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RSS2014 Vol. 38, No. 1
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2014, 38(1): 1-5.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.001
[Abstract]
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Abstract:
In order to optimize the process parameters in laser welding of high-strength galvanized steel with powder filling, orthogonal experimental tests were used to analyze such process parameters as laser power, welding speed and the defocusing distance. The test results show that the accumulation of the molten mass and the welding holes might occur at low welding speed; the defocusing distance should be increased to achieve the effective addition of the powder. The optimization process parameters for laser welding of high-strength galvanized steel with powder filling were 1500W laser power, 30mm/s welding speed and 12mm defocusing distance. Under these welding conditions, good weld performance was obtained and the base material was broken in tensile fracture tests.
In order to optimize the process parameters in laser welding of high-strength galvanized steel with powder filling, orthogonal experimental tests were used to analyze such process parameters as laser power, welding speed and the defocusing distance. The test results show that the accumulation of the molten mass and the welding holes might occur at low welding speed; the defocusing distance should be increased to achieve the effective addition of the powder. The optimization process parameters for laser welding of high-strength galvanized steel with powder filling were 1500W laser power, 30mm/s welding speed and 12mm defocusing distance. Under these welding conditions, good weld performance was obtained and the base material was broken in tensile fracture tests.
2014, 38(1): 6-10.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.002
Abstract:
An active multi-mode-interferometer (MMI) waveguide configuration was introduced and designed for single transverse mode laser diode with high output power. By using InAs/InGaAs/GaAs quantum dots (QD) as the active region, 1.3μm QD laser diode with the 1×1 MMI waveguide configuration was fabricated. It was demonstrated that the QD laser diode with the active MMI configuration exhibited improved heat dissipation and optical performance compared to the device with regular uniform waveguide structure. At a continuous wave injection current of 0.5A, a high output power of 114mW was obtained from the narrow waveguide while the laser diode emitting at 1332nm. The systematic study shows that the device with MMI waveguide configuration is instructive device for the fabrication of single transverse mode light emitting devices with high output power.
An active multi-mode-interferometer (MMI) waveguide configuration was introduced and designed for single transverse mode laser diode with high output power. By using InAs/InGaAs/GaAs quantum dots (QD) as the active region, 1.3μm QD laser diode with the 1×1 MMI waveguide configuration was fabricated. It was demonstrated that the QD laser diode with the active MMI configuration exhibited improved heat dissipation and optical performance compared to the device with regular uniform waveguide structure. At a continuous wave injection current of 0.5A, a high output power of 114mW was obtained from the narrow waveguide while the laser diode emitting at 1332nm. The systematic study shows that the device with MMI waveguide configuration is instructive device for the fabrication of single transverse mode light emitting devices with high output power.
2014, 38(1): 11-16.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.003
Abstract:
In order to improve the homogeneity of metallurgical reaction on the bonding interface between seam and steel so as to improve the tensile strength of a specimen, the effect of V-shaped grooves on properties of laser welding-brazing steel-aluminum butt joints was discussed by means of simulation combined with experiments. Frist, the temperature field of laser welding steel-aluminum butt was simulated by means of ANSYS. It was found that the temperature gradient on the bonding interface when there was a V-shaped groove on galvanized steel was lower than that when there was no grooves on galvanized steel. Then the experiments were carried out for laser welding steel-aluminum butt joints with and without V-shaped grooves on galvanized steel respectively, and the specimens were subjected to a tensile test. The result showed that distribution of intermetallic compounds on the bonding interface between the seam and galvanized steel with a V-shaped groove was more uniform than that without grooves. The V-shaped groove on the base material made the fracture far away from the bonding interface and the mechanical property of the joint was improved significantly.
In order to improve the homogeneity of metallurgical reaction on the bonding interface between seam and steel so as to improve the tensile strength of a specimen, the effect of V-shaped grooves on properties of laser welding-brazing steel-aluminum butt joints was discussed by means of simulation combined with experiments. Frist, the temperature field of laser welding steel-aluminum butt was simulated by means of ANSYS. It was found that the temperature gradient on the bonding interface when there was a V-shaped groove on galvanized steel was lower than that when there was no grooves on galvanized steel. Then the experiments were carried out for laser welding steel-aluminum butt joints with and without V-shaped grooves on galvanized steel respectively, and the specimens were subjected to a tensile test. The result showed that distribution of intermetallic compounds on the bonding interface between the seam and galvanized steel with a V-shaped groove was more uniform than that without grooves. The V-shaped groove on the base material made the fracture far away from the bonding interface and the mechanical property of the joint was improved significantly.
2014, 38(1): 17-20.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.004
Abstract:
In order to study the thermal effect of the neodymium-doped microsphere array caused by the pumping laser diode array (LDA), a thermal-flow-solid coupling model was established with FLUENT6.3.26 software, and the dependence of the temperature of neodymium-doped microsphere array on its size, fluid velocity, pump frequency and the number of microsphere layers was analyzed by means of finite element analysis. Analysis results show that the laser has short thermal recovery time and the cooling effect has nothing to do with the number of layers. The cooling effect of the microspheres in the small size isn't improved by increasing velocity. The maximum one-way optical path difference of Nd3+microsphere in 2mm and 4mm diameter was 3.1nm and 51.9nm respectively at a repetition rate of 1Hz. The results show that the neodymium-doped microsphere array laser has a highly efficient cooling capacity and is beneficial to the thermal management of a microsphere array laser.
