Underwater long-distance imaging system based on super-bunching light field

Abstract

The invention discloses an underwater long-distance imaging system based on a super-bunching light field, and relates to the technical field of underwater optical imaging, the underwater long-distance imaging system comprises a super-continuum light source, a light emitting module, a light receiving module, a noise generation module, a data acquisition module and a data processing module, the super-continuum light source comprises a super-continuum laser and a frequency selector, the light emitting module comprises a reflector I, a reflector II and a lens I, the light receiving module comprises a lens II, a lens III, a reflector III, a lens IV and a lens V, the noise generation module comprises a signal generator and a light emitting diode, and the data acquisition module comprises a single photon tester I and a single photon tester II. And the data processing module comprises a digital analyzer and a computer. According to the underwater long-distance imaging system based on the super-bunching light field, the anti-interference performance on water noise and the image quality of underwater imaging are improved, and meanwhile the underwater imaging distance is increased.

Description

Technical Field

[0001] The invention relates to the technical field of underwater optical imaging, and in particular to an underwater long-distance imaging system based on a super-bunched light field. Background Art

[0002] The ocean occupies about 71% of the earth's surface, of which 95% is undeveloped. In various applications, underwater imaging technology is essential for understanding and exploring the ocean. For example, in the military, it can be used to map the environment around submarines and underwater minesweeping; in civilian use, it can be used for marine mineral exploration and underwater rescue; in scientific research, this technology is used for in-situ detection of marine organisms and underwater archaeology. At present, underwater imaging technology includes acoustic imaging and optical imaging. The propagation of sound waves underwater will not be significantly affected by water and impurities, and the underwater environment has less attenuation on sound waves. Therefore, acoustic imaging has the advantages of long detection range and wide coverage, but the disadvantages of acoustic imaging are low resolution, slow transmission speed, and long imaging time, which limit its application in actual sea areas. On the contrary, optical imaging has the ability to obtain intuitive and high-resolution images underwater, but light will be affected by seawater during underwater propagation, resulting in greater absorption and scattering, thereby affecting the image quality and the imaging distance. Therefore, improving the quality and distance of optical underwater imaging is an important research topic.

[0003] Underwater imaging technology focuses on reducing the impact of water absorption and scattering of light signals on the quality of underwater images, especially in turbid water. Suspended turbid particles will greatly increase the attenuation of light signals and generate large environmental noise to interfere with effective signals. Common underwater imaging systems include polarization imaging systems, laser synchronous scanning imaging systems, range-gated imaging systems, and correlation imaging systems. The imaging distance of polarization imaging is relatively short, the laser synchronous scanning imaging system is relatively complex and has extremely high requirements for equipment, and the range-gated imaging has high requirements for pulse width and gating. The correlation imaging system has the advantages of simple structure and long imaging distance. The present invention adds single-photon detection technology based on this imaging system, which greatly compresses the amount of data.

[0004] In the correlation imaging system, the number of correlated photon pairs is an important parameter for imaging. The supercontinuum light used in the present invention has the characteristic of beam emission compared to ordinary lasers, that is, there are multiple photons with time correlation characteristics in the same pulse, and a certain number of correlated photons can be maintained even under strong attenuation, providing more correlated photon pairs for imaging, eliminating the interference of environmental noise to a greater extent, and thus greatly improving the imaging quality. At the same time, the supercontinuum light emits a light signal with a very large frequency range, and the absorption attenuation of blue and green light in the underwater environment is relatively small. The research can be carried out by actually selecting light signals of different frequencies, providing more options for underwater imaging, and at the same time, the light power can be controlled by changing the light source current to change the size of the echo signal.

[0005] Single-photon detection technology is used to detect optical signals. This technology has the ability to respond to echo signals as low as a single photon level, which can greatly enhance the underwater imaging system's ability to detect weak signals, thereby improving imaging quality and imaging distance. At the same time, single-photon detection has a picosecond time resolution capability, which effectively improves the distance resolution accuracy of the underwater imaging system. Summary of the invention

[0006] The purpose of the present invention is to provide an underwater long-distance imaging system based on a super-bunched light field, so as to solve the problems of poor imaging quality and low resolution caused by underwater environmental noise in existing underwater imaging.

