Map
WeChat
Email alert
RSS2019 Vol. 43, No. 5
column
Display Method:
[Abstract]
[PDF 287KB]
2019, 43(5): 591-596.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.001
[FullText HTML]
Abstract:
In order to solve the difficult problem of locating large size multi-blind holes in laser processing, local pictures were taken by industrial cameras. According to the structure and distribution characteristics of blind holes in meshes, blind holes in local images were detected by least square fitting circle method. Neighborhood feature was used to find feature points in a network. By using feature point matching to realize local localization as a whole, the precise and efficient positioning of the workpiece was realized. The results show that, neighborhood feature method has a positioning accuracy of 0.02mm for blind holes in meshes. Effective positioning of blind holes is realized. It solves the problem of difficult positioning of dot processing parts. This study provides a basis for further research on laser processing in blind holes.
In order to solve the difficult problem of locating large size multi-blind holes in laser processing, local pictures were taken by industrial cameras. According to the structure and distribution characteristics of blind holes in meshes, blind holes in local images were detected by least square fitting circle method. Neighborhood feature was used to find feature points in a network. By using feature point matching to realize local localization as a whole, the precise and efficient positioning of the workpiece was realized. The results show that, neighborhood feature method has a positioning accuracy of 0.02mm for blind holes in meshes. Effective positioning of blind holes is realized. It solves the problem of difficult positioning of dot processing parts. This study provides a basis for further research on laser processing in blind holes.
2019, 43(5): 597-600.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.002
Abstract:
In order to meet the application requirements of military long-distance laser rangefinders for solid-state lasers with small volume and high peak power, a small air-cooled LD-pumped Nd:YAG solid-state laser was designed by using short cavity length and orthogonal polarization electro-optic Q-switched technology. The prototype was verified by experiments. The results show that, the laser with weight of 630g, repetition frequency of 20Hz, output energy of 85mJ, pulse width of 3.9ns, laser peak power of 21.8MW and beam divergence angle of 1.9mrad meets the requirements of miniaturization and high peak power. The laser has strong environmental adaptability and has been applied in engineering.
In order to meet the application requirements of military long-distance laser rangefinders for solid-state lasers with small volume and high peak power, a small air-cooled LD-pumped Nd:YAG solid-state laser was designed by using short cavity length and orthogonal polarization electro-optic Q-switched technology. The prototype was verified by experiments. The results show that, the laser with weight of 630g, repetition frequency of 20Hz, output energy of 85mJ, pulse width of 3.9ns, laser peak power of 21.8MW and beam divergence angle of 1.9mrad meets the requirements of miniaturization and high peak power. The laser has strong environmental adaptability and has been applied in engineering.
2019, 43(5): 601-607.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.003
Abstract:
In order to detect its components rapidly in the production of compound fertilizer and guide the production, laser-induced breakdown spectroscopy (LIBS) and support vector machine (SVM) were used to quantitatively analyze phosphorus (P) in compound fertilizer. In the experiment, 58 compound fertilizer samples were analyzed by three characteristic spectra of PⅠ 213.5nm, PⅠ 214.9nm and PⅠ 215.4nm. 58 samples were divided into training set (43 samples) and test set (15 samples) by random selection method. The grid search method was used to optimize the parameters of the quantitative analysis model of P element in compound fertilizer. The SVM analysis model was constructed. The results show that, the correlation coefficient R2 of the calibration model of training set is 0.981. It shows that the correlation between the reference value and the predicted value of the training set is high. The correlation coefficient R2 between the reference value and the predicted value of phosphorus (P) in the samples is 0.992. The mean square error is 4.95×10-5. SVM model has strong applicability. The average absolute error and relative error of the training set are 5.9×10-4 and 3.99×10-3, respectively. The average absolute error and relative error of the test set are 5.6×10-4 and 3.28×10-3, respectively. The combination of SVM algorithm and LIBS technology can realize the rapid detection of phosphorus in compound fertilizer. This study provides a reference for rapid determination of element content in compound fertilizer.
In order to detect its components rapidly in the production of compound fertilizer and guide the production, laser-induced breakdown spectroscopy (LIBS) and support vector machine (SVM) were used to quantitatively analyze phosphorus (P) in compound fertilizer. In the experiment, 58 compound fertilizer samples were analyzed by three characteristic spectra of PⅠ 213.5nm, PⅠ 214.9nm and PⅠ 215.4nm. 58 samples were divided into training set (43 samples) and test set (15 samples) by random selection method. The grid search method was used to optimize the parameters of the quantitative analysis model of P element in compound fertilizer. The SVM analysis model was constructed. The results show that, the correlation coefficient R2 of the calibration model of training set is 0.981. It shows that the correlation between the reference value and the predicted value of the training set is high. The correlation coefficient R2 between the reference value and the predicted value of phosphorus (P) in the samples is 0.992. The mean square error is 4.95×10-5. SVM model has strong applicability. The average absolute error and relative error of the training set are 5.9×10-4 and 3.99×10-3, respectively. The average absolute error and relative error of the test set are 5.6×10-4 and 3.28×10-3, respectively. The combination of SVM algorithm and LIBS technology can realize the rapid detection of phosphorus in compound fertilizer. This study provides a reference for rapid determination of element content in compound fertilizer.
2019, 43(5): 608-613.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.004
Abstract:
When detecting vibration with a phase sensitive optical time domain reflectometer, if the incident laser power is high, the photo detector might be saturated so that the front end of optical fiber become insensitive to vibration sensing; if the laser power is relatively low, long-distance detection might be impossible. In order to solve this problem, a new type of sensor structure was used to conduct theoretical analysis and experimental verification. According to the incident of high or low power, optical fiber was segmented and detected. Through corresponding data processing, the whole process sensitivity of optical fiber vibration was realized. At the same time, in order to further improve the vibration sensitivity and signal-to-noise ratio of the system, the results of avalanche diode detection and low noise photodiode detection were compared and analyzed. The experimental results of acoustooptic modulator and semiconductor optical amplifier were compared. The results show that, when the measuring distance is 38km, compared with avalanche diode detection, the use of low noise photodiodes and erbium-doped fiber amplifiers has a higher signal-to-noise ratio. Compared with acoustooptic modulators, a higher signal-to-noise ratio can be obtained by using semiconductor optical amplifiers. The new sensing structure provides a good reference for scientific research and engineering application in the field of optical fiber sensors.