In order to study the thermal effect of the neodymium-doped microsphere array caused by the pumping laser diode array (LDA), a thermal-flow-solid coupling model was established with FLUENT6.3.26 software, and the dependence of the temperature of neodymium-doped microsphere array on its size, fluid velocity, pump frequency and the number of microsphere layers was analyzed by means of finite element analysis. Analysis results show that the laser has short thermal recovery time and the cooling effect has nothing to do with the number of layers. The cooling effect of the microspheres in the small size isn't improved by increasing velocity. The maximum one-way optical path difference of Nd3+microsphere in 2mm and 4mm diameter was 3.1nm and 51.9nm respectively at a repetition rate of 1Hz. The results show that the neodymium-doped microsphere array laser has a highly efficient cooling capacity and is beneficial to the thermal management of a microsphere array laser.
2014, 38(1): 21-25.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.005
Abstract:
In order to study the interference mechanism of high-frequency laser to laser guided weapons, according to the principle of high-frequency laser interference,a series of related theoretical models such as semi-active laser seeker coded identification model, time door model, multi-signal processing model and interference signal modulation processing model were established. Then the 3σ criterion was proposed for interfering the seeker effectively. Based on this, the study of the effect of multi-source interference and signal characteristics of the effect of high repetition frequency laser interference were studied. According to the simulation system testing, the results show that the multi-source interference and interference signal frequency modulation can effectively enhance the interference effect. While the interference effect of the interference signal amplitude modulation is not obvious. The research results will provide the evaluation of high-frequency laser interference effect and provide theoretical references for application of high-frequency laser interference system.
In order to study the interference mechanism of high-frequency laser to laser guided weapons, according to the principle of high-frequency laser interference,a series of related theoretical models such as semi-active laser seeker coded identification model, time door model, multi-signal processing model and interference signal modulation processing model were established. Then the 3σ criterion was proposed for interfering the seeker effectively. Based on this, the study of the effect of multi-source interference and signal characteristics of the effect of high repetition frequency laser interference were studied. According to the simulation system testing, the results show that the multi-source interference and interference signal frequency modulation can effectively enhance the interference effect. While the interference effect of the interference signal amplitude modulation is not obvious. The research results will provide the evaluation of high-frequency laser interference effect and provide theoretical references for application of high-frequency laser interference system.
2014, 38(1): 26-29.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.006
Abstract:
According to transmission characteristics of optical energy in ultraviolet light-emitting diode(LED) scattering communication, the beam divergence angle has a certain influence on scattering link structure and received photon energy. The action effect of the beam and scatterers was strengthened with the transmit array composed by a plurality of LEDs. With the effects of different scattering on the beam divergence angle, the changing of the photon energy was analyzed. In order to study the UV communication performance more accurately, pulse modulation method and measures to increase the transmission power of UV scattering communication were studied, the solution of LED array driving circuit and the pulse position modulation (PPM) were given, scattering communication system transmission of UV-LED was tested outdoor. The experimental results showed that, in the short distance communication, large scattering angle made the light area of scatterers increase and more effective of scattering, the amount of photons arriving at receiving was increased. In the actual communication applications, the scattering optical communication was higher flexibility and real-time, appropriate optical processing can be used to optimize the structure of the optical path for increasing the transmission distance. The result provides a correct guidance for larger transmission distance and better transmission effect.
According to transmission characteristics of optical energy in ultraviolet light-emitting diode(LED) scattering communication, the beam divergence angle has a certain influence on scattering link structure and received photon energy. The action effect of the beam and scatterers was strengthened with the transmit array composed by a plurality of LEDs. With the effects of different scattering on the beam divergence angle, the changing of the photon energy was analyzed. In order to study the UV communication performance more accurately, pulse modulation method and measures to increase the transmission power of UV scattering communication were studied, the solution of LED array driving circuit and the pulse position modulation (PPM) were given, scattering communication system transmission of UV-LED was tested outdoor. The experimental results showed that, in the short distance communication, large scattering angle made the light area of scatterers increase and more effective of scattering, the amount of photons arriving at receiving was increased. In the actual communication applications, the scattering optical communication was higher flexibility and real-time, appropriate optical processing can be used to optimize the structure of the optical path for increasing the transmission distance. The result provides a correct guidance for larger transmission distance and better transmission effect.
2014, 38(1): 30-34.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.007
Abstract:
In order to interpolate these missing data of 3-D measurement quickly and accurately and achieve further comparison study, the estimation method of fast interpolation of 3-D data based on priority was proposed. This algorithm was used to interpolate both the data of simulation experiment and twenty frames vibrating speaker. Compared with other common interpolation algorithm, this new algorithm is time-saving and its result is much better. It can be used to handle large amounts of data of 3-D shape measurement.
In order to interpolate these missing data of 3-D measurement quickly and accurately and achieve further comparison study, the estimation method of fast interpolation of 3-D data based on priority was proposed. This algorithm was used to interpolate both the data of simulation experiment and twenty frames vibrating speaker. Compared with other common interpolation algorithm, this new algorithm is time-saving and its result is much better. It can be used to handle large amounts of data of 3-D shape measurement.
2014, 38(1): 39-43.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.009
Abstract:
In order to obtain phase information, many unfavorable factors such as noise, breakpoint and under sampling must be overcome. Aimed at too low sampling frequency and high fringe density, the root cause of the undersampling problem, unwrapping algorithm based on segmentation and zooming principle was introduced. After enlarging interference fringe whose density is too high by interpolation method, the phase was unwrapped. The simulation and experimental results show the feasibility of the proposed algorithm. It turns out that it is an effective unwrapping algorithm for undersampled wrapped phase.