[0007] To achieve the above-mentioned purpose, the present invention provides an underwater long-distance imaging system based on a super-bunched light field, comprising a supercontinuum light source, a light transmitting module, a light receiving module, a noise generating module, a data acquisition module and a data processing module, wherein the supercontinuum light source comprises a supercontinuum laser and a frequency selector, the light transmitting module comprises a reflector 1, a reflector 2 and a lens 1, the light receiving module comprises a lens 2, a lens 3, a reflector 3, a lens 4 and a lens 5, the noise generating module comprises a signal generator and a light emitting diode, the data acquiring module comprises a single photon tester 1 and a single photon tester 2, and the data processing module comprises a digital analyzer and a computer.

[0008] Preferably, a supercontinuum light source is used to generate an optical signal with a superbunching effect, and the optical signal has a strong photon correlation effect; the supercontinuum laser emits white light of continuous frequency, and an optical signal of a fixed frequency range is outputted by a frequency selector and transmitted to the optical transmission module.

[0009] Preferably, the correlation effect between photons is characterized by a second-order correlation function, and the specific formula is as follows:

[0010]

[0011] Among them, I(t) represents the intensity of the photon at time t, and τ is the time delay.

[0012] Preferably, the optical transmission module divides the optical signal output by the frequency selector into two signals through the light reflected by reflector one and the weak light transmitted by reflector one. One signal is used as a reference optical path and is detected by single-photon detector one; the other signal is used as a detection optical path and is emitted by reflector two and lens one to the surface of the underwater target to be measured.

[0013] Preferably, the splitting ratio of the reference light and the detection light is 1:30.

[0014] Preferably, the light receiving module collects the light signal scattered back by the underwater target to be measured and receives it through the single photon detector 2.

[0015] Preferably, the reflector three is controlled by a scanning system, and the scanning mirror control program in the scanning system sets the scanning starting point, ending point, scanning step length and moving time interval, controls the x-axis scanning, and when the x-axis scan ends a row, controls the step length of the y-axis, manually moves it to the next row on the y-axis, and continues to control the program to scan the x-axis, thereby completing the scanning of the entire target.

[0016] Preferably, the signal generator generates a noise signal to control the light emitting diode to light up and down irregularly.

[0017] Preferably, the time digital analyzer is used to receive light signals detected by single-photon detector one and single-photon detector two, and to mark each pulse signal in the two light signals detected by single-photon detector one and single-photon detector two with time to generate a document, and output it to a computer to correlate and calculate the two signals, so as to obtain the relevant intensity information of each pixel point within a certain time, and restore the image information of the underwater target to be measured.

[0018] Preferably, the image information is processed to obtain an image, and the quality of the image is measured by the peak signal-to-noise ratio, and the specific calculation formula is as follows:

[0019]

[0020] in:

[0021]

[0022] Among them, MSE is the mean square error, H and W are the number of pixels in the horizontal and vertical coordinate directions of the image, H*W is the total number of pixels in the image, X is the pixel value of the original image, Y is the pixel value of the image, and i and j are the horizontal and vertical coordinates of the pixel, respectively.

[0023] Therefore, the underwater long-distance imaging system based on the super-focused light field using the above structure has the following beneficial effects:

[0024] (1) The present invention adopts supercontinuum light as the emitting light source and utilizes the superbunching effect produced by it to emit more photons at the same time. It has a strong photon correlation characteristic and can effectively eliminate the interference of noise signals, greatly improving the anti-interference ability of underwater imaging. At the same time, it also improves the image quality and resolution of underwater imaging. By increasing the output light power, the underwater imaging distance can also be greatly improved.

[0025] (2) The present invention uses a single-photon detector to detect photon pulses as low as a single-photon level, and can detect each photon diffusely reflected by the target object. A time digital analyzer is used to perform ps-level time marking on the detected photon information, providing more accurate photon time information, and screening out more accurate dual-photon numbers during data processing, greatly improving the imaging quality.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of an embodiment of an underwater long-distance imaging system based on a super-bunched light field of the present invention;

[0028] Figure 2 The results of testing the second-order correlation emitted by the supercontinuum light source used in this method are shown in Figure 2.