When detecting vibration with a phase sensitive optical time domain reflectometer, if the incident laser power is high, the photo detector might be saturated so that the front end of optical fiber become insensitive to vibration sensing; if the laser power is relatively low, long-distance detection might be impossible. In order to solve this problem, a new type of sensor structure was used to conduct theoretical analysis and experimental verification. According to the incident of high or low power, optical fiber was segmented and detected. Through corresponding data processing, the whole process sensitivity of optical fiber vibration was realized. At the same time, in order to further improve the vibration sensitivity and signal-to-noise ratio of the system, the results of avalanche diode detection and low noise photodiode detection were compared and analyzed. The experimental results of acoustooptic modulator and semiconductor optical amplifier were compared. The results show that, when the measuring distance is 38km, compared with avalanche diode detection, the use of low noise photodiodes and erbium-doped fiber amplifiers has a higher signal-to-noise ratio. Compared with acoustooptic modulators, a higher signal-to-noise ratio can be obtained by using semiconductor optical amplifiers. The new sensing structure provides a good reference for scientific research and engineering application in the field of optical fiber sensors.
2019, 43(5): 614-618.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.005
Abstract:
Metal-graphene photonic crystal-metal composite structures can achieve multi-band absorption. In order to understand the absorption characteristics of the composite structure, the influence of visible band structure parameters on multi-band absorption characteristics was studied with transfer matrix method. The results show that, central wavelength of each absorption band is independent of the chemical potential of graphene. The number of absorption bands is related to the number of periodic units of graphene photonic crystals and the optical thickness of dielectric layer. The larger the number of periodic elements, the greater the optical thickness of the dielectric layer, the more the number of absorption bands. The influence of the thickness of the two metal layers on the absorption characteristics is different. In order to make the optical absorption as high as possible, the metal layer on the side of the substrate should be as thick as possible. The thickness of the metal layer on the side of the incident space has an optimal value. When the parameters are selected reasonably at normal incidence, the absorption rate of each main absorption peak can be more than 90%. The results provide a reference for the development of multi-band optical absorbers based on graphene.
Metal-graphene photonic crystal-metal composite structures can achieve multi-band absorption. In order to understand the absorption characteristics of the composite structure, the influence of visible band structure parameters on multi-band absorption characteristics was studied with transfer matrix method. The results show that, central wavelength of each absorption band is independent of the chemical potential of graphene. The number of absorption bands is related to the number of periodic units of graphene photonic crystals and the optical thickness of dielectric layer. The larger the number of periodic elements, the greater the optical thickness of the dielectric layer, the more the number of absorption bands. The influence of the thickness of the two metal layers on the absorption characteristics is different. In order to make the optical absorption as high as possible, the metal layer on the side of the substrate should be as thick as possible. The thickness of the metal layer on the side of the incident space has an optimal value. When the parameters are selected reasonably at normal incidence, the absorption rate of each main absorption peak can be more than 90%. The results provide a reference for the development of multi-band optical absorbers based on graphene.
2019, 43(5): 619-623.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.006
Abstract:
In order to improve the accuracy of dynamic 3-D shape measurement by fringe projection, the windowed Fourier analysis was used to reduce the phase shift error caused by motion. Firstly, the actual phase shift between deformed fringes was estimated by windowed Fourier analysis. Then, the phase distribution of the deformed fringes was estimated with high precision by the least square method. Finally, 3-D shape of the scene was obtained from the estimated phase calculation. The influence of object motion on phase shift was analyzed theoretically. The phase shift estimation accuracy of the proposed method was studied by simulation. An experimental system was built to verify the results. The phase recovery accuracy of the proposed method is 0.1673rad. Compared with the existing methods, this method is obviously improved. The results show that the method is effective.
In order to improve the accuracy of dynamic 3-D shape measurement by fringe projection, the windowed Fourier analysis was used to reduce the phase shift error caused by motion. Firstly, the actual phase shift between deformed fringes was estimated by windowed Fourier analysis. Then, the phase distribution of the deformed fringes was estimated with high precision by the least square method. Finally, 3-D shape of the scene was obtained from the estimated phase calculation. The influence of object motion on phase shift was analyzed theoretically. The phase shift estimation accuracy of the proposed method was studied by simulation. An experimental system was built to verify the results. The phase recovery accuracy of the proposed method is 0.1673rad. Compared with the existing methods, this method is obviously improved. The results show that the method is effective.
2019, 43(5): 624-628.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.007
Abstract:
In order to investigate the surface powder adhesion process of 316L stainless steel by laser direct metal deposition, the type of powder adhesion was analyzed by high-speed camera. The influence of powder feeding rate, gas flow rate and linear energy density on powder adhesion in single-channel multilayer deposition was studied quantitatively by single factor test method. The results show that, adhesion powder mainly includes two types: molten solution escaping from molten pool and unmelted powder adhesion. With the increase of powder feeding rate and the decrease of powder feeding gas flow rate, the adhesion degree of powder on the side surface of thin-walled parts increases. However, the degree of powder adhesion is insensitive to the change of laser linear energy density. With laser power of 700W, scanning speed of 700mm/min, powder feeding rate of 13.54g/min, powder feeding gas flow rate of 14L/min and defocusing rate of +22mm, powder adhesion on the surface of thin-walled parts by laser direct metal deposition is less. The results can be used as an important basis for improving the surface quality of 316L stainless steel products.
