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RSS2016 Vol. 40, No. 4
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2016, 40(4): 461-465.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.001
[Abstract]
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Abstract:
In order to cope with changeable environment and complex requirements of strontium optical lattice clock experiments, laser power should be stabilized and controlled in time sequence in some laser paths. Acousto-optic modulation was adopted to stabilize the laser power based on the principle that diffraction efficiency of acousto-optic crystal varies with the change of driving radio frequency power. A feedback control system was established to realize active stabilization of laser power and timing control of power. The result shows that laser power can be set at arbitrary levels within its setting range according to time sequence. When the control system is enabled, the relative laser power stability is improved from 10-2 to 10-4 compared with the disabled state. The advantage of the system is power stability with timing control.
In order to cope with changeable environment and complex requirements of strontium optical lattice clock experiments, laser power should be stabilized and controlled in time sequence in some laser paths. Acousto-optic modulation was adopted to stabilize the laser power based on the principle that diffraction efficiency of acousto-optic crystal varies with the change of driving radio frequency power. A feedback control system was established to realize active stabilization of laser power and timing control of power. The result shows that laser power can be set at arbitrary levels within its setting range according to time sequence. When the control system is enabled, the relative laser power stability is improved from 10-2 to 10-4 compared with the disabled state. The advantage of the system is power stability with timing control.
2016, 40(4): 466-471.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.002
Abstract:
In order to meet the requirements of increasing precision, processing size and processing efficiency of 3-D laser micromachining, after theoretical analysis and calculation, a dynamic focusing system was designed combining the dynamic focusing lens with the 2-D galvanometer scanning system. A large scale 3-D laser dynamic focusing scanning processing system was proposed with the combination of the dynamic focusing system and a high precision X-Y-Z 3-D working stage. Telecentric f- lens was designed with focal length of 100mm, field angle of 15, aperture size of 7mm, back focal length of 137mm and relative distortion of less than 0.5%. And a dynamic focusing system was designed with aperture size of 8mm, optical leverage ratio of 1:8 and back focal length of 800mm40mm. ZEMAX was used to analyze and evaluate the optical design and system performance of the dynamic focusing lens and telecentric f- lens. The results show that, after layer stitching with the process control software, large-scale (460mm310mm50mm) 3-D dynamic focusing precision UV laser micromachining system is achieved. In 3-D scanning range, laser beam spot diameter remains always less than 10m and meets the needs of large-scale 3-D precision laser micromachining.
In order to meet the requirements of increasing precision, processing size and processing efficiency of 3-D laser micromachining, after theoretical analysis and calculation, a dynamic focusing system was designed combining the dynamic focusing lens with the 2-D galvanometer scanning system. A large scale 3-D laser dynamic focusing scanning processing system was proposed with the combination of the dynamic focusing system and a high precision X-Y-Z 3-D working stage. Telecentric f- lens was designed with focal length of 100mm, field angle of 15, aperture size of 7mm, back focal length of 137mm and relative distortion of less than 0.5%. And a dynamic focusing system was designed with aperture size of 8mm, optical leverage ratio of 1:8 and back focal length of 800mm40mm. ZEMAX was used to analyze and evaluate the optical design and system performance of the dynamic focusing lens and telecentric f- lens. The results show that, after layer stitching with the process control software, large-scale (460mm310mm50mm) 3-D dynamic focusing precision UV laser micromachining system is achieved. In 3-D scanning range, laser beam spot diameter remains always less than 10m and meets the needs of large-scale 3-D precision laser micromachining.
2016, 40(4): 472-475.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.003
Abstract:
In order to develop a compact instrument to measure the thickness of isotropic uniform thin films, applying a common normal incident path and thin-film interference principle, the film thickness was calculated inversely by fitting the measured reflectance spectrum with nonlinear optimization algorithm. The relative error between the thickness of a SiO2/Si thin film measured by the proposed instrument and that measured by the commercial ellipsometer was less than 0.5%, and the time for a single measurement was about 70ms. Experimental results show that the proposed instrument has advantages of insensitivity to measuring distance, concise light path, compact structure and excellent repeatability. The study has great significance for online measurement of thin film thickness.
In order to develop a compact instrument to measure the thickness of isotropic uniform thin films, applying a common normal incident path and thin-film interference principle, the film thickness was calculated inversely by fitting the measured reflectance spectrum with nonlinear optimization algorithm. The relative error between the thickness of a SiO2/Si thin film measured by the proposed instrument and that measured by the commercial ellipsometer was less than 0.5%, and the time for a single measurement was about 70ms. Experimental results show that the proposed instrument has advantages of insensitivity to measuring distance, concise light path, compact structure and excellent repeatability. The study has great significance for online measurement of thin film thickness.
2016, 40(4): 476-478.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.004
Abstract:
In order to study the temperature-dependant properties of a birefringent filter made by uniaxial crystals LiNbO3,the relationship between birefringence and thickness of LiNbO3 with the change of temperature was characterized by numerical simulation. Transmission spectrum of the designed LiNbO3 birefringence filter was tested and investigated by using Ultra-6600 spectrophotometer. The results show that, in different bandwidths, a certain incident angle can be found to make center wavelength of the filter is insensitive to temperature. Further, the birefringence filter maintains temperature stability. The results show that, temperature stability of filter and precision of the LiNbO3 filter can be improved by adjusting the direction of incident light.
In order to study the temperature-dependant properties of a birefringent filter made by uniaxial crystals LiNbO3,the relationship between birefringence and thickness of LiNbO3 with the change of temperature was characterized by numerical simulation. Transmission spectrum of the designed LiNbO3 birefringence filter was tested and investigated by using Ultra-6600 spectrophotometer. The results show that, in different bandwidths, a certain incident angle can be found to make center wavelength of the filter is insensitive to temperature. Further, the birefringence filter maintains temperature stability. The results show that, temperature stability of filter and precision of the LiNbO3 filter can be improved by adjusting the direction of incident light.
2016, 40(4): 479-482.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.005
Abstract:
In order to suppress speckle noise in laser imaging, a laser microscopic speckle analysis and evaluation system was built by using the gray level co-occurrence matrix. In this system, a 405nm wavelength laser was used as light source of the microscopic system and the vibration of an sample driven by a voice coil motor through voltage was used to control the size of laser speckle noise. At the same time, a CCD image sensor was used to collect laser speckle noise under different driving voltages. Through analyzing the characteristic parameters such as angular second moment, contrast, entropy and inverse difference moment of laser speckle noise, the characteristics of laser speckle noise were appropriately characterized. The results show that the gray level co-occurrence matrix method can be used to evaluate the speckle in laser microscopic imaging.
