Map
WeChat
Email alert
RSS2018 Vol. 42, No. 5
Display Method:
[Abstract]
[PDF 272KB]
2018, 42(5): 583-587.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.001
[FullText HTML]
Abstract:
Coaxial auxiliary gas blowing structure has important effect on the efficiency of deep hole machining by femtosecond laser, but there is poor effect of slag removal in the process. In order to improve the capacity of slag removal, ANSYS CFD software was used to simulate the distribution of flow field with coaxial gas blowing, paraxial gas blowing and double-channel gas blowing. Experimental platform of double-channel auxiliary gas blowing was designed. After theoretical analysis and experimental verification, the distribution of dynamic flow field and velocity vector of micropore inner and around the micropores were obtained. The hole morphologies were obtained after micropore treatment assisted by coaxial, paraxial and double-channel gas blowing structures. The results show that double-channel auxiliary gas blowing can not only improve processing efficiency but also help to clean the workpiece surface. It is of great significance to the realization of high efficiency deep hole processing by femtosecond laser.
Coaxial auxiliary gas blowing structure has important effect on the efficiency of deep hole machining by femtosecond laser, but there is poor effect of slag removal in the process. In order to improve the capacity of slag removal, ANSYS CFD software was used to simulate the distribution of flow field with coaxial gas blowing, paraxial gas blowing and double-channel gas blowing. Experimental platform of double-channel auxiliary gas blowing was designed. After theoretical analysis and experimental verification, the distribution of dynamic flow field and velocity vector of micropore inner and around the micropores were obtained. The hole morphologies were obtained after micropore treatment assisted by coaxial, paraxial and double-channel gas blowing structures. The results show that double-channel auxiliary gas blowing can not only improve processing efficiency but also help to clean the workpiece surface. It is of great significance to the realization of high efficiency deep hole processing by femtosecond laser.
2018, 42(5): 588-592.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.002
Abstract:
Because of good flexibility, fast speed and high measurement precision, airborne laser bathymetry technology has gradually replaced the traditional method of measuring the depth of water and plays an important role in depth measurement of water in the river and offshore waters, as well as the mapping of underwater topography and geomorphology. Airborne laser bathymetry technology is introduced. Working principle of airborne laser bathymetry system and two main methods of signal processing are expounded. Two methods and the latest application research are summarized. Key research techniques of airborne laser bathymetry and future development are summed up and prospected. The data processing methods for echo signal in the future are explained.
Because of good flexibility, fast speed and high measurement precision, airborne laser bathymetry technology has gradually replaced the traditional method of measuring the depth of water and plays an important role in depth measurement of water in the river and offshore waters, as well as the mapping of underwater topography and geomorphology. Airborne laser bathymetry technology is introduced. Working principle of airborne laser bathymetry system and two main methods of signal processing are expounded. Two methods and the latest application research are summarized. Key research techniques of airborne laser bathymetry and future development are summed up and prospected. The data processing methods for echo signal in the future are explained.
Research of SF6 detection by means of differential photoacoustic spectroscopy with tunable CO2 laser
2018, 42(5): 593-598.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.003
Abstract:
In order to monitor SF6 gas concentration in electric power site effectively, based on wavelength tunable CO2 laser, a set of SF6 trace gas detection system under atmospheric environment was designed by means of photoacoustic spectroscopy gas detection technology. Differential photoacoustic spectroscopy technique was proposed to improve detection sensitivity of photoacoustic system. The results show that resonant center frequency of the designed SF6 gas detection photoacoustic system is 1066Hz, quality factor is 32.04 and photoacoustic pool constant is 89.74 Pa·m·W-1. Sensitivity of SF6 gas detection at laser spectral line 10P12 is 0.06×10-6(volume fraction) by using single spectrum photoacoustic method. Sensitivity of photoacoustic system at 10P12 and 10P16 and at 3W modulated light increases to 0.02×10-6(volume fraction) after using differential photoacoustic spectroscopy gas technology. Differential photoacoustic spectroscopy can effectively reduce noise effect and enhance the sensitivity of photoacoustic detection system. It has practical value.
In order to monitor SF6 gas concentration in electric power site effectively, based on wavelength tunable CO2 laser, a set of SF6 trace gas detection system under atmospheric environment was designed by means of photoacoustic spectroscopy gas detection technology. Differential photoacoustic spectroscopy technique was proposed to improve detection sensitivity of photoacoustic system. The results show that resonant center frequency of the designed SF6 gas detection photoacoustic system is 1066Hz, quality factor is 32.04 and photoacoustic pool constant is 89.74 Pa·m·W-1. Sensitivity of SF6 gas detection at laser spectral line 10P12 is 0.06×10-6(volume fraction) by using single spectrum photoacoustic method. Sensitivity of photoacoustic system at 10P12 and 10P16 and at 3W modulated light increases to 0.02×10-6(volume fraction) after using differential photoacoustic spectroscopy gas technology. Differential photoacoustic spectroscopy can effectively reduce noise effect and enhance the sensitivity of photoacoustic detection system. It has practical value.