In order to obtain phase information, many unfavorable factors such as noise, breakpoint and under sampling must be overcome. Aimed at too low sampling frequency and high fringe density, the root cause of the undersampling problem, unwrapping algorithm based on segmentation and zooming principle was introduced. After enlarging interference fringe whose density is too high by interpolation method, the phase was unwrapped. The simulation and experimental results show the feasibility of the proposed algorithm. It turns out that it is an effective unwrapping algorithm for undersampled wrapped phase.
2014, 38(1): 44-48.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.010
Abstract:
In order to solve the difficult problem of finding, identifying and tracking a low altitude, slow speed small target, a new technology of array propelled laser imaging method was proposed. With range-gated imaging model, different images of the scene were obtained by the moving forward vehicle system. According to the principle of plane array propelled imaging method, a 3-D reconstruction calculation about the successive range-gated images was introduced. Aiming at the characteristics of a low altitude, slow speed small target, the basic parameters of imaging detection system were designed. The performance of the system was studied including array elements, pulse repetition frequency, pulse duration, atmospheric attenuation and signal to noise. The results show that in low-flying area, this technology can be used to quickly imaging for 3-D observation scene, shortening the time required for images generation and could provide a guideline for the future system realization.
In order to solve the difficult problem of finding, identifying and tracking a low altitude, slow speed small target, a new technology of array propelled laser imaging method was proposed. With range-gated imaging model, different images of the scene were obtained by the moving forward vehicle system. According to the principle of plane array propelled imaging method, a 3-D reconstruction calculation about the successive range-gated images was introduced. Aiming at the characteristics of a low altitude, slow speed small target, the basic parameters of imaging detection system were designed. The performance of the system was studied including array elements, pulse repetition frequency, pulse duration, atmospheric attenuation and signal to noise. The results show that in low-flying area, this technology can be used to quickly imaging for 3-D observation scene, shortening the time required for images generation and could provide a guideline for the future system realization.
2014, 38(1): 49-53.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.011
Abstract:
A retro-focus Michelson type shearing speckle interferometry imaging system was proposed to extend the field of view (FOV) for a speckle shearing interferometer. The retro-focus imaging system includes negative lens group and television lens. Analysis of the optical setup was taken out and the simulation was demonstrated by ZEMAX software. The phase shifting unit was a plane mirror attached with a piezo, the non-uniform phase difference caused by the tilted mirror was discussed. The equal-step Carre algorithm was used to calculate the phase map so that the non-uniform phase error was avoided. The experiment results of center loaded metal plane show this method can achieve large FOV detection system. A 70°FOV imaging system can be implemented by using three plano-concave lenses with -75mm focus length and the FOV can be adjusted by changing the focus length and number of lenses.
A retro-focus Michelson type shearing speckle interferometry imaging system was proposed to extend the field of view (FOV) for a speckle shearing interferometer. The retro-focus imaging system includes negative lens group and television lens. Analysis of the optical setup was taken out and the simulation was demonstrated by ZEMAX software. The phase shifting unit was a plane mirror attached with a piezo, the non-uniform phase difference caused by the tilted mirror was discussed. The equal-step Carre algorithm was used to calculate the phase map so that the non-uniform phase error was avoided. The experiment results of center loaded metal plane show this method can achieve large FOV detection system. A 70°FOV imaging system can be implemented by using three plano-concave lenses with -75mm focus length and the FOV can be adjusted by changing the focus length and number of lenses.
2014, 38(1): 54-57.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.012
Abstract:
In order to realize an optical filter with all-fiber structure and tunable center wavelength, a novel tunable optical filter made of the third-order high birefringence fiber loop mirror and electromagnetic force based cantilever tuning unit was proposed. The transmission process of the loop mirror and the principle of the cantilever tuning unit were analyzed. The pass-band can be tuned by controlling the input current of the cantilever tuning unit. Thus it turns out that the filter possesses the characteristics of good tunability, fine output spectrum, etc.As a result, it can be used for selectively output of light-wave at different wavelengths.
In order to realize an optical filter with all-fiber structure and tunable center wavelength, a novel tunable optical filter made of the third-order high birefringence fiber loop mirror and electromagnetic force based cantilever tuning unit was proposed. The transmission process of the loop mirror and the principle of the cantilever tuning unit were analyzed. The pass-band can be tuned by controlling the input current of the cantilever tuning unit. Thus it turns out that the filter possesses the characteristics of good tunability, fine output spectrum, etc.As a result, it can be used for selectively output of light-wave at different wavelengths.
2014, 38(1): 58-64.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.013
Abstract:
To study the propagation of Rayleigh waves in a hollow cylinder, a finite element algorithm is put forward to simulate laser inducing Rayleigh waves in a hollow cylinder based on the thermoelastic mechanism. The Rayleigh waves induced by line laser source in hollow cylinders with different source-thickness and different radius were simulated and typical results were presented. Simulation results show that in the uniform thin hollow cylinder, the composition of ultrasonic waves is partly determined by the thickness of the hollow cylinder, and in a certain range, the ultrasonic waves are changing when the thickness of the hollow cylinder is changing; in the non-uniform hollow cylinder, the thickness of the source-thickness has a great influence on the generation of ultrasonic waves, and to some extent, it can determine the components of the waves. This work will provide a useful guidance for the further application of laser ultrasonic in the cylinder nondestructive testing field.