In order to suppress speckle noise in laser imaging, a laser microscopic speckle analysis and evaluation system was built by using the gray level co-occurrence matrix. In this system, a 405nm wavelength laser was used as light source of the microscopic system and the vibration of an sample driven by a voice coil motor through voltage was used to control the size of laser speckle noise. At the same time, a CCD image sensor was used to collect laser speckle noise under different driving voltages. Through analyzing the characteristic parameters such as angular second moment, contrast, entropy and inverse difference moment of laser speckle noise, the characteristics of laser speckle noise were appropriately characterized. The results show that the gray level co-occurrence matrix method can be used to evaluate the speckle in laser microscopic imaging.
2016, 40(4): 483-486.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.006
Abstract:
In order to improve the efficiency of marking vector texts in laser marking systems, an optimized algorithm of linear approximation for TrueType font outline was proposed by analyzing the structure of TrueType font outline and properties of Bezier curve. Theoretical analysis and experimental verification were carried out. Firstly, Bezier curves in the outline of TrueType fonts were divided on the basis of de Casteljau recursive algorithm. Then they were replaced with the lines between start and end points. Finally, all the lines were interpolated to generate laser marking point. Through comparison between linear approximation contours and standard TrueType outlines, the results show that the algorithm can generate fewer nodes and improve the efficiency of marking vector texts under the condition of meeting accuracy.
In order to improve the efficiency of marking vector texts in laser marking systems, an optimized algorithm of linear approximation for TrueType font outline was proposed by analyzing the structure of TrueType font outline and properties of Bezier curve. Theoretical analysis and experimental verification were carried out. Firstly, Bezier curves in the outline of TrueType fonts were divided on the basis of de Casteljau recursive algorithm. Then they were replaced with the lines between start and end points. Finally, all the lines were interpolated to generate laser marking point. Through comparison between linear approximation contours and standard TrueType outlines, the results show that the algorithm can generate fewer nodes and improve the efficiency of marking vector texts under the condition of meeting accuracy.
2016, 40(4): 487-490.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.007
Abstract:
In order to obtain the birefringence of nematic liquid crystal, a novel measurement method was put forward based on Michelson interference principle. A wedge-shaped cell was put into the Michelson interferometer. The refractive indexes of ordinary and extraordinary lights were accurately measured by adjusting the polarized direction of incident light. The results show that this method is simple and with high precision by converting the measurement of refractive index to the measurement of length and the counts of interference fringes. This method is very important for theoretical research and practical development of liquid crystal display devices and has some promotional value in the production of liquid crystal materials and liquid crystal devices.
In order to obtain the birefringence of nematic liquid crystal, a novel measurement method was put forward based on Michelson interference principle. A wedge-shaped cell was put into the Michelson interferometer. The refractive indexes of ordinary and extraordinary lights were accurately measured by adjusting the polarized direction of incident light. The results show that this method is simple and with high precision by converting the measurement of refractive index to the measurement of length and the counts of interference fringes. This method is very important for theoretical research and practical development of liquid crystal display devices and has some promotional value in the production of liquid crystal materials and liquid crystal devices.
2016, 40(4): 491-495.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.008
Abstract:
Transmission function of double grating monochromator plays an important role in rotational Raman lidar's simulation calculation of echo signal,the analysis of temperature inversion sensitivity,the selection of temperature inversion formula and so on. In order to study algorithm of double grating monochromator transmittance function, the sectional area ratio between light spot and output optical fiber was expressed by a variable. And then transmission function was given by the relationship of phase, intersection, tangent between light spot and output optical fiber cross section. 532nm double grating monochromator transmission function was analyzed in theory and verified in experiments. The results show that, central wavelength of 532nm double grating monochromator transmission curve is 529.0nm,530.3nm,533.8nm and 535.1nm respectively and the bandwidth is 0.48nm. The simulated echo signal and the measured echo signal are basically consistent. The calculation method of double grating monochromator transmittance function is correct.
Transmission function of double grating monochromator plays an important role in rotational Raman lidar's simulation calculation of echo signal,the analysis of temperature inversion sensitivity,the selection of temperature inversion formula and so on. In order to study algorithm of double grating monochromator transmittance function, the sectional area ratio between light spot and output optical fiber was expressed by a variable. And then transmission function was given by the relationship of phase, intersection, tangent between light spot and output optical fiber cross section. 532nm double grating monochromator transmission function was analyzed in theory and verified in experiments. The results show that, central wavelength of 532nm double grating monochromator transmission curve is 529.0nm,530.3nm,533.8nm and 535.1nm respectively and the bandwidth is 0.48nm. The simulated echo signal and the measured echo signal are basically consistent. The calculation method of double grating monochromator transmittance function is correct.
2016, 40(4): 496-499.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.009
Abstract:
In order to measure thickness of a specimen with a continuous wave terahertz imaging system based on photomixing, its 2-D thickness was measured by means of the phase information obtained from the imaging system. A continuous wave terahertz imaging system based on photomixing was established by using two external cavity laser diodes. The specimen was placed on the X-Y motorized precision translation stage and point-to-point scanning images were generated. Both the amplitude and phase information can be obtained simultaneously through the system. The signal-to-noise ratio of the system was 68dB at the frequency of 0.47THz. The deviation between the calculated result and the actual measurement was less than 0.02mm. The influences of the interference of plane specimen and transmission intensity on thickness measurement accuracy were analyzed. The results show that, the higher refractive index of the plane specimen is, the greater interference influence on thickness measurement becomes. The accuracy increases with the increase of terahertz transmission. The accuracy of thickness is better than 2.0% when the transmission coefficient is higher than 0.5.