[0029] Figure 3 This is a comparison chart of the number of photons emitted by ordinary lasers and supercontinuum light sources in one cycle and their probability of occurrence under the same conditions;

[0030] Figure 4 This is a single- and double-photon imaging diagram when the method is used to add environmental noise at a distance of ten meters under the condition of low-power emission light;

[0031] Figure 5 The peak signal-to-noise ratio of the single-photon and double-photon images obtained by this method when the ambient noise is increased;

[0032] Figure numerals: 1011, supercontinuum laser; 1012, frequency selector; 1021, reflector one; 1022, single-photon detector one; 1031, reflector two; 1032, lens one; 104, underwater target to be measured; 1051, lens two; 1052, lens three; 1053, reflector three; 1054, lens four; 1055, lens five; 1056, single-photon detector two; 1061, time digital analyzer; 1062, computer; 1071, light-emitting diode; 1072, signal generator. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0034] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0035] Example

[0036] See also Figure 1-5 The present invention provides an underwater long-distance imaging system based on a super-bunched light field, including a super-continuum light source, a light transmitting module, a light receiving module, a noise generating module, a data acquisition module and a data processing module.

[0037] The supercontinuum light source includes a supercontinuum laser 1011 and a frequency selector 1012, which is used to generate an optical signal with a superbunching effect, and the optical signal has a strong photon correlation effect. Since the underwater environment has a small absorption attenuation of optical signals in the blue-green light frequency band, the present invention selects this range for experimentation, and the frequency selector 1012 is controlled by software to emit 532nm green light output to the optical transmission module.

[0038] The supercontinuum laser 1011 emits white light of continuous frequency, and the frequency selector 1012 outputs an optical signal of a fixed frequency range to the optical transmission module, and the optical power is adjusted by controlling the current. The supercontinuum light source has an optical pulse signal of continuous frequency, and the optical signal of a certain frequency range can be selectively used through the frequency selector 1012. At the same time, it has a changeable optical pulse repetition rate, and its characteristics make it applicable to a wider range of situations. Supercontinuum light has the characteristic of being able to generate and emit more photons at the same time, so it has more correlated photon pairs and has good correlation characteristics.

[0039] Compared with ordinary lasers, supercontinuum light sources can emit more photons at the same time and can better use the photon correlation effect to eliminate the influence of environmental noise, thereby improving imaging quality.

[0040] For the supercontinuum laser 1011, the events of emitting single photons, double photons and multiple photons are random, and the situation of each photon entering the reference optical path and the detection optical path is also random, which means that there are situations where there are no photons in both paths, or only one of them has photons, or both paths have photons. When the computer 1062 performs correlation calculation on the two-path signal, only when the two paths receive photons within a certain time difference range, it is regarded as a double photon carrying effective image information, which largely excludes the noise photon information in the detection optical path.

[0041] The second-order correlation function is a method based on photon statistics, which is calculated by the relationship between photon intensity in the time domain. The second-order correlation function is used to characterize the correlation effect between photons. The specific formula is as follows:

[0042]

[0043] Where I(t) represents the intensity of the photon at time t, and τ is the time delay. (2) (0) represents the ratio of the probability of detecting two photons arriving at the same time to the probability of two independent photons arriving at the same time within a given time. (2) When (0) is much larger than 2, it means that there is obvious photon aggregation phenomenon, such as Figure 2 As shown in , there is an obvious super bunching effect at this time, and the correlation between photons is enhanced. Figure 3 As shown, under the superbunching effect, the probability of two-photon emission of the light source of this system is much greater than that of ordinary lasers. This feature provides the imaging system with more available correlated photon pairs, thus reflecting the advantage of the system in the field of underwater photon imaging.