To study the propagation of Rayleigh waves in a hollow cylinder, a finite element algorithm is put forward to simulate laser inducing Rayleigh waves in a hollow cylinder based on the thermoelastic mechanism. The Rayleigh waves induced by line laser source in hollow cylinders with different source-thickness and different radius were simulated and typical results were presented. Simulation results show that in the uniform thin hollow cylinder, the composition of ultrasonic waves is partly determined by the thickness of the hollow cylinder, and in a certain range, the ultrasonic waves are changing when the thickness of the hollow cylinder is changing; in the non-uniform hollow cylinder, the thickness of the source-thickness has a great influence on the generation of ultrasonic waves, and to some extent, it can determine the components of the waves. This work will provide a useful guidance for the further application of laser ultrasonic in the cylinder nondestructive testing field.
2014, 38(1): 65-69.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.014
Abstract:
In order to propose a novel method to measure the mass fraction of fructose, plane wave expansion method for photonic crystal was adopted. A 2-D photonic crystal with a square lattice and triangle lattice of circular cylinders was designed in the Si background semiconductor material. The TE mode and TM mode band gap structure characteristics of square lattice and triangular lattice air hole structure photonic crystal were achieved.The results show that for isotropic photonic crystal of either square or triangular array arrangement, it is easier for the dielectric air type photonic crystal to form TE-polarized mode band gap in high-frequency region. Lattice structure has a certain impact on photonic band gap, TE mode band gap is much larger than the TM mode in both square and triangular structure photonic crystal. The photonic band gap changes with the difference of the mass fraction of the fructose solutions, which are used as the dielectric material in the air hole.
In order to propose a novel method to measure the mass fraction of fructose, plane wave expansion method for photonic crystal was adopted. A 2-D photonic crystal with a square lattice and triangle lattice of circular cylinders was designed in the Si background semiconductor material. The TE mode and TM mode band gap structure characteristics of square lattice and triangular lattice air hole structure photonic crystal were achieved.The results show that for isotropic photonic crystal of either square or triangular array arrangement, it is easier for the dielectric air type photonic crystal to form TE-polarized mode band gap in high-frequency region. Lattice structure has a certain impact on photonic band gap, TE mode band gap is much larger than the TM mode in both square and triangular structure photonic crystal. The photonic band gap changes with the difference of the mass fraction of the fructose solutions, which are used as the dielectric material in the air hole.
2014, 38(1): 70-75.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.015
Abstract:
Interferometric fiber-optic gyroscopes require the optical sources should have high output power, broad bandwidth, as well as good mean wavelength stability within a large temperature range. To meet the temperature demands from -45℃ to 70℃, a bandpass filter as well as a Faraday rotation mirror was incorporated in the double-pass backward Er-doped superfluorescent fiber source, which, together with the optimization of the performance of fiber and other optical components in such a large temperature range, improved the output mean wavelength of the superfluorescent fiber source a lot. The effects of filters with different central wavelengths and bandwidths, as well as fiber length on mean wavelength stability and output bandwidth were modeled. Based on the simulation result about bandpass filters and fiber length, after optimizing the whole superfluorescent fiber source, the output power reached 32mW; the output bandwidth was 12.5nm. From -45℃ to 70℃, the mean wavelength variation of the superfluorescent fiber source was controlled to 23.5×10-6, and the output power variation was 0.65%. According to the investigation, among all superfluorescent fiber sources with mean wavelength stability lower than 0.5×10-6/℃, the 32mW output power is pretty high; the thermal coefficient of 0.2×10-6/℃ is also an excellent result reported for a whole superfluorescent fiber source with output power above 30mW in the 115℃ temperature range, which satisfies the demands of interferometric fiber-optic gyroscopes.
Interferometric fiber-optic gyroscopes require the optical sources should have high output power, broad bandwidth, as well as good mean wavelength stability within a large temperature range. To meet the temperature demands from -45℃ to 70℃, a bandpass filter as well as a Faraday rotation mirror was incorporated in the double-pass backward Er-doped superfluorescent fiber source, which, together with the optimization of the performance of fiber and other optical components in such a large temperature range, improved the output mean wavelength of the superfluorescent fiber source a lot. The effects of filters with different central wavelengths and bandwidths, as well as fiber length on mean wavelength stability and output bandwidth were modeled. Based on the simulation result about bandpass filters and fiber length, after optimizing the whole superfluorescent fiber source, the output power reached 32mW; the output bandwidth was 12.5nm. From -45℃ to 70℃, the mean wavelength variation of the superfluorescent fiber source was controlled to 23.5×10-6, and the output power variation was 0.65%. According to the investigation, among all superfluorescent fiber sources with mean wavelength stability lower than 0.5×10-6/℃, the 32mW output power is pretty high; the thermal coefficient of 0.2×10-6/℃ is also an excellent result reported for a whole superfluorescent fiber source with output power above 30mW in the 115℃ temperature range, which satisfies the demands of interferometric fiber-optic gyroscopes.
2014, 38(1): 76-78.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.016
Abstract:
In order to obtain polarization images without true polarization images, firstly, the degree of polarization of various objects were found in experiments, and a database of degree of polarization was built. Then, objects in the infrared images were classified by means of K-means clustering algorithm. Finally, the polarization images were calculated from the clustering images. The results verify the simulation algorithm is feasible. The effect of the simulated images is good, it is easy to distinguish artificial object from natural objects. Image simulation is important for better and more convenient research of polarization properties of objects and the establishment of a database of polarization.