2018, 42(5): 599-604.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.004
Abstract:
In order to improve the performance of cladding layer, image processing technology was used to detect the temperature field of laser molten pool. A color CCD industrial camera was used to collect the image data and median filtering method was used to remove the image noise. After processing, the image data were calibrated by high-precision HG-2 standard high temperature blackbody furnace, and temperature fitting formula was obtained. The original images were transformed into pseudo color images by image processing, which reflected temperature distribution and change rule in each area of the molten pool. The results show that the maximum error between the temperature calculated by the fitting formula and the actual temperature is 1.23%. The detection precision meets the demand of the field application, and temperature detection of molten pool is realized.
In order to improve the performance of cladding layer, image processing technology was used to detect the temperature field of laser molten pool. A color CCD industrial camera was used to collect the image data and median filtering method was used to remove the image noise. After processing, the image data were calibrated by high-precision HG-2 standard high temperature blackbody furnace, and temperature fitting formula was obtained. The original images were transformed into pseudo color images by image processing, which reflected temperature distribution and change rule in each area of the molten pool. The results show that the maximum error between the temperature calculated by the fitting formula and the actual temperature is 1.23%. The detection precision meets the demand of the field application, and temperature detection of molten pool is realized.
2018, 42(5): 605-610.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.005
Abstract:
In order to obtain a better decision method of laser cladding sequence selection in laser cladding remanufacturing process, finite element method was used to analyze transient solution of temperature field of multichannel laser cladding heat transfer model of flat substrate. The reliability of whole numerical simulation process was verified by temperature measurement system based on thermocouple. An evaluation selection method was proposed. Numerical simulation was used to analyze and evaluate the transient temperature field of the matrix, and select laser scanning sequence during the cladding process according to evaluation criteria. It was the trajectory optimization method. The results show that experimental hardness data are 625.38HV, 620.58HV, 623.34HV, 680.09HV, 673.58HV and 683.01HV of one way successive method and evaluation selection method respectively. The average deformation values are 0.9722mm and 0.6458mm respectively. Evaluation selection method has the most uniform temperature field and the maximum temperature gradient around the pool, which can produce larger cladding layer hardness, smaller microstructure scale and smaller measurement deformation. This method provides an important reference value for sequential selection of laser cladding.
In order to obtain a better decision method of laser cladding sequence selection in laser cladding remanufacturing process, finite element method was used to analyze transient solution of temperature field of multichannel laser cladding heat transfer model of flat substrate. The reliability of whole numerical simulation process was verified by temperature measurement system based on thermocouple. An evaluation selection method was proposed. Numerical simulation was used to analyze and evaluate the transient temperature field of the matrix, and select laser scanning sequence during the cladding process according to evaluation criteria. It was the trajectory optimization method. The results show that experimental hardness data are 625.38HV, 620.58HV, 623.34HV, 680.09HV, 673.58HV and 683.01HV of one way successive method and evaluation selection method respectively. The average deformation values are 0.9722mm and 0.6458mm respectively. Evaluation selection method has the most uniform temperature field and the maximum temperature gradient around the pool, which can produce larger cladding layer hardness, smaller microstructure scale and smaller measurement deformation. This method provides an important reference value for sequential selection of laser cladding.
2018, 42(5): 611-616.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.006
Abstract:
In order to study effect of parameters of radio frequency(RF) intensity modulation laser signal sources, especially modulation index, on anti-atmospheric turbulence interference, phase change of the RF intensity modulation laser signal passing through atmospheric turbulence was analyzed theoretically and verified experimentally. A Mach-Zehnder interferometer was built, and two interference beams were single frequency light without modulation and dual frequency light with modulation respectively. The contrast of interference fringes was taken as the criterion of signal phase fluctuation. The contrast of interference fringes with the change of modulation depth were compared under different atmospheric turbulence conditions.The atmospheric turbulence was generated by the simulation of spatial light modulator. The contrast of interference fringes with and without atmospheric turbulence was compared under four modulation depths of 26.32%, 42.04%, 67.59% and 85.04%, respectively. The results show that, the deeper the modulation level of modulation signal is, the stronger its ability to resist atmospheric turbulence is. The conclusion has some reference significance for the selection of dual frequency lidar light sources.
In order to study effect of parameters of radio frequency(RF) intensity modulation laser signal sources, especially modulation index, on anti-atmospheric turbulence interference, phase change of the RF intensity modulation laser signal passing through atmospheric turbulence was analyzed theoretically and verified experimentally. A Mach-Zehnder interferometer was built, and two interference beams were single frequency light without modulation and dual frequency light with modulation respectively. The contrast of interference fringes was taken as the criterion of signal phase fluctuation. The contrast of interference fringes with the change of modulation depth were compared under different atmospheric turbulence conditions.The atmospheric turbulence was generated by the simulation of spatial light modulator. The contrast of interference fringes with and without atmospheric turbulence was compared under four modulation depths of 26.32%, 42.04%, 67.59% and 85.04%, respectively. The results show that, the deeper the modulation level of modulation signal is, the stronger its ability to resist atmospheric turbulence is. The conclusion has some reference significance for the selection of dual frequency lidar light sources.
2018, 42(5): 617-621.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.007
Abstract:
In order to optimize the structure parameters of the device, the period, height and duty ratio of grating structure were taken as the optimized particles. By using particle swarm optimization algorithm and rigorous coupled wave analysis algorithm, fitness values of the particles in particle swarm were compared. After theoretical analysis and simulative optimization of the structure of metal-medium grating filter, the optimal parameters were found in a certain range. The results show that, according to MATLAB simulation results, structure parameters are optimized:period is 0.300μm, the thickness of metal grating is 0.035μm, the thickness of dielectric grating is 0.400μm and grating duty ratio is 0.77. When TM light is vertically incident, the transmission rate of structure to red light in 0.65μm wavelength is 80.27% and the transmission rate of the side bands is less than 15%. This structure achieves high transmission to specific wavelength light and then achieves light filtering. This structure provides the reference for the design, fabrication and practical application of sub-wavelength gratings.