In order to measure thickness of a specimen with a continuous wave terahertz imaging system based on photomixing, its 2-D thickness was measured by means of the phase information obtained from the imaging system. A continuous wave terahertz imaging system based on photomixing was established by using two external cavity laser diodes. The specimen was placed on the X-Y motorized precision translation stage and point-to-point scanning images were generated. Both the amplitude and phase information can be obtained simultaneously through the system. The signal-to-noise ratio of the system was 68dB at the frequency of 0.47THz. The deviation between the calculated result and the actual measurement was less than 0.02mm. The influences of the interference of plane specimen and transmission intensity on thickness measurement accuracy were analyzed. The results show that, the higher refractive index of the plane specimen is, the greater interference influence on thickness measurement becomes. The accuracy increases with the increase of terahertz transmission. The accuracy of thickness is better than 2.0% when the transmission coefficient is higher than 0.5.
2016, 40(4): 500-505.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.010
Abstract:
In order to meet the demand for high pixels, miniaturization and without stray light of a modern mobile phone lens, a three-unit 5106 pixel optical system based on CODEV software was designed by optical plastic aspherical technology and Monte Carlo ray tracing method. Stray light was analyzed based on LightTools software. After theoretical analysis and experimental verification, the results show that the F number of lens is 2.6, the full field of view angle is 72.9, the total length of system is 3.1mm. Performance test results of the final assembled products meet design requirements and have no unacceptable stray light.
In order to meet the demand for high pixels, miniaturization and without stray light of a modern mobile phone lens, a three-unit 5106 pixel optical system based on CODEV software was designed by optical plastic aspherical technology and Monte Carlo ray tracing method. Stray light was analyzed based on LightTools software. After theoretical analysis and experimental verification, the results show that the F number of lens is 2.6, the full field of view angle is 72.9, the total length of system is 3.1mm. Performance test results of the final assembled products meet design requirements and have no unacceptable stray light.
2016, 40(4): 506-511.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.011
Abstract:
With the development of micro-nano fabrication,the measurement of thermo-physical property of micro-nano material becomes more significant. At first, the basic principle of measurement of the thermo-physical property of micro-nano material with femtosecond laser and the means of realization were introduced. And then, two-temperature model, hyperbolic two-step model, hyperbolic one-step model, parabolic one-step model, dual-phase-lag model and parabolic two-step model were compared. Secondly, the characteristics of the measurement of the thermo-physical property of micro-nano material with femtosecond laser were introduced. Thirdly, three common system such as single-color femtosecond laser pump in front and probe system, two-color femtosecond laser pump in front and probe system, and single-color femtosecond laser pump and probe system in different side were introduced. Finally, the direction of future research in measurement of the thermo-physical property of materials was pointed out.
With the development of micro-nano fabrication,the measurement of thermo-physical property of micro-nano material becomes more significant. At first, the basic principle of measurement of the thermo-physical property of micro-nano material with femtosecond laser and the means of realization were introduced. And then, two-temperature model, hyperbolic two-step model, hyperbolic one-step model, parabolic one-step model, dual-phase-lag model and parabolic two-step model were compared. Secondly, the characteristics of the measurement of the thermo-physical property of micro-nano material with femtosecond laser were introduced. Thirdly, three common system such as single-color femtosecond laser pump in front and probe system, two-color femtosecond laser pump in front and probe system, and single-color femtosecond laser pump and probe system in different side were introduced. Finally, the direction of future research in measurement of the thermo-physical property of materials was pointed out.
2016, 40(4): 512-515.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.012
Abstract:
To explore the potential application of micro-textures on the surface of cemented carbide material by laser texturing, process tests of laser texturing were carried out on the surface of YG6X cemented carbide cutters by using single factor analysis method. Crater micro-textures with approximate 270m diameter and 6m height were obtained. The experimental results show that laser pulse width, pump voltage and air pressure have important effects on the textured topography dimensions and quality of the convex textures. Pulse width and pumping voltage can increases the dimension of convex textures greatly, gas pressure can significantly reduce the height of convex textures about 43%. However, micro-cracks exist from the center to the surrounding of micro-texture materials on cemented carbide by laser texturing. Furthermore, micro-texture materials by laser texturing on cemented carbide show uneven distribution with bigger hole and cavity in the center, but have close bonding strength with substrate.
To explore the potential application of micro-textures on the surface of cemented carbide material by laser texturing, process tests of laser texturing were carried out on the surface of YG6X cemented carbide cutters by using single factor analysis method. Crater micro-textures with approximate 270m diameter and 6m height were obtained. The experimental results show that laser pulse width, pump voltage and air pressure have important effects on the textured topography dimensions and quality of the convex textures. Pulse width and pumping voltage can increases the dimension of convex textures greatly, gas pressure can significantly reduce the height of convex textures about 43%. However, micro-cracks exist from the center to the surrounding of micro-texture materials on cemented carbide by laser texturing. Furthermore, micro-texture materials by laser texturing on cemented carbide show uneven distribution with bigger hole and cavity in the center, but have close bonding strength with substrate.
2016, 40(4): 516-520.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.013
Abstract:
In order to study laser irradiation temperature effect of a focal plane array detector under laser irradiation, 3-D analysis model of InSb infrared focal plane array detectors with complex multilayer structure was established based on ANSYS software, and 3-D temperature field and temperature effect of InSb infrared focal plane array induced by Gaussian pulse laser was simulated. The simulation results show that, the maximum temperature occurs in InSb chip, locating at the uppermost layer of the InSb detector. When the maximum temperature of InSb chip reaches the melting temperature 798K of InSb material, hot melting damage for the detector would happen and the melting damage threshold was also influenced by the laser pulse wide width and spot radius of laser. Temperature field distribution of each layer material in InSb detector shows non-consecutive high temperature extreme areas. The main reason is that, Indium bump and underfill, which are the alternative distribution in the middle layers of InSb focal plane array detectors, have different thermal properties. And then, extreme heat region of InSb chip, underfill and silicon readout circuit has high-temperature distribution similar to complementary in cloud map of detector temperature field. The research is useful for studying stress field distribution caused by temperature effect and improving laser protective performance of detector.
In order to study laser irradiation temperature effect of a focal plane array detector under laser irradiation, 3-D analysis model of InSb infrared focal plane array detectors with complex multilayer structure was established based on ANSYS software, and 3-D temperature field and temperature effect of InSb infrared focal plane array induced by Gaussian pulse laser was simulated. The simulation results show that, the maximum temperature occurs in InSb chip, locating at the uppermost layer of the InSb detector. When the maximum temperature of InSb chip reaches the melting temperature 798K of InSb material, hot melting damage for the detector would happen and the melting damage threshold was also influenced by the laser pulse wide width and spot radius of laser. Temperature field distribution of each layer material in InSb detector shows non-consecutive high temperature extreme areas. The main reason is that, Indium bump and underfill, which are the alternative distribution in the middle layers of InSb focal plane array detectors, have different thermal properties. And then, extreme heat region of InSb chip, underfill and silicon readout circuit has high-temperature distribution similar to complementary in cloud map of detector temperature field. The research is useful for studying stress field distribution caused by temperature effect and improving laser protective performance of detector.
