs to be resampled first, data is reconstructed according to the sequence of angle-space coordinates, and finally a five-dimensional light field matrix is obtained; then processing the five-dimensional light field matrix by using a digital refocusing algorithm to obtain a refocusing light field image; and then, decoding the refocused light field image by utilizing a wavefront coding decoding algorithm, namely performing convolution operation on a decoding function and the refocused light field image in a space domain or performing equivalent operation in a frequency domain to obtain a clear composite imaging system decoding image.
Further, the refocusing algorithm comprises a shift and sum algorithm and a frequency domain refocusing algorithm; the decoding algorithm of the wavefront coding comprises wiener filtering, inverse filtering, Kalman filtering, Lucy-Richardson filtering and wavelet analysis.
Furthermore, the wavefront coding imaging lens is composed of a four-piece imaging lens and a phase plate, and the phase plate is a cubic phase plate or a non-rotational symmetric phase plate.
Furthermore, the wavefront coding imaging lens is composed of a four-piece type imaging lens and a liquid crystal spatial light modulator.
Furthermore, the defocus amount of the microlens array is related to parameters of the photoelectric imaging system, after the focal length of the imaging main lens, the size of the imaging main lens, the focal length of the microlens array unit, the size of the microlens array unit, the pixel size of the area array detector, the reflectivity of the area array detector and the distance between the microlens array and the area array detector are set, a relation curve between the surface single-pixel incident power of the area array detector and the defocus amount of the microlens array is calculated, and a relation curve between the system echo power and the defocus amount of the microlens array, the defocus amount corresponding to the minimum value point in the relation curve of the echo power is an optimal value, and if a plurality of minimum value points exist, the defocus amount corresponding to the minimum value point in which the wave power is the minimum is retrieved is the optimal value.
Further, the structure of the photoelectric imaging system is a transmission structure, a reflection structure or a coaxial Cassegrain structure.
A photoelectric imaging method is based on the photoelectric imaging system with the laser defense function to carry out photoelectric imaging.
Compared with the prior art, the invention has the remarkable advantages that: 1) the non-focusing structure of the system is utilized to weaken cat eye echo formed by the reflection of the surface of the detector, the micro-lens array angle is utilized to sample the intermediate image of the wavefront coding, the dispersion degree of the imaging facula is enlarged, the blind threshold of the laser is improved, and the focal depth of the system is improved on the premise of keeping the imaging quality of the photoelectric system. 2) The method comprises the steps of firstly resampling original data of a light field by using a reconstruction algorithm, reconstructing the data according to the sequence of angle-space coordinates to obtain a five-dimensional light field matrix, then processing the resampled five-dimensional light field matrix by using a digital refocusing algorithm to obtain a refocused light field image, and finally performing wavefront decoding on the refocused light field image to recover a clear image, thereby further improving the imaging quality.
Drawings
Fig. 1 is a schematic configuration diagram of a light field imaging system.
Fig. 2 is a schematic structural diagram of a wavefront coding photoelectric imaging system.
Fig. 3 is a schematic structural diagram of the photoelectric imaging system of the present invention.
Fig. 4 is a flow chart of the algorithm of the photoelectric imaging system of the invention.
FIG. 5 is a diagram of the maximum single pixel incident power P of a Conventional imaging system (Conventional), wavefront coded imaging system (WFC), light field imaging system (LFC), and Composite imaging system (Composite) detectorpixelAccording to defocus amount W20Variation plot of ± 10 λ.
FIG. 6 shows the Conventional imaging system (Conventional), wavefront coded imaging system (WFC), light field imaging system (LFC) and Composite imaging system (Composite) echo detector received power PdecAccording to defocus amount W20Variation plot of ± 10 λ.
Fig. 7 is a graph comparing the imaging effect of a conventional imaging system and a composite imaging system.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The invention discloses a photoelectric imaging system with a laser defense function, which is a photoelectric imaging system combining wavefront coding and light field imaging. The system mainly comprises a wavefront coding imaging lens (comprising a group of lenses of a phase plate), a micro-lens array, an area array detector, an image processing device and an output display device, and the system structure is shown in figure 3. Incident laser is modulated by the wavefront coding imaging lens to generate a diffraction-free Airy beam, and the beam is subjected to angle discrete sampling by the micro-lens array near the focal plane and is finally received by the area array detector. The area array detector sends the received blurred intermediate image (original light field image) after angle sampling to a signal processor for processing such as refocusing, decoding and the like to form a clear digital image for outputting and result displaying.