In order to optimize the structure parameters of the device, the period, height and duty ratio of grating structure were taken as the optimized particles. By using particle swarm optimization algorithm and rigorous coupled wave analysis algorithm, fitness values of the particles in particle swarm were compared. After theoretical analysis and simulative optimization of the structure of metal-medium grating filter, the optimal parameters were found in a certain range. The results show that, according to MATLAB simulation results, structure parameters are optimized:period is 0.300μm, the thickness of metal grating is 0.035μm, the thickness of dielectric grating is 0.400μm and grating duty ratio is 0.77. When TM light is vertically incident, the transmission rate of structure to red light in 0.65μm wavelength is 80.27% and the transmission rate of the side bands is less than 15%. This structure achieves high transmission to specific wavelength light and then achieves light filtering. This structure provides the reference for the design, fabrication and practical application of sub-wavelength gratings.
2018, 42(5): 622-626.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.008
Abstract:
In order to realize palladium free electroless nickel plating on the surface of the ceramic matrix, the mixed solution of 10g/L NiSO4·6H2O and 45g/L NaH2PO2 was used as activation solution and was coated on the surface of the matrix. The substrate was activated by laser scanning, and then electroless nickel was carried out. The effect of laser power, spot diameter and scanning rate on coating coverage was studied. The microstructure of coarsening, activation and plating was observed by a scanning electron microscope. The composition analysis of the substrate surface after activation and plating was analyzed. The adhesion, electrical conductivity and solderability of the coating were detected. The results show that, when laser power is 3W, the diameter of the spot is 2mm and scanning rate is 5mm/s, a layer of Ni particles with an average diameter of 0.1μm is generated on the substrate surface. The coating coverage is 100%. Micro surface of the coating is smooth and dense and the diameter of the cell is above 10μm. Mass fraction of P in plating layer is 0.0771, with good wear resistance and corrosion resistance for the amorphous structure. The coating has strong adhesion and good weldability. It is good conductor with the resistivity of 7.67×10-5Ω·cm. With low cost and pollution-free, the process can realize local electroless nickel plating on the surface of ceramic matrix. By controlling the motion of laser, all kinds of fine graphics can be deposited on the surface of the matrix. The process has a certain practical value.
In order to realize palladium free electroless nickel plating on the surface of the ceramic matrix, the mixed solution of 10g/L NiSO4·6H2O and 45g/L NaH2PO2 was used as activation solution and was coated on the surface of the matrix. The substrate was activated by laser scanning, and then electroless nickel was carried out. The effect of laser power, spot diameter and scanning rate on coating coverage was studied. The microstructure of coarsening, activation and plating was observed by a scanning electron microscope. The composition analysis of the substrate surface after activation and plating was analyzed. The adhesion, electrical conductivity and solderability of the coating were detected. The results show that, when laser power is 3W, the diameter of the spot is 2mm and scanning rate is 5mm/s, a layer of Ni particles with an average diameter of 0.1μm is generated on the substrate surface. The coating coverage is 100%. Micro surface of the coating is smooth and dense and the diameter of the cell is above 10μm. Mass fraction of P in plating layer is 0.0771, with good wear resistance and corrosion resistance for the amorphous structure. The coating has strong adhesion and good weldability. It is good conductor with the resistivity of 7.67×10-5Ω·cm. With low cost and pollution-free, the process can realize local electroless nickel plating on the surface of ceramic matrix. By controlling the motion of laser, all kinds of fine graphics can be deposited on the surface of the matrix. The process has a certain practical value.
2018, 42(5): 627-632.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.009
Abstract:
In order to select optimal detection spectrum for infrared warning satellites, a method of determining the detection spectrum based on the contrast between the target and background was adopted. In comprehensive consideration of the target, background, direction of detection and detector parameters, radiation intensity under different conditions, different observation angles and different wavelength ranges, various earth/atmospheric background radiation, the contrast between the HTV-2 aircraft target and background were analyzed theoretically and simulated under different conditions. The results show that, for HTV-2 like vehicles, at the observation of waist-level viewing, under the two conditions of 30km height, Ma=7 and 50km height, Ma=17, the contrast between the target and background is larger in the range of 2.65μm to 2.85μm. The results are of great reference value for the selection of spectrum in the detection of this kind of targets.
In order to select optimal detection spectrum for infrared warning satellites, a method of determining the detection spectrum based on the contrast between the target and background was adopted. In comprehensive consideration of the target, background, direction of detection and detector parameters, radiation intensity under different conditions, different observation angles and different wavelength ranges, various earth/atmospheric background radiation, the contrast between the HTV-2 aircraft target and background were analyzed theoretically and simulated under different conditions. The results show that, for HTV-2 like vehicles, at the observation of waist-level viewing, under the two conditions of 30km height, Ma=7 and 50km height, Ma=17, the contrast between the target and background is larger in the range of 2.65μm to 2.85μm. The results are of great reference value for the selection of spectrum in the detection of this kind of targets.