2016, 40(4): 521-525.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.014
Abstract:
To solve the quality degradation problem of fog polarization imaging, an improved defogging method was proposed based on physical model of atmospheric scattering and dark passage principle of polarization images. Firstly, based on atmospheric scattering model, fog polarization imaging mechanism was analyzed and effect of atmospheric polarization on defogging was explained. Secondly, based on edge detection operator and closing operation, sky region of fog polarization image was obtained, and light intensity of infinity atmospheric and degree of polarization of atmospheric were estimated. At last, to solve the existing factors in the image such as noise interference, radiation intensity information of the degraded image was restored by modifying the degree of polarization and light intensity distribution of atmospheric. After theoretical analysis and experimental verification, good results of foggy image restoration were achieved. The results show that the algorithm can accurately obtain the sky region and improve the contrast and sharpness of the image, and improve the degradation of the image. Therefore, the algorithm can effectively inhibit the degradation of the image caused by fog, and improved target detection and identification capability of remote sensing.
To solve the quality degradation problem of fog polarization imaging, an improved defogging method was proposed based on physical model of atmospheric scattering and dark passage principle of polarization images. Firstly, based on atmospheric scattering model, fog polarization imaging mechanism was analyzed and effect of atmospheric polarization on defogging was explained. Secondly, based on edge detection operator and closing operation, sky region of fog polarization image was obtained, and light intensity of infinity atmospheric and degree of polarization of atmospheric were estimated. At last, to solve the existing factors in the image such as noise interference, radiation intensity information of the degraded image was restored by modifying the degree of polarization and light intensity distribution of atmospheric. After theoretical analysis and experimental verification, good results of foggy image restoration were achieved. The results show that the algorithm can accurately obtain the sky region and improve the contrast and sharpness of the image, and improve the degradation of the image. Therefore, the algorithm can effectively inhibit the degradation of the image caused by fog, and improved target detection and identification capability of remote sensing.
2016, 40(4): 526-530.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.015
Abstract:
In order to develop new material applied in food, medicine and biological engineering based on selective laser sintering rapid prototyping, the sucrose was used to carry out thermal gravity and differential-thermal analysis by thermal gravity/differential calorimetry. Sucrose powder and starch-sucrose mixed powder was sintered by using SLS300 rapid prototyping machine and after experimental analysis, the sinter quality was assessed. The results show that when the heating temperature is between 187℃ and 220℃,sucrose can guarantee good forming quality. The modified sugar mixture material by starch can accumulate forming and its surface quality is better than that of single sugar powder sintering molding. The dimension error is 2.1% and the maximum bending strength is 0.5620MPa. It meets the requirements of the general strength of food. The study has important significance for 3-D printing technology application in the field of food.
In order to develop new material applied in food, medicine and biological engineering based on selective laser sintering rapid prototyping, the sucrose was used to carry out thermal gravity and differential-thermal analysis by thermal gravity/differential calorimetry. Sucrose powder and starch-sucrose mixed powder was sintered by using SLS300 rapid prototyping machine and after experimental analysis, the sinter quality was assessed. The results show that when the heating temperature is between 187℃ and 220℃,sucrose can guarantee good forming quality. The modified sugar mixture material by starch can accumulate forming and its surface quality is better than that of single sugar powder sintering molding. The dimension error is 2.1% and the maximum bending strength is 0.5620MPa. It meets the requirements of the general strength of food. The study has important significance for 3-D printing technology application in the field of food.
2016, 40(4): 531-535.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.016
Abstract:
To decrease the byte loss probability of data burst, reduce the time delay cost and grantee the high usage efficiency of channel resource, a novel contention resolution was proposed based on segment redundant recombination in optical burst switching(OBS) networks. In this scheme, a special channel type called back-off channel was classified. When two bursts contents, the lower priority one will be separated and the segments will be sent back to upstream node by back-off channels. To grantee high efficient usage of channel resources, the segments will be cloned as many copies to fill the void of data channels. These copies will be recombined with the original data burst as virtual burst which can be separated flexibly. Moreover, the priority of the burst on back-off contention was set to the lowest to balance out the cost of segmentation copies. The simulation results show that, this contention resolution method reduces packet loss rate and time delay in OBS networks effectively, and use the channel resources efficiently.
To decrease the byte loss probability of data burst, reduce the time delay cost and grantee the high usage efficiency of channel resource, a novel contention resolution was proposed based on segment redundant recombination in optical burst switching(OBS) networks. In this scheme, a special channel type called back-off channel was classified. When two bursts contents, the lower priority one will be separated and the segments will be sent back to upstream node by back-off channels. To grantee high efficient usage of channel resources, the segments will be cloned as many copies to fill the void of data channels. These copies will be recombined with the original data burst as virtual burst which can be separated flexibly. Moreover, the priority of the burst on back-off contention was set to the lowest to balance out the cost of segmentation copies. The simulation results show that, this contention resolution method reduces packet loss rate and time delay in OBS networks effectively, and use the channel resources efficiently.
2016, 40(4): 536-540.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.017
Abstract:
In order to reduce the cost and the size of a sensing system, a 4-element fiber laser hydrophone time division multiplexing array was established by using high-speed optical switches based on the characteristics of fiber laser sensing elements. The selective pulse width and the loss of the time division multiplexing array were analyzed after theoretical analysis and experimental verification. Because of time delay of the interferometer and switch speed of the optical switches, sampling frequency was limited. The acoustic detecting experiments show that the multiplexing signal can be acquired and demutiplexed correctly. The crosstalk between adjacent channels of the 4-element fiber laser hydrophone array is -17dB.