In order to investigate the surface powder adhesion process of 316L stainless steel by laser direct metal deposition, the type of powder adhesion was analyzed by high-speed camera. The influence of powder feeding rate, gas flow rate and linear energy density on powder adhesion in single-channel multilayer deposition was studied quantitatively by single factor test method. The results show that, adhesion powder mainly includes two types: molten solution escaping from molten pool and unmelted powder adhesion. With the increase of powder feeding rate and the decrease of powder feeding gas flow rate, the adhesion degree of powder on the side surface of thin-walled parts increases. However, the degree of powder adhesion is insensitive to the change of laser linear energy density. With laser power of 700W, scanning speed of 700mm/min, powder feeding rate of 13.54g/min, powder feeding gas flow rate of 14L/min and defocusing rate of +22mm, powder adhesion on the surface of thin-walled parts by laser direct metal deposition is less. The results can be used as an important basis for improving the surface quality of 316L stainless steel products.
2019, 43(5): 629-634.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.008
Abstract:
In order to obtain attosecond pulses in X-ray range, the method of generating high intensity harmonic spectra and attosecond pulses by combining ultraviolet and chirped laser beams was introduced. The theoretical analysis was carried out. The results show that, when forward chirp parameter is introduced, harmonic cut-off energy has a slight extension and the efficiency of harmonic radiation decreases significantly. When negative chirp parameter is introduced, harmonic cut-off energy is extended and harmonic radiation efficiency is enhanced under the condition of forward chirp. When a 125nm ultraviolet light source is introduced into the chirped laser, the efficiency of harmonic radiation is obviously enhanced because of the effect of resonance-enhanced ionization. Driven by ultraviolet-forward chirp, harmonic radiation intensity is enhanced 25 times and harmonic cut-off energy is extended. A 382eV platform area is formed. Driven by ultraviolet-negative chirp, harmonic cut-off energy does not changed significantly but the efficiency of harmonic radiation is 110 times higher. A 410eV platform area is formed. By superposing the harmonics in the combined field, a series of single attosecond pulses within 70as can be obtained. This study is helpful for the development of attosecond science.
In order to obtain attosecond pulses in X-ray range, the method of generating high intensity harmonic spectra and attosecond pulses by combining ultraviolet and chirped laser beams was introduced. The theoretical analysis was carried out. The results show that, when forward chirp parameter is introduced, harmonic cut-off energy has a slight extension and the efficiency of harmonic radiation decreases significantly. When negative chirp parameter is introduced, harmonic cut-off energy is extended and harmonic radiation efficiency is enhanced under the condition of forward chirp. When a 125nm ultraviolet light source is introduced into the chirped laser, the efficiency of harmonic radiation is obviously enhanced because of the effect of resonance-enhanced ionization. Driven by ultraviolet-forward chirp, harmonic radiation intensity is enhanced 25 times and harmonic cut-off energy is extended. A 382eV platform area is formed. Driven by ultraviolet-negative chirp, harmonic cut-off energy does not changed significantly but the efficiency of harmonic radiation is 110 times higher. A 410eV platform area is formed. By superposing the harmonics in the combined field, a series of single attosecond pulses within 70as can be obtained. This study is helpful for the development of attosecond science.
2019, 43(5): 635-640.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.009
Abstract:
In order to improve the analysis accuracy of hyperspectral remote sensing technology, the diffraction efficiency of partial structural errors of rectangular gratings was analyzed by using scalar diffraction theory. The influence of grating local period and slit width error on diffraction efficiency was calculated. The results show that, when the processing error makes the local slit width of grating wider, the main maxima intensity (excluding zero order) of the grating decreases. This error has a relatively small effect on the intensity of the diffracted light at ±1 order. With the increase of the error, the higher the diffraction order, the faster the intensity of the light decreases. With the increase of the error, relative to the effect on ±1 order diffraction light, the higher the order, the faster the principal maximum diffraction intensity increases. This study provides a reference for the control of local period and slit width error in processing rectangular gratings.
In order to improve the analysis accuracy of hyperspectral remote sensing technology, the diffraction efficiency of partial structural errors of rectangular gratings was analyzed by using scalar diffraction theory. The influence of grating local period and slit width error on diffraction efficiency was calculated. The results show that, when the processing error makes the local slit width of grating wider, the main maxima intensity (excluding zero order) of the grating decreases. This error has a relatively small effect on the intensity of the diffracted light at ±1 order. With the increase of the error, the higher the diffraction order, the faster the intensity of the light decreases. With the increase of the error, relative to the effect on ±1 order diffraction light, the higher the order, the faster the principal maximum diffraction intensity increases. This study provides a reference for the control of local period and slit width error in processing rectangular gratings.
2019, 43(5): 641-645.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.010
Abstract:
In order to study dispersion compensation of optical differential phase shift keying (DPSK) modulation format in high-speed optical fiber transmission system, dispersion compensation principle of dispersion compensation fiber was used to compensate the dispersion of 40Gbit/s optical fiber transmission system. The spectrum characteristics of three DPSK modulation formats in 40Gbit/s single channel optical fiber transmission system were analyzed. The dispersion tolerance of three codes was simulated. When considering the nonlinearity of optical fibers, dispersion compensation schemes of three modulation schemes were simulated. The results show that, optical non-return-to-zero differential phase shift keying (NRZ-DPSK) signal has the best dispersion tolerance, but it is greatly affected by non-linearity. 33% return-to-zero differential phase shift keying signal has poor dispersion tolerance, but the effect of dispersion compensation is better than that of NRZ-DPSK. Carrier-suppressed return-to-zero differential phase shift keying signals can suppress both dispersion and nonlinearity. Three DPSK modulation schemes have the best dispersion compensation effect in symmetrical compensation scheme 2. This simulation study has reference significance for dispersion compensation of optical DPSK signal in optical fiber.
