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RSS2011 Vol. 35, No. 3
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2011, 35(3): 289-292.
doi: 10.3969/j.issn.1001-3806.2011.03.001
[Abstract]
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Abstract:
Optical absorption method is effective for trace methane detection and is extensively used in foul gas measurement and alarm in case of coal mining tunnel. In order to obtain a monochromatic light source for detecting the methane absorption at 1653nm wavelength, a 1653nm distributed feedback(DFB)laser was obtained from multi quantum well material design and epitaxy to device package with technologies such as metal-organic chemical vapor deposition epitaxy and nanoimprint lithography. The laser demonstrated 52dB side mode suppression ratio, 14.9% external quantum efficiency，no more than 12mA threshold current, 0.11nm@20dB line width matching the absorption band of methane at 1653nm, and stable optical and electrical characteristics. Less than 1.3% error was obtained for detection of methane with gas volume fraction from 0.005 to 0.05, based on the DFB laser. The result shows that the device is suitable for trace methane detection in engineering by means of harmonic detection and can be manufactured in mass production.
Optical absorption method is effective for trace methane detection and is extensively used in foul gas measurement and alarm in case of coal mining tunnel. In order to obtain a monochromatic light source for detecting the methane absorption at 1653nm wavelength, a 1653nm distributed feedback(DFB)laser was obtained from multi quantum well material design and epitaxy to device package with technologies such as metal-organic chemical vapor deposition epitaxy and nanoimprint lithography. The laser demonstrated 52dB side mode suppression ratio, 14.9% external quantum efficiency，no more than 12mA threshold current, 0.11nm@20dB line width matching the absorption band of methane at 1653nm, and stable optical and electrical characteristics. Less than 1.3% error was obtained for detection of methane with gas volume fraction from 0.005 to 0.05, based on the DFB laser. The result shows that the device is suitable for trace methane detection in engineering by means of harmonic detection and can be manufactured in mass production.
2011, 35(3): 293-298,304.
doi: 10.3969/j.issn.1001-3806.2011.03.002
Abstract:
Liquid crystal based beam steering technology has advantages of high accuracy，low power consumption and random-access pointing etc. Firstly, the worldwide research status was introduced. Secondly, the basic principle and performance indexes，in company with the research progress and bottleneck, of beam steering system based on liquid crystal were described in detail. Combining liquid crystal material with wide-angle step-steering devices, a few techniques for wide-angle beam steering were compared. Finally, the development trend of novel liquid crystal based beam steering technology was previewed.
Liquid crystal based beam steering technology has advantages of high accuracy，low power consumption and random-access pointing etc. Firstly, the worldwide research status was introduced. Secondly, the basic principle and performance indexes，in company with the research progress and bottleneck, of beam steering system based on liquid crystal were described in detail. Combining liquid crystal material with wide-angle step-steering devices, a few techniques for wide-angle beam steering were compared. Finally, the development trend of novel liquid crystal based beam steering technology was previewed.
2011, 35(3): 299-301,311.
doi: 10.3969/j.issn.1001-3806.2011.03.003
Abstract:
In order to suppress the high-frequency noise contained in the wavelet ridge obtained from the laser interference velocity measurement system and improve the system accuracy, a method based on empirical mode decomposition was proposed . Theoretical analysis and experimental results show that this method can significantly suppress the high-frequency noise. The measurement error is 42.3% of the original one before optimization. This method improves the system accuracy of the all-fiber displacement interferometer system for any reflector and it is applicable in signal denoising in time-frequency analysis.
In order to suppress the high-frequency noise contained in the wavelet ridge obtained from the laser interference velocity measurement system and improve the system accuracy, a method based on empirical mode decomposition was proposed . Theoretical analysis and experimental results show that this method can significantly suppress the high-frequency noise. The measurement error is 42.3% of the original one before optimization. This method improves the system accuracy of the all-fiber displacement interferometer system for any reflector and it is applicable in signal denoising in time-frequency analysis.
2011, 35(3): 302-304.
doi: 10.3969/j.issn.1001-3806.2011.03.004
Abstract:
In order to study effect of phosphor on welding quality of high strength steel, 4.8mm thick P-added high strength interstitial free steel M250P1 was welded with a 12kW CO2 laser. For different welding parameters, different welding nodes were obtained, and their tensile dynamic property, microstructure and scanning electron microscope energy spectrum were observed. The results show that: for given welding parameters, the weld joints show good tensile and forming property, however, crack is prone to happen on the fusion zone because of the toughness reduction induced by phosphorus microsegregation in the fusion zone. The phosphorus element in the fusion zone hadn't enough time to diffuse and aggregated on the grain boundary when the fusion metal was quickly cooled after weld.
In order to study effect of phosphor on welding quality of high strength steel, 4.8mm thick P-added high strength interstitial free steel M250P1 was welded with a 12kW CO2 laser. For different welding parameters, different welding nodes were obtained, and their tensile dynamic property, microstructure and scanning electron microscope energy spectrum were observed. The results show that: for given welding parameters, the weld joints show good tensile and forming property, however, crack is prone to happen on the fusion zone because of the toughness reduction induced by phosphorus microsegregation in the fusion zone. The phosphorus element in the fusion zone hadn't enough time to diffuse and aggregated on the grain boundary when the fusion metal was quickly cooled after weld.
2011, 35(3): 305-307,333.
doi: 10.3969/j.issn.1001-3806.2011.03.005
Abstract:
In order to study the thermal effect of rectangular Nd:GGG heat capacity laser crystal, the semianalytical analysis of thermal conductive anisotropic material was introduced. Through the analysis of working characteristic of laser crystal, thermal model according to actual working state was established, thermal effect of a rectangular Nd:GGG crystal was investigated and the expressions of temperature field inside laser crystal in the pump stage and cooling stage were obtained. The effect of width and thickness of the crystal on temperature field was analyzed quantitatively. Results show that a maximum temperature rise of 169.1℃ is obtained in the center of the pump surface after LD-pumped for 4s with an output power of 8100W and a pulse frequency of 500Hz and a pulse width of 0.2ms. The maximum temperature rise decreases to 0.97% 120s later after the pumping stops. The results can offer theoretical basis for the optimization design of heat capacity lasers.