In order to reduce the cost and the size of a sensing system, a 4-element fiber laser hydrophone time division multiplexing array was established by using high-speed optical switches based on the characteristics of fiber laser sensing elements. The selective pulse width and the loss of the time division multiplexing array were analyzed after theoretical analysis and experimental verification. Because of time delay of the interferometer and switch speed of the optical switches, sampling frequency was limited. The acoustic detecting experiments show that the multiplexing signal can be acquired and demutiplexed correctly. The crosstalk between adjacent channels of the 4-element fiber laser hydrophone array is -17dB.
2016, 40(4): 541-544.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.018
Abstract:
In order to solve drift problem of distributed optical fiber temperature sensorfor detection of blast of hot air tubes, a new solution of light center frequency matching (LCFM) method was proposed after theoretical derivation and experimental verification. By measuring the difference between the incident optical current and the reference photo current to adjust F-P light filter bandwidth, filter center frequency can always be kept in pass-band range of the filter. The match of filter bandwidth and light center frequency was achieved. The curves between Raman ratio and distance substantially coincided at different ambient temperatures when using frequency matching method. The linearity of the distributed optical fiber temperature sensor was about 0.52%. The experimental results show that LCFM method can reduce temperature drift of a fiber optical sensor and does not affect the linearity of the sensor. It is of great significance for achieving effective temperature measurement on hot air tube surface to combined center frequency matching mothod with distributed optical fiber temperature sensing technology.
In order to solve drift problem of distributed optical fiber temperature sensorfor detection of blast of hot air tubes, a new solution of light center frequency matching (LCFM) method was proposed after theoretical derivation and experimental verification. By measuring the difference between the incident optical current and the reference photo current to adjust F-P light filter bandwidth, filter center frequency can always be kept in pass-band range of the filter. The match of filter bandwidth and light center frequency was achieved. The curves between Raman ratio and distance substantially coincided at different ambient temperatures when using frequency matching method. The linearity of the distributed optical fiber temperature sensor was about 0.52%. The experimental results show that LCFM method can reduce temperature drift of a fiber optical sensor and does not affect the linearity of the sensor. It is of great significance for achieving effective temperature measurement on hot air tube surface to combined center frequency matching mothod with distributed optical fiber temperature sensing technology.
2016, 40(4): 545-549.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.019
Abstract:
In order to investigate influence of electronic tube radio frequency(RF) power frequency fluctuation of 2kW RF slab CO2 laser on output beam, the influences of RF frequency on laser input and output characteristics were analyzed through equivalent circuit analysis and experiment measurement. When frequency offset was 2MHz, real component of load impedance had the change of 0.01%. RF frequency drift had little effect on equivalent circuit parameters of discharge portion. When using the radio frequency of 79.4MHz, 80.0MHz, 80.7MHz, 81.4MHz, 82.0MHz and 82.7MHz, with corresponding output power of 81.4MHz design frequency set as benchmark, with the duty cycle set as 80%, laser power decreased about 150W with frequency drift of 1MHz. The computational results were consistent with the experimental results well. The results show thatthe impedance matching problem caused by frequency fluctuation is a major factor that deteriorates the RF slab laser performance. This problem can be solved by improving the matching network.
In order to investigate influence of electronic tube radio frequency(RF) power frequency fluctuation of 2kW RF slab CO2 laser on output beam, the influences of RF frequency on laser input and output characteristics were analyzed through equivalent circuit analysis and experiment measurement. When frequency offset was 2MHz, real component of load impedance had the change of 0.01%. RF frequency drift had little effect on equivalent circuit parameters of discharge portion. When using the radio frequency of 79.4MHz, 80.0MHz, 80.7MHz, 81.4MHz, 82.0MHz and 82.7MHz, with corresponding output power of 81.4MHz design frequency set as benchmark, with the duty cycle set as 80%, laser power decreased about 150W with frequency drift of 1MHz. The computational results were consistent with the experimental results well. The results show thatthe impedance matching problem caused by frequency fluctuation is a major factor that deteriorates the RF slab laser performance. This problem can be solved by improving the matching network.
2016, 40(4): 550-554.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.020
Abstract:
Tool surface with micro texture has good effect of anti-friction, increases adhesion resistance and abrasion resistance of the tool, and prolongs its life. Laser processing technology had obvious advantages in the preparation of micro texture on tool surface. The ideal surface micro texture of a tool can be obtained by laser processing technology under the reasonable processing conditions. In order to find the effects of laser energy density, frequency, laser beam scanning speed and scanning times on the dimension of tool surface micro groove, experiments were carried out under the condition of single factor of UV laser. The experiment at the preparation of micro texture on ceramic tool surface with 355nm wavelength UV laser was carried out. The reasonable condition parameters were determined. The study has guiding significance for working out suitable micro textures and improving the performance of ceramic tools.
Tool surface with micro texture has good effect of anti-friction, increases adhesion resistance and abrasion resistance of the tool, and prolongs its life. Laser processing technology had obvious advantages in the preparation of micro texture on tool surface. The ideal surface micro texture of a tool can be obtained by laser processing technology under the reasonable processing conditions. In order to find the effects of laser energy density, frequency, laser beam scanning speed and scanning times on the dimension of tool surface micro groove, experiments were carried out under the condition of single factor of UV laser. The experiment at the preparation of micro texture on ceramic tool surface with 355nm wavelength UV laser was carried out. The reasonable condition parameters were determined. The study has guiding significance for working out suitable micro textures and improving the performance of ceramic tools.
2016, 40(4): 555-559.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.021
Abstract:
In order to solve the problems for measurement and modeling of gas turbine blade trailing edge contour, a least-square circle fitting method based on probability density was proposed. After several times of fitting data repeatedly, each fitting center coordinate and radius was obtained. The maximum value of probability density distribution was looked as the optimal value. The errors of fitting data were analyzed by data simulation after theoretical analysis and experimental verification. The feasibility and robustness of the method were verified. The results show that the fitting of blade trailing edge contour and the estimation of parameter data are realized. The fitting error is 0.01mm. The optimal center coordinates and radius of circle fitting is obtained. For the blade trailing edge composed of straight line segments and short arcs, the fitting result is effective and accurate in the case of unknowing the point of tangent and arc equation. The method has an important guiding significance to precision measurement, machining accuracy and parameter design of blade trailing edge contour.