In order to study dispersion compensation of optical differential phase shift keying (DPSK) modulation format in high-speed optical fiber transmission system, dispersion compensation principle of dispersion compensation fiber was used to compensate the dispersion of 40Gbit/s optical fiber transmission system. The spectrum characteristics of three DPSK modulation formats in 40Gbit/s single channel optical fiber transmission system were analyzed. The dispersion tolerance of three codes was simulated. When considering the nonlinearity of optical fibers, dispersion compensation schemes of three modulation schemes were simulated. The results show that, optical non-return-to-zero differential phase shift keying (NRZ-DPSK) signal has the best dispersion tolerance, but it is greatly affected by non-linearity. 33% return-to-zero differential phase shift keying signal has poor dispersion tolerance, but the effect of dispersion compensation is better than that of NRZ-DPSK. Carrier-suppressed return-to-zero differential phase shift keying signals can suppress both dispersion and nonlinearity. Three DPSK modulation schemes have the best dispersion compensation effect in symmetrical compensation scheme 2. This simulation study has reference significance for dispersion compensation of optical DPSK signal in optical fiber.
2019, 43(5): 646-649.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.011
Abstract:
In order to obtain high power 780nm laser with simple structure and relatively low cost, the method of out-of-cavity frequency doubling with single frequency doubling crystal was adopted. After continuous wavelength laser generated by distributed feedback semiconductor lasers was injected into the optical fiber amplifier, quasi-phase matching was performed through periodically polarized lithium niobate crystals. The saturated absorption spectra of rubidium were obtained. The results show that, 1.2W frequency doubling light is produced and the laser has high output power. This result is helpful for the miniaturization of cold atomic physics experiments such as rubidium atomic clock and atomic interferometer.
In order to obtain high power 780nm laser with simple structure and relatively low cost, the method of out-of-cavity frequency doubling with single frequency doubling crystal was adopted. After continuous wavelength laser generated by distributed feedback semiconductor lasers was injected into the optical fiber amplifier, quasi-phase matching was performed through periodically polarized lithium niobate crystals. The saturated absorption spectra of rubidium were obtained. The results show that, 1.2W frequency doubling light is produced and the laser has high output power. This result is helpful for the miniaturization of cold atomic physics experiments such as rubidium atomic clock and atomic interferometer.
2019, 43(5): 650-654.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.012
Abstract:
In order to make a laser work stably, a temperature control system with fast control speed, high precision and tunable performance was designed and implemented. ATmega328P was used as the processor in the system. Self-tuning proportional-integral-differential (PID) coefficients was determined by particle swarm optimization. A closed-loop negative feedback PID structure was used to control the temperature of the laser. The results show that, under the control of this system, the laser can reach the target temperature in about 15s. The temperature error after reaching the target temperature is about (±0.01℃). It can be maintained for a long time. The output power of the laser fluctuates very little. The variance is only 568.49μW. The system can effectively control the temperature of butterfly packaging laser.
In order to make a laser work stably, a temperature control system with fast control speed, high precision and tunable performance was designed and implemented. ATmega328P was used as the processor in the system. Self-tuning proportional-integral-differential (PID) coefficients was determined by particle swarm optimization. A closed-loop negative feedback PID structure was used to control the temperature of the laser. The results show that, under the control of this system, the laser can reach the target temperature in about 15s. The temperature error after reaching the target temperature is about (±0.01℃). It can be maintained for a long time. The output power of the laser fluctuates very little. The variance is only 568.49μW. The system can effectively control the temperature of butterfly packaging laser.
2019, 43(5): 655-659.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.013
Abstract:
In order to overcome the limitation of maximum coupling efficiency in the coupling package of optical emission sub-modules of distributed feedback laser lasers, the wedge-shaped truncated optical fiber microlens was used to replace the discrete lens in direct coupling scheme.A wedge-shaped truncated end-face model with inclined angle of 0.6rad, coupling distance of 60μm and half-width of 15μm was obtained. On this basis, compared with discrete and direct coupling, longitudinal, transverse and angular migration errors were discussed.The results show that, when longitudinal coupling distance is -21.45μm~56.79μm and angular coupling angle ranges from -8.3°~8.5°, the coupling efficiency is always greater than 70%. The overall tolerance of structure is high and the coupling efficiency is 84.40%.This research can provide a new solution of secondary emission module of coupling package device for the next generation distributed feedback lasers.
In order to overcome the limitation of maximum coupling efficiency in the coupling package of optical emission sub-modules of distributed feedback laser lasers, the wedge-shaped truncated optical fiber microlens was used to replace the discrete lens in direct coupling scheme.A wedge-shaped truncated end-face model with inclined angle of 0.6rad, coupling distance of 60μm and half-width of 15μm was obtained. On this basis, compared with discrete and direct coupling, longitudinal, transverse and angular migration errors were discussed.The results show that, when longitudinal coupling distance is -21.45μm~56.79μm and angular coupling angle ranges from -8.3°~8.5°, the coupling efficiency is always greater than 70%. The overall tolerance of structure is high and the coupling efficiency is 84.40%.This research can provide a new solution of secondary emission module of coupling package device for the next generation distributed feedback lasers.
2019, 43(5): 660-665.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.014
Abstract:
In order to solve the problem that convolutional neural network detection of pedestrians was slow, and did not meet the real-time requirement when performing continuous pedestrian detection, pedestrian detection algorithm of history-based region with convolutional neural network was used. Current image was detected by using the detection result in the previous image. The detection process was optimized, and the detection result of the previous image was used as reference information for extracting region proposals of the current image. Convolution feature of the current image was filtered by using the gray value difference map of the current image and the previous image to reduce the sliding window searching area. The results of Caltech pedestrian detection data set show that the algorithm combined with historical information is 2.5 times faster than the advanced algorithm, and the detection accuracy is increased by 1.5%. The algorithm implements real-time pedestrian detection, and the designed network can effectively detect small target pedestrians.
In order to solve the problem that convolutional neural network detection of pedestrians was slow, and did not meet the real-time requirement when performing continuous pedestrian detection, pedestrian detection algorithm of history-based region with convolutional neural network was used. Current image was detected by using the detection result in the previous image. The detection process was optimized, and the detection result of the previous image was used as reference information for extracting region proposals of the current image. Convolution feature of the current image was filtered by using the gray value difference map of the current image and the previous image to reduce the sliding window searching area. The results of Caltech pedestrian detection data set show that the algorithm combined with historical information is 2.5 times faster than the advanced algorithm, and the detection accuracy is increased by 1.5%. The algorithm implements real-time pedestrian detection, and the designed network can effectively detect small target pedestrians.