[0044] The optical transmission module includes a reflector 1021, a reflector 1031 and a lens 1032. The optical transmission module divides the optical signal output by the frequency selector 1012 into two signals through the light reflected by the reflector 1021 and the weak light transmitted by the reflector 1021. One signal is used as a reference optical path and is detected by the single photon detector 1022 to provide reference photon information; the other signal is used as a detection optical path and is emitted by the reflector 1031 and the lens 1032 to the surface of the underwater target 104 to be measured.

[0045] The reflector 1021 is selected to replace the beam splitter to split the light output by the frequency selector 1012 into two beams, so that the beam splitting ratio of the reference optical path and the detection optical path is 1:30, which is far higher than the beam splitting ratio that can be achieved by the beam splitter. In this case, more optical signals can be transmitted to the underwater target 104 to be measured. In the case of weak optical signals, the reference signal is guaranteed to be valid while a higher power optical signal is transmitted to the target object.

[0046] The optical receiving module includes lens 2 1051 , lens 3 1052 , reflector 3 1053 , lens 4 1054 and lens 5 1055 , which are used to collect the optical signal scattered back by the underwater target 104 and receive it through single photon detector 2 1056 .

[0047] Reflector three 1053 is controlled by a scanning system. The scanning system is a system that controls the reflector by a dual-axis. The scanning mirror control program in the scanning system sets the scanning start point, end point, scanning step length and moving time interval, and controls the x-axis scanning. When the x-axis scans a line, the y-axis step length is controlled, and it is manually moved to the next line on the y-axis. The control program continues to scan the x-axis, thereby completing the scanning of the entire target.

[0048] The noise generating module includes a signal generator 1072 and a light emitting diode 1071, which is used to generate a noise signal to simulate the photon information generated by the underwater environmental noise mixed in the detection light received by the light receiving module. The signal generator 1072 generates a noise signal to control the light emitting diode 1071 to light up and down irregularly.

[0049] The data acquisition module includes a single photon tester 1 and a single photon tester 2, which are used to detect the optical signals of the reference optical path and the detection optical path respectively. The single photon tester 1 and the single photon tester 2 detect photon pulses and can respond to photon pulses at the single photon level. They have the ability to detect every photon, which can effectively improve the detection efficiency.

[0050] The data processing module includes a digital analyzer and a computer 1062. The time digital analyzer 1061 can record the light pulses detected by the single photon tester 1 and the single photon tester 2 with a time of up to ps, so as to obtain the number of photons recovered within a certain integration time, which is reflected as photon intensity information. The time digital analyzer 1061 is used to receive the light signals detected by the single photon detector 1 1022 and the single photon detector 2 1056, and annotate each pulse signal in the two light signals detected by the single photon detector 1 1022 and the single photon detector 2 1056 with time to generate a document, and output it to the computer 1062 to associate and operate the two signals, obtain the relevant intensity information of each pixel point within a certain time, and restore the image information of the underwater target 104 to be measured.

[0051] Under the superbunching effect, the two collected signals are correlated. When photons appear in both signals within a certain period of time, they are regarded as one valid photon, so as to screen out the correlated photon pairs. The number of photon pairs is used to represent the photon intensity information of the pixel point, and imaging is performed using the intensity information.

[0052] The image information is processed to obtain an image, and the image quality is measured by the peak signal-to-noise ratio. The specific calculation formula is as follows:

[0053]

[0054] in:

[0055]

[0056] Where MSE is the mean square error, H and W are the number of pixels in the horizontal and vertical coordinates of the image, H*W is the total number of pixels in the image, X is the pixel value of the original image, Y is the pixel value of the image, and i and j are the horizontal and vertical coordinates of the pixel. The larger the calculated peak signal-to-noise ratio value, the better the image quality. Figure 5 As shown in the figure, the imaging quality of single-photon and double-photon imaging changes with the increase of noise signal, which proves the imaging advantage of this system in removing noise.

[0057] This system uses a super-bunched light field as a light source, which has the ability to generate a large number of photons emitted simultaneously. By utilizing the photon correlation characteristics, it can effectively eliminate the influence of ambient light and background noise. The reference signal and the detection signal are collected through a single-photon detector, and the data is correlated and processed to extract the relevant intensity information of the underwater target 104 to be measured, thereby restoring the image information of the underwater target 104 to be measured.