In order to obtain polarization images without true polarization images, firstly, the degree of polarization of various objects were found in experiments, and a database of degree of polarization was built. Then, objects in the infrared images were classified by means of K-means clustering algorithm. Finally, the polarization images were calculated from the clustering images. The results verify the simulation algorithm is feasible. The effect of the simulated images is good, it is easy to distinguish artificial object from natural objects. Image simulation is important for better and more convenient research of polarization properties of objects and the establishment of a database of polarization.
2014, 38(1): 79-82.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.017
Abstract:
In order to expand the ultraviolet range of an imaging spectrometer, a Wollaston prism was designed based on the birefringent material of α-BBO crystal. After theoretical analysis and simulation, the data graphs were obtained for some parameters. The splitting angle of the BBO-Wollaston prism has the non-linear relationship with the longer wavelength in the ultraviolet region, but beneficial to the stability of the beam angle in the entire spectral region; larger structure angle will make the field of view angle becomes smaller, and larger structural angle and width will help to promote the spectral resolution. Comprehensive research show that it is proper to design a α-BBO crystal Wollaston prism in thickness from 6mm to 8mm, with the structure angle α≤15°and the angle of incidence smaller than 1°in the ultraviolet to visible band. The results provide a theoretical basis for the further development of imaging spectrometers used in ultraviolet spectrum range.
In order to expand the ultraviolet range of an imaging spectrometer, a Wollaston prism was designed based on the birefringent material of α-BBO crystal. After theoretical analysis and simulation, the data graphs were obtained for some parameters. The splitting angle of the BBO-Wollaston prism has the non-linear relationship with the longer wavelength in the ultraviolet region, but beneficial to the stability of the beam angle in the entire spectral region; larger structure angle will make the field of view angle becomes smaller, and larger structural angle and width will help to promote the spectral resolution. Comprehensive research show that it is proper to design a α-BBO crystal Wollaston prism in thickness from 6mm to 8mm, with the structure angle α≤15°and the angle of incidence smaller than 1°in the ultraviolet to visible band. The results provide a theoretical basis for the further development of imaging spectrometers used in ultraviolet spectrum range.
2014, 38(1): 83-86.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.018
Abstract:
There is an optimal length of gain medium in a laser diode (LD) end-pumped laser. The laser output performance will be worsened for too long or too short crystal. In order to study the influence of thermally induced losses on the optimal gain medium length, the method of combining theoretical analysis and experiments was adopted. Through theoretical analysis of the balance between gain and losses in the laser medium, the optimal gain length of Nd:GYSGG was calculated to be 7.8mm. With experiments of laser crystals of different lengths, the best laser output performance was conformed at 8mm. The maximum output energy is about 2.4mJ with pump energy of 7.6mJ at the repetition rate of 1kHz, corresponding to the optical efficiency of 31.6%. The results show that the investigation is significant for design and optimization of end-pumped Nd:GYSGG lasers.
There is an optimal length of gain medium in a laser diode (LD) end-pumped laser. The laser output performance will be worsened for too long or too short crystal. In order to study the influence of thermally induced losses on the optimal gain medium length, the method of combining theoretical analysis and experiments was adopted. Through theoretical analysis of the balance between gain and losses in the laser medium, the optimal gain length of Nd:GYSGG was calculated to be 7.8mm. With experiments of laser crystals of different lengths, the best laser output performance was conformed at 8mm. The maximum output energy is about 2.4mJ with pump energy of 7.6mJ at the repetition rate of 1kHz, corresponding to the optical efficiency of 31.6%. The results show that the investigation is significant for design and optimization of end-pumped Nd:GYSGG lasers.
2014, 38(1): 87-90.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.019
Abstract:
In the discrete numerical calculation of diffraction distribution, the total number of sampling points following sampling theorem increases with the augment of propagating distance. Although the traditional zero-padding method resolves this problem, the calculation load increases inevitably and PC's memory can not afford. A novel frequency shift interpolation, i.e., utilizing frequency spectrum calculation after shift in Fourier domain, was proposed. In the method, more sufficient spectrum components can be got without the increase of sampling number. A complete diffraction distribution is accomplished by splicing the light field obtained by spectrum of each shifted interpolation. The results show that the proposed method successfully evades the great sampling number caused by larger diffracting distance. Comparing with traditional zero-padding method, calculation load is decreased notably and the requirement to memory in numerical calculation is depressed.
In the discrete numerical calculation of diffraction distribution, the total number of sampling points following sampling theorem increases with the augment of propagating distance. Although the traditional zero-padding method resolves this problem, the calculation load increases inevitably and PC's memory can not afford. A novel frequency shift interpolation, i.e., utilizing frequency spectrum calculation after shift in Fourier domain, was proposed. In the method, more sufficient spectrum components can be got without the increase of sampling number. A complete diffraction distribution is accomplished by splicing the light field obtained by spectrum of each shifted interpolation. The results show that the proposed method successfully evades the great sampling number caused by larger diffracting distance. Comparing with traditional zero-padding method, calculation load is decreased notably and the requirement to memory in numerical calculation is depressed.