2019, 43(5): 666-671.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.015
Abstract:
In order to realize optical true time-delay(TDD) system of large-scale 2-D phased array antenna(PAA), a binary silicon-based integrated binary optical delay line technology based on silicon-based photonics was adopted. A 2-D PAA N×N TDD network was proposed. By using the symmetry of 2-D PAA structure and the independent control of row and column delays, the complexity of TDD networks can be reduced to (N-1)/2 (when N is odd) or N/2 (when N is even). Delay control scheme and the design of integrated delay chip were analyzed theoretically. Four kinds of silicon-based binary TDD chips were designed and implemented by taking 8×8 2-D phased array as an example. The delay of chips was measured. The beam scanning characteristics of 2-D phased array antenna were simulated and analyzed for the measured delay. The results show that TDD can satisfy the beam pointing requirement of PAA (angle error is less than 0.5°). The use of integrated optics technology greatly reduces the volume and the cost of the system. This study provides a feasible method for realizing TDD network of large-scale 2-D PAA.
In order to realize optical true time-delay(TDD) system of large-scale 2-D phased array antenna(PAA), a binary silicon-based integrated binary optical delay line technology based on silicon-based photonics was adopted. A 2-D PAA N×N TDD network was proposed. By using the symmetry of 2-D PAA structure and the independent control of row and column delays, the complexity of TDD networks can be reduced to (N-1)/2 (when N is odd) or N/2 (when N is even). Delay control scheme and the design of integrated delay chip were analyzed theoretically. Four kinds of silicon-based binary TDD chips were designed and implemented by taking 8×8 2-D phased array as an example. The delay of chips was measured. The beam scanning characteristics of 2-D phased array antenna were simulated and analyzed for the measured delay. The results show that TDD can satisfy the beam pointing requirement of PAA (angle error is less than 0.5°). The use of integrated optics technology greatly reduces the volume and the cost of the system. This study provides a feasible method for realizing TDD network of large-scale 2-D PAA.
2019, 43(5): 672-675.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.016
Abstract:
In order to realize wavelength tunability of mode-locked fiber laser, a passively mode-locked ytterbium-doped fiber laser with ring cavity was constructed with a semiconductor saturable absorber mirror (SESAM). Without any polarization controllers and tunable filters in the cavity, by changing the distance between the end face of the optical fiber jumper and the SESAM, the stable tunability of the spectrum was achieved between 1029.5nm and 1042.7nm. The fundamental frequency repetition rate was 18.0MHz, the pulse width was 130ps, and the signal-to-noise ratio of mode-locked pulse was 44dB. The results show that, the mode-locked fiber laser has a high signal-to-noise ratio and a wide tunable range. This study provides an important reference for the development of tunable passively mode-locked fiber lasers.
In order to realize wavelength tunability of mode-locked fiber laser, a passively mode-locked ytterbium-doped fiber laser with ring cavity was constructed with a semiconductor saturable absorber mirror (SESAM). Without any polarization controllers and tunable filters in the cavity, by changing the distance between the end face of the optical fiber jumper and the SESAM, the stable tunability of the spectrum was achieved between 1029.5nm and 1042.7nm. The fundamental frequency repetition rate was 18.0MHz, the pulse width was 130ps, and the signal-to-noise ratio of mode-locked pulse was 44dB. The results show that, the mode-locked fiber laser has a high signal-to-noise ratio and a wide tunable range. This study provides an important reference for the development of tunable passively mode-locked fiber lasers.
2019, 43(5): 676-680.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.017
Abstract:
In order to prove that the non-destructive detection of apple surface defect combining optical fiber spectroscopy with pattern recognition was effective, an optical fiber spectrum acquisition system was used to collect spectral data of apples with and without surface defect. Standard normal variation (SNV) and first derivative were used to preprocess the original spectral data. Principal component analysis (PCA) was used to reduce the dimension of the pre-processed spectral data to extract the characteristic spectra of apples with surface defect. By using k nearest neighbor (KNN) pattern recognition method and partial least squares discriminant analysis method, recognition model of apple defect was established. The results show that, the first eight principal components with cumulative contribution over 99% are selected as the characteristic spectral data of the sample set by using principal component analysis and the dimensionality reduction of spectral data is well realized. By using first order derivative+KNN recognition model for correction set and SNV+KNN recognition model for prediction concentration, the recognition rate of normal apples and defected apples is 96.0%. The feasibility of non-destructive detection of apple surface defect based on optical fiber spectroscopy and pattern recognition is verified.
In order to prove that the non-destructive detection of apple surface defect combining optical fiber spectroscopy with pattern recognition was effective, an optical fiber spectrum acquisition system was used to collect spectral data of apples with and without surface defect. Standard normal variation (SNV) and first derivative were used to preprocess the original spectral data. Principal component analysis (PCA) was used to reduce the dimension of the pre-processed spectral data to extract the characteristic spectra of apples with surface defect. By using k nearest neighbor (KNN) pattern recognition method and partial least squares discriminant analysis method, recognition model of apple defect was established. The results show that, the first eight principal components with cumulative contribution over 99% are selected as the characteristic spectral data of the sample set by using principal component analysis and the dimensionality reduction of spectral data is well realized. By using first order derivative+KNN recognition model for correction set and SNV+KNN recognition model for prediction concentration, the recognition rate of normal apples and defected apples is 96.0%. The feasibility of non-destructive detection of apple surface defect based on optical fiber spectroscopy and pattern recognition is verified.