In order to study the thermal effect of rectangular Nd:GGG heat capacity laser crystal, the semianalytical analysis of thermal conductive anisotropic material was introduced. Through the analysis of working characteristic of laser crystal, thermal model according to actual working state was established, thermal effect of a rectangular Nd:GGG crystal was investigated and the expressions of temperature field inside laser crystal in the pump stage and cooling stage were obtained. The effect of width and thickness of the crystal on temperature field was analyzed quantitatively. Results show that a maximum temperature rise of 169.1℃ is obtained in the center of the pump surface after LD-pumped for 4s with an output power of 8100W and a pulse frequency of 500Hz and a pulse width of 0.2ms. The maximum temperature rise decreases to 0.97% 120s later after the pumping stops. The results can offer theoretical basis for the optimization design of heat capacity lasers.
2011, 35(3): 308-311.
doi: 10.3969/j.issn.1001-3806.2011.03.006
Abstract:
Research progress of laser induced damage of coating at 193nm was reviewed. After some typical damage morphologies from UV to DUV were compared, the possible reasons for the laser damage of the coating were put forward. The absorption of oxide coating at 193nm was responsible for the massive damage, while the damage of fluoride coating at 193nm was induced by local deposit defects. The dependence of the laser induced damage threshold on the thin film preparation parameters was known according to the damage analysis of the specimen. The methods to enhance the laser induced damage threshold were summarized by material chose, coating design and deposition process.
Research progress of laser induced damage of coating at 193nm was reviewed. After some typical damage morphologies from UV to DUV were compared, the possible reasons for the laser damage of the coating were put forward. The absorption of oxide coating at 193nm was responsible for the massive damage, while the damage of fluoride coating at 193nm was induced by local deposit defects. The dependence of the laser induced damage threshold on the thin film preparation parameters was known according to the damage analysis of the specimen. The methods to enhance the laser induced damage threshold were summarized by material chose, coating design and deposition process.
2011, 35(3): 312-314,411.
doi: 10.3969/j.issn.1001-3806.2011.03.007
Abstract:
To study the property of an open photonic crystal cavity, the new open cavity, formed by 30 vertex angle of the photonic crystal and air tank alternately was analyzed based on the plane wave expansion method and finite-difference time-domain method. It was found that the open cavity structure had negative refraction property in both the normalized frequency bands (0.3006~0.35 and 0.6755~0.6851), and a zero-optical path closed-loop could be formed with the air tank in the frequency range of negative refraction; and there was a high transmission rate in the photonic crystal and air tank boundaries, so resonance could happen at a certain wavelength. The results indicate that the refractive index can be measured with high sensitivity using this open photonic crystal cavity whose resonance wavelength varies with the refractive index.
To study the property of an open photonic crystal cavity, the new open cavity, formed by 30 vertex angle of the photonic crystal and air tank alternately was analyzed based on the plane wave expansion method and finite-difference time-domain method. It was found that the open cavity structure had negative refraction property in both the normalized frequency bands (0.3006~0.35 and 0.6755~0.6851), and a zero-optical path closed-loop could be formed with the air tank in the frequency range of negative refraction; and there was a high transmission rate in the photonic crystal and air tank boundaries, so resonance could happen at a certain wavelength. The results indicate that the refractive index can be measured with high sensitivity using this open photonic crystal cavity whose resonance wavelength varies with the refractive index.
2011, 35(3): 315-318.
doi: 10.3969/j.issn.1001-3806.2011.03.008
Abstract:
In order to study the size of melt pool in laser cladding, a system for monitoring the melt pool was constructed with a CCD camera and special image-processing software developed on VISUAL C++. The edge and geometric parameters of the melt pool were obtained in real-time. The width of the clad layer was obtained in time after calibration correction coefficients of the experimental detection system. Experiment results indicate that the width of melt pool can be detected accurately, and the presented system is useful for online detection of the clad quality.
In order to study the size of melt pool in laser cladding, a system for monitoring the melt pool was constructed with a CCD camera and special image-processing software developed on VISUAL C++. The edge and geometric parameters of the melt pool were obtained in real-time. The width of the clad layer was obtained in time after calibration correction coefficients of the experimental detection system. Experiment results indicate that the width of melt pool can be detected accurately, and the presented system is useful for online detection of the clad quality.
2011, 35(3): 319-321,325.
doi: 10.3969/j.issn.1001-3806.2011.03.009
Abstract:
In order to find more simple and stable chaos anti-control methods of a laser system, the characteristics of an erbium-doped fiber ring laser was simulated based on delay feedback and various periodic phenomena and chaotic behaviors were observed. It was found that chaotic control of erbium-doped fiber ring laser could be realized with delay feedback. These results are useful for simplifying chaos anti-control in secret communication.
In order to find more simple and stable chaos anti-control methods of a laser system, the characteristics of an erbium-doped fiber ring laser was simulated based on delay feedback and various periodic phenomena and chaotic behaviors were observed. It was found that chaotic control of erbium-doped fiber ring laser could be realized with delay feedback. These results are useful for simplifying chaos anti-control in secret communication.
2011, 35(3): 322-325.
doi: 10.3969/j.issn.1001-3806.2011.03.010
Abstract:
In order to eliminate effect of inhomogeneous light spot, light intensity randomness, beam off-axis in the process of online large-spot laser energy measurement，a simple method was introduced. The laser beam was collected with a common diffusive plate and its spot was decreased so that its spatial information was eliminated and only the intensity information was reserved. At the same time, the sampling spots were laid in the region diffusive light could reach so as to eliminate effect of transmission section and polarization state. Furthermore, the distance between sampling spots and the diffusive plate was much greater than beam size to eliminate the effect of insufficiency of the sensor receiving angle. Laser energy was obtained by a photoelectric integrator. Experiment results indicate that the response in the laser detection surface is coincident and partial intensity change and laser divergence have little effect on the measurement result. The above suggested method can eliminate effect of many factors and ensure the measurement accuracy.
In order to eliminate effect of inhomogeneous light spot, light intensity randomness, beam off-axis in the process of online large-spot laser energy measurement，a simple method was introduced. The laser beam was collected with a common diffusive plate and its spot was decreased so that its spatial information was eliminated and only the intensity information was reserved. At the same time, the sampling spots were laid in the region diffusive light could reach so as to eliminate effect of transmission section and polarization state. Furthermore, the distance between sampling spots and the diffusive plate was much greater than beam size to eliminate the effect of insufficiency of the sensor receiving angle. Laser energy was obtained by a photoelectric integrator. Experiment results indicate that the response in the laser detection surface is coincident and partial intensity change and laser divergence have little effect on the measurement result. The above suggested method can eliminate effect of many factors and ensure the measurement accuracy.