2018, 42(5): 633-637.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.010
Abstract:
In order to measure the line-width of distributed feedback(DFB) diode single mode semiconductor laser, novel optical fiber self-heterodyne measurement scheme based on Mach-Zehnder interference structure was adopted and a set of all fiber time-delay self-heterodyne measurement system was designed. After theoretical analysis, narrow band line-width measurement system with time-delay fiber length of 900m, 3000m and 6000m was set up. A DFB single mode laser source with center wavelength of 1550nm and nominal line-width of 800kHz was tested. The measured line-width values of laser were 951.566kHz, 832.471kHz and 802.221kHz respectively. The designed scheme is verified by simulation. The results show that, compared with the simulation results, narrowband line-width measurement system with the length of 6000m is optimal, and its error is within 3%, which proves the rationality and accuracy of self-heterodyne interference principle. All fiber frequency shift delay self-heterodyne method has advantages and practical value for measuring the line-width of DFB lasers.
In order to measure the line-width of distributed feedback(DFB) diode single mode semiconductor laser, novel optical fiber self-heterodyne measurement scheme based on Mach-Zehnder interference structure was adopted and a set of all fiber time-delay self-heterodyne measurement system was designed. After theoretical analysis, narrow band line-width measurement system with time-delay fiber length of 900m, 3000m and 6000m was set up. A DFB single mode laser source with center wavelength of 1550nm and nominal line-width of 800kHz was tested. The measured line-width values of laser were 951.566kHz, 832.471kHz and 802.221kHz respectively. The designed scheme is verified by simulation. The results show that, compared with the simulation results, narrowband line-width measurement system with the length of 6000m is optimal, and its error is within 3%, which proves the rationality and accuracy of self-heterodyne interference principle. All fiber frequency shift delay self-heterodyne method has advantages and practical value for measuring the line-width of DFB lasers.
2018, 42(5): 638-645.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.011
Abstract:
In order to enhance output power of a fiber laser, thulium doped fiber with large mode area was used to suppress the nonlinear effect. Optimizing parameters of a thulium-doped fiber in an inhomogeneous Bragg structure, a fiber with mode area of 719μm2 was obtained under the condition of single-mode transmission. Based on this fiber, a theoretical model for large mode area thulium-doped fiber amplifiers pumped by 793nm wavelength was established. Because large mode area fiber can reduce optical power density and suppress Stokes light power, compared with the ordinary single-mode fiber amplifier, this kind of fiber amplifiers under high pump power can get higher output power. The results show that, when pump power is 100W, compared with the conventional single-mode fiber, the conversion efficiency increases 5% and reaches 40%, and the output power reaches 41.01W. The research is of great value for design of actual thulium-doped fiber amplifiers.
In order to enhance output power of a fiber laser, thulium doped fiber with large mode area was used to suppress the nonlinear effect. Optimizing parameters of a thulium-doped fiber in an inhomogeneous Bragg structure, a fiber with mode area of 719μm2 was obtained under the condition of single-mode transmission. Based on this fiber, a theoretical model for large mode area thulium-doped fiber amplifiers pumped by 793nm wavelength was established. Because large mode area fiber can reduce optical power density and suppress Stokes light power, compared with the ordinary single-mode fiber amplifier, this kind of fiber amplifiers under high pump power can get higher output power. The results show that, when pump power is 100W, compared with the conventional single-mode fiber, the conversion efficiency increases 5% and reaches 40%, and the output power reaches 41.01W. The research is of great value for design of actual thulium-doped fiber amplifiers.
2018, 42(5): 646-650.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.012
Abstract:
In order to solve the problem of low precision of indoor location algorithm, a set of visible light indoor positioning device which has illuminating function at the same time was designed. First of all, the layout of the indoor light source was arranged according to international standard of illumination. Secondly, a visible light transceiver system of intensity modulation/direct modulation (IM/DM) and an indoor positioning system platform with STM32 as core processor were designed. Finally, the calibration of target coordinates and regions was realized by using the method of multi point calibration relative positioning. The results show that, under the conditions suitable for illumination, measurement error is less than 10cm. The measurement error of partial location area is 3cm or even 0cm. Error resolution is 0.1cm, and relative error is less than 10cm. The research provides a scheme for current indoor positioning technology.
In order to solve the problem of low precision of indoor location algorithm, a set of visible light indoor positioning device which has illuminating function at the same time was designed. First of all, the layout of the indoor light source was arranged according to international standard of illumination. Secondly, a visible light transceiver system of intensity modulation/direct modulation (IM/DM) and an indoor positioning system platform with STM32 as core processor were designed. Finally, the calibration of target coordinates and regions was realized by using the method of multi point calibration relative positioning. The results show that, under the conditions suitable for illumination, measurement error is less than 10cm. The measurement error of partial location area is 3cm or even 0cm. Error resolution is 0.1cm, and relative error is less than 10cm. The research provides a scheme for current indoor positioning technology.
2018, 42(5): 651-654.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.013
Abstract:
In order to investigate output power balance mechanism of Nd:YVO4 microchip dual-frequency lasers (DFL), the relationships among pump current, operating temperature and dual-mode wavelengths of microchip lasers were analyzed by means of experiments. With the increase of pump current of DFL, the balance of DFL power was re-achieved by lowering the temperature of laser crystal. Finally, the power-balanced temperature of DFL with different pump currents and the relationship between dual-frequency power product and pump current of DFL were obtained. The result shows that, the power-balanced temperature of DFL signal is negatively correlated with pump current sectionally, and dual frequency power product is positively correlated with pump current. It indicated that, power-balanced power-adjustable dual-frequency laser signal output can be achieved by changing pump current and controlling temperature.