2019, 43(5): 681-685.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.018
Abstract:
In order to improve the effect of laser technology in the treatment of pigmentary diseases and other biomedical application, 1064nm/ 532nm/ 570nm three-wavelength lasers were developed. Electro-optic Q-switched Nd:YAG laser was used to obtain 1064nm pulse laser with narrow pulse width of 11ns. Output of 532nm laser was obtained by using KTP non-linear crystal for optical extra-cavity frequency doubling. With solid dye block as laser gain medium and frequency doubling light as pump light, yellow light output with a central wavelength of 570nm was obtained, and the light-to-light conversion efficiency was 61.3%. The results show that, by changing the injection voltage of xenon lamp, output characteristics of 1064nm laser pulse can be adjusted. By increasing the cavity length of the solid dye laser, output spectral characteristics of the dye laser can be adjusted. The research results are of great significance to the flexible application of lasers.
In order to improve the effect of laser technology in the treatment of pigmentary diseases and other biomedical application, 1064nm/ 532nm/ 570nm three-wavelength lasers were developed. Electro-optic Q-switched Nd:YAG laser was used to obtain 1064nm pulse laser with narrow pulse width of 11ns. Output of 532nm laser was obtained by using KTP non-linear crystal for optical extra-cavity frequency doubling. With solid dye block as laser gain medium and frequency doubling light as pump light, yellow light output with a central wavelength of 570nm was obtained, and the light-to-light conversion efficiency was 61.3%. The results show that, by changing the injection voltage of xenon lamp, output characteristics of 1064nm laser pulse can be adjusted. By increasing the cavity length of the solid dye laser, output spectral characteristics of the dye laser can be adjusted. The research results are of great significance to the flexible application of lasers.
2019, 43(5): 686-690.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.019
Abstract:
Traditional wireless communication will inevitably interfere with signals in electromagnetic sensitive scenarios. In order not to affect the stability and reliability of communication systems, combined with insensitive characteristic of visible light to electromagnetic field, a smart and lighting system with visible light as information carrier was built in electromagnetic sensitive environment. Firstly, 3-D space of 0.5m×0.5m×0.3m was used as room model and reasonable layout optimization method of indoor light source was carried out to make it meet the international indoor lighting standards. Secondly, the upstream and downlink of system and the signal frame structure were designed. The stable information transmission was realized. Finally, the physical model of the system was built and the system was debugged. The results show that the system can stably realize real-time monitoring and data transmission of lighting and indoor environment parameters. Bit error rate is less than 10-6. It can stably communicate for more than 10h. This study provides a reference for the layout parameters of large scenes.
Traditional wireless communication will inevitably interfere with signals in electromagnetic sensitive scenarios. In order not to affect the stability and reliability of communication systems, combined with insensitive characteristic of visible light to electromagnetic field, a smart and lighting system with visible light as information carrier was built in electromagnetic sensitive environment. Firstly, 3-D space of 0.5m×0.5m×0.3m was used as room model and reasonable layout optimization method of indoor light source was carried out to make it meet the international indoor lighting standards. Secondly, the upstream and downlink of system and the signal frame structure were designed. The stable information transmission was realized. Finally, the physical model of the system was built and the system was debugged. The results show that the system can stably realize real-time monitoring and data transmission of lighting and indoor environment parameters. Bit error rate is less than 10-6. It can stably communicate for more than 10h. This study provides a reference for the layout parameters of large scenes.
2019, 43(5): 691-696.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.020
Abstract:
In order to make full use of 3-D spatial information in continuous visual images and solve the positioning problem of unmanned aerial vehicles(UAV) during autonomous landing, based on the principle of dense 3-D point cloud method and optical flow method, a localization method based on the image space of the same object at different time was proposed. By means of theoretical calculation and graphic annotation, and calculating the movement of a single pixel and the whole image, the deformations and quantities of continuous frame images were decomposed into spatial relative motion information of UAV and reference objects. Combining with the known motion parameters of the reference object, the position and attitude information of UAV was calculated. The spatial positioning method of UAV based on optical vision image was completed. This study provides a reference for the vision system to independently realize spatial positioning in the process of UAV landing and recovery.
In order to make full use of 3-D spatial information in continuous visual images and solve the positioning problem of unmanned aerial vehicles(UAV) during autonomous landing, based on the principle of dense 3-D point cloud method and optical flow method, a localization method based on the image space of the same object at different time was proposed. By means of theoretical calculation and graphic annotation, and calculating the movement of a single pixel and the whole image, the deformations and quantities of continuous frame images were decomposed into spatial relative motion information of UAV and reference objects. Combining with the known motion parameters of the reference object, the position and attitude information of UAV was calculated. The spatial positioning method of UAV based on optical vision image was completed. This study provides a reference for the vision system to independently realize spatial positioning in the process of UAV landing and recovery.
2019, 43(5): 697-701.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.021
Abstract:
In order to accurately measure volume fraction of the escaping ammonia at high temperature, tunable diode laser absorption spectroscopy, wavelength modulation spectroscopy (WMS) and long-path technology were used. A set of miniaturized measurement instrument for escaped ammonia gas at high temperature was developed. In order to reduce the adsorption effect of escaping ammonia and improve the detection sensitivity, a new type of sample absorption cell with high temperature and long optical path was developed. On the basis of the laser driving module developed earlier, phase-locked loop chip 74HC4046 was used as an adjustable sinusoidal modulation signal source. EPM7064 was used as phase shifting and frequency doubling logic control chip. At the same time, two AD630 chips were used as simultaneous demodulation multiplier of the first demodulation (WMS-1f) and the second demodulation (WMS-2f). The synchronous demodulation of 1f and 2f absorption signals was realized. In addition, STM32F429 was used as main controller and the demodulated and filtered signal was input to AD7606 for analog-to-digital conversion. Digital filtering and volume fraction inversion were performed. The results show that linear fitting coefficients of volume fraction of ammonia gas with WMS-1f amplitude, WMS-2f amplitude and the normalized amplitude of WMS-2f/WMS-1f are 0.998, 0.997 and 0.998, respectively. Allen variance shows that when the optimization time is 228s, the lowest volume fraction is 0.496×10-6. In the range of volume fraction 20×10-6~100×10-6, the measurement error is less than ±2%. The instrument can provide high precision raw data for high temperature measurement of ammonia escaping from coal-fired power plants.