2011, 35(3): 326-329.
doi: 10.3969/j.issn.1001-3806.2011.03.011
Abstract:
At present, it is a considerable shortage of natural calcite and it has some defects and restrictions in application. In order to alleviate the shortage of polarized prism material，the new alternative birefringence material-BBO was studied. Based on the light total reflection principle at the interface, the polarizing prisms with Lippich and Glan-Taylor style were designed. The value range of their structural angles and corresponding field angles, in particular the corresponding theoretical value in the frequency band from 230nm to 800nm were put forward. The result shows that this kind of material has good applicability and larger view angles in the ultraviolet wave band.This work lays the foundation for further research and development of new material polarized devices.
At present, it is a considerable shortage of natural calcite and it has some defects and restrictions in application. In order to alleviate the shortage of polarized prism material，the new alternative birefringence material-BBO was studied. Based on the light total reflection principle at the interface, the polarizing prisms with Lippich and Glan-Taylor style were designed. The value range of their structural angles and corresponding field angles, in particular the corresponding theoretical value in the frequency band from 230nm to 800nm were put forward. The result shows that this kind of material has good applicability and larger view angles in the ultraviolet wave band.This work lays the foundation for further research and development of new material polarized devices.
2011, 35(3): 330-333.
doi: 10.3969/j.issn.1001-3806.2011.03.012
Abstract:
In order to investigate a digital modulation applicable for underwater wireless optical communication (UWOC), the model of the UWOC channel was analyzed. The packet error rate, bandwidth efficiency and energy efficiency of the channel based on multilevel digital pulse interval modulation (MDPIM) was deduced. Comparison was carried out between different modulation modes. Both power efficiency and bandwidth efficiency are the highest for MDPIM. The results help to determine the modulation suitable for underwater wireless optical communication.
In order to investigate a digital modulation applicable for underwater wireless optical communication (UWOC), the model of the UWOC channel was analyzed. The packet error rate, bandwidth efficiency and energy efficiency of the channel based on multilevel digital pulse interval modulation (MDPIM) was deduced. Comparison was carried out between different modulation modes. Both power efficiency and bandwidth efficiency are the highest for MDPIM. The results help to determine the modulation suitable for underwater wireless optical communication.
2011, 35(3): 334-337.
doi: 10.3969/j.issn.1001-3806.2011.03.013
Abstract:
In order to study the processing quality of the laser hardened workpiece, a dynamic detecting system of laser hardening was developed in which a CCD camera was used to capture the thermal radiation images in laser hardening process. The oversaturated phenomenon can be eliminated during the detecting process by selecting the CCD model reasonably. The images of the object were taken by the CCD camera. Then the image data were analyzed by a computer so that image processing made the gray value distribution display clearly, and the hardened band width was obtained by pseudo-color and threshold segmentation processing, which made the software system was developed successfully. The experimental results show that this system can accurately measure the hardened band width, which will contribute to a closed-loop control system for laser hardening for improvement in hardening quality.
In order to study the processing quality of the laser hardened workpiece, a dynamic detecting system of laser hardening was developed in which a CCD camera was used to capture the thermal radiation images in laser hardening process. The oversaturated phenomenon can be eliminated during the detecting process by selecting the CCD model reasonably. The images of the object were taken by the CCD camera. Then the image data were analyzed by a computer so that image processing made the gray value distribution display clearly, and the hardened band width was obtained by pseudo-color and threshold segmentation processing, which made the software system was developed successfully. The experimental results show that this system can accurately measure the hardened band width, which will contribute to a closed-loop control system for laser hardening for improvement in hardening quality.
2011, 35(3): 338-342,379.
doi: 10.3969/j.issn.1001-3806.2011.03.014
Abstract:
The development of all-solid-state Raman laser and optical parametric oscillation(OPO) laser were summarized during the past five years. The principle and crystal of Raman laser and OPO laser were compared. An all-solid-state Raman lasers has advantages in beam quality and optical stability. While, an OPO laser has a larger tuning range and higher output power. Finally, the future development of all-solid-state Raman and OPO lasers was put forward.
The development of all-solid-state Raman laser and optical parametric oscillation(OPO) laser were summarized during the past five years. The principle and crystal of Raman laser and OPO laser were compared. An all-solid-state Raman lasers has advantages in beam quality and optical stability. While, an OPO laser has a larger tuning range and higher output power. Finally, the future development of all-solid-state Raman and OPO lasers was put forward.
2011, 35(3): 343-347.
doi: 10.3969/j.issn.1001-3806.2011.03.015
Abstract:
In order to solve the problem of deflection control of deflection algorithm, a deflection routing algorithm was proposed based on priority and load balancing in optical burst switching(OBS)networks. When conflict occurs, low priority bursts are segmented at first. Then, the contention part of bursts is deflected to free links. The algorithm selects many candidate routes on which the current maximum number of residual hops less than the maximum number of hops of the source-to-destination nodes. Finally, the algorithm chooses the best route that balances the assigned wavelengths of every links from candidate routes. This algorithm was analyzed in theory and simulated, and a series of data including the packet loss probability and the delay changing with network loads were obtained. Simulation results show that the delay of the proposed algorithm is located between the shortest path deflection routing algorithm and load-balancing deflection routing algorithm. It can efficiently reduce the packet loss probability of the entire network and protect the integrity of some high priority bursts. So the scheme can efficiently improve the performance of OBS networks.
In order to solve the problem of deflection control of deflection algorithm, a deflection routing algorithm was proposed based on priority and load balancing in optical burst switching(OBS)networks. When conflict occurs, low priority bursts are segmented at first. Then, the contention part of bursts is deflected to free links. The algorithm selects many candidate routes on which the current maximum number of residual hops less than the maximum number of hops of the source-to-destination nodes. Finally, the algorithm chooses the best route that balances the assigned wavelengths of every links from candidate routes. This algorithm was analyzed in theory and simulated, and a series of data including the packet loss probability and the delay changing with network loads were obtained. Simulation results show that the delay of the proposed algorithm is located between the shortest path deflection routing algorithm and load-balancing deflection routing algorithm. It can efficiently reduce the packet loss probability of the entire network and protect the integrity of some high priority bursts. So the scheme can efficiently improve the performance of OBS networks.