In order to investigate output power balance mechanism of Nd:YVO4 microchip dual-frequency lasers (DFL), the relationships among pump current, operating temperature and dual-mode wavelengths of microchip lasers were analyzed by means of experiments. With the increase of pump current of DFL, the balance of DFL power was re-achieved by lowering the temperature of laser crystal. Finally, the power-balanced temperature of DFL with different pump currents and the relationship between dual-frequency power product and pump current of DFL were obtained. The result shows that, the power-balanced temperature of DFL signal is negatively correlated with pump current sectionally, and dual frequency power product is positively correlated with pump current. It indicated that, power-balanced power-adjustable dual-frequency laser signal output can be achieved by changing pump current and controlling temperature.
2018, 42(5): 655-658.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.014
Abstract:
In order to improve optical processing speed and the feasibility of optical realization in interference encryption technology, based on the idea of interference encryption principle and image processing method of grating filter, 4f system double image optical encryption technology based on grating filter was designed. The mature image additiion and subtraction 4f system based on grating filtering was used to transform two encrypting images into two real values of white noise. The feasibility and effectiveness of the method were verified by theoretical simulation. The results show that the method is simple, practical, safe and easy to implement.
In order to improve optical processing speed and the feasibility of optical realization in interference encryption technology, based on the idea of interference encryption principle and image processing method of grating filter, 4f system double image optical encryption technology based on grating filter was designed. The mature image additiion and subtraction 4f system based on grating filtering was used to transform two encrypting images into two real values of white noise. The feasibility and effectiveness of the method were verified by theoretical simulation. The results show that the method is simple, practical, safe and easy to implement.
2018, 42(5): 659-665.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.015
Abstract:
In order to optimize the phase difference of the all-optical logic gates, the phase difference of all-optical logic exclusive OR (XOR) gates was studied. Firstly, the refined sectionalized model was used simulate the dynamic process of quantum-dot semiconductor optical amplifier (QD-SOA). Secondly, the Newton method and the four-order Runge-Kutta method were used to solve the three-level transition rate equations and the light field transfer equations. Finally, an all-optical logic XOR gate based on quantum-dot semiconductor optical amplifier Mach-Zehnder interferometer (QD-SOA-MZI) was implemented. The influence of the length of the active regions, the maximum modal gain, input pump power and input pump pulse width on phase difference of probe signal through two arms of the interferometer was studied in detail. Moreover, the relationship between phase difference of the probe signal and output optical power was also discussed. The results show that, with the increase of the length of the active regions, the maximum modal gain and input pump power can lead to improve phase difference of probe signal through two arms of the interferometer. With the increase of input pump pulse width, phase difference of probe signal through two arms of the interferometer increases at first and then decreases. When the length of the active region is 2.0mm, the maximum modal gain is 3000m-1, the input pump power is 5dBm, and input pump pulse width is 1.0ps, the maximum phase difference of probe signal through two arms of the interferometer increases 0.3277π. Output optical power also can be improved by the increase of probe signal phase difference. Phase difference of the detected light can be increased by optimizing the parameters. Output light power increases with the increase of the phase difference of the probe. This study provides a reference for improving the quality of conversion signals.
In order to optimize the phase difference of the all-optical logic gates, the phase difference of all-optical logic exclusive OR (XOR) gates was studied. Firstly, the refined sectionalized model was used simulate the dynamic process of quantum-dot semiconductor optical amplifier (QD-SOA). Secondly, the Newton method and the four-order Runge-Kutta method were used to solve the three-level transition rate equations and the light field transfer equations. Finally, an all-optical logic XOR gate based on quantum-dot semiconductor optical amplifier Mach-Zehnder interferometer (QD-SOA-MZI) was implemented. The influence of the length of the active regions, the maximum modal gain, input pump power and input pump pulse width on phase difference of probe signal through two arms of the interferometer was studied in detail. Moreover, the relationship between phase difference of the probe signal and output optical power was also discussed. The results show that, with the increase of the length of the active regions, the maximum modal gain and input pump power can lead to improve phase difference of probe signal through two arms of the interferometer. With the increase of input pump pulse width, phase difference of probe signal through two arms of the interferometer increases at first and then decreases. When the length of the active region is 2.0mm, the maximum modal gain is 3000m-1, the input pump power is 5dBm, and input pump pulse width is 1.0ps, the maximum phase difference of probe signal through two arms of the interferometer increases 0.3277π. Output optical power also can be improved by the increase of probe signal phase difference. Phase difference of the detected light can be increased by optimizing the parameters. Output light power increases with the increase of the phase difference of the probe. This study provides a reference for improving the quality of conversion signals.