Because the original light field image data collected by the area array detector contains five-dimensional light field image information (two-dimensional angle, two-dimensional position and one-dimensional color) of the space of the object to be shot and consists of a macropixel array, the method is not favorable for observation and post-processing, and a signal processor is required to carry out secondary transformation and decoding on the macropixel array. The algorithm flow of the quadratic transformation and decoding is shown in fig. 4, and first, a five-dimensional light field image needs to be resampled, and data is reconstructed according to the sequence of the angle-space coordinates, so that a five-dimensional light field matrix is finally obtained. And then processing the resampled five-dimensional light field matrix by using a digital refocusing algorithm to obtain a refocusing light field image. The refocusing algorithm, such as shift and sum algorithm, is used to process the light field data, and the obtained refocused light field image is still in a fuzzy state, which is mainly caused by cubic phase modulation, so that the refocused image needs to be decoded, and the wavefront coding decoding algorithm, such as wiener filtering algorithm, is used to process the refocused image. And finally, performing convolution operation on the decoding function and the refocusing light field image in a space domain or performing equivalent operation in a frequency domain to obtain a clear composite imaging system decoding image, wherein the image details can be reproduced.
The original light field image of the composite imaging system is a set of a series of circular macro-pixel arrays, which is similar to the light field imaging system, and the difference is that the macro-pixel size of the light field imaging system depends on the position of a reference object plane, namely the defocusing amount of a light field detector; the macro-pixel size of the composite imaging system can be kept stable in a larger focal depth range and is approximately equal to the size of the micro-lens unit, so that the utilization rate of the detector can be ensured, macro-pixel overlapping is not easy to generate, and the composite imaging system has outstanding depth of field continuation characteristic of the wavefront coding imaging system and excellent laser defense performance of the light field imaging system.
An embodiment of a photo imaging system with laser defense is given below. The parameters of the composite imaging system are set as shown in table 1, the wavefront coding imaging lens is composed of a four-piece imaging lens and a cubic phase plate, the focal length of the equivalent imaging main lens is 100mm, the modulation coefficient of the phase plate is alpha 100, the distance from the micro-lens array to the surface array detector is fixed to be 100mm, and the defocusing size of the micro-lens array is determined by the following simulation process: according to the parameters of the imaging system, a relation curve of the single-pixel incident power on the surface of the detector and the defocusing amount of the micro-lens array and a relation curve of the system echo power and the defocusing amount of the micro-lens array are obtained through calculation, the defocusing amount corresponding to the minimum value point in the relation curve of the echo power is an optimal value, and if a plurality of minimum value points exist, the defocusing amount corresponding to the minimum value point with the minimum wave power is an optimal value.
TABLE 1 parameters of a composite imaging system
The initial simulation conditions are as follows: the incident laser power is 60W, the wavelength is 532nm, the Gaussian beam waist size is 5mm, the beam waist distance optical system is 500m, the equivalent area of the area array detector is phi 50mm, and the area array detector and the emitted laser are located at the same position.
FIG. 6 shows the maximum single-pixel incident power P of four imaging system detectorspixelAnd echo detector received power P at 500mdecAccording to defocus amount W20Variation curve of ± 10 λ.
As can be seen from the analysis of fig. 5, although the maximum single-pixel incident power can be significantly reduced by defocus in the Conventional imaging system (Conventional), the imaging quality is rapidly degraded and is not recoverable. The wavefront coding imaging system (WFC) can greatly reduce the peak power density of an image plane detector light spot, so that the maximum single-pixel incident power of the image plane detector light spot is reduced by more than one magnitudeDue to the diffraction-free characteristic of the Airy beam, the energy density at the center of the beam is concentrated, and the anti-laser blinding performance of the system cannot be further remarkably improved by image plane defocusing operation; the light field imaging system (LFC) can disperse the focused light field on the surface of the detector, reduce the maximum single-pixel incident power by more than two orders of magnitude, but along with the increase of the defocusing amount, the maximum single-pixel incident power P of the detectorpixelThere will be fluctuations that result in a focal depth extension that is less than that of the wavefront coding system. For a Composite imaging system (Composite), the anti-laser blinding performance of the system is similar to that of a light field imaging system (LFC) due to the co-action of the cubic phase plate and the microlens array.