In order to solve the problems for measurement and modeling of gas turbine blade trailing edge contour, a least-square circle fitting method based on probability density was proposed. After several times of fitting data repeatedly, each fitting center coordinate and radius was obtained. The maximum value of probability density distribution was looked as the optimal value. The errors of fitting data were analyzed by data simulation after theoretical analysis and experimental verification. The feasibility and robustness of the method were verified. The results show that the fitting of blade trailing edge contour and the estimation of parameter data are realized. The fitting error is 0.01mm. The optimal center coordinates and radius of circle fitting is obtained. For the blade trailing edge composed of straight line segments and short arcs, the fitting result is effective and accurate in the case of unknowing the point of tangent and arc equation. The method has an important guiding significance to precision measurement, machining accuracy and parameter design of blade trailing edge contour.
2016, 40(4): 560-564.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.022
Abstract:
In order to design a beam expander or beam compressor with a single ellipsoidal lens, the comprehensive learning strategy particle swarm algorithm was introduced. The refraction characteristics of an ellipsoidal surface expressed by the vector form of refraction law was theoretically analyzed. Fitness data formula in the comprehensive learning strategy particle swarm optimizer was gotten. A single ellipsoidal beam-expanding lens with length less than 170mm and shrinkage rate of 14.16 was designed. The process of beam-shrinking or beam-expanding was simulated by using the ray tracing method. Simulation results show that a single ellipsoidal lens can play the role in compressing beam or expanding beam, and the comprehensive learning particle swarm algorithm can be applied to the design of beam expanders/compressors. The results is helpful in simplifying beam expanding/compressing systems and designing a single expanding/compressing beam lens to meet different requirements.
In order to design a beam expander or beam compressor with a single ellipsoidal lens, the comprehensive learning strategy particle swarm algorithm was introduced. The refraction characteristics of an ellipsoidal surface expressed by the vector form of refraction law was theoretically analyzed. Fitness data formula in the comprehensive learning strategy particle swarm optimizer was gotten. A single ellipsoidal beam-expanding lens with length less than 170mm and shrinkage rate of 14.16 was designed. The process of beam-shrinking or beam-expanding was simulated by using the ray tracing method. Simulation results show that a single ellipsoidal lens can play the role in compressing beam or expanding beam, and the comprehensive learning particle swarm algorithm can be applied to the design of beam expanders/compressors. The results is helpful in simplifying beam expanding/compressing systems and designing a single expanding/compressing beam lens to meet different requirements.
2016, 40(4): 565-570.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.023
Abstract:
In order to ensure the zero-mean property of measurement matrix during the process of acquiring wideband signal by using photonic compressive sensing, a parallel structure based on Mach-Zehnder modulators was used to implement the mixing function of input signal and zero-mean random sequence. At the same time, digital domain compensation was employed to reduce the negative effect of modulator nonlinearity on recovery performance. In this way the system had an improved recovery performance within a certain range. The results show that the improved photonic compressive sensing performs better when acquiring wideband sparse signals.
In order to ensure the zero-mean property of measurement matrix during the process of acquiring wideband signal by using photonic compressive sensing, a parallel structure based on Mach-Zehnder modulators was used to implement the mixing function of input signal and zero-mean random sequence. At the same time, digital domain compensation was employed to reduce the negative effect of modulator nonlinearity on recovery performance. In this way the system had an improved recovery performance within a certain range. The results show that the improved photonic compressive sensing performs better when acquiring wideband sparse signals.
2016, 40(4): 571-575.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.024
Abstract:
In order to validate the impact of saturable absorber on output performance of thulium-doped mode-locked fiber laser, the effect of parameters of saturable absorber was numerically studied based on the coupled Ginzburg-Landau equation. The time domain and frequency domain characteristics of thulium-doped mode-locked fiber laser modulated by high modulation depth saturable absorber were discussed. The results show that pulse width is shortened and time-bandwidth product decreases effectively by choosing high modulation depth saturable absorber with suitable modulation depth. The result would provide some design guidelines for the developing of the steady, ultrafast mid-infrared fiber lasers.
In order to validate the impact of saturable absorber on output performance of thulium-doped mode-locked fiber laser, the effect of parameters of saturable absorber was numerically studied based on the coupled Ginzburg-Landau equation. The time domain and frequency domain characteristics of thulium-doped mode-locked fiber laser modulated by high modulation depth saturable absorber were discussed. The results show that pulse width is shortened and time-bandwidth product decreases effectively by choosing high modulation depth saturable absorber with suitable modulation depth. The result would provide some design guidelines for the developing of the steady, ultrafast mid-infrared fiber lasers.
2016, 40(4): 576-581.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.025
Abstract:
In order to capture 3-D image instantaneously by transmitting single laser pulse of array lidar, solve the problem of multi-channel ranging, a 25-channel concurrent ranging system was developed. A multi-core parallel processor was consisted of four measuring units and one data multiplexing unit. Each measuring units contained 8-channel trans-impedance amplifiers, 8-channel high speed comparators, a TDC-GPX chip, and a STM32 microprocessor. Multi-channel data package and upload were completed by field-programmable gate array(FPGA) in multiplexing unit. Experimental results indicate that range error is less than 25cm. The ranging system has the feature of openness, ranging channel can be increased easily, and circuit boards are interchangeable. Error correction method based on distance is presented. The correction of ranging data can be accessed directly by single laser pulse detection without the repetition of measurement. The study gives the foundation for researching and manufacturing of array lidar with higher precision.
In order to capture 3-D image instantaneously by transmitting single laser pulse of array lidar, solve the problem of multi-channel ranging, a 25-channel concurrent ranging system was developed. A multi-core parallel processor was consisted of four measuring units and one data multiplexing unit. Each measuring units contained 8-channel trans-impedance amplifiers, 8-channel high speed comparators, a TDC-GPX chip, and a STM32 microprocessor. Multi-channel data package and upload were completed by field-programmable gate array(FPGA) in multiplexing unit. Experimental results indicate that range error is less than 25cm. The ranging system has the feature of openness, ranging channel can be increased easily, and circuit boards are interchangeable. Error correction method based on distance is presented. The correction of ranging data can be accessed directly by single laser pulse detection without the repetition of measurement. The study gives the foundation for researching and manufacturing of array lidar with higher precision.
2016, 40(4): 582-585.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.026
Abstract:
In order to improve configuration of a widely tunable low-frequency optical radio frequency(RF) generation system and reduce phase noise of the system, a simplified system design was demonstrated with fewer components and improved phase noise performance by using an amplitude modulator. After theoretical analysis and experimental verification, the data of system phase noise and frequency offset was obtained under low-frequency radio signal conditions. The results show that, excess phase noise due to acoustic vibrations of optical fibers can be successfully eliminated by mechanical isolation. The study has some value and practical significance in the field of optical communication in the future.