2014, 38(1): 91-95.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.020
Abstract:
In order to study the influence of laser shock peening on the thermal stability property of A356 Al alloy, after laser shock peening A356 Al alloy workpieces with Nd:YAG laser and annealing them at 220℃ their microstructure, micro-hardness and residual stress were studied. A series of experimental data were got. The results showed that laser shock peening can effectively improve the thermal stability of A356 Al alloys. The large residual compressive stress was induced by laser shock peening on the surface, micro-hardness and the surface dislocation density was increased significantly; the grain was refined obviously. After annealing, the residual compressive stress was decreased by 30.68%, the dislocation density (full width at half maximum) was decreased from 1.63°to 1.51°, and the micro-hardness was decreased by 19.42%, the grain size on the surface layer was grown up slightly. However, compared to the matrix, the scale was less. The results were helpful to expand application fields of laser shock peening and A356 Al alloy.
In order to study the influence of laser shock peening on the thermal stability property of A356 Al alloy, after laser shock peening A356 Al alloy workpieces with Nd:YAG laser and annealing them at 220℃ their microstructure, micro-hardness and residual stress were studied. A series of experimental data were got. The results showed that laser shock peening can effectively improve the thermal stability of A356 Al alloys. The large residual compressive stress was induced by laser shock peening on the surface, micro-hardness and the surface dislocation density was increased significantly; the grain was refined obviously. After annealing, the residual compressive stress was decreased by 30.68%, the dislocation density (full width at half maximum) was decreased from 1.63°to 1.51°, and the micro-hardness was decreased by 19.42%, the grain size on the surface layer was grown up slightly. However, compared to the matrix, the scale was less. The results were helpful to expand application fields of laser shock peening and A356 Al alloy.
2014, 38(1): 96-100.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.021
Abstract:
In order to improve the relative density of parts made of selective laser sintering (SLS), cold isostatic pressing (CIP) was carried out for densification. Numerical simulations of CIP SLS parts were made based on Drucker-Prager-cap model. Theoretical analysis and experimental verification were conducted based on simulation results. The results show the relative density of SLS parts was enhanced obviously. The contraction of the parts was uniform. The errors between experimental results and wanted dimensions of main dimensions were within 0.41mm, which indicated the simulation results accorded with the experiment results. The post-process of CIP SLS parts develops the application field of powder laser rapid prototype that lays the technical and experimental foundation for engineering practice.
In order to improve the relative density of parts made of selective laser sintering (SLS), cold isostatic pressing (CIP) was carried out for densification. Numerical simulations of CIP SLS parts were made based on Drucker-Prager-cap model. Theoretical analysis and experimental verification were conducted based on simulation results. The results show the relative density of SLS parts was enhanced obviously. The contraction of the parts was uniform. The errors between experimental results and wanted dimensions of main dimensions were within 0.41mm, which indicated the simulation results accorded with the experiment results. The post-process of CIP SLS parts develops the application field of powder laser rapid prototype that lays the technical and experimental foundation for engineering practice.
2014, 38(1): 101-104.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.022
Abstract:
In order to compensate dispersion in an optical communication system, a single channel dispersion compensation system which used of dispersion compensating fiber was designed and simulated. The system was optimized by a fiber loop mirror so that it economized the cost, and the effect of dispersion compensation was fine. The simulation results such as Q factor and eye diagram were given and analyzed in this system with different velocity of 2.5Gbit/s and 10Gbit/s, and their input power were obtained. When the system's velocity is 2.5Gbit/s, the optimum input power is 13dBm, and Q factor is 172.88; When the system's velocity is 10Gbit/s, the input power is 6dBm and the corresponding Q factor is 45.96. The obtained results are helpful for the application of dispersion compensation in an optical communication system.
In order to compensate dispersion in an optical communication system, a single channel dispersion compensation system which used of dispersion compensating fiber was designed and simulated. The system was optimized by a fiber loop mirror so that it economized the cost, and the effect of dispersion compensation was fine. The simulation results such as Q factor and eye diagram were given and analyzed in this system with different velocity of 2.5Gbit/s and 10Gbit/s, and their input power were obtained. When the system's velocity is 2.5Gbit/s, the optimum input power is 13dBm, and Q factor is 172.88; When the system's velocity is 10Gbit/s, the input power is 6dBm and the corresponding Q factor is 45.96. The obtained results are helpful for the application of dispersion compensation in an optical communication system.
2014, 38(1): 105-108.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.023
Abstract:
To optimize the fiber laser cavity, an Yb3+-doped double-cladding photonic crystal fiber (PCF) was pumped with a 110W multimode LD at central wavelength of 976nm, and the PCF laser characteristics were examined. A dichroic flat mirror and a dichroic flat-concave mirror were used as the back cavity-mirror respectively. There happened the model competition phenomenon in the first laser. And the line width of the PCF laser with a flat-concave mirror as the back cavity-mirror was about 5nm, while another one was above 10nm. Besides, slope efficiency of the former was 11%, and the latter's was just 9%. It has stable model, narrower emission line width and higher slope efficiency in the PCF-laser with a flat-concave mirror as the back cavity-mirror.
To optimize the fiber laser cavity, an Yb3+-doped double-cladding photonic crystal fiber (PCF) was pumped with a 110W multimode LD at central wavelength of 976nm, and the PCF laser characteristics were examined. A dichroic flat mirror and a dichroic flat-concave mirror were used as the back cavity-mirror respectively. There happened the model competition phenomenon in the first laser. And the line width of the PCF laser with a flat-concave mirror as the back cavity-mirror was about 5nm, while another one was above 10nm. Besides, slope efficiency of the former was 11%, and the latter's was just 9%. It has stable model, narrower emission line width and higher slope efficiency in the PCF-laser with a flat-concave mirror as the back cavity-mirror.