2018, 42(5): 666-672.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.016
Abstract:
In order to reduce the computational complexity of convolution neural network, improve the over-fitting phenomenon in the process of feature extraction and solve the problem that the classic network model can not effectively deal with large size images, deep feature extraction and classification recognition algorithm based on weighting and dimension reduction was adopted. Based on recognition contribution rate of two features, the results of dimensionality reduction of principal component analysis (PCA) and random projection (RP) method were fused with weighted average, then the results were provided to convolution neural network and the high-level features of image classification were extracted. Euclidean distance classifier was used to classify the recognition objects. After theoretical analysis and experimental verification, the results show that the weight ratio of PCA matrix and RP reduction matrix is 6:4, and the recognition rate is over 96% after the preprocess of data by weighting and dimension reduction. This algorithm improves the accuracy effectively, makes large size pictures having good recognition effect in deep learning network and improves the adaptability of network.
In order to reduce the computational complexity of convolution neural network, improve the over-fitting phenomenon in the process of feature extraction and solve the problem that the classic network model can not effectively deal with large size images, deep feature extraction and classification recognition algorithm based on weighting and dimension reduction was adopted. Based on recognition contribution rate of two features, the results of dimensionality reduction of principal component analysis (PCA) and random projection (RP) method were fused with weighted average, then the results were provided to convolution neural network and the high-level features of image classification were extracted. Euclidean distance classifier was used to classify the recognition objects. After theoretical analysis and experimental verification, the results show that the weight ratio of PCA matrix and RP reduction matrix is 6:4, and the recognition rate is over 96% after the preprocess of data by weighting and dimension reduction. This algorithm improves the accuracy effectively, makes large size pictures having good recognition effect in deep learning network and improves the adaptability of network.
2018, 42(5): 673-680.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.017
Abstract:
As one hot spot in the field of laser research, yellow lasers have achieved fruitful research results and extensive application. With the development of self-Raman crystal, which can be used as laser crystal and Raman crystal at the same time, the research upsurge of self-Raman yellow lasers has been set off gradually. The research progress of solid self-Raman yellow lasers in recent ten years is summarized. According to the way of laser operation, yellow lasers are divided into continuous lasers and pulsed lasers. By classifying and comparing the advantages and disadvantages of lasers with different working modes, it is clear that future research trend of self-Raman yellow laser would adopt multiple methods. The characteristics of compact structure, low threshold and so on will make yellow lasers have great potential in the field of biological medicine. Future research will focus on high conversion, high stability, low cost and miniaturization. The study provides the reference for the future research direction.
As one hot spot in the field of laser research, yellow lasers have achieved fruitful research results and extensive application. With the development of self-Raman crystal, which can be used as laser crystal and Raman crystal at the same time, the research upsurge of self-Raman yellow lasers has been set off gradually. The research progress of solid self-Raman yellow lasers in recent ten years is summarized. According to the way of laser operation, yellow lasers are divided into continuous lasers and pulsed lasers. By classifying and comparing the advantages and disadvantages of lasers with different working modes, it is clear that future research trend of self-Raman yellow laser would adopt multiple methods. The characteristics of compact structure, low threshold and so on will make yellow lasers have great potential in the field of biological medicine. Future research will focus on high conversion, high stability, low cost and miniaturization. The study provides the reference for the future research direction.
2018, 42(5): 681-686.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.018
Abstract:
Meta-surface is optical flat film based on sub-wavelength structure, which can regulate phase, amplitude and polarization of incident beam in sub-wavelength range. In order to replace the traditional surface optical elements, one new type of mata-surface was designed by using the transmission phase regulation theory and the generalized reflection law. Program simulation was carried out and the data of beam focused and regulated by the sub-wavelength structure were obtained. The results show that, when the length of long and short axis of elliptical element of mata-surface is longer, equivalent refractive index of material increases at the same time and the applicable wavelength range increases to 0.7μm~1.2μm. By optimizing the mata-surface structure parameters, phase regulation within wide wave band can be realized, and the optimization of the focused light field can be obtained. To a certain extent, it can replace traditional optical elements to realize optical focusing. The results have some reference value in super-resolution imaging and photolithography. It can simplify the optical path in some special demands that sub-wavelength structure can regulate the beams. Compared with the traditional optical elements, mata-surface has the advantages of thickness.
Meta-surface is optical flat film based on sub-wavelength structure, which can regulate phase, amplitude and polarization of incident beam in sub-wavelength range. In order to replace the traditional surface optical elements, one new type of mata-surface was designed by using the transmission phase regulation theory and the generalized reflection law. Program simulation was carried out and the data of beam focused and regulated by the sub-wavelength structure were obtained. The results show that, when the length of long and short axis of elliptical element of mata-surface is longer, equivalent refractive index of material increases at the same time and the applicable wavelength range increases to 0.7μm~1.2μm. By optimizing the mata-surface structure parameters, phase regulation within wide wave band can be realized, and the optimization of the focused light field can be obtained. To a certain extent, it can replace traditional optical elements to realize optical focusing. The results have some reference value in super-resolution imaging and photolithography. It can simplify the optical path in some special demands that sub-wavelength structure can regulate the beams. Compared with the traditional optical elements, mata-surface has the advantages of thickness.
2018, 42(5): 687-691.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.019
Abstract:
In order to improve the recycling precision and recycling rate of unmanned aerial vehicles (UAV) in complex environment, a precise recycling method of UAV based on laser terminal guidance was adopted. The principle and process of precise UAV recycling by means of laser terminal guidance were analyzed and verified. The relationship between the guide distance of UAV and laser guidance light radiation field and the relationship between yaw angle information of UAV departure and system precise recycling were discussed. The results show that in the range of rough guide distance of 1km to 2km from the landing point, keeping a constant laser guided field of 40m, the UAV can quickly enter the laser radiation field, adjust yaw angle information and improve the reliability of recycling. In the range of middle distance, the relationship between laser radiation field and landing distance changes linearly, which is beneficial for transferring from the rough guidance to the precise guidance. In the range of precise guide distance within 500m and constant laser guided field of 20m, the system can improve the precision of recycling. The scheme is applied to UAV recycling system, which can significantly improve the recycling precision of UAV in complex environment.
In order to improve the recycling precision and recycling rate of unmanned aerial vehicles (UAV) in complex environment, a precise recycling method of UAV based on laser terminal guidance was adopted. The principle and process of precise UAV recycling by means of laser terminal guidance were analyzed and verified. The relationship between the guide distance of UAV and laser guidance light radiation field and the relationship between yaw angle information of UAV departure and system precise recycling were discussed. The results show that in the range of rough guide distance of 1km to 2km from the landing point, keeping a constant laser guided field of 40m, the UAV can quickly enter the laser radiation field, adjust yaw angle information and improve the reliability of recycling. In the range of middle distance, the relationship between laser radiation field and landing distance changes linearly, which is beneficial for transferring from the rough guidance to the precise guidance. In the range of precise guide distance within 500m and constant laser guided field of 20m, the system can improve the precision of recycling. The scheme is applied to UAV recycling system, which can significantly improve the recycling precision of UAV in complex environment.
2018, 42(5): 692-698.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.020
Abstract:
Because spatial resolution of hyper-spectral images is low, a large number of the mixed pixels were in hyper-spectral images. The presence of the mixed pixels is one of the main reasons of the low accuracy of target classification in hyper-spectral images. Hyper spectral pixel unmixing is of great importance in hyper-spectral remote sensing image processing. Hyper-spectral unmixing is divided into two methods:linear and nonlinear spectral unmixing. Linear spectral unmixing has been studied most widely. Two steps of linear spectral mixing are summed up:firstly, spectral signals of ground objects in the pure pixels are extracted, that is, end-members are extracted. It is the key step. The weighted linear combination of end-members is used to unmix the spectral image of the mixed pixels, that is, the abundance inversion. Main progress of end-member extraction and abundances inversion is briefly introduced, and several typical algorithms for end-member extraction are introduced. Through summing-up, contrasting and analyzing, the characteristics of different endmember extraction methods are summarized. The prospect of hyperspectral unmixing is prospected.
Because spatial resolution of hyper-spectral images is low, a large number of the mixed pixels were in hyper-spectral images. The presence of the mixed pixels is one of the main reasons of the low accuracy of target classification in hyper-spectral images. Hyper spectral pixel unmixing is of great importance in hyper-spectral remote sensing image processing. Hyper-spectral unmixing is divided into two methods:linear and nonlinear spectral unmixing. Linear spectral unmixing has been studied most widely. Two steps of linear spectral mixing are summed up:firstly, spectral signals of ground objects in the pure pixels are extracted, that is, end-members are extracted. It is the key step. The weighted linear combination of end-members is used to unmix the spectral image of the mixed pixels, that is, the abundance inversion. Main progress of end-member extraction and abundances inversion is briefly introduced, and several typical algorithms for end-member extraction are introduced. Through summing-up, contrasting and analyzing, the characteristics of different endmember extraction methods are summarized. The prospect of hyperspectral unmixing is prospected.
2018, 42(5): 699-703.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.021
Abstract:
In order to reduce influence of polarization mode dispersion(PMD) on the quality of transmission signal, an optical circulator was applied in the front-end of the optical amplifier of the optical transmission network. The effect of PMD in optical transmission network was simulated. After PMD suppression, transmission eye diagram opened more obviously. Transmission performance of the system was improved to a certain extent.The PMD in the optical transmission network was suppressed to a certain extent, and the quality of signal was effectively improved. The results show that the bit error rate of PMD decreases about one time with and without the optical circulator. The optical circulator has a significant inhibitory effect on PMD in the optical transport network. The polarization delay at different transmission speeds is compensated equivalently with this scheme so that the PMD is compensated finally.
In order to reduce influence of polarization mode dispersion(PMD) on the quality of transmission signal, an optical circulator was applied in the front-end of the optical amplifier of the optical transmission network. The effect of PMD in optical transmission network was simulated. After PMD suppression, transmission eye diagram opened more obviously. Transmission performance of the system was improved to a certain extent.The PMD in the optical transmission network was suppressed to a certain extent, and the quality of signal was effectively improved. The results show that the bit error rate of PMD decreases about one time with and without the optical circulator. The optical circulator has a significant inhibitory effect on PMD in the optical transport network. The polarization delay at different transmission speeds is compensated equivalently with this scheme so that the PMD is compensated finally.
2018, 42(5): 704-708.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.022
Abstract:
In order to obtain tunable absorption spectra under TE wave, an absorber was designed based on plasma metamaterial. The absorption spectra and the distribution of surface current of the absorber were computed by means of full-wave simulation. The effect of structural parameters c, v and incident angle θ on absorption spectra was also discussed. The simulated results demonstrate that not only the tunable absorption spectra can be obtained in the proposed absorber but also the properties of absorption can be improved by exciting the different plasma resonance structures. Changing the structural parameters of c and v, the absorption bandwidth can be widened and its location can be tuned at same time. The incident angle θ has little effect on the absorption spectra. The proposed absorber has good angular stability.