As can be seen from fig. 6, although defocusing in the Conventional imaging system (Conventional) can significantly reduce the received power of the echo detector, the imaging quality is rapidly degraded and is not recoverable. For a wave-front coding imaging system (WFC), due to the modulation effect of a cubic phase, the central light intensity of an echo is in a non-rotational symmetric structure, the size of the echo is obviously increased along with the increase of defocusing amount, and the change rule of the echo is basically consistent with that of a conventional system; for a light field imaging system (LFC), due to coherent superposition of echo components of all micro mirror units, the echo intensity has periodic fluctuation to a certain degree, but the whole system still keeps a single-light spot structure, and the system has a strong negative defocusing echo enhancement effect at the moment. Wherein, the contrast is the non-defocus state, and the negative defocus (W)206 lambda) the echo detector receive power of the light field imaging system is increased by more than two orders of magnitude. For a Composite imaging system (Composite), on the one hand, the central light intensity of the echo is distributed in a non-rotationally symmetric-periodic manner due to the combined action of the cubic phase plate and the microlens array. Along with the increase of the defocusing amount, the size of the echo and the offset of the center of the peak light intensity are gradually increased, the receiving power of the echo detector is reduced, the receiving power of the detector of the negative defocusing composite imaging system is stable, and no magnitude level fluctuation exists. Compared with a light field imaging system, the peak value of the negative defocusing power curve of the composite imaging system is reduced by more than one magnitude, and the negative defocusing enhancement effect of the system echo is effectively improved.
Analyzing the images 5 and 6, comprehensively considering the improvement of the laser defense performance of the system and the stability of the system, setting the defocusing amount of the micro-lens array of the composite imaging system to be optimal at 6 lambda, and compared with a conventional imaging system without defocusing, reducing the maximum single-pixel incident power on the detector surface from 16101.96mW to 120.25mW and reducing the amplitude to 99.3% respectively by adopting the composite imaging system designed by the structural parameters; the receiving power of the echo detector is reduced to 3.51mW from 722.74mW, and the amplitude reduction is 99.5%.
In order to evaluate the imaging quality of the composite imaging system designed by the parameters in the field depth image reconstruction, the three characters B, C and D are respectively arranged at different field depth positions in the object space, the corresponding object distances are 125mm, 150mm and 200mm, the three characters are respectively imaged by a variable-focus conventional imaging system, and after the composite imaging system is used for imaging for once, the three characters are decoded and reconstructed by adopting the calculation algorithm of FIG. 4, and the imaging effects of the three characters are compared as shown in FIG. 7. Fig. 7(a) - (c) show the imaging effect of the conventional imaging system on B, C, D letters in triple focus, respectively, with focusing parameters γ of 2.9, 1 and 0.55, respectively, and corresponding focused object planes of 125mm, 150mm and 200mm, respectively. The result shows that except the object plane of focus, the other object planes of depth of field are all in a fuzzy state, the details cannot be identified, and the depth of field of the single-focus image of the system is smaller. Fig. 7(d) shows the intermediate image after the light field refocusing algorithm of the composite imaging system, and the blurring degree of the image is relatively uniform due to the effect of the cubic phase modulation. Fig. 7(e) shows a clear image reproduced after the inverse filtering decoding of fig. 7(d), and it can be seen that B, C, D three letters at different depths of field are clearly displayed on one image, which illustrates that the composite imaging system has a better depth of field extension capability than the conventional imaging system.
In conclusion, the invention not only can maintain the high imaging quality of the large-area array photoelectric imaging system, but also has the performance of cat eye effect inhibition and laser blinding threshold promotion which are far superior to the performance of the conventional photoelectric imaging system, well solves the contradiction between the maintenance of the high-quality imaging performance and the performance of laser defense of the conventional photoelectric imaging system, and has wide application adaptability.