2011, 35(3): 348-351.
doi: 10.3969/j.issn.1001-3806.2011.03.016
Abstract:
To study effect of wave aberration on tiling results, far-field characteristic parameters for two-pair gratings with wave aberration were calculated by means of analogy calculation. On the basis of a certain evaluation criterion, the tiling accuracy of the mosaic gratings was obtained. Calculation results show that for the wave aberration with the coma of 0.5, the maximum piston-error of the tiling precision is about 0.42 grating period, and the maximum tip-tip error is 0.52rad approximately, which are lower than those of gratings without wave aberration. The result is useful for preparation of large aperture compression mosaic gratings.
To study effect of wave aberration on tiling results, far-field characteristic parameters for two-pair gratings with wave aberration were calculated by means of analogy calculation. On the basis of a certain evaluation criterion, the tiling accuracy of the mosaic gratings was obtained. Calculation results show that for the wave aberration with the coma of 0.5, the maximum piston-error of the tiling precision is about 0.42 grating period, and the maximum tip-tip error is 0.52rad approximately, which are lower than those of gratings without wave aberration. The result is useful for preparation of large aperture compression mosaic gratings.
2011, 35(3): 352-355,387.
doi: 10.3969/j.issn.1001-3806.2011.03.017
Abstract:
Particle size inverse algorithm is the key technology for laser particle size analyzer based on Mie theory. Because the independent model iterative inverse algorithm was so sensitive to noise that it can not be used in actual particle size measurement, five-spot triple smoothing algorithm was proposed to conduct independent model iterative inversion. With VISUAL C++6.0 as development platform, the software was written and simulation was carried out. The simulation result was compared with actual distribution. The distribution error of special particle size D10, D90 was less than 5%, and the distribution error of special particle size D50 was less than 3%. The results show that only the inversion data after smoothing processing can reveal the actual distribution of particle size. The inversion result distortion induced by the optical energy detection error can be overcome. This algorithm can satisfy the requirements of high accuracy, anti-jamming and stability for particle size measurement in modern power industry.
Particle size inverse algorithm is the key technology for laser particle size analyzer based on Mie theory. Because the independent model iterative inverse algorithm was so sensitive to noise that it can not be used in actual particle size measurement, five-spot triple smoothing algorithm was proposed to conduct independent model iterative inversion. With VISUAL C++6.0 as development platform, the software was written and simulation was carried out. The simulation result was compared with actual distribution. The distribution error of special particle size D10, D90 was less than 5%, and the distribution error of special particle size D50 was less than 3%. The results show that only the inversion data after smoothing processing can reveal the actual distribution of particle size. The inversion result distortion induced by the optical energy detection error can be overcome. This algorithm can satisfy the requirements of high accuracy, anti-jamming and stability for particle size measurement in modern power industry.
2011, 35(3): 356-359.
doi: 10.3969/j.issn.1001-3806.2011.03.018
Abstract:
For the coherent detection of laser beams in free space, a new 24 90 optical hybrid for freely propagating laser beams was proposed based on the diffraction and polarization characteristics of a subwavelength polarization grating. It mainly consists of a subwavelength polarization grating, two half-wave-plates and two polarization splitters. The split and recombination of the signal beam and the local oscillator beam are achieved through the subwavelength polarization grating. The desired phase relation is obtained when orthogonally polarized beam components of the left-circularly and right-circularly polarized light are spatially separated under given conditions so that the rigid phase requirement for the beam splitters in traditional space optical hybrids is avoided and stable phase output can be obtained easily. It has potential applications in field of free-space laser coherent communication.
For the coherent detection of laser beams in free space, a new 24 90 optical hybrid for freely propagating laser beams was proposed based on the diffraction and polarization characteristics of a subwavelength polarization grating. It mainly consists of a subwavelength polarization grating, two half-wave-plates and two polarization splitters. The split and recombination of the signal beam and the local oscillator beam are achieved through the subwavelength polarization grating. The desired phase relation is obtained when orthogonally polarized beam components of the left-circularly and right-circularly polarized light are spatially separated under given conditions so that the rigid phase requirement for the beam splitters in traditional space optical hybrids is avoided and stable phase output can be obtained easily. It has potential applications in field of free-space laser coherent communication.
2011, 35(3): 360-363.
doi: 10.3969/j.issn.1001-3806.2011.03.019
Abstract:
An integrated control system was designed for carbon monoxide gas detection, emission and recycling based on tunable diode laser absorption spectroscopy. A MCU MC9S12DG128B was embedded in the system as its core controller to produce laser modulation signal. By collecting optical power and the second harmonic of the absorbed gas, the gas composition and concentration was analyzed, and then the information of the gas concentration was uploaded to a real-time industrial computer. The results show that the laser detection of gases with high sensitivity and selectivity, fast response, continuous analysis and anti-jamming performance, and it meets the requirements in the industrial field.
An integrated control system was designed for carbon monoxide gas detection, emission and recycling based on tunable diode laser absorption spectroscopy. A MCU MC9S12DG128B was embedded in the system as its core controller to produce laser modulation signal. By collecting optical power and the second harmonic of the absorbed gas, the gas composition and concentration was analyzed, and then the information of the gas concentration was uploaded to a real-time industrial computer. The results show that the laser detection of gases with high sensitivity and selectivity, fast response, continuous analysis and anti-jamming performance, and it meets the requirements in the industrial field.
2011, 35(3): 364-367,383.
doi: 10.3969/j.issn.1001-3806.2011.03.020
Abstract:
In order to study the deposition of 52Cr atomic interacted by a focused near-resonant Gaussian standing-laser at 425.55nm wavelength, 3-D simulation was carried out based on both particle-optics and wave-mechanical approaches. The results show that the deposited nano-grating has uniform period along laser vector direction, and similar structure along the direction perpendicular to laser vector. In addition, the deposited nano-grating may be split with the increase of laser power. Due to the wave property, the simulated nano-grating presents obvious interference side peak. All the simulation results provide abundant theory for experiments.