2014, 38(1): 109-113.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.024
Abstract:
In order to improve measuring precision of thread based on machine vision, tangential and vertical projection measuring methods were discussed in theory, and verified experimentally, mainly related to the matter of extending helicoidal surface shade error when measuring thread profile with both the methods. After introducing the tangential and vertical projection measurement methods, the error sources were analyzed which cause principle error in measuring thread. The shade error calculating formula was given that caused from measuring thread with vertical projection measurement, and the effect that the shade error and the error caused by different lead angle was studied in measuring thread profile experiments. The result shows that the helix angle measurement error caused by extend helicoids shade error can reached over 1°when measuring larger-size helical pitch by vertical projection measurement, it can't be ignored for helix angle measurement.
In order to improve measuring precision of thread based on machine vision, tangential and vertical projection measuring methods were discussed in theory, and verified experimentally, mainly related to the matter of extending helicoidal surface shade error when measuring thread profile with both the methods. After introducing the tangential and vertical projection measurement methods, the error sources were analyzed which cause principle error in measuring thread. The shade error calculating formula was given that caused from measuring thread with vertical projection measurement, and the effect that the shade error and the error caused by different lead angle was studied in measuring thread profile experiments. The result shows that the helix angle measurement error caused by extend helicoids shade error can reached over 1°when measuring larger-size helical pitch by vertical projection measurement, it can't be ignored for helix angle measurement.
2014, 38(1): 114-118.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.025
Abstract:
In order to design a novel fan-shaped semiconductor micro-ring laser based on an elliptical mirror reflector, ray tracing and finite-difference time-domain method were applied to approach theoretical analysis and design simulation. Compared with the common triangular ring cavity, due to the introduction of the elliptical mirror reflector that the specular reflection loss of this new micro-cavity is very low (1%), the power transmission rate is 93% and the high Q value is also achieved. At the resonance wavelength of 1576.36nm, Q value reaches 23318.6. The results show that this novel type of micro-ring laser has a bigger chance to exhibit directional bistablility, and can be further used to the field of all-optical signal processing.
In order to design a novel fan-shaped semiconductor micro-ring laser based on an elliptical mirror reflector, ray tracing and finite-difference time-domain method were applied to approach theoretical analysis and design simulation. Compared with the common triangular ring cavity, due to the introduction of the elliptical mirror reflector that the specular reflection loss of this new micro-cavity is very low (1%), the power transmission rate is 93% and the high Q value is also achieved. At the resonance wavelength of 1576.36nm, Q value reaches 23318.6. The results show that this novel type of micro-ring laser has a bigger chance to exhibit directional bistablility, and can be further used to the field of all-optical signal processing.
2014, 38(1): 119-123.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.026
Abstract:
Phase comparison of the heterodyne signal determines the performance of the heterodyne interferometer to some extent, such as precision and resolution. To resolve the conflict between the resolution and the velocity, methods used presently to design the phase comparator were introduced and analyzed. Key design points to achieve high measureable velocity with fine resolution were discussed. Solutions to the problems were also proposed. The full period sampling method based on field-programmable gate array(FPGA) can improve the precision of autocorrelation and the zero-across detection with frequency mixing can improve the test speed.
Phase comparison of the heterodyne signal determines the performance of the heterodyne interferometer to some extent, such as precision and resolution. To resolve the conflict between the resolution and the velocity, methods used presently to design the phase comparator were introduced and analyzed. Key design points to achieve high measureable velocity with fine resolution were discussed. Solutions to the problems were also proposed. The full period sampling method based on field-programmable gate array(FPGA) can improve the precision of autocorrelation and the zero-across detection with frequency mixing can improve the test speed.
2014, 38(1): 124-127.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.027
Abstract:
In order to reduce the wavelength drift of the time division multiplexing passive optical network (TDM-PON) upstream traffic,based on a architecture with optical power equalization of the upstream traffic in a TDM-PON, using single mode laser injection locking Fabry-Perot laser diode (F-P LD) of optical network unit (ONU), the mode-locking characteristics of Fabry-Perot output laser wavelength was discussed, such as the range of injection-locking, the influence of driving current on mode-locking characteristics, the influence of temperature variation on the wavelength with or without injection-locking. The results show that, for such a laser, when the driving current is 9mA, the injection-locking wavelength range is 0.38nm which is larger than the 0.25nm upstream wavelength drift of the ONU caused by the 5℃ change of environmental temperature. The identical and stable wavelength of the ONU upstream traffic and the low noise after the optical power equalization were achieved by the injection-locking F-P LD.
In order to reduce the wavelength drift of the time division multiplexing passive optical network (TDM-PON) upstream traffic,based on a architecture with optical power equalization of the upstream traffic in a TDM-PON, using single mode laser injection locking Fabry-Perot laser diode (F-P LD) of optical network unit (ONU), the mode-locking characteristics of Fabry-Perot output laser wavelength was discussed, such as the range of injection-locking, the influence of driving current on mode-locking characteristics, the influence of temperature variation on the wavelength with or without injection-locking. The results show that, for such a laser, when the driving current is 9mA, the injection-locking wavelength range is 0.38nm which is larger than the 0.25nm upstream wavelength drift of the ONU caused by the 5℃ change of environmental temperature. The identical and stable wavelength of the ONU upstream traffic and the low noise after the optical power equalization were achieved by the injection-locking F-P LD.
