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RSS2015 Vol. 39, No. 6
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2015, 39(6): 735-740.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.001
[Abstract]
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Abstract:
In order to study the orientation behaviors of CO molecules induced by chirped terahertz pulse, the time-dependent Schrdinger equation was solved by means of rigid rotor approximation for theoretical analysis. In order to achieve high degree of molecular orientation in chirped terahertz pulse at a low intensity, the method by utilizing chirped terahertz pulse in combination with femtosecond laser pulse was proposed. The results show that the molecular orientation degree can be enhanced about 81%, and that the orientation efficiency decreases with the rise of temperature in finite temperature range. Compared with the few-cycle terahertz pulse, chirped terahertz pulse has more advantages in inducing molecular orientation. The result is meaningful to enhance the CO orientation degree.
In order to study the orientation behaviors of CO molecules induced by chirped terahertz pulse, the time-dependent Schrdinger equation was solved by means of rigid rotor approximation for theoretical analysis. In order to achieve high degree of molecular orientation in chirped terahertz pulse at a low intensity, the method by utilizing chirped terahertz pulse in combination with femtosecond laser pulse was proposed. The results show that the molecular orientation degree can be enhanced about 81%, and that the orientation efficiency decreases with the rise of temperature in finite temperature range. Compared with the few-cycle terahertz pulse, chirped terahertz pulse has more advantages in inducing molecular orientation. The result is meaningful to enhance the CO orientation degree.
2015, 39(6): 741-744.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.002
Abstract:
In order to study the performance of Lyot fiber depolarizers, 2-section, 3-section and 4-section Lyot fiber depolarizers were analyzed by means of Jones matrix. After theoretical analysis and experimental verification, the mathematical expression of the dependence of the degree of polarization on the section number of a multi-section Lyot fiber depolarizer was obtained. A conclusion was made that the degree of polarization decreased substantially with the increase of section number of a fiber depolarizer. The experiment results show that the degree of polarization of a 4-section Lyot fiber depolarizer is one quarter of a 2-section fiber depolarizer. The standard deviation decreases from 0.0951 to 0.0245. The experimental results prove the mathematical expressions are correct. The results prove the correctness of the theory and provide theoretical guidance for the actual production of multi-section Lyot depolarizers.
In order to study the performance of Lyot fiber depolarizers, 2-section, 3-section and 4-section Lyot fiber depolarizers were analyzed by means of Jones matrix. After theoretical analysis and experimental verification, the mathematical expression of the dependence of the degree of polarization on the section number of a multi-section Lyot fiber depolarizer was obtained. A conclusion was made that the degree of polarization decreased substantially with the increase of section number of a fiber depolarizer. The experiment results show that the degree of polarization of a 4-section Lyot fiber depolarizer is one quarter of a 2-section fiber depolarizer. The standard deviation decreases from 0.0951 to 0.0245. The experimental results prove the mathematical expressions are correct. The results prove the correctness of the theory and provide theoretical guidance for the actual production of multi-section Lyot depolarizers.
2015, 39(6): 745-750.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.003
Abstract:
In order to combine the spectral shape difference information and the polynomial kernel function global information, exploit the object feature fully and improve the accuracy of anomaly detection, anomaly detection method was proposed based on weighted combination kernel RX algorithm. A spectral angle kernel function was added to Gaussian kernel function in the anomaly detection method. Because the kernels' parameter and the weighting parameter will affect the efficiency of the algorithm, the random function selection, the hill climbing method and the particle swarm optimization algorithm were implemented for setting the above parameters. Experiment results show that at a constant false alarm rate, it is the best to set the parameters by means of the particle swarm algorithm. Target detection rate is 83.5% by using the weighted combination kernel RX algorithm, higher than that by means of the traditional kernel RX algorithm.
In order to combine the spectral shape difference information and the polynomial kernel function global information, exploit the object feature fully and improve the accuracy of anomaly detection, anomaly detection method was proposed based on weighted combination kernel RX algorithm. A spectral angle kernel function was added to Gaussian kernel function in the anomaly detection method. Because the kernels' parameter and the weighting parameter will affect the efficiency of the algorithm, the random function selection, the hill climbing method and the particle swarm optimization algorithm were implemented for setting the above parameters. Experiment results show that at a constant false alarm rate, it is the best to set the parameters by means of the particle swarm algorithm. Target detection rate is 83.5% by using the weighted combination kernel RX algorithm, higher than that by means of the traditional kernel RX algorithm.