[0058] Therefore, the present invention adopts the above-mentioned structure of the underwater long-distance imaging system based on the super-bunched light field, and utilizes the particularity of the correlated photon pairs of the weak-power light source and the supercontinuum light itself to realize the detection and imaging of long-distance underwater targets, improves the anti-interference ability to water noise and the image quality of underwater imaging, and at the same time increases the underwater imaging distance.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. An underwater long-distance imaging system based on a super-bunched light field, characterized by: It includes a supercontinuum light source, a light emitting module, a light receiving module, a noise generating module, a data acquisition module and a data processing module. The supercontinuum light source includes a supercontinuum laser and a frequency selector. The light emitting module includes a reflector 1, a reflector 2 and a lens 1. The light receiving module includes a lens 2, a lens 3, a reflector 3, a lens 4 and a lens 5. The noise generating module includes a signal generator and a light emitting diode. The data acquisition module includes a single photon tester 1 and a single photon tester 2. The data processing module includes a digital analyzer and a computer.

2. The underwater long-distance imaging system based on super-focused light field according to claim 1, characterized in that: The supercontinuum light source is used to generate an optical signal with a superbunching effect, and the optical signal has a strong photon correlation effect; the supercontinuum laser emits white light of continuous frequency, and the optical signal of a fixed frequency range is output by the frequency selector and transmitted to the optical transmission module.

3. The underwater long-distance imaging system based on super-focused light field according to claim 2, characterized in that: The correlation effect between photons is characterized by the second-order correlation function. The specific formula is as follows: Among them, I(t) represents the intensity of the photon at time t, and τ is the time delay.

4. The underwater long-distance imaging system based on super-focused light field according to claim 3, characterized in that: The optical transmitting module divides the optical signal output by the frequency selector into two signals through the light reflected by reflector 1 and the weak light transmitted by reflector 1. One signal is used as a reference optical path and is detected by single-photon detector 1; the other signal is used as a detection optical path and is emitted by reflector 2 and lens 1 to the surface of the underwater target to be measured.

5. The underwater long-distance imaging system based on super-focused light field according to claim 4, characterized in that: The splitting ratio of reference light and detection light is 1:

30.

6. The underwater long-distance imaging system based on super-focused light field according to claim 5, characterized in that: The optical receiving module collects the optical signal scattered back by the underwater target to be detected and receives it through the single photon detector 2.

7. The underwater long-distance imaging system based on super-focused light field according to claim 6, characterized in that: The reflector is controlled by a scanning system. The scanning mirror control program in the scanning system sets the scanning start point, end point, scanning step length and moving time interval to control the x-axis scanning. When the x-axis scans a line, the y-axis step length is controlled and manually moved to the next line on the y-axis. The control program continues to scan the x-axis to complete the scanning of the entire target.

8. The underwater long-distance imaging system based on super-focused light field according to claim 7, characterized in that: The signal generator generates a noise signal to control the light emitting diode to light up and down irregularly.

9. The underwater long-distance imaging system based on super-focused light field according to claim 8, characterized in that: The time digital analyzer is used to receive the light signals detected by the single photon detector 1 and the single photon detector 2, and to mark each pulse signal in the two light signals detected by the single photon detector 1 and the single photon detector 2 with time to generate a document, and output it to the computer to correlate and calculate the two signals, so as to obtain the relevant intensity information of each pixel point within a certain time, and restore the image information of the underwater target to be measured.

10. The underwater long-distance imaging system based on super-focused light field according to claim 9, characterized in that: The image information is processed to obtain an image, and the image quality is measured by the peak signal-to-noise ratio. The specific calculation formula is as follows: in: Among them, MSE is the mean square error, H and W are the number of pixels in the horizontal and vertical coordinate directions of the image, H*W is the total number of pixels in the image, X is the pixel value of the original image, Y is the pixel value of the image, and i and j are the horizontal and vertical coordinates of the pixel, respectively.

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