In order to improve configuration of a widely tunable low-frequency optical radio frequency(RF) generation system and reduce phase noise of the system, a simplified system design was demonstrated with fewer components and improved phase noise performance by using an amplitude modulator. After theoretical analysis and experimental verification, the data of system phase noise and frequency offset was obtained under low-frequency radio signal conditions. The results show that, excess phase noise due to acoustic vibrations of optical fibers can be successfully eliminated by mechanical isolation. The study has some value and practical significance in the field of optical communication in the future.
2016, 40(4): 586-591.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.027
Abstract:
The output voltage of a traditional high voltage charging power supply of CO2 laser in LC resonant charging configuration drops with the increase of operating frequency, which affect the stability of laser output and the beam quality. Meanwhile, traditional high voltage charging power supply has huge size and weight which is disadvantageous to small size and weight of the device. In order to resolve the problems, a 36kV/10kW high frequency and high voltage charging power supply was studied by using a full bridge inverter circuit and a series resonant soft switch circuit. Three phase 380V alternating current (AC) was used as the energy system, high power intelligent power module(IPM) was used as full bridge inverter circuit. High voltage pulse signal was obtained by the inverter AC signal through series resonant circuit and high frequency pulse transformer. High voltage pulse charged power supply for load capacitor through rectifier. Voltage and current double closed-loop control system was used in the charging power. After sampling and amplification, the output voltage and current were fed back to the power supply control chip SG3525. SG3525 controlled the duty cycle of pulse width modulation driving signal by feedback signal. Experimental results show that the output voltage of the charging power supply is 37kV, output peak power is 13.05kW, and charging efficiency is 0.826 when laser discharge frequency is 25Hz. The high frequency and high voltage charging power supply is suit for high voltage charging power of CO2 laser.
The output voltage of a traditional high voltage charging power supply of CO2 laser in LC resonant charging configuration drops with the increase of operating frequency, which affect the stability of laser output and the beam quality. Meanwhile, traditional high voltage charging power supply has huge size and weight which is disadvantageous to small size and weight of the device. In order to resolve the problems, a 36kV/10kW high frequency and high voltage charging power supply was studied by using a full bridge inverter circuit and a series resonant soft switch circuit. Three phase 380V alternating current (AC) was used as the energy system, high power intelligent power module(IPM) was used as full bridge inverter circuit. High voltage pulse signal was obtained by the inverter AC signal through series resonant circuit and high frequency pulse transformer. High voltage pulse charged power supply for load capacitor through rectifier. Voltage and current double closed-loop control system was used in the charging power. After sampling and amplification, the output voltage and current were fed back to the power supply control chip SG3525. SG3525 controlled the duty cycle of pulse width modulation driving signal by feedback signal. Experimental results show that the output voltage of the charging power supply is 37kV, output peak power is 13.05kW, and charging efficiency is 0.826 when laser discharge frequency is 25Hz. The high frequency and high voltage charging power supply is suit for high voltage charging power of CO2 laser.
2016, 40(4): 592-595.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.028
Abstract:
In order to realize the laser energy attenuation, a cascade three-set disc attenuator was proposed to achieve wide range of attenuation of laser energy. In the attenuation system, exact rotation of attenuation plates was achieved with the stepper motor driven by the pulse generated by the STM32 timer and with the position decided by the Hall sensor. The opto-mecahanical parts, motor driver and rotation control mechanism were analyzed. The experimental results show that attenuation range is 0%~97.51%. Reliability and repeatability of the system are verified. The results are helpful for high power laser attenuation.
In order to realize the laser energy attenuation, a cascade three-set disc attenuator was proposed to achieve wide range of attenuation of laser energy. In the attenuation system, exact rotation of attenuation plates was achieved with the stepper motor driven by the pulse generated by the STM32 timer and with the position decided by the Hall sensor. The opto-mecahanical parts, motor driver and rotation control mechanism were analyzed. The experimental results show that attenuation range is 0%~97.51%. Reliability and repeatability of the system are verified. The results are helpful for high power laser attenuation.
2016, 40(4): 596-600.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.029
Abstract:
To explore new structures of comb filters, a new Sagnac loop filter based on the sampled fiber Bragg grating was proposed. Using the theory of Jones matrix, the theoretical model of filter was established. Theoretical analysis and numerical simulation of transmission spectra of the proposed filter were carried on. By choosing the different value of the sampled fiber Bragg grating length L, optical fiber ring arm length difference L, and the sampling period P, six kinds of narrow-band comb transmission spectrums with discrete spectral lines, high reflectivity, and equal interval can be obtained. The spectrums have good wavelength selectivity and good channel isolation. The simulation results show that this filter can be used in the multi-channel narrow band filter of the wavelength division multiplexing system, dual-wavelengthfiber laser, and the distributed sensing system, etc. It provides a certain reference for the filter combining fiber Bragg grating with the structure of the Sagnac loop in research and application.
To explore new structures of comb filters, a new Sagnac loop filter based on the sampled fiber Bragg grating was proposed. Using the theory of Jones matrix, the theoretical model of filter was established. Theoretical analysis and numerical simulation of transmission spectra of the proposed filter were carried on. By choosing the different value of the sampled fiber Bragg grating length L, optical fiber ring arm length difference L, and the sampling period P, six kinds of narrow-band comb transmission spectrums with discrete spectral lines, high reflectivity, and equal interval can be obtained. The spectrums have good wavelength selectivity and good channel isolation. The simulation results show that this filter can be used in the multi-channel narrow band filter of the wavelength division multiplexing system, dual-wavelengthfiber laser, and the distributed sensing system, etc. It provides a certain reference for the filter combining fiber Bragg grating with the structure of the Sagnac loop in research and application.