In order to study the deposition of 52Cr atomic interacted by a focused near-resonant Gaussian standing-laser at 425.55nm wavelength, 3-D simulation was carried out based on both particle-optics and wave-mechanical approaches. The results show that the deposited nano-grating has uniform period along laser vector direction, and similar structure along the direction perpendicular to laser vector. In addition, the deposited nano-grating may be split with the increase of laser power. Due to the wave property, the simulated nano-grating presents obvious interference side peak. All the simulation results provide abundant theory for experiments.
2011, 35(3): 368-371.
doi: 10.3969/j.issn.1001-3806.2011.03.021
Abstract:
A remote monitor system was designed to manage the data of fiber amplifiers based on simple network management protocol (SNMP). On the management side, there was a friendly user management interface made by SNMP++. Meanwhile, MSP430, a single chip microcomputer and CS8900A, a network interface card driver chip were used as supporting hardware on the agent side. Private nodes of management information base file were made, which represented objects of the fiber amplifier needing management. Through the union test with an actual fiber amplifier, corresponding private nodes of this system could be managed in the user management interface. It shows that this remote monitor system can be used to manage a fiber amplifier.
A remote monitor system was designed to manage the data of fiber amplifiers based on simple network management protocol (SNMP). On the management side, there was a friendly user management interface made by SNMP++. Meanwhile, MSP430, a single chip microcomputer and CS8900A, a network interface card driver chip were used as supporting hardware on the agent side. Private nodes of management information base file were made, which represented objects of the fiber amplifier needing management. Through the union test with an actual fiber amplifier, corresponding private nodes of this system could be managed in the user management interface. It shows that this remote monitor system can be used to manage a fiber amplifier.
2011, 35(3): 372-375,397.
doi: 10.3969/j.issn.1001-3806.2011.03.022
Abstract:
A bitmap laser marking method based on bitmap vectorization was developed to overcome the difficulties of traditional bitmap marking method used in a laser marking system. In this method, the edge or skeleton of the bitmap was extracted in the form of digital curves firstly, then the polygonal approximating method was adopted to vectorize above digital curves, finally the vectorized data was engraved by means of continuous marking method. The involved algorithm of polygonal approximation of digital curves, consisting of Freeman chain code generating, approximate digital straight line segments extracting and polygonal approximating, was emphatically discussed. The experimental results show that the approximating algorithm works well. The practical application shows that the precision and the speed of bitmap marking can be largely improved with this marking method.
A bitmap laser marking method based on bitmap vectorization was developed to overcome the difficulties of traditional bitmap marking method used in a laser marking system. In this method, the edge or skeleton of the bitmap was extracted in the form of digital curves firstly, then the polygonal approximating method was adopted to vectorize above digital curves, finally the vectorized data was engraved by means of continuous marking method. The involved algorithm of polygonal approximation of digital curves, consisting of Freeman chain code generating, approximate digital straight line segments extracting and polygonal approximating, was emphatically discussed. The experimental results show that the approximating algorithm works well. The practical application shows that the precision and the speed of bitmap marking can be largely improved with this marking method.
2011, 35(3): 376-379.
doi: 10.3969/j.issn.1001-3806.2011.03.023
Abstract:
In order to detect underwater pipeline leakage and locate leakage points in real-time, an in-line distributed optical fiber sensor was developed based on the principle of Sagnac interferometers. The measuring principle and the leaking source location method for the detection system were analyzed. The effect of the pipeline pressure on the performance of the system was studied . The results verify that the system can obtain optimal performance when the pipeline pressure is more than 0.35MPa, and the error is less than 1.17%; the leakage points can not be located when the pressure is less than 0.35MPa. The conclusion is that the system can realize underwater pipeline leakage detection and locate leakage accurately when the pressure is more than 0.35MPa.
In order to detect underwater pipeline leakage and locate leakage points in real-time, an in-line distributed optical fiber sensor was developed based on the principle of Sagnac interferometers. The measuring principle and the leaking source location method for the detection system were analyzed. The effect of the pipeline pressure on the performance of the system was studied . The results verify that the system can obtain optimal performance when the pipeline pressure is more than 0.35MPa, and the error is less than 1.17%; the leakage points can not be located when the pressure is less than 0.35MPa. The conclusion is that the system can realize underwater pipeline leakage detection and locate leakage accurately when the pressure is more than 0.35MPa.
2011, 35(3): 380-383.
doi: 10.3969/j.issn.1001-3806.2011.03.024
Abstract:
In order to study the generation mechanism of scattering characteristics of dielectric random surfaces, on the basis of Kirchhoff approximation, light intensity scattered from rough dielectric surfaces was calculated by means of Monte-Carlo method. The geometric profile of rough surfaces obeys Gaussian distribution. All of the surfaces have the same correlation length. With the increase of rms height, the distribution of the scattered intensity is broadened, decreased at its peak value and moved backward. The above phenomena were induced by the combination of the local slope and the reflecting index of local slope. This result provides reference to the research under more complex conditions.
In order to study the generation mechanism of scattering characteristics of dielectric random surfaces, on the basis of Kirchhoff approximation, light intensity scattered from rough dielectric surfaces was calculated by means of Monte-Carlo method. The geometric profile of rough surfaces obeys Gaussian distribution. All of the surfaces have the same correlation length. With the increase of rms height, the distribution of the scattered intensity is broadened, decreased at its peak value and moved backward. The above phenomena were induced by the combination of the local slope and the reflecting index of local slope. This result provides reference to the research under more complex conditions.
2011, 35(3): 384-387.
doi: 10.3969/j.issn.1001-3806.2011.03.025
Abstract:
In order to study the effect of the laser electromagnetic field on the electron in vacuum，based on the Lorentz equation，the motion track of electrons was simulated，and the electrons were accelerated in the laser electromagnetic field. Then the radiant energy spectrum was obtained according to the flux density generated by the motive electron. Finally the radiant characteristics of the relativistic electrons were analyzed. It is shown that Gaussian laser electromagnetic field has beneficial effect on vacuum electron acceleration，and its maximum speed along the optical axis is up to 0.9c.
In order to study the effect of the laser electromagnetic field on the electron in vacuum，based on the Lorentz equation，the motion track of electrons was simulated，and the electrons were accelerated in the laser electromagnetic field. Then the radiant energy spectrum was obtained according to the flux density generated by the motive electron. Finally the radiant characteristics of the relativistic electrons were analyzed. It is shown that Gaussian laser electromagnetic field has beneficial effect on vacuum electron acceleration，and its maximum speed along the optical axis is up to 0.9c.