2014, 38(1): 128-131.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.028
Abstract:
The refractive index of K9 glass was measured with the third-order harmonic technique, in which two parallel femtosecond laser beams with equal energy were involved. In addition, theoretical analysis and experimental verification were performed, and the refractive index of K9 cylindrical mirror and the measurement accuray were obtained by processing the experimental data before and after putting the sample into the light path. Furthermore, the refractive index of two pieces of attenuators has also been measured. It turned out that the measured refractive index of the sample was in good agreement with the actual data, which verified the validity of this technique to measure the linear refractive index of materials. Compared with the traditional measuring methods, this technique can be operated simply, which has no limit on the range of the refractive index, and the sample is processed easily. Thus, the method of third-order harmonic has very important practical value.
The refractive index of K9 glass was measured with the third-order harmonic technique, in which two parallel femtosecond laser beams with equal energy were involved. In addition, theoretical analysis and experimental verification were performed, and the refractive index of K9 cylindrical mirror and the measurement accuray were obtained by processing the experimental data before and after putting the sample into the light path. Furthermore, the refractive index of two pieces of attenuators has also been measured. It turned out that the measured refractive index of the sample was in good agreement with the actual data, which verified the validity of this technique to measure the linear refractive index of materials. Compared with the traditional measuring methods, this technique can be operated simply, which has no limit on the range of the refractive index, and the sample is processed easily. Thus, the method of third-order harmonic has very important practical value.
2014, 38(1): 132-136.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.029
Abstract:
In order to improve the wear resistance of the clad layer, the powder mixture of stellite-6 and tungsten carbide (WC) in the range of 0~0.47 mass fraction of WC was deposited on mild steel plates by CO2 laser cladding system. The phase constitution, microstructure, hardness and wear resistance of the clad layer were studied with an X-ray diffractometer, energy dispersive spectroscopy, scanning electron microscope, laser microscope, Vickers hardness tester and wear tester. According to the analyzed results, the microstructure of the clad layer consists of hypoeutectic structure and undissolved tungsten carbides dispersed in the matrix of the Co-based alloy. The Vickers hardness increases with the increase of WC weight fraction. On the other hand, the crack sensitivity of the laser clad layer is low.
In order to improve the wear resistance of the clad layer, the powder mixture of stellite-6 and tungsten carbide (WC) in the range of 0~0.47 mass fraction of WC was deposited on mild steel plates by CO2 laser cladding system. The phase constitution, microstructure, hardness and wear resistance of the clad layer were studied with an X-ray diffractometer, energy dispersive spectroscopy, scanning electron microscope, laser microscope, Vickers hardness tester and wear tester. According to the analyzed results, the microstructure of the clad layer consists of hypoeutectic structure and undissolved tungsten carbides dispersed in the matrix of the Co-based alloy. The Vickers hardness increases with the increase of WC weight fraction. On the other hand, the crack sensitivity of the laser clad layer is low.
2014, 38(1): 137-140.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.030
Abstract:
Fire image enhancement plays an important role in the system of fire detection based on images. A deficit of traditional fuzzy enhancement algorithms is the high computation cost. To solve this problem, a novel algorithm was proposed utilizing the 3-D look-up table (LUT) and a novel image fuzzy enhancement arithmetic operator. It firstly transforms the color space of fire images from red, green and blue to hue, intensity, saturaiton(HIS) and builds LUT for the variables I and S. Then enhances them through LUT and transforms the color space of fire images back to HIS space. Experimental results show that the new algorithm has significantly improved the running speed. It's helpful to the real-time detection of fire.
Fire image enhancement plays an important role in the system of fire detection based on images. A deficit of traditional fuzzy enhancement algorithms is the high computation cost. To solve this problem, a novel algorithm was proposed utilizing the 3-D look-up table (LUT) and a novel image fuzzy enhancement arithmetic operator. It firstly transforms the color space of fire images from red, green and blue to hue, intensity, saturaiton(HIS) and builds LUT for the variables I and S. Then enhances them through LUT and transforms the color space of fire images back to HIS space. Experimental results show that the new algorithm has significantly improved the running speed. It's helpful to the real-time detection of fire.
2014, 38(1): 141-144.
doi: 10.7510/jgjs.issn.1001-3806.2014.01.031
Abstract:
In order to study transmission characteristics of non-paraxial partially coherent Hermitian-cosine-Gaussian beam, the Wigner distribution function was used to analyze the characteristics in spatial and time domain. Their analytical propagation expressions with the three parameters of f,fσ,g were obtained for describing the space domain and frequency domain at the same time. The calculated results show that f and fσ play key roles in determining the non-paraxiality partially coherent Hermite-cosine-Gaussian beams, when g is constant. On the other hand, when g is changing, it can not preserve their shape while propagating in free space.
In order to study transmission characteristics of non-paraxial partially coherent Hermitian-cosine-Gaussian beam, the Wigner distribution function was used to analyze the characteristics in spatial and time domain. Their analytical propagation expressions with the three parameters of f,fσ,g were obtained for describing the space domain and frequency domain at the same time. The calculated results show that f and fσ play key roles in determining the non-paraxiality partially coherent Hermite-cosine-Gaussian beams, when g is constant. On the other hand, when g is changing, it can not preserve their shape while propagating in free space.