Simulation of propagation characteristics of stress wave in copper films with laser shock processing
2016, 40(4): 601-605.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.030
Abstract:
In order to study the propagation characteristics of shock wave, shock processing of copper films under the different processing parameters was simulated with finite element software. Propagation characteristics of dynamic stress wave in film-substrate system were analyzed by using stress wave theory. The results show that when the laser energy is 30mJ, shock waves are elastic. The maximum velocity of particles in thin film with the single shock is -0.018mm/s, the change of the velocity and the residual strain of particles in films is little with three shocks. When laser energy is 120mJ, shock waves are elastic-plastic. The maximum velocity of particles and the largest depth of the residual strain in the films with three shocks are respectively 26.44% lower and 35.48% higher than those with single shock. These have guiding significance to the study of propagation characteristics of shock wave.
In order to study the propagation characteristics of shock wave, shock processing of copper films under the different processing parameters was simulated with finite element software. Propagation characteristics of dynamic stress wave in film-substrate system were analyzed by using stress wave theory. The results show that when the laser energy is 30mJ, shock waves are elastic. The maximum velocity of particles in thin film with the single shock is -0.018mm/s, the change of the velocity and the residual strain of particles in films is little with three shocks. When laser energy is 120mJ, shock waves are elastic-plastic. The maximum velocity of particles and the largest depth of the residual strain in the films with three shocks are respectively 26.44% lower and 35.48% higher than those with single shock. These have guiding significance to the study of propagation characteristics of shock wave.
2016, 40(4): 606-609.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.031
Abstract:
In order to study the temperature distribution for laser butt welding of dissimilar metal steel/aluminum, a mathematical model was established and welding temperature field was also simulated by ANSYS software. Temperature distribution at different time and the thermal cycling profile at the node on specimen surface were obtained. The effect of welding speed on welding temperature field was studied. The results were compared with the actual welding. The results show that, the welding temperature field is asymmetrically distributed and the temperature gradient in steel side is greater than that in aluminum side; With the increase of welding speed, the maximum temperature reduces gradually and weld width also decreases gradually. The weld shapes obtained from simulation and experiments are consistent, and the error is less than 5%. The study can verify the accuracy of simulation results.
In order to study the temperature distribution for laser butt welding of dissimilar metal steel/aluminum, a mathematical model was established and welding temperature field was also simulated by ANSYS software. Temperature distribution at different time and the thermal cycling profile at the node on specimen surface were obtained. The effect of welding speed on welding temperature field was studied. The results were compared with the actual welding. The results show that, the welding temperature field is asymmetrically distributed and the temperature gradient in steel side is greater than that in aluminum side; With the increase of welding speed, the maximum temperature reduces gradually and weld width also decreases gradually. The weld shapes obtained from simulation and experiments are consistent, and the error is less than 5%. The study can verify the accuracy of simulation results.
Thermal characteristics of spontaneous emission spectra from external-cavity surface-emitting lasers
2016, 40(4): 610-614.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.032
Abstract:
Thermal effect is the main reason limiting output power and beam quality of vertical-external-cavity surface-emitting lasers (VECSELs). To optimize the quantum design in active regions of gain chip, decrease thermal effect and upgrade slope efficiencies and output laser power, thermal characteristics of a VECSEL at 980nm wavelength were investigated experimentally by means of photoluminescence. The edge-emitting and surface-emitting spectra at different heatsink temperatures were obtained. The results indicate that the redshift rate of the edge-emitting spectra, which revels the intrinsic properties of quantum wells in active region, is 0.5nm/K with increasing temperature, while the redshift rate of the surface-emitting spectra, which are modulated by multiple-layer structure of the gain chip, is only 0.1nm/K with increasing temperature. The experiments also show that the surface-emitting spectra are split into several modes because of the restriction from the micro-cavities in gain chips of VECSELs. In the design of VECSEL gain chip, according to the above thermal characteristics of VECSELs, performance of a laser could be improved significantly by prebiasing emission wavelengths of quantum wells and cavity lengths of micro-cavities.
Thermal effect is the main reason limiting output power and beam quality of vertical-external-cavity surface-emitting lasers (VECSELs). To optimize the quantum design in active regions of gain chip, decrease thermal effect and upgrade slope efficiencies and output laser power, thermal characteristics of a VECSEL at 980nm wavelength were investigated experimentally by means of photoluminescence. The edge-emitting and surface-emitting spectra at different heatsink temperatures were obtained. The results indicate that the redshift rate of the edge-emitting spectra, which revels the intrinsic properties of quantum wells in active region, is 0.5nm/K with increasing temperature, while the redshift rate of the surface-emitting spectra, which are modulated by multiple-layer structure of the gain chip, is only 0.1nm/K with increasing temperature. The experiments also show that the surface-emitting spectra are split into several modes because of the restriction from the micro-cavities in gain chips of VECSELs. In the design of VECSEL gain chip, according to the above thermal characteristics of VECSELs, performance of a laser could be improved significantly by prebiasing emission wavelengths of quantum wells and cavity lengths of micro-cavities.
2016, 40(4): 615-618.
doi: 10.7510/jgjs.issn.1001-3806.2016.04.033
Abstract:
In order to optimize the phase sensitive optical time-domain reflectometer (-OTDR) system, a multi-intrusion detection system was built based on -OTDR principle. The effect of laser linewidth on system performance was studied theoretically and experimentally. 7km sensing optical fiber was used in system experiment. The theoretical analysis shows that with the increase of the laser linewidth, the ripples of backward coherent Rayleigh scattering detected by the system become gradually smooth, and the signal-to-noise ratio and location accuracy of system also decrease, so that the system can't locate and identify interference information. The experimental results show that when laser linewidth changes from 5kHz to 200kHz,the ripple of backward coherent Rayleigh scattering detected by the system also becomes gradually smooth, the signal to noise ratio of system decrease from 12dB to 3dB. The results of experiment is in agreement with the results of theoretical very well.
In order to optimize the phase sensitive optical time-domain reflectometer (-OTDR) system, a multi-intrusion detection system was built based on -OTDR principle. The effect of laser linewidth on system performance was studied theoretically and experimentally. 7km sensing optical fiber was used in system experiment. The theoretical analysis shows that with the increase of the laser linewidth, the ripples of backward coherent Rayleigh scattering detected by the system become gradually smooth, and the signal-to-noise ratio and location accuracy of system also decrease, so that the system can't locate and identify interference information. The experimental results show that when laser linewidth changes from 5kHz to 200kHz,the ripple of backward coherent Rayleigh scattering detected by the system also becomes gradually smooth, the signal to noise ratio of system decrease from 12dB to 3dB. The results of experiment is in agreement with the results of theoretical very well.