2011, 35(3): 388-390,402.
doi: 10.3969/j.issn.1001-3806.2011.03.026
Abstract:
In order to study the effect of channel code technology on bit error rate (BER) performance of wireless optical communication subcarrier systems, based on noise characteristics of wireless optical communication, atmospheric channel model was found. Low density parity check(LDPC)code was introduced as the channel code in wireless optical communication, the error rate of wireless optical communication using subcarrier modulation was simulated under different scintillation distribution, and the BER performance between LDPC code coded and uncoded systems of binary phase shift keying (BPSK)and quaternary phase shift keying(QPSK)system was compared. The simulation results show that error performance of the BPSK system is better than that of QPSK system, and LDPC code has excellent error correction capabilities with a larger coding gain, and has some applicable values in the field of wireless optical communication.
In order to study the effect of channel code technology on bit error rate (BER) performance of wireless optical communication subcarrier systems, based on noise characteristics of wireless optical communication, atmospheric channel model was found. Low density parity check(LDPC)code was introduced as the channel code in wireless optical communication, the error rate of wireless optical communication using subcarrier modulation was simulated under different scintillation distribution, and the BER performance between LDPC code coded and uncoded systems of binary phase shift keying (BPSK)and quaternary phase shift keying(QPSK)system was compared. The simulation results show that error performance of the BPSK system is better than that of QPSK system, and LDPC code has excellent error correction capabilities with a larger coding gain, and has some applicable values in the field of wireless optical communication.
2011, 35(3): 391-394.
doi: 10.3969/j.issn.1001-3806.2011.03.027
Abstract:
In order to develop the direction property of a multi-element linear ultrasonic transducer array, the effect of its dominant frequency, element number and space between the elements on its direction was studied based on the multi-element phase-controlled technique. These results show that for good direction property, a large size array could be used when the main frequency of the transducer is low; on the contrary, for high frequency transducers, a smaller size array should be used. This is beneficial for photoacoustic detection and imaging.
In order to develop the direction property of a multi-element linear ultrasonic transducer array, the effect of its dominant frequency, element number and space between the elements on its direction was studied based on the multi-element phase-controlled technique. These results show that for good direction property, a large size array could be used when the main frequency of the transducer is low; on the contrary, for high frequency transducers, a smaller size array should be used. This is beneficial for photoacoustic detection and imaging.
2011, 35(3): 395-397.
doi: 10.3969/j.issn.1001-3806.2011.03.028
Abstract:
To improve the welding efficiency and reduce cost, the possibility of the penetration improvement on the welding joints by low-power pulsed laser with activating fluxes was studied. Based on the research of low-power pulsed laser welding of SUS304 stainless steel with five activating fluxes (TiO2, SiO2,Cr2O3, CaF2, NaF), the effect of the fluxes on the penetration of joints, as well as the mechanism of penetration improvement, was studied, and the relevant data was received. The results show that the penetration can be changed with all the activating fluxes, among which TiO2 and SiO2 can deepen the penetration by 38.290% and 17.175% respectively. Meanwhile the depth/width ratios are improved in different degrees by Cr2O3, TiO2 and SiO2, however the fluoride has little effect on this ratio. The existence of activating fluxes not only improves the absorption rate of laser power, but also changes the convection of the welding pool, which makes the microstructures within the welding vary. The result is helpful for the further application of the activating fluxes in the laser technique.
To improve the welding efficiency and reduce cost, the possibility of the penetration improvement on the welding joints by low-power pulsed laser with activating fluxes was studied. Based on the research of low-power pulsed laser welding of SUS304 stainless steel with five activating fluxes (TiO2, SiO2,Cr2O3, CaF2, NaF), the effect of the fluxes on the penetration of joints, as well as the mechanism of penetration improvement, was studied, and the relevant data was received. The results show that the penetration can be changed with all the activating fluxes, among which TiO2 and SiO2 can deepen the penetration by 38.290% and 17.175% respectively. Meanwhile the depth/width ratios are improved in different degrees by Cr2O3, TiO2 and SiO2, however the fluoride has little effect on this ratio. The existence of activating fluxes not only improves the absorption rate of laser power, but also changes the convection of the welding pool, which makes the microstructures within the welding vary. The result is helpful for the further application of the activating fluxes in the laser technique.
2011, 35(3): 398-402.
doi: 10.3969/j.issn.1001-3806.2011.03.029
Abstract:
In order to study of output characteristics of a laser diode pumped passively Q-switched Nd:YAG/GdVO4 intracavity Raman laser, taking Nd:YAG as the gain crystal, GdVO4 as the Raman medium, and two Cr4+:YAG crystals with different initial transmissions as the saturable absorber respectively, the passively Q-switched operation of the Nd:YAG/GdVO4 Raman laser at 1174nm was investigated and compared. The average power, pulse energy, pulse width and pulse repletion rate of diode pumped passively Q-switched Nd:GdVO4 self-Raman laser at 1174nm with respect to the injected pump power were measured. The obtained maximum output average power was 150.6mW with respect to injected power of 5.2W and the corresponding conversion efficiency was 2.9% in the case of the initial transmission of 91%. The theoretical results were obtained according to the rate equations, in which the Gaussian distribution of the intracavity photon density of the fundamental and Raman laser and the initial population inversion density were taken into account. The obtained theoretical results were in agreement with the experimental results on the whole.
In order to study of output characteristics of a laser diode pumped passively Q-switched Nd:YAG/GdVO4 intracavity Raman laser, taking Nd:YAG as the gain crystal, GdVO4 as the Raman medium, and two Cr4+:YAG crystals with different initial transmissions as the saturable absorber respectively, the passively Q-switched operation of the Nd:YAG/GdVO4 Raman laser at 1174nm was investigated and compared. The average power, pulse energy, pulse width and pulse repletion rate of diode pumped passively Q-switched Nd:GdVO4 self-Raman laser at 1174nm with respect to the injected pump power were measured. The obtained maximum output average power was 150.6mW with respect to injected power of 5.2W and the corresponding conversion efficiency was 2.9% in the case of the initial transmission of 91%. The theoretical results were obtained according to the rate equations, in which the Gaussian distribution of the intracavity photon density of the fundamental and Raman laser and the initial population inversion density were taken into account. The obtained theoretical results were in agreement with the experimental results on the whole.