The parameters of the components in the scheme of the composite imaging system consisting of the phase plate and the microlens array can be changed, such as the number, the size and the focal length of the main lens, the number, the size, the focal length and the defocusing amount of the microlens, the number and the size of the detector and the like. The phase plate is not limited to the cubic phase plate with cubic function described in the embodiment of the invention, and the phase function form of the substituted non-rotational symmetric phase plate can be selected, and parameters such as the modulation coefficient of the phase plate can also be selected according to the engineering application requirements. Since the liquid crystal spatial light modulator has the characteristic of flexibly generating different phase modulation functions, the phase plate can be replaced by the liquid crystal spatial light modulator, and the principle of the liquid crystal spatial light modulator is the same as that of the embodiment. The wavefront coding decoding algorithm according to the present invention is not limited to the wiener filtering described in the embodiment, and includes, for example: inverse filtering, modified wiener filtering, kalman filtering, Lucy-Richardson filtering, wavelet analysis, and other modified algorithms, the refocusing algorithm for light field imaging is not limited to the shift and sum algorithm described in the embodiments, and further includes such algorithms as: 2D frequency line, 4D frequency planar equal frequency domain refocusing algorithm. The imaging system structure described in the present invention is not limited to the conventional transmissive structure described in the embodiments, but includes a reflective or coaxial cassegrain type imaging structure.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application.
Claims (8)
1. The photoelectric imaging system with the laser defense function is characterized in that the photoelectric imaging system is a combined wavefront coding and light field imaging system and comprises a wavefront coding imaging lens, a micro lens array, an area array detector, an image processing device and an output display device, incident laser is modulated by the wavefront coding imaging lens to generate a diffraction-free Airy light beam, the light beam is subjected to angle discrete sampling by the micro lens array near a focal plane and finally received by the area array detector, the area array detector sends a received blurred intermediate image after the angle discrete sampling to a signal processor for refocusing and decoding processing to form a clear digital image, and the clear digital image is output and displayed by the output display device.
2. The photoelectric imaging system with the laser defense function according to claim 1, wherein the intermediate image received by the signal processor is an original light field image, and includes five-dimensional light field image information including a space of an object to be photographed, and the five-dimensional light field image is resampled first, and data is reconstructed in an angle-space coordinate order, so that a five-dimensional light field matrix is finally obtained; then processing the five-dimensional light field matrix by using a digital refocusing algorithm to obtain a refocused light field image; and then, decoding the refocused light field image by utilizing a wavefront coding decoding algorithm, namely performing convolution operation on a decoding function and the refocused light field image in a space domain or performing equivalent operation in a frequency domain to obtain a clear composite imaging system decoding image.
3. The optoelectronic imaging system with laser defense function as claimed in claim 2, wherein the refocusing algorithm comprises shift and sum algorithm and frequency domain refocusing algorithm; the decoding algorithm of the wavefront coding comprises wiener filtering, inverse filtering, Kalman filtering, Lucy-Richardson filtering and wavelet analysis.
4. The optoelectronic imaging system with laser defense function as claimed in claim 1, wherein the wavefront coding imaging lens is composed of a four-piece imaging lens and a phase plate, and the phase plate is a cubic phase plate or a non-rotational symmetric phase plate.
5. The optoelectronic imaging system with laser defense function as claimed in claim 1, wherein the wavefront coding imaging lens is composed of a four-piece imaging lens and a liquid crystal spatial light modulator.
6. The photoelectric imaging system with the laser defense function according to claim 1, wherein the defocus amount of the microlens array is related to parameters of the photoelectric imaging system, and after the focal length of the imaging main lens, the size of the imaging main lens, the focal length of the microlens array unit, the size of the microlens array unit, the pixel size of the area array detector, the reflectivity of the area array detector and the distance from the microlens array to the area array detector are set, a relation curve between the incident power of a single pixel on the surface of the area array detector and the defocus amount of the microlens array is calculated, and a relation curve between the system echo power and the defocus amount of the microlens array is calculated, and the defocus amount corresponding to the minimum value in the relation curve of the echo power is an optimal value, and if a plurality of minimum value points exist, the defocus amount corresponding to the minimum value point in which the wave power is retrieved is an optimal value.
7. The optoelectronic imaging system with laser defense function as claimed in claim 1, wherein the structure of the optoelectronic imaging system is a transmissive structure, a reflective structure or a coaxial Cassegrain structure.
8. A photoelectric imaging method, characterized in that the photoelectric imaging system with laser defense function according to any one of claims 1 to 7 is used for photoelectric imaging.
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