2015, 39(6): 751-755.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.004
Abstract:
In order to obtain light guide plate(LGP) with uniform surface illumination efficiently, using the design method based on gray image processing technique and using TracePro software, the model with two unilateral incident light-emitting diodes was analyzed theoretically and verified by simulation. Simulation data of output surface illumination was obtained. The results show that LGP designed by the method presented in this paper can reach 86.7% of illumination uniformity, conforming to the standard of Commission Internationale de I'Eclairage. The illumination uniformity can improved to 91.9% after modifying the gray image locally. This study is helpful for the design of LGP with high illumination uniformity more effectively.
In order to obtain light guide plate(LGP) with uniform surface illumination efficiently, using the design method based on gray image processing technique and using TracePro software, the model with two unilateral incident light-emitting diodes was analyzed theoretically and verified by simulation. Simulation data of output surface illumination was obtained. The results show that LGP designed by the method presented in this paper can reach 86.7% of illumination uniformity, conforming to the standard of Commission Internationale de I'Eclairage. The illumination uniformity can improved to 91.9% after modifying the gray image locally. This study is helpful for the design of LGP with high illumination uniformity more effectively.
2015, 39(6): 756-760.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.005
Abstract:
Because of the effect of nonlinear polarization of transmission fiber, coupling ratio between local oscillator and quantum signal in a quantum key distribution system is decreased, signal jitters which leads to polarization multiplexing is increased, and security and stability of the system are decreased. To enhance technical performance of polarization encodement of quantum optics, after theoretical analysis and numerical simulation, operational experiment scheme was proposed to solve the polarization jitters caused by nonlinear polarization coupling of fiber. The results show that signal stability of polarization multiplexing enhances and transmission capacity of quantum key distribution increases to 61% by using feedback of spectral test results to control fiber nonlinear polarization coupling ratio between local oscillator and quantum signal. The research is helpful for practical application of polarization coding technology in quantum key distribution.
Because of the effect of nonlinear polarization of transmission fiber, coupling ratio between local oscillator and quantum signal in a quantum key distribution system is decreased, signal jitters which leads to polarization multiplexing is increased, and security and stability of the system are decreased. To enhance technical performance of polarization encodement of quantum optics, after theoretical analysis and numerical simulation, operational experiment scheme was proposed to solve the polarization jitters caused by nonlinear polarization coupling of fiber. The results show that signal stability of polarization multiplexing enhances and transmission capacity of quantum key distribution increases to 61% by using feedback of spectral test results to control fiber nonlinear polarization coupling ratio between local oscillator and quantum signal. The research is helpful for practical application of polarization coding technology in quantum key distribution.
2015, 39(6): 761-764.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.006
Abstract:
In order to optimize the phase noise characteristics and improve the performance of an optoelectronic oscillator (OEO), the relation among the phase noise of an OEO, the spectra line-width and optical power was studied by theoretical analysis and experimental verification. The spectral performance and phase noise of microwave signals generated by the OEO were measured respectively, under the conditions of equal optical power and different spectra line-widths. And then, phase noise of microwave signals was measured under the conditions of fixed spectral line-width and different laser power. The results indicate that the narrower spectral line-width and the higher laser power, the better phase noise and spectral characteristics of microwave signals. Furthermore, compared with the spectral line-width, the laser power has greater effect on phase noise beyond 1kHz frequency offset. The result is helpful for improving phase noise of photoelectric oscillator.
In order to optimize the phase noise characteristics and improve the performance of an optoelectronic oscillator (OEO), the relation among the phase noise of an OEO, the spectra line-width and optical power was studied by theoretical analysis and experimental verification. The spectral performance and phase noise of microwave signals generated by the OEO were measured respectively, under the conditions of equal optical power and different spectra line-widths. And then, phase noise of microwave signals was measured under the conditions of fixed spectral line-width and different laser power. The results indicate that the narrower spectral line-width and the higher laser power, the better phase noise and spectral characteristics of microwave signals. Furthermore, compared with the spectral line-width, the laser power has greater effect on phase noise beyond 1kHz frequency offset. The result is helpful for improving phase noise of photoelectric oscillator.
2015, 39(6): 765-768.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.007
Abstract:
In order to study ultrafast dynamics of high power laser ablation of silica, the dynamic process of monocrystalline silicon ablated by nanosecond (ns) and femtosecond (fs) laser was investigated by the technology of ultrafast time-resolved optical diagnosis. The time-resolved shadowgraphs of the formation and evolution process of plasma expansion, material ejection and shock waves were obtained. For ns laser, material ejection occurs at 200ns ~300ns of delay time with gas-liquid mixture and at 1060ns of delay time with droplet ejection. For fs laser, material ejection occurs at 1ns~2ns of delay time with plasma. The result shows that the dynamic process of laser ablation is significantly different between by fs laser and by ns laser, especially the time of material ejection and the state and size of ejection particles. The results indicate that the process of material ejection induced by ns and fs laser is discontinuous and show that the material ejection is caused by different ablation mechanisms in