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RSS2015 Vol. 39, No. 5
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2015, 39(5): 585-589.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.001
[Abstract]
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Abstract:
To achieve azimuthally polarized beam, hybrid grating mirror was designed based on rigorous coupled wave analysis method. At first, amorphous Ge grating with high depth-to-width ratio was obtained by studying the etching characteristics of pseudo Bosch process on Ge grating. And then, dielectric-metal hybrid grating mirror was obtained after the randomly distributed Ge nanoneedle was introduced at the bottom of gate groove, and gold film and dielectric protective film were coated in turn. Finally, 550W azimuthally polarized beam was generated when hybrid grating mirror was used as the rear mirror of a fast axial flow CO2 laser. The results show that hybrid grating mirror has high polarization selectivity because of the introduction of nano-pillars as well as gold ridge.
To achieve azimuthally polarized beam, hybrid grating mirror was designed based on rigorous coupled wave analysis method. At first, amorphous Ge grating with high depth-to-width ratio was obtained by studying the etching characteristics of pseudo Bosch process on Ge grating. And then, dielectric-metal hybrid grating mirror was obtained after the randomly distributed Ge nanoneedle was introduced at the bottom of gate groove, and gold film and dielectric protective film were coated in turn. Finally, 550W azimuthally polarized beam was generated when hybrid grating mirror was used as the rear mirror of a fast axial flow CO2 laser. The results show that hybrid grating mirror has high polarization selectivity because of the introduction of nano-pillars as well as gold ridge.
2015, 39(5): 590-593.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.002
Abstract:
In order to improve the situation of the metal powder radiation existing in the current powder feeding broadband laser cladding nozzles and the low utilization rate, a collimation hood of powder feeding nozzle for broadband laser cladding was designed. A flow channel was designed to realize the uniformity of inside-laser powder feeding, to ensure that the powder was heated evenly and the divergence of powder beam was small. FLUENT software was used to analyze the internal fluid of collimation gas cover, to determine the inside cavity and the outlet size of device, to reduce the turbulence at the exit and to achieve better collimation effect. The experiment of the new powder feeding device was conducted to verify the effectiveness of gas collimator device. The results indicate that the best collimation could be achieved when width of the collimated gas curtain is 1.5 times of the width of powder beam.
In order to improve the situation of the metal powder radiation existing in the current powder feeding broadband laser cladding nozzles and the low utilization rate, a collimation hood of powder feeding nozzle for broadband laser cladding was designed. A flow channel was designed to realize the uniformity of inside-laser powder feeding, to ensure that the powder was heated evenly and the divergence of powder beam was small. FLUENT software was used to analyze the internal fluid of collimation gas cover, to determine the inside cavity and the outlet size of device, to reduce the turbulence at the exit and to achieve better collimation effect. The experiment of the new powder feeding device was conducted to verify the effectiveness of gas collimator device. The results indicate that the best collimation could be achieved when width of the collimated gas curtain is 1.5 times of the width of powder beam.
2015, 39(5): 594-597.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.003
Abstract:
In order to obtain a rotator with low surface roughness and variable radii, based on the technology of laser cladding manufacturing process with coaxial inside-beam powder feeding, the advantages of coaxial inside-beam power feeding accumulation and the influence of the posture, increment in z axis (z) and laser power of the laser head on the surface roughness were analyzed theoretically and verified experimentally. In the accumulation process, laser head was kept perpendicular to the molten surface, z and laser power were effectively controlled. Finally, a fine rotator was obtained with low roughness, i.e.,Ra=0.497m~2.163m;Rz=1.992m~7.447m. Experimental results show that this method is applicable for laser accumulation on vertical surfaces and the molding parts have lower roughness.
In order to obtain a rotator with low surface roughness and variable radii, based on the technology of laser cladding manufacturing process with coaxial inside-beam powder feeding, the advantages of coaxial inside-beam power feeding accumulation and the influence of the posture, increment in z axis (z) and laser power of the laser head on the surface roughness were analyzed theoretically and verified experimentally. In the accumulation process, laser head was kept perpendicular to the molten surface, z and laser power were effectively controlled. Finally, a fine rotator was obtained with low roughness, i.e.,Ra=0.497m~2.163m;Rz=1.992m~7.447m. Experimental results show that this method is applicable for laser accumulation on vertical surfaces and the molding parts have lower roughness.
2015, 39(5): 598-602.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.004
Abstract:
In order to expand the application fields of free space optical communication, a steady and practical communication system of retro-modulation was designed. Based on acousto-optic modulator (AOM) and the reverse link of light, transistor-transistor logic gate level was send to control AOM by using field programmable gate arrays. By using quaternary modulation method combining binary frequency shift keying and binary pulse width modulation, by using the encryption and error correction methods of redundancy checking replacement and improved Hamming code, reverse modulation laser communication indoor was realized. The results show that serial communication rate of the communication system is 115.2kbit/s, high frequency carrier is 1MHz and bit error rate is less than 10-6. Its confidentiality is good. While, it also proves that the maximum carrier wave of laser externally-modulated reverse communication system can reach about 5MHz.
In order to expand the application fields of free space optical communication, a steady and practical communication system of retro-modulation was designed. Based on acousto-optic modulator (AOM) and the reverse link of light, transistor-transistor logic gate level was send to control AOM by using field programmable gate arrays. By using quaternary modulation method combining binary frequency shift keying and binary pulse width modulation, by using the encryption and error correction methods of redundancy checking replacement and improved Hamming code, reverse modulation laser communication indoor was realized. The results show that serial communication rate of the communication system is 115.2kbit/s, high frequency carrier is 1MHz and bit error rate is less than 10-6. Its confidentiality is good. While, it also proves that the maximum carrier wave of laser externally-modulated reverse communication system can reach about 5MHz.
2015, 39(5): 603-609.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.005
Abstract:
In large size space coordinate measuring system, theodolite measuring system is widely used due to wide measurement range, non-contact measurement and portability. In order to reduce the cost and the error sources of a traditional theodolite measurement system, a novel laser theodolite measurement system based on non-orthogonal shaft system was proposed. Firstly, according to the transform relationship of the non-orthogonal shaft system during the measurement, the orientation mathematical model of visual collimation axis of non-orthogonal shaft laser theodolites was derived. Based on intersection measurement principle of double theodolites,measurement system of non-orthogonal shaft system laser theodolites was built and the coordinates of spatial point were obtained. Finally, after simulation and experiments, the accuracy of measurement model was verified. The experiment results show that, measurement accuracy of spatial point measured with non-orthogonal shafting laser theodolites can achieve 1mm at Pauta criterion within the measurement radius of 3m. The measurement system is especially suitable for the measurement of large volume or large space.
In large size space coordinate measuring system, theodolite measuring system is widely used due to wide measurement range, non-contact measurement and portability. In order to reduce the cost and the error sources of a traditional theodolite measurement system, a novel laser theodolite measurement system based on non-orthogonal shaft system was proposed. Firstly, according to the transform relationship of the non-orthogonal shaft system during the measurement, the orientation mathematical model of visual collimation axis of non-orthogonal shaft laser theodolites was derived. Based on intersection measurement principle of double theodolites,measurement system of non-orthogonal shaft system laser theodolites was built and the coordinates of spatial point were obtained. Finally, after simulation and experiments, the accuracy of measurement model was verified. The experiment results show that, measurement accuracy of spatial point measured with non-orthogonal shafting laser theodolites can achieve 1mm at Pauta criterion within the measurement radius of 3m. The measurement system is especially suitable for the measurement of large volume or large space.
2015, 39(5): 610-616.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.006
Abstract:
In order to analyze the frequency features of commonly used wavelets, such as complex Morlet wavelet, Fan wavelet, real Mexican hat wavelet in frequency domain, wavelet transform and 3-D surface shape measurement method based on the structured light illumination were used in reconstruction of the object to be measured. Theoretical analysis and experimental verification were carried out. By comparing the capability of eliminating fringe nonlinearity and noise of 1-D and 2-D Morlet wavelets, 1-D and 2-D Mexican hat wavelets and 2-D Fan wavelet, and comparing the demodulation accuracy of different fringe phases, the reconstructed accuracies of the same fringe based on different wavelet demodulations were obtained. The results show that the capability of eliminating the noise of 2-D wavelet is stronger than 1-D wavelet. Mexican hat wavelet is suitable for demodulating fringe pattern with phase mutation. The research provides the theoretical reference for the application of wavelet transform profilometry.
In order to analyze the frequency features of commonly used wavelets, such as complex Morlet wavelet, Fan wavelet, real Mexican hat wavelet in frequency domain, wavelet transform and 3-D surface shape measurement method based on the structured light illumination were used in reconstruction of the object to be measured. Theoretical analysis and experimental verification were carried out. By comparing the capability of eliminating fringe nonlinearity and noise of 1-D and 2-D Morlet wavelets, 1-D and 2-D Mexican hat wavelets and 2-D Fan wavelet, and comparing the demodulation accuracy of different fringe phases, the reconstructed accuracies of the same fringe based on different wavelet demodulations were obtained. The results show that the capability of eliminating the noise of 2-D wavelet is stronger than 1-D wavelet. Mexican hat wavelet is suitable for demodulating fringe pattern with phase mutation. The research provides the theoretical reference for the application of wavelet transform profilometry.
2015, 39(5): 617-620.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.007
Abstract:
In order to design three-port wavelength-division demultiplexer based on square lattice photonic crystal waveguide, wavelength-division demultiplexer was analyzed theoretically by using the characteristics of photonic band gap of photonic crystal and the transmission characteristics of slow light mode in photonic crystal, by using plane wave expansion method and finite difference time domain method. The spectral and spatial characteristics of wavelength-division demultiplexer were calculated numerically. The results show that adjusting the position of the column at the first row adjacent to the waveguide will change the frequency of slow light transmitted in three parts of waveguide. Based on the transmission characteristics of slow light, provided a reasonable structure design, the light beams at different frequencies can output from different output terminals, and the purpose of demultiplexing can be achieved.
In order to design three-port wavelength-division demultiplexer based on square lattice photonic crystal waveguide, wavelength-division demultiplexer was analyzed theoretically by using the characteristics of photonic band gap of photonic crystal and the transmission characteristics of slow light mode in photonic crystal, by using plane wave expansion method and finite difference time domain method. The spectral and spatial characteristics of wavelength-division demultiplexer were calculated numerically. The results show that adjusting the position of the column at the first row adjacent to the waveguide will change the frequency of slow light transmitted in three parts of waveguide. Based on the transmission characteristics of slow light, provided a reasonable structure design, the light beams at different frequencies can output from different output terminals, and the purpose of demultiplexing can be achieved.
2015, 39(5): 621-624.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.008
Abstract:
In order to get pure annular end-pumping beam to generate Laguerre-Gaussian beams from solid-state lasers, a method with axicon shaping system was put forward. At first, the solid pump light from LD source was collimated by the lens and was coupled into a axicon and a focal lens. And then, the shaping system was obtained and hollow beam with variable size was formed. Based on geometrical optics, theoretical analysis and numerical simulation were made with the aid of the software ZEMAX . The phenomenon of the invariant dark region of annular pump light was also investigated. The results show that power conversion efficiency could reach up to 64.5% by using the system with uncoated axicon.
In order to get pure annular end-pumping beam to generate Laguerre-Gaussian beams from solid-state lasers, a method with axicon shaping system was put forward. At first, the solid pump light from LD source was collimated by the lens and was coupled into a axicon and a focal lens. And then, the shaping system was obtained and hollow beam with variable size was formed. Based on geometrical optics, theoretical analysis and numerical simulation were made with the aid of the software ZEMAX . The phenomenon of the invariant dark region of annular pump light was also investigated. The results show that power conversion efficiency could reach up to 64.5% by using the system with uncoated axicon.
2015, 39(5): 625-630.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.009
Abstract:
In order to study influence of welding parameters on root humps in high power fiber laser welding, effect of laser power, welding speed, defocus, flow rate of bottom shielding gas and welding position on root humps was studied based on a single variable method. The results show that, with the increase of laser power, root humps tend to increase at first and then decrease. When welding speed increases, root hump height increases at first and then decreases, root hump spacing decreases significantly. When defocus is near 0mm, root hump tendency is obvious. Under the appropriate flow rate of bottom shielding gas, root hump tendency is reduced. The optimal rate is 15L/min. When welding orientation is 60, root hump tendency decreases to a certain extent. The results show that reasonable welding parameters can eliminate root hump efficiently.
In order to study influence of welding parameters on root humps in high power fiber laser welding, effect of laser power, welding speed, defocus, flow rate of bottom shielding gas and welding position on root humps was studied based on a single variable method. The results show that, with the increase of laser power, root humps tend to increase at first and then decrease. When welding speed increases, root hump height increases at first and then decreases, root hump spacing decreases significantly. When defocus is near 0mm, root hump tendency is obvious. Under the appropriate flow rate of bottom shielding gas, root hump tendency is reduced. The optimal rate is 15L/min. When welding orientation is 60, root hump tendency decreases to a certain extent. The results show that reasonable welding parameters can eliminate root hump efficiently.
2015, 39(5): 631-636.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.010
Abstract:
Research progress of laser cladding on magnesium alloy was reviewed. The process characteristics and process method were introduced. Then effects of process parameters on the performance of laser cladding layers were described. The main material system of laser cladding on magnesium alloys, the microstructure and the properties of laser cladding layers in recent years were also summarized. Finally the future development was also predicated.
Research progress of laser cladding on magnesium alloy was reviewed. The process characteristics and process method were introduced. Then effects of process parameters on the performance of laser cladding layers were described. The main material system of laser cladding on magnesium alloys, the microstructure and the properties of laser cladding layers in recent years were also summarized. Finally the future development was also predicated.
2015, 39(5): 637-641.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.011
Abstract:
In order to study effect of material dispersion on transmission characteristics of a Fabry-Perot interferometer (F-PI), transmission spectrum of the F-PI was calculated based on the Lorentz oscillator mode and the effect of dispersion intensity 0, attenuation coefficient and resonant frequency 0 on longitudinal mode interval was investigated. The results show that the interval between longitudinal modes at low and high frequency band decreases with the increasing of 0 and increases with the increase of . For the longitudinal modes near 0, the interval between longitudinal modes increases with the increase of 0 at first and then decreases. When 0 is small, the interval between longitudinal modes decreases with the increase of and increases with the increase of 0 at first and then decreases when 0 is big, the interval between longitudinal modes increases with the increase of at first and then decreases, and decreases with the increase of 0. The results are helpful for design and research of lasers.
In order to study effect of material dispersion on transmission characteristics of a Fabry-Perot interferometer (F-PI), transmission spectrum of the F-PI was calculated based on the Lorentz oscillator mode and the effect of dispersion intensity 0, attenuation coefficient and resonant frequency 0 on longitudinal mode interval was investigated. The results show that the interval between longitudinal modes at low and high frequency band decreases with the increasing of 0 and increases with the increase of . For the longitudinal modes near 0, the interval between longitudinal modes increases with the increase of 0 at first and then decreases. When 0 is small, the interval between longitudinal modes decreases with the increase of and increases with the increase of 0 at first and then decreases when 0 is big, the interval between longitudinal modes increases with the increase of at first and then decreases, and decreases with the increase of 0. The results are helpful for design and research of lasers.
2015, 39(5): 642-647.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.012
Abstract:
In a structured light vision measurement system, the extraction accuracy and speed of laser stripes directly affect the final accuracy of measurement results. In order to reach strong anti-interference ability, good stability and low computation cost at the same time, an optimal Steger algorithm was proposed to extract center points of laser stripes. The gradient threshold segmentation was used to get the effective stripe area. The optimal scanning method and the gray centroid method were used extract the stripe center coarsely. Then, Hessian matrix method was used to extract pure stripe center. The principle of the laser stripes extraction was analyzed in theory and the hardware and software design were verified by experiments. Good experimental data was obtained. The experimental results show that this method has high extraction accuracy and fast speed compared with the traditional method. The research is helpful for high precision and real-time performance of flexible sensors.
In a structured light vision measurement system, the extraction accuracy and speed of laser stripes directly affect the final accuracy of measurement results. In order to reach strong anti-interference ability, good stability and low computation cost at the same time, an optimal Steger algorithm was proposed to extract center points of laser stripes. The gradient threshold segmentation was used to get the effective stripe area. The optimal scanning method and the gray centroid method were used extract the stripe center coarsely. Then, Hessian matrix method was used to extract pure stripe center. The principle of the laser stripes extraction was analyzed in theory and the hardware and software design were verified by experiments. Good experimental data was obtained. The experimental results show that this method has high extraction accuracy and fast speed compared with the traditional method. The research is helpful for high precision and real-time performance of flexible sensors.
2015, 39(5): 648-653.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.013
Abstract:
In order to analyze the relationship between static and dynamic temperature field distribution of catalyst substrate and various experimental parameters in graphene fabrication with laser-induced chemical vapor deposition, the finite element model was established by using ANSYS software and 532nm laser model was loaded as the heat source. The data of temperature field distribution and the needing time for achieving reaction temperature under different parameters were obtained. The results show that under the influence of the property of substrate, laser power, the size of substrate area, the focus spot diameter and the reaction gas flow, the substrate temperature field distribution and the needing time for achieving reaction temperature are different. It can be used as the reference in high quality graphene fabrication experiment. The dynamic temperature field distribution under the conditions of continuous wave laser(wavelength of 532nm, power of 3W, focused spot diameter of 50m, movement speed of 1mm/s), nickel foil substrate, 10mL/min methane and 5mL/min hydrogen conforms to the pattern graphene growth mechanism fabricated by laser chemical vapor deposition.
In order to analyze the relationship between static and dynamic temperature field distribution of catalyst substrate and various experimental parameters in graphene fabrication with laser-induced chemical vapor deposition, the finite element model was established by using ANSYS software and 532nm laser model was loaded as the heat source. The data of temperature field distribution and the needing time for achieving reaction temperature under different parameters were obtained. The results show that under the influence of the property of substrate, laser power, the size of substrate area, the focus spot diameter and the reaction gas flow, the substrate temperature field distribution and the needing time for achieving reaction temperature are different. It can be used as the reference in high quality graphene fabrication experiment. The dynamic temperature field distribution under the conditions of continuous wave laser(wavelength of 532nm, power of 3W, focused spot diameter of 50m, movement speed of 1mm/s), nickel foil substrate, 10mL/min methane and 5mL/min hydrogen conforms to the pattern graphene growth mechanism fabricated by laser chemical vapor deposition.
2015, 39(5): 654-657.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.014
Abstract:
In order to study effect of multiple quantum well (MQW) on threshold current of a semiconductor ring laser (SRL), the function relationship between threshold current of SRL and MQW structural parameters was analyzed based on the oscillation condition of a conventional Fabry-Perot laser. An optimal expression of quantum well number was derived. Equivalent model of SRL was founded by utilizing device simulation software ATLAS. The effect of quantum well number, well width and barrier thickness on threshold current density of SRL were simulated and analyzed at various operating temperatures. The simulation results show that threshold current decreases firstly and then increases with increasing of well number and well width. A set of optimal values existed. After determining the appropriate well number and well width, the barrier with relatively narrower thickness can further reduce the threshold current. For GaAs/AlGaAs material system and device structure, the optimal parameters are M=3, dw=20nm, and db=10nm respectively.
In order to study effect of multiple quantum well (MQW) on threshold current of a semiconductor ring laser (SRL), the function relationship between threshold current of SRL and MQW structural parameters was analyzed based on the oscillation condition of a conventional Fabry-Perot laser. An optimal expression of quantum well number was derived. Equivalent model of SRL was founded by utilizing device simulation software ATLAS. The effect of quantum well number, well width and barrier thickness on threshold current density of SRL were simulated and analyzed at various operating temperatures. The simulation results show that threshold current decreases firstly and then increases with increasing of well number and well width. A set of optimal values existed. After determining the appropriate well number and well width, the barrier with relatively narrower thickness can further reduce the threshold current. For GaAs/AlGaAs material system and device structure, the optimal parameters are M=3, dw=20nm, and db=10nm respectively.
2015, 39(5): 658-661.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.015
Abstract:
In order to study influence of mechanical-stress on quartz filter output, based on the elasto-optical effect of quartz crystal, the relationship between birefringence of quartz crystal and mechanical stress in different directions was analyzed. After numerical simulation, the experimental system was set up by using UV-visible spectrophotometer of Ultra-6600 series and the transmission spectrum of a Lyot quartz birefringence filter was studied and investigated. Theoretical simulation and experimental results show that central wavelength of the Lyot quartz crystal birefringence filter will drift under mechanical stress at different directions. The drifts of central wavelength of a Lyot quartz crystal birefringence filter are 0.4nm, 0.6nm and 1nm respectively when mechanical stress is 0.0025N/m2 along the direction of Ox1 axis, Ox2 axis, Ox3 axis. The research is helpful for manufacture, design and application of quartz birefringence filters.
In order to study influence of mechanical-stress on quartz filter output, based on the elasto-optical effect of quartz crystal, the relationship between birefringence of quartz crystal and mechanical stress in different directions was analyzed. After numerical simulation, the experimental system was set up by using UV-visible spectrophotometer of Ultra-6600 series and the transmission spectrum of a Lyot quartz birefringence filter was studied and investigated. Theoretical simulation and experimental results show that central wavelength of the Lyot quartz crystal birefringence filter will drift under mechanical stress at different directions. The drifts of central wavelength of a Lyot quartz crystal birefringence filter are 0.4nm, 0.6nm and 1nm respectively when mechanical stress is 0.0025N/m2 along the direction of Ox1 axis, Ox2 axis, Ox3 axis. The research is helpful for manufacture, design and application of quartz birefringence filters.
2015, 39(5): 662-665.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.016
Abstract:
In order to filter the noise in infrared images effectively, an improved non-local mean filtering (INLMF) algorithm was proposed. In the traditional non-local means filtering (NLMF) algorithm, the square image blocks of fixed size cannot depict the image details effectively. For overcoming the defects of NLMF, a novel adaptive classification method of image blocks, combing with gray scale information of image pixels, was put forward. The divided image block in size and shape depended on the actual distribution of gray scale information. And then, structure similarity (SSIM) factor was introduced to improve the calculation method of image blocks weights. Two infrared monitoring images were filtered by two traditional NLMF algorithms and the new INLMF algorithm. The theoretical and experimental results show that the performance of INLMF is superior to the others. It is helpful for enhancing the filtering effects of infrared images.
In order to filter the noise in infrared images effectively, an improved non-local mean filtering (INLMF) algorithm was proposed. In the traditional non-local means filtering (NLMF) algorithm, the square image blocks of fixed size cannot depict the image details effectively. For overcoming the defects of NLMF, a novel adaptive classification method of image blocks, combing with gray scale information of image pixels, was put forward. The divided image block in size and shape depended on the actual distribution of gray scale information. And then, structure similarity (SSIM) factor was introduced to improve the calculation method of image blocks weights. Two infrared monitoring images were filtered by two traditional NLMF algorithms and the new INLMF algorithm. The theoretical and experimental results show that the performance of INLMF is superior to the others. It is helpful for enhancing the filtering effects of infrared images.
2015, 39(5): 666-668.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.017
Abstract:
In order to eliminate the speckle in laser microscopic imaging system, effect of optical fiber vibration on microscopic speckle images was studied by comparing the speckle dark ratio. In this experiment, with laser at 532nm wavelength as light source of the microscopic system, with the optical fiber vibration to eliminate the image speckle and a CCD image sensor acquisition system to collect the microscopic images of the sample surface, images dark ratios were analyzed at different vibration voltages. The results show that with the increase of the vibration voltage, the speckle dark ratio of the images will reduce gradually. When the voltage is 2.6V, the image speckle dark ratio can reach 5.64%, speckle contrast is 4.17% close to human eye resolution of 4%. This method can achieve good speckle elimination effect.
In order to eliminate the speckle in laser microscopic imaging system, effect of optical fiber vibration on microscopic speckle images was studied by comparing the speckle dark ratio. In this experiment, with laser at 532nm wavelength as light source of the microscopic system, with the optical fiber vibration to eliminate the image speckle and a CCD image sensor acquisition system to collect the microscopic images of the sample surface, images dark ratios were analyzed at different vibration voltages. The results show that with the increase of the vibration voltage, the speckle dark ratio of the images will reduce gradually. When the voltage is 2.6V, the image speckle dark ratio can reach 5.64%, speckle contrast is 4.17% close to human eye resolution of 4%. This method can achieve good speckle elimination effect.
2015, 39(5): 669-673.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.018
Abstract:
In order to get better results of 3-D laser scanning image denoising, an improved sparse representation denoising algorithm was proposed by combining histogram structural similarity (HSSIM) and residual ratio threshold. The initial over-complete dictionary was applied in the sparse decomposition. The reconstruction error was replaced by similarity factor as fidelity factor. Then the residual ratio threshold was used as the iteration termination of the orthogonal matching pursuit algorithm to reconstruct the denoised image. Finally, the performance data of denoised image, such as peak signal-to-noise ratio(PSNR) and HSSIM, were obtained. The experimental results show that the proposed method could provide better PSNR and HSSIM results compared with the image denoising methods using db2 wavelet transform, multiscale curve wave transform and discrete cosine transform. Meanwhile, the structural features can be reserved effectively by the proposed method.
In order to get better results of 3-D laser scanning image denoising, an improved sparse representation denoising algorithm was proposed by combining histogram structural similarity (HSSIM) and residual ratio threshold. The initial over-complete dictionary was applied in the sparse decomposition. The reconstruction error was replaced by similarity factor as fidelity factor. Then the residual ratio threshold was used as the iteration termination of the orthogonal matching pursuit algorithm to reconstruct the denoised image. Finally, the performance data of denoised image, such as peak signal-to-noise ratio(PSNR) and HSSIM, were obtained. The experimental results show that the proposed method could provide better PSNR and HSSIM results compared with the image denoising methods using db2 wavelet transform, multiscale curve wave transform and discrete cosine transform. Meanwhile, the structural features can be reserved effectively by the proposed method.
2015, 39(5): 674-678.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.019
Abstract:
In order to evaluate jamming effect of high-repetition rate laser, the laser jamming mechanisms of laser seekers with different amplification circuits were analyzed. The traction effect of high-repetition rate laser jamming was described. The necessity of large dynamic range signal amplification in laser seekers was studied. The principles of two different amplification circuits were introduced. The jamming effect of high-repetition rate laser was analyzed based on automatic gain control circuit and log-ratio amplifier circuit. The research indicates that high-repetition rate laser jamming was an effective method of laser countermeasure. The action effects were different because of different amplifying circuits of laser seekers. An automatic gain control circuit could not amplify signal instantly because of gain adjustment time and guided signal would be shielded by high-repetition rate laser jamming. A log-ratio amplifier circuit could broad the signal pulse width and decreases the signal-to-noise ratio and four branches signal consistency, which make high-repetition rate laser jam a seeker easily. The results will be helpful for evaluation of jamming effect of high-repetition rate laser.
In order to evaluate jamming effect of high-repetition rate laser, the laser jamming mechanisms of laser seekers with different amplification circuits were analyzed. The traction effect of high-repetition rate laser jamming was described. The necessity of large dynamic range signal amplification in laser seekers was studied. The principles of two different amplification circuits were introduced. The jamming effect of high-repetition rate laser was analyzed based on automatic gain control circuit and log-ratio amplifier circuit. The research indicates that high-repetition rate laser jamming was an effective method of laser countermeasure. The action effects were different because of different amplifying circuits of laser seekers. An automatic gain control circuit could not amplify signal instantly because of gain adjustment time and guided signal would be shielded by high-repetition rate laser jamming. A log-ratio amplifier circuit could broad the signal pulse width and decreases the signal-to-noise ratio and four branches signal consistency, which make high-repetition rate laser jam a seeker easily. The results will be helpful for evaluation of jamming effect of high-repetition rate laser.
2015, 39(5): 679-684.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.020
Abstract:
In order to study the dynamical behaviors of self-Q-switched erbium-doped fiber lasers, all-fiber self-Q-switched erbium-doped fiber lasers with linear cavity configuration and ring cavity configuration were constructed. Theoretical analysis and experimental verification were also carried out. In the experiment, when pump power reached the threshold, output laser was observed by oscilloscope with the increase of pump power. Linear cavity laser output experienced two operation states of continuous wave (CW) and self-Q-switched in turn and failed to appear CW operation state again because of the constraint of pump power. Ring cavity laser output experienced self-Q-switched operation state at first and then CW operation state. For linear cavity, self-Q-switched pulses can be obtained with pulse width from 8s to 100s and repetition rate from 2.5kHz to 54kHz in pump power range from 21mW to 190mW. For ring cavity, self-Q-switched pulses can be obtained with pulse width about 165s and repetition rate about 3kHz at pump power range from 16.2mW to 110mW. The results show that dynamical behaviors of output laser are different because cavity configurations of self-Q-switched erbium-doped fiber laser are different. Although both linear and ring cavities have self-Q-switched pulse output, the range of self-Q-switched pulse is wider for linear cavity.
In order to study the dynamical behaviors of self-Q-switched erbium-doped fiber lasers, all-fiber self-Q-switched erbium-doped fiber lasers with linear cavity configuration and ring cavity configuration were constructed. Theoretical analysis and experimental verification were also carried out. In the experiment, when pump power reached the threshold, output laser was observed by oscilloscope with the increase of pump power. Linear cavity laser output experienced two operation states of continuous wave (CW) and self-Q-switched in turn and failed to appear CW operation state again because of the constraint of pump power. Ring cavity laser output experienced self-Q-switched operation state at first and then CW operation state. For linear cavity, self-Q-switched pulses can be obtained with pulse width from 8s to 100s and repetition rate from 2.5kHz to 54kHz in pump power range from 21mW to 190mW. For ring cavity, self-Q-switched pulses can be obtained with pulse width about 165s and repetition rate about 3kHz at pump power range from 16.2mW to 110mW. The results show that dynamical behaviors of output laser are different because cavity configurations of self-Q-switched erbium-doped fiber laser are different. Although both linear and ring cavities have self-Q-switched pulse output, the range of self-Q-switched pulse is wider for linear cavity.
2015, 39(5): 685-688.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.021
Abstract:
An object's surface temperature distribution and surface information can be obtained generally through infrared and visible image fusion. In order to find out internal heat source within an object, an image fusion strategy between infrared and X-ray images based on wavelet transform was proposed because wavelet transform has better multi-resolution properties in time domain and frequency domain. Firstly, the infrared color image was transformed into gray-scale image. Then, Mallat algorithm was employed to decompose the infrared and X-ray images. The fusion image was gotten by the rules of low frequency coefficient averaging and high frequency coefficient absolute value maximizing. The colored temperature information of infrared images was transferred to the fused wavelet images by using YIQ space transform. Finally, the fused image was evaluated quantitatively by image entropy, standard deviation and average gradient. The experiment results show that the fused image integrates infrared and X-ray image information, which reflects not only the component's surface temperature distribution but also its clear inner structure.
An object's surface temperature distribution and surface information can be obtained generally through infrared and visible image fusion. In order to find out internal heat source within an object, an image fusion strategy between infrared and X-ray images based on wavelet transform was proposed because wavelet transform has better multi-resolution properties in time domain and frequency domain. Firstly, the infrared color image was transformed into gray-scale image. Then, Mallat algorithm was employed to decompose the infrared and X-ray images. The fusion image was gotten by the rules of low frequency coefficient averaging and high frequency coefficient absolute value maximizing. The colored temperature information of infrared images was transferred to the fused wavelet images by using YIQ space transform. Finally, the fused image was evaluated quantitatively by image entropy, standard deviation and average gradient. The experiment results show that the fused image integrates infrared and X-ray image information, which reflects not only the component's surface temperature distribution but also its clear inner structure.
2015, 39(5): 689-693.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.022
Abstract:
In order to explore effect of wedge end on the characteristics of fiber transfer, wedge-shaped micro/nano fiber was studied and coupling efficiency of two wedge-shaped micro/nano fibers was calculated by using COMSOL Multiphysics numerical simulation software. Energy distribution of a single wedge-shaped micro-nano fiber and coupling efficiency of two fibers were obtained. The results show that more energy is distributed on the surface of the fiber core when it gets closer to the fiber tip. Along the direction of transmission, there is an increase of energy density of the wedge at first and then a decrease. Fresnel reflection of wedge-shaped end has a little influence on coupling efficiency and the whole variation. Coupling efficiency would decrease with the increase of axial displacement and radial displacement, and would decrease at first and then increase with the increase of wedge angle. The study of micro/nano fiber will lay the foundation in fiber optic sensing field.
In order to explore effect of wedge end on the characteristics of fiber transfer, wedge-shaped micro/nano fiber was studied and coupling efficiency of two wedge-shaped micro/nano fibers was calculated by using COMSOL Multiphysics numerical simulation software. Energy distribution of a single wedge-shaped micro-nano fiber and coupling efficiency of two fibers were obtained. The results show that more energy is distributed on the surface of the fiber core when it gets closer to the fiber tip. Along the direction of transmission, there is an increase of energy density of the wedge at first and then a decrease. Fresnel reflection of wedge-shaped end has a little influence on coupling efficiency and the whole variation. Coupling efficiency would decrease with the increase of axial displacement and radial displacement, and would decrease at first and then increase with the increase of wedge angle. The study of micro/nano fiber will lay the foundation in fiber optic sensing field.
2015, 39(5): 694-696.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.023
Abstract:
In order to design a polarization splitter based on lithium niobate photonic wires, the splitter was analyzed and optimized by using the electromagnetic simulation software based on finite element method and the optimal design result of compact structure size was gotten. The effects of the changes of waveguide width on the transmission of the splitter were analyzed with the consideration of the common process error. The results show that the bandwidth and power transmittance of the polarization splitter have the strong relationship with the waveguide coupling length.
In order to design a polarization splitter based on lithium niobate photonic wires, the splitter was analyzed and optimized by using the electromagnetic simulation software based on finite element method and the optimal design result of compact structure size was gotten. The effects of the changes of waveguide width on the transmission of the splitter were analyzed with the consideration of the common process error. The results show that the bandwidth and power transmittance of the polarization splitter have the strong relationship with the waveguide coupling length.
2015, 39(5): 697-701.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.024
Abstract:
In order to obtain high-fidelity 3-D images, an adaptive mean filtering algorithm for high resolution 3-D images was proposed. Firstly, a high-precision 3-D linear laser measuring system consisting of a laser, two high-resolution 3-D cameras, two linear motors and a computer was established to measure the texture of leather. After theoretical analysis and experimental verification of the high-resolution 3-D texture images (dots per inch 1000) collected by the measuring system, the data of high-fidelity three dimensional images after filtering were gotten. The effect of the adaptive mean filtering algorithm was compared with the effects of mean filtering method and wavelet threshold filtering method. The results show that the adaptive mean filtering algorithm can remove noise of 3-D images effectively, select the appropriate filtering window automatically, and also keep details and edge information of high resolution images. Finally, the high resolution 3-D texture images with high fidelity would be obtained. The experimental results are very helpful for denoising processing of high resolution images.
In order to obtain high-fidelity 3-D images, an adaptive mean filtering algorithm for high resolution 3-D images was proposed. Firstly, a high-precision 3-D linear laser measuring system consisting of a laser, two high-resolution 3-D cameras, two linear motors and a computer was established to measure the texture of leather. After theoretical analysis and experimental verification of the high-resolution 3-D texture images (dots per inch 1000) collected by the measuring system, the data of high-fidelity three dimensional images after filtering were gotten. The effect of the adaptive mean filtering algorithm was compared with the effects of mean filtering method and wavelet threshold filtering method. The results show that the adaptive mean filtering algorithm can remove noise of 3-D images effectively, select the appropriate filtering window automatically, and also keep details and edge information of high resolution images. Finally, the high resolution 3-D texture images with high fidelity would be obtained. The experimental results are very helpful for denoising processing of high resolution images.
2015, 39(5): 702-705.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.025
Abstract:
To study effect of the matching of z-axis single increment (z) with single cladding layer height on laser cladding forming, experiments of laser cladding forming were carried out at different z. The relationship curves of different z, single cladding layer height and defocusing were obtained after theoretical analysis and experimental verification. The results show that the optimal range of z is based on the second cladding layer height. In this range, the process of cladding would reach a steady forming state by feedback regulation. A recommended value of z(0.5d2 z 0.6d2) is provided.
To study effect of the matching of z-axis single increment (z) with single cladding layer height on laser cladding forming, experiments of laser cladding forming were carried out at different z. The relationship curves of different z, single cladding layer height and defocusing were obtained after theoretical analysis and experimental verification. The results show that the optimal range of z is based on the second cladding layer height. In this range, the process of cladding would reach a steady forming state by feedback regulation. A recommended value of z(0.5d2 z 0.6d2) is provided.
2015, 39(5): 706-711.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.026
Abstract:
Aiming at the high stability requirements for light amplification in optical packet and circuit (OPCI) nodes, two main schemes of electrical and optical control for Er3+-doped fiber amplifier (EDFA) gain control were clarified. The principle of electrical automatic gain control was put forward with/without fine tuning of EDFA. The recent study progress of EDFA gain control was summarized. The specific control process of each control scheme was analyzed. The stage achievements by using these control schemes were shown.
Aiming at the high stability requirements for light amplification in optical packet and circuit (OPCI) nodes, two main schemes of electrical and optical control for Er3+-doped fiber amplifier (EDFA) gain control were clarified. The principle of electrical automatic gain control was put forward with/without fine tuning of EDFA. The recent study progress of EDFA gain control was summarized. The specific control process of each control scheme was analyzed. The stage achievements by using these control schemes were shown.
2015, 39(5): 712-716.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.027
Abstract:
Coherent beam was an important method to obtain high power and high beam quality laser. In order to analyze the characteristics of fiber laser beam combination, influence of fiber laser array structure, phase random jitter, fiber spacing, transmission distance and other factors on coherent combination was discussed by comparing the intensity distribution at different propagation distance. Power in the bucket for coherent beam was evaluated. The result shows that intensity distribution of different fiber laser array is different when the propagation distance is near. Intensity distribution is close to Gaussian distribution with the increasing of propagation distance. The number of the maximum intensity distribution points in the axis has the close relationship with the circular number of fiber laser array. The coherent effect is better if the random phase difference of the laser array is smaller. These results are reference to the study of fiber laser coherent combination.
Coherent beam was an important method to obtain high power and high beam quality laser. In order to analyze the characteristics of fiber laser beam combination, influence of fiber laser array structure, phase random jitter, fiber spacing, transmission distance and other factors on coherent combination was discussed by comparing the intensity distribution at different propagation distance. Power in the bucket for coherent beam was evaluated. The result shows that intensity distribution of different fiber laser array is different when the propagation distance is near. Intensity distribution is close to Gaussian distribution with the increasing of propagation distance. The number of the maximum intensity distribution points in the axis has the close relationship with the circular number of fiber laser array. The coherent effect is better if the random phase difference of the laser array is smaller. These results are reference to the study of fiber laser coherent combination.
2015, 39(5): 717-722.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.028
Abstract:
In order to solve the problem that 2-D minimum error threshold segmentation (METS) method had poor segment robust performance on an image which presents skew distribution and heavy-tailed distribution, an improved 2-D METS method was proposed based on mean absolute deviation from the median. Considering that the median was a more robust estimator of gray level than the mean in 1-D histogram of skew distribution and heavy-tailed distribution, variance in 2-D METS was replaced by mean absolute deviation from the median. In order to improve the computational speed, a 2-D algorithm was decomposed into two 1-D algorithms. Experimental results show that, compared with 2-D Otsu method, 2-D METS method and other classical algorithms, the improved 2-D METS method based on mean absolute deviation has more accurate segmentation results and more robust performance for 1-D histogram with skew distribution and heavy-tailed distribution.
In order to solve the problem that 2-D minimum error threshold segmentation (METS) method had poor segment robust performance on an image which presents skew distribution and heavy-tailed distribution, an improved 2-D METS method was proposed based on mean absolute deviation from the median. Considering that the median was a more robust estimator of gray level than the mean in 1-D histogram of skew distribution and heavy-tailed distribution, variance in 2-D METS was replaced by mean absolute deviation from the median. In order to improve the computational speed, a 2-D algorithm was decomposed into two 1-D algorithms. Experimental results show that, compared with 2-D Otsu method, 2-D METS method and other classical algorithms, the improved 2-D METS method based on mean absolute deviation has more accurate segmentation results and more robust performance for 1-D histogram with skew distribution and heavy-tailed distribution.
2015, 39(5): 723-726.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.029
Abstract:
In order to study the phase characteristics of Laguerre-Gaussian vortex beam during propagation, the vortex beam was obtained by means of spiral phase plates. Based on Fresnel diffraction integral formula, the phase change of the beam in the propagation process and the stability of vortex beam phase singularities at integer order and fractional order were studied by theoretical derivation and numerical simulation. When the beam was transmitted a certain distance, phase contours of the light field on the observation plane became from diverging rays into petal-shaped arcs. The results show that if topological charge of the vortex beam is integer order, the phase singularity of the beam assumes stability in the propagation process. The phase singularity of fractional order is unstable, intensity distribution on the observation plane is obvious asymmetric and the central darkness gradually disappears. The research results supply theoretical foundation and practical guidance for the application of optical micro manipulation and information coding techniques.
In order to study the phase characteristics of Laguerre-Gaussian vortex beam during propagation, the vortex beam was obtained by means of spiral phase plates. Based on Fresnel diffraction integral formula, the phase change of the beam in the propagation process and the stability of vortex beam phase singularities at integer order and fractional order were studied by theoretical derivation and numerical simulation. When the beam was transmitted a certain distance, phase contours of the light field on the observation plane became from diverging rays into petal-shaped arcs. The results show that if topological charge of the vortex beam is integer order, the phase singularity of the beam assumes stability in the propagation process. The phase singularity of fractional order is unstable, intensity distribution on the observation plane is obvious asymmetric and the central darkness gradually disappears. The research results supply theoretical foundation and practical guidance for the application of optical micro manipulation and information coding techniques.
2015, 39(5): 727-730.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.030
Abstract:
In order to study the influence factors of output power of Cr,Tm,Ho:YAG lasers, the variation of laser pumped threshold and output power were obtained using the cooling of water temperature to change the controllable factor. The relationship among the cooling temperature, frequency and power was analyzed. The results show that laser threshold increases with the rise of temperature and frequency. The increase of cooling temperature and repetition frequency will result in the decrease of laser output efficiency. When repetition frequency is 20Hz, output power of laser reaches 10.1W, output power of fiber end is 7.3W and total coupling rate is 72%. With single pulse energy of 2.0J~2.5J and repeat frequency of 20Hz~25Hz, Cr,Tm,Ho:YAG laser can achieve the desired result of crushing human kidney stones.
In order to study the influence factors of output power of Cr,Tm,Ho:YAG lasers, the variation of laser pumped threshold and output power were obtained using the cooling of water temperature to change the controllable factor. The relationship among the cooling temperature, frequency and power was analyzed. The results show that laser threshold increases with the rise of temperature and frequency. The increase of cooling temperature and repetition frequency will result in the decrease of laser output efficiency. When repetition frequency is 20Hz, output power of laser reaches 10.1W, output power of fiber end is 7.3W and total coupling rate is 72%. With single pulse energy of 2.0J~2.5J and repeat frequency of 20Hz~25Hz, Cr,Tm,Ho:YAG laser can achieve the desired result of crushing human kidney stones.
2015, 39(5): 731-734.
doi: 10.7510/jgjs.issn.1001-3806.2015.05.031
Abstract:
In order to study influence of gradient-index medium on propagation property of complex variable sinh-Gaussian beam, propagation field of complex variable sinh-Gaussian beam in a gradient-index medium was deduced by means of generalized Huygens-Fresnel diffraction integral method. The expressions of spot size and its change rate were deduced by using the definitions of spatial second-order matrix. Then, the numerical stimulation and analysis were made. The results show that the spot size and its change rate changes with the increasing of propagation distance periodically and the periodical cycles are determined by gradient-index parameters. With the changing of beam parameters, the spot location and the periodical cycle are constant, but the oscillation amplitude of the spot size will change. The spot size and its location can be changed by adjusting these parameters. The study is helpful for development and application of high-power semiconductor lasers.
In order to study influence of gradient-index medium on propagation property of complex variable sinh-Gaussian beam, propagation field of complex variable sinh-Gaussian beam in a gradient-index medium was deduced by means of generalized Huygens-Fresnel diffraction integral method. The expressions of spot size and its change rate were deduced by using the definitions of spatial second-order matrix. Then, the numerical stimulation and analysis were made. The results show that the spot size and its change rate changes with the increasing of propagation distance periodically and the periodical cycles are determined by gradient-index parameters. With the changing of beam parameters, the spot location and the periodical cycle are constant, but the oscillation amplitude of the spot size will change. The spot size and its location can be changed by adjusting these parameters. The study is helpful for development and application of high-power semiconductor lasers.