2011, 35(3): 403-406.
doi: 10.3969/j.issn.1001-3806.2011.03.030
Abstract:
In order to improve the signal-to-noise ratio (SNR) of surface acoustic waves (SAWs) in laser ultrasonic test, laser array, obtained by the temporal and spatial modulation of the line sources, was used to irradiate on the aluminum plate, and the physical processes, including the generation of SAWs (giant SAWs) with huge displacement amplitude and the interactions between the giant SAWs and the surface breaking crack were simulated by means of the finite element method. The numerical results demonstrate that the displacement amplitude of the giant SAWs generated by the laser array increases in proportion with the number of laser array elements. Besides, the amplitude of the reflected SAWs, generated by the interactions between the giant SAWs and the surface breaking crack, is also increased as the numbers of the line sources increased. The results can provide some hints for the utilization of the thermoelastic laser array to improve SNR of the SAWs.
In order to improve the signal-to-noise ratio (SNR) of surface acoustic waves (SAWs) in laser ultrasonic test, laser array, obtained by the temporal and spatial modulation of the line sources, was used to irradiate on the aluminum plate, and the physical processes, including the generation of SAWs (giant SAWs) with huge displacement amplitude and the interactions between the giant SAWs and the surface breaking crack were simulated by means of the finite element method. The numerical results demonstrate that the displacement amplitude of the giant SAWs generated by the laser array increases in proportion with the number of laser array elements. Besides, the amplitude of the reflected SAWs, generated by the interactions between the giant SAWs and the surface breaking crack, is also increased as the numbers of the line sources increased. The results can provide some hints for the utilization of the thermoelastic laser array to improve SNR of the SAWs.
2011, 35(3): 407-411.
doi: 10.3969/j.issn.1001-3806.2011.03.031
Abstract:
Based on the principle of the non-diffracting beam, a new electronic target was designed for guidance of a shield machine. The system constitution and the measurement principle of attitude angles of the electronic target were discussed. Since the accurate optic center of optic system in the electronic target was difficult to find, a new calibration method was proposed. The spot center location of the incident laser of the total station in CCD fixed in the electronic target and the angle data of the total station were combined, and a mapping database was set up. During guidance of the shield machine, the actual slope angle, rolling angle and horizontal azimuth angle of the electronic target and the center of the head of shield machine were computed by the space angle of the incident laser interpolated by the actual spot center location and the angles of electronic gradienter. The experiment shows that high calibration precision is achieved by the calibration method, and high measurement precision is gained during measurement of electronic target.
Based on the principle of the non-diffracting beam, a new electronic target was designed for guidance of a shield machine. The system constitution and the measurement principle of attitude angles of the electronic target were discussed. Since the accurate optic center of optic system in the electronic target was difficult to find, a new calibration method was proposed. The spot center location of the incident laser of the total station in CCD fixed in the electronic target and the angle data of the total station were combined, and a mapping database was set up. During guidance of the shield machine, the actual slope angle, rolling angle and horizontal azimuth angle of the electronic target and the center of the head of shield machine were computed by the space angle of the incident laser interpolated by the actual spot center location and the angles of electronic gradienter. The experiment shows that high calibration precision is achieved by the calibration method, and high measurement precision is gained during measurement of electronic target.
2011, 35(3): 412-414,417.
doi: 10.3969/j.issn.1001-3806.2011.03.032
Abstract:
In order to resolve the low output energy of active mode-locked laser and instability of passive mode-locked laser, Cr4+:YAG passive mode-locker and acousto-optic active mode-locker were used jointly for Nd:YAG laser mode-locking. The output characteristics of passively mode-locked by Cr4+:YAG only, actively mode-locked by acousto-optic mode-locker only and mode-locked by Cr4+:YAG and acousto-optic jointly were analyzed and compared through experiments. Results showed that the joint mode-locking method gave good resolution to the low output energy and stability, and the mode-lock amplitude and energy fluctuation were less than 5％, with the depth of mode locking of 100%, pulse width less than 450ps and output energy near 200mJ at 1064nm wavelength. Adding KTP crystal out of the cavity, the output conversion efficiency was about 41% at 532nm wavelength．The results show the possibility of actively-passively mode-locked technology and it is helpful for the development of mode-locking technology.
In order to resolve the low output energy of active mode-locked laser and instability of passive mode-locked laser, Cr4+:YAG passive mode-locker and acousto-optic active mode-locker were used jointly for Nd:YAG laser mode-locking. The output characteristics of passively mode-locked by Cr4+:YAG only, actively mode-locked by acousto-optic mode-locker only and mode-locked by Cr4+:YAG and acousto-optic jointly were analyzed and compared through experiments. Results showed that the joint mode-locking method gave good resolution to the low output energy and stability, and the mode-lock amplitude and energy fluctuation were less than 5％, with the depth of mode locking of 100%, pulse width less than 450ps and output energy near 200mJ at 1064nm wavelength. Adding KTP crystal out of the cavity, the output conversion efficiency was about 41% at 532nm wavelength．The results show the possibility of actively-passively mode-locked technology and it is helpful for the development of mode-locking technology.
2011, 35(3): 415-417.
doi: 10.3969/j.issn.1001-3806.2011.03.033
Abstract:
To study the material commonly used in the interval of soft X-ray multilayer, soft X-ray multilayer with high reflectivity were designed with the special design program prepared by the Lawrence-Livermore National Laboratory. The results show that Molybdenum has good optical property in a wide waveband. Besides at optimum wavelength of 12.44nm, molybdenum has high reflectivity at other wavelengths except 4.36nm. Multilayer consisting of uranium and other spacing layer material, with uranium as an absorption layer, also has higher reflectivity in a large wavelength range. The results are helpful for selection of multilayer material.
To study the material commonly used in the interval of soft X-ray multilayer, soft X-ray multilayer with high reflectivity were designed with the special design program prepared by the Lawrence-Livermore National Laboratory. The results show that Molybdenum has good optical property in a wide waveband. Besides at optimum wavelength of 12.44nm, molybdenum has high reflectivity at other wavelengths except 4.36nm. Multilayer consisting of uranium and other spacing layer material, with uranium as an absorption layer, also has higher reflectivity in a large wavelength range. The results are helpful for selection of multilayer material.