In order to obtain tunable absorption spectra under TE wave, an absorber was designed based on plasma metamaterial. The absorption spectra and the distribution of surface current of the absorber were computed by means of full-wave simulation. The effect of structural parameters c, v and incident angle θ on absorption spectra was also discussed. The simulated results demonstrate that not only the tunable absorption spectra can be obtained in the proposed absorber but also the properties of absorption can be improved by exciting the different plasma resonance structures. Changing the structural parameters of c and v, the absorption bandwidth can be widened and its location can be tuned at same time. The incident angle θ has little effect on the absorption spectra. The proposed absorber has good angular stability.
2018, 42(5): 709-712.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.023
Abstract:
To study the influence of impurity particles on light propagation in air, a finite element method was used to analyze the distribution of light intensity at the boundary of impurity particles at the presence of multiple impurity particles. The intensity difference data between different particles was acquired. A general solution was provided to solve the problem of complex impurity particles. After theoretical analysis and experimental verification, the results show that, for sphere particles, while there are two impurity particles at the same time, the particles passing through the impurity present a trend from low to high, and the intensity reaches the maximum in the area where the impurity particles are in contact with each other. For cube impurity particles, the intensity distribution exhibits a strong fluctuation property, and the intensity of light is 100 times more than that of sphere impurity particles. The research model has strong portability and can be widely applied to lots of fields. This result is helpful for the subsequent development of light propagation in air.
To study the influence of impurity particles on light propagation in air, a finite element method was used to analyze the distribution of light intensity at the boundary of impurity particles at the presence of multiple impurity particles. The intensity difference data between different particles was acquired. A general solution was provided to solve the problem of complex impurity particles. After theoretical analysis and experimental verification, the results show that, for sphere particles, while there are two impurity particles at the same time, the particles passing through the impurity present a trend from low to high, and the intensity reaches the maximum in the area where the impurity particles are in contact with each other. For cube impurity particles, the intensity distribution exhibits a strong fluctuation property, and the intensity of light is 100 times more than that of sphere impurity particles. The research model has strong portability and can be widely applied to lots of fields. This result is helpful for the subsequent development of light propagation in air.
2018, 42(5): 713-717.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.024
Abstract:
In order to detect the refractive index of surface plasmon resonance (SPR) with high sensitivity, a SPR sensing structure based on single core photonic crystal fiber with large core was proposed. The full vector finite element method was used to simulate and analyze its sensing characteristics. The results show that the structure has a wide range of refractive index sensing range (1.36~1.55). At the same time, the structure has high sensing sensitivity and the average sensitivity is 12139nm/RIU. With refractive index of 1.36~1.42, the linear sensor sensitivity is 5646.4nm/RIU and linearity is 0.9317. With refractive index of 1.42~1.57, the linear sensor sensitivity is 15326.8nm/RIU and linearity is 0.98738. Sensing characteristics appear in obvious linear subsections. The results provide an important theoretical basis for the realization of high sensitive photonic crystal fiber SPR sensors.
In order to detect the refractive index of surface plasmon resonance (SPR) with high sensitivity, a SPR sensing structure based on single core photonic crystal fiber with large core was proposed. The full vector finite element method was used to simulate and analyze its sensing characteristics. The results show that the structure has a wide range of refractive index sensing range (1.36~1.55). At the same time, the structure has high sensing sensitivity and the average sensitivity is 12139nm/RIU. With refractive index of 1.36~1.42, the linear sensor sensitivity is 5646.4nm/RIU and linearity is 0.9317. With refractive index of 1.42~1.57, the linear sensor sensitivity is 15326.8nm/RIU and linearity is 0.98738. Sensing characteristics appear in obvious linear subsections. The results provide an important theoretical basis for the realization of high sensitive photonic crystal fiber SPR sensors.
2018, 42(5): 718-726.
doi: 10.7510/jgjs.issn.1001-3806.2018.05.025
Abstract:
In order to obtain rich image detail information, a wide dynamic acquisition circuit is often used in an infrared imaging system. However, most of the display devices are only 8 bits, how to compress wide dynamic images into low dynamic images and preserve detail information as much as possible is one of the key technologies of infrared image display. Current mainstream infrared image processing algorithms, such as mapping, image stratification and gradient domain are introduced, and the advantages and disadvantages of the 3 algorithms are analyzed. Contrast analysis is made with the same infrared image, and the improved opinions of all the algorithms are proposed. Image stratification algorithm needs to reduce time complexity in the case of inhibition of halo and gradient inversion. Gradient domain algorithm needs to suppress background noise and then the details are further improved.
In order to obtain rich image detail information, a wide dynamic acquisition circuit is often used in an infrared imaging system. However, most of the display devices are only 8 bits, how to compress wide dynamic images into low dynamic images and preserve detail information as much as possible is one of the key technologies of infrared image display. Current mainstream infrared image processing algorithms, such as mapping, image stratification and gradient domain are introduced, and the advantages and disadvantages of the 3 algorithms are analyzed. Contrast analysis is made with the same infrared image, and the improved opinions of all the algorithms are proposed. Image stratification algorithm needs to reduce time complexity in the case of inhibition of halo and gradient inversion. Gradient domain algorithm needs to suppress background noise and then the details are further improved.