In order to accurately measure volume fraction of the escaping ammonia at high temperature, tunable diode laser absorption spectroscopy, wavelength modulation spectroscopy (WMS) and long-path technology were used. A set of miniaturized measurement instrument for escaped ammonia gas at high temperature was developed. In order to reduce the adsorption effect of escaping ammonia and improve the detection sensitivity, a new type of sample absorption cell with high temperature and long optical path was developed. On the basis of the laser driving module developed earlier, phase-locked loop chip 74HC4046 was used as an adjustable sinusoidal modulation signal source. EPM7064 was used as phase shifting and frequency doubling logic control chip. At the same time, two AD630 chips were used as simultaneous demodulation multiplier of the first demodulation (WMS-1f) and the second demodulation (WMS-2f). The synchronous demodulation of 1f and 2f absorption signals was realized. In addition, STM32F429 was used as main controller and the demodulated and filtered signal was input to AD7606 for analog-to-digital conversion. Digital filtering and volume fraction inversion were performed. The results show that linear fitting coefficients of volume fraction of ammonia gas with WMS-1f amplitude, WMS-2f amplitude and the normalized amplitude of WMS-2f/WMS-1f are 0.998, 0.997 and 0.998, respectively. Allen variance shows that when the optimization time is 228s, the lowest volume fraction is 0.496×10-6. In the range of volume fraction 20×10-6~100×10-6, the measurement error is less than ±2%. The instrument can provide high precision raw data for high temperature measurement of ammonia escaping from coal-fired power plants.
2019, 43(5): 702-707.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.022
Abstract:
The measurement of the size of the atomized field is of great significance for testing and evaluating the spray performance. It is very important to summarize and analyze the technical means of optical particle size measurement. Firstly, the basic principle of spray and mathematical representation of particle size are introduced. The principles and characteristics of the mainstream and emerging optical methods of particle size measurement, such as light scattering, structured laser illumination planar imaging, phase Doppler analyzer, laser holography and dual spectral imaging, are discussed in detail. At the same time, the typical applications of these testing methods are listed. On this basis, the problems existing in the spray field test are summarized and compared respectively, and the specific suggestions on how to select the test method properly are put forward.
The measurement of the size of the atomized field is of great significance for testing and evaluating the spray performance. It is very important to summarize and analyze the technical means of optical particle size measurement. Firstly, the basic principle of spray and mathematical representation of particle size are introduced. The principles and characteristics of the mainstream and emerging optical methods of particle size measurement, such as light scattering, structured laser illumination planar imaging, phase Doppler analyzer, laser holography and dual spectral imaging, are discussed in detail. At the same time, the typical applications of these testing methods are listed. On this basis, the problems existing in the spray field test are summarized and compared respectively, and the specific suggestions on how to select the test method properly are put forward.
2019, 43(5): 708-712.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.023
Abstract:
In order to slow down oxidation of silver particles, improve stability and maintain high signal intensity, silver particles were coated with graphene. An experimental study was carried out to slow down the oxidation rate of silver particles by using ultra-thin graphene. In the experiment, the concentration of R6G solution as low as 10-11mol/L could still be detected after the substrate was placed for one month. The results show that the presence of graphene makes the graphene/silver particle composite structure possess both electromagnetic and chemical enhancement mechanisms. The detection sensitivity of the substrate is improved. The enhancement effect of the basement has nearly doubled with the decay rate of time. The stability of Raman substrate is improved. This method is economical and simple. It can be widely applied to various silver-based Raman substrates and will not destroy the original structure of the base.
In order to slow down oxidation of silver particles, improve stability and maintain high signal intensity, silver particles were coated with graphene. An experimental study was carried out to slow down the oxidation rate of silver particles by using ultra-thin graphene. In the experiment, the concentration of R6G solution as low as 10-11mol/L could still be detected after the substrate was placed for one month. The results show that the presence of graphene makes the graphene/silver particle composite structure possess both electromagnetic and chemical enhancement mechanisms. The detection sensitivity of the substrate is improved. The enhancement effect of the basement has nearly doubled with the decay rate of time. The stability of Raman substrate is improved. This method is economical and simple. It can be widely applied to various silver-based Raman substrates and will not destroy the original structure of the base.
Super-resolution reconstruction of remote sensing images based on the improved point spread function
2019, 43(5): 713-718.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.024
Abstract:
In order to improve the quality of remote sensing image reconstruction in spatial domain, point spread function of improved projection onto convex set (POCS) algorithm was adopted and an improved POCS super-resolution reconstruction algorithm was proposed. Firstly, the basic principle and implementation steps of POCS algorithm were given. On this basis, the algorithm was improved and the reconstructed high-resolution initial frames were detected on edge. The improved point spread function (PSF) was applied to the detected edge pixels. The horizontal and vertical direction coefficients of PSF corresponding to the pixels at the edge were set with different weights according to the change of the slope of the edge. Finally, two sets of data sets were used to verify the effectiveness of the improved POCS algorithm. The results show that the improved POCS algorithm effectively improves the effect of image reconstruction. The average absolute errors of two groups increase by 0.79% and 0.26%, respectively. It achieves the goal of improving the quality of image reconstruction. The algorithm has good practical application value.
In order to improve the quality of remote sensing image reconstruction in spatial domain, point spread function of improved projection onto convex set (POCS) algorithm was adopted and an improved POCS super-resolution reconstruction algorithm was proposed. Firstly, the basic principle and implementation steps of POCS algorithm were given. On this basis, the algorithm was improved and the reconstructed high-resolution initial frames were detected on edge. The improved point spread function (PSF) was applied to the detected edge pixels. The horizontal and vertical direction coefficients of PSF corresponding to the pixels at the edge were set with different weights according to the change of the slope of the edge. Finally, two sets of data sets were used to verify the effectiveness of the improved POCS algorithm. The results show that the improved POCS algorithm effectively improves the effect of image reconstruction. The average absolute errors of two groups increase by 0.79% and 0.26%, respectively. It achieves the goal of improving the quality of image reconstruction. The algorithm has good practical application value.