2011, 35(3): 418-421,424.
doi: 10.3969/j.issn.1001-3806.2011.03.034
Abstract:
To elucidate the effect of field curvature on laser-induced far-field diffraction and its mechanism, the effect of field curvature on the far-field diffraction ring pattern after Gaussian beam propagating through self-defocusing liquid crystal was simulated based on Kirchhoff diffraction integral. Without considering the filed curvature effect, the central spot of the far-field diffraction ring will turn out to be bright and dark alternatively with the incident laser intensity increasing. With divergent beam traversing thin self-defocusing medium, the central spot will turn out to be darkened, while brightened with the convergent case. Finally the phenomena were explained based on the amplitude and phase factors in the integral expression of Kirchhoff diffraction. The phenomena are attributed to the interaction between the wave-curvature and the nonlinear phase factor.
To elucidate the effect of field curvature on laser-induced far-field diffraction and its mechanism, the effect of field curvature on the far-field diffraction ring pattern after Gaussian beam propagating through self-defocusing liquid crystal was simulated based on Kirchhoff diffraction integral. Without considering the filed curvature effect, the central spot of the far-field diffraction ring will turn out to be bright and dark alternatively with the incident laser intensity increasing. With divergent beam traversing thin self-defocusing medium, the central spot will turn out to be darkened, while brightened with the convergent case. Finally the phenomena were explained based on the amplitude and phase factors in the integral expression of Kirchhoff diffraction. The phenomena are attributed to the interaction between the wave-curvature and the nonlinear phase factor.
2011, 35(3): 422-424.
doi: 10.3969/j.issn.1001-3806.2011.03.035
Abstract:
In order to find a route set from multi-source to multi-purpose nodes in a communication network in accordance with the bandwidth-delay constraints at minimum total cost according to the characteristics of quality of service multicast routing, combined with genetic algorithm optimization characteristics, solving the bandwidth-delay constraints with two-layer genetic algorithm, the cost data of the route set was obtained. The results show that the proposed algorithm can effectively find an optimal solution for multicast routing problem.
In order to find a route set from multi-source to multi-purpose nodes in a communication network in accordance with the bandwidth-delay constraints at minimum total cost according to the characteristics of quality of service multicast routing, combined with genetic algorithm optimization characteristics, solving the bandwidth-delay constraints with two-layer genetic algorithm, the cost data of the route set was obtained. The results show that the proposed algorithm can effectively find an optimal solution for multicast routing problem.
2011, 35(3): 425-427,432.
doi: 10.3969/j.issn.1001-3806.2011.03.036
Abstract:
To investigate the change of microstructure and properties, laser transformation hardening was carried out on 1Cr18Ni9Ti stainless steel, and the microstructure and properties of laser transformation hardened layers were investigated by means of scanning electron microscope, X-ray diffractometer, microhardnessmeter, abrasive wear testing machine, potentiostat etc. The hardness, wear resistance, corrosion resistance data of laser transformation hardening layer were obtained by theoretical analysis and experimental verification. The result indicated that the laser transformation hardening layer was mainly consisted of austenite, martensite, Fe-(Cr, Ni), Fe etc. With the increase of the laser power, the average microhardness of laser hardening layers increased first and then decreased. The average microhardness reached the highest (223.5HK) when laser power was 750W. Wear resistance reached the best (whose wear rate is 56% of the substrate) when the power was 550W. Corrosion resistance was improved after laser transformation hardening, passivation current density of the smallest dimension was 33% of the substrate, the maximum length of the passive zone of stability was seven times of the substrate. The results are helpful to study the change of microstructure and properties of 1Cr18Ni9Ti stainless steel.
To investigate the change of microstructure and properties, laser transformation hardening was carried out on 1Cr18Ni9Ti stainless steel, and the microstructure and properties of laser transformation hardened layers were investigated by means of scanning electron microscope, X-ray diffractometer, microhardnessmeter, abrasive wear testing machine, potentiostat etc. The hardness, wear resistance, corrosion resistance data of laser transformation hardening layer were obtained by theoretical analysis and experimental verification. The result indicated that the laser transformation hardening layer was mainly consisted of austenite, martensite, Fe-(Cr, Ni), Fe etc. With the increase of the laser power, the average microhardness of laser hardening layers increased first and then decreased. The average microhardness reached the highest (223.5HK) when laser power was 750W. Wear resistance reached the best (whose wear rate is 56% of the substrate) when the power was 550W. Corrosion resistance was improved after laser transformation hardening, passivation current density of the smallest dimension was 33% of the substrate, the maximum length of the passive zone of stability was seven times of the substrate. The results are helpful to study the change of microstructure and properties of 1Cr18Ni9Ti stainless steel.
2011, 35(3): 428-432.
doi: 10.3969/j.issn.1001-3806.2011.03.037
Abstract:
In order to deal with the disadvantages of fixed-threshold method in skin color segmentation, a new algorithm based on 2-D Otsu and YCgCr color space was proposed after analysis and comparison of different color spaces and skin color models. Firstly, the skin color sample images compensated with light were transferred from RGB to YCgCr color space and the 2-D Gaussian skin color model was established based on the 179221 skin pixels. Secondly, the image to be segmented was light compensated and transferred from RGB to YCgCr color space. Thirdly, skin color similarity degree was computed based on the 2-D Gaussian model and the skin color similarity image was obtained. Finally, an improved 2-D Otsu method was used into segmentation of the skin color similarity image. Theoretical analysis and experimental results show that the new skin color segmentation method is superior to the traditional methods based on a fixed-threshold in pertinence and anti-noise robustness.
In order to deal with the disadvantages of fixed-threshold method in skin color segmentation, a new algorithm based on 2-D Otsu and YCgCr color space was proposed after analysis and comparison of different color spaces and skin color models. Firstly, the skin color sample images compensated with light were transferred from RGB to YCgCr color space and the 2-D Gaussian skin color model was established based on the 179221 skin pixels. Secondly, the image to be segmented was light compensated and transferred from RGB to YCgCr color space. Thirdly, skin color similarity degree was computed based on the 2-D Gaussian model and the skin color similarity image was obtained. Finally, an improved 2-D Otsu method was used into segmentation of the skin color similarity image. Theoretical analysis and experimental results show that the new skin color segmentation method is superior to the traditional methods based on a fixed-threshold in pertinence and anti-noise robustness.