2019, 43(5): 719-723.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.025
Abstract:
In order to study the B2Σ+~X2Σ+ spectra of CN radical and temperature under different conditions, laser-induced breakdown spectroscopy was used to break high purity graphite in air environment and produce CN free radicals. Emission spectra of B2Σ+~X2Σ+ were measured by high resolution spectrometer. The spectra of CN radicals under different conditions were studied by changing laser energy and laser focus position. The results show that, when laser energy is tuned from 30mJ to 50mJ and the increasing step size is 5mJ, spectral intensity increases with the increase of laser energy. When single pulse energy is 50mJ, spectral intensity reaches its maximum. In addition, when the distance between the upper surface of graphite and laser focal point is 8mm, signal-to-noise ratio reaches the maximum. LIFBASE software is used to fit the spectral data. The vibration temperature of CN radical is about 104K. The rotating temperature is about 4000K. Vibration temperature of CN radicals decreases and rotational temperature increases with the increase of distance. These results play an important role in studying cosmic stars and exploring high temperature chemical reaction.
In order to study the B2Σ+~X2Σ+ spectra of CN radical and temperature under different conditions, laser-induced breakdown spectroscopy was used to break high purity graphite in air environment and produce CN free radicals. Emission spectra of B2Σ+~X2Σ+ were measured by high resolution spectrometer. The spectra of CN radicals under different conditions were studied by changing laser energy and laser focus position. The results show that, when laser energy is tuned from 30mJ to 50mJ and the increasing step size is 5mJ, spectral intensity increases with the increase of laser energy. When single pulse energy is 50mJ, spectral intensity reaches its maximum. In addition, when the distance between the upper surface of graphite and laser focal point is 8mm, signal-to-noise ratio reaches the maximum. LIFBASE software is used to fit the spectral data. The vibration temperature of CN radical is about 104K. The rotating temperature is about 4000K. Vibration temperature of CN radicals decreases and rotational temperature increases with the increase of distance. These results play an important role in studying cosmic stars and exploring high temperature chemical reaction.
2019, 43(5): 724-728.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.026
Abstract:
In order to optimize beam quality of high power slab lasers, the oscillation of some high-order modes in the cavity was limited by increasing the size of unilateral fundamental mode beam. For semiconductor side-pumped slab lasers, horizontal and vertical thermal focal lengths of the laser under pumping were measured. The equivalent model of thermal lens was established. By using flat-flat cavity as reference, a flat-concave cavity with enlarged dimension of unilateral fundamental modes in both horizontal and vertical directions was designed. It was verified that, for slab lasers with fixed cross-section size of laser medium, expanding the size of one-sided fundamental mode can limit the higher-order mode and optimize the beam quality. A method for further optimizing the performance of slab lasers was proposed. The results show that, when the length of flat-concave cavity is 370mm and the output power is 59.9W, horizontal M2 factor is significantly optimized from 115.6 for flat-flat cavity to 32.9 and vertical M2 factor is significantly optimized from 116.4 to 60.9. This research has practical significance for obtaining high quality output of slab lasers and the related application.
In order to optimize beam quality of high power slab lasers, the oscillation of some high-order modes in the cavity was limited by increasing the size of unilateral fundamental mode beam. For semiconductor side-pumped slab lasers, horizontal and vertical thermal focal lengths of the laser under pumping were measured. The equivalent model of thermal lens was established. By using flat-flat cavity as reference, a flat-concave cavity with enlarged dimension of unilateral fundamental modes in both horizontal and vertical directions was designed. It was verified that, for slab lasers with fixed cross-section size of laser medium, expanding the size of one-sided fundamental mode can limit the higher-order mode and optimize the beam quality. A method for further optimizing the performance of slab lasers was proposed. The results show that, when the length of flat-concave cavity is 370mm and the output power is 59.9W, horizontal M2 factor is significantly optimized from 115.6 for flat-flat cavity to 32.9 and vertical M2 factor is significantly optimized from 116.4 to 60.9. This research has practical significance for obtaining high quality output of slab lasers and the related application.
2019, 43(5): 729-734.
doi: 10.7510/jgjs.issn.1001-3806.2019.05.027
Abstract:
During the transmission of femtosecond laser pulses, a long-distance self-guided light channel is formed because of the interaction between Kerr self-focusing and plasma defocusing. This process is called femtosecond laser filamentation. The fluorescence radiation induced by femtosecond laser filamentation in flames provides new possibility for combustion diagnosis. It provides useful information for understanding combustion process, improving combustion efficiency and reducing pollutant generation. Aiming at the application of femtosecond laser filamentation-induced fluorescence radiation in combustion diagnosis, the propagation characteristics and filamentation dynamics of femtosecond laser in flame are introduced. The mechanism of femtosecond laser filamentation-induced non-linear spectroscopy and its application in diagnosis of high temperature combustion field are summarized. The challenges and application prospects of femtosecond laser filamentation in this field are also discussed.
During the transmission of femtosecond laser pulses, a long-distance self-guided light channel is formed because of the interaction between Kerr self-focusing and plasma defocusing. This process is called femtosecond laser filamentation. The fluorescence radiation induced by femtosecond laser filamentation in flames provides new possibility for combustion diagnosis. It provides useful information for understanding combustion process, improving combustion efficiency and reducing pollutant generation. Aiming at the application of femtosecond laser filamentation-induced fluorescence radiation in combustion diagnosis, the propagation characteristics and filamentation dynamics of femtosecond laser in flame are introduced. The mechanism of femtosecond laser filamentation-induced non-linear spectroscopy and its application in diagnosis of high temperature combustion field are summarized. The challenges and application prospects of femtosecond laser filamentation in this field are also discussed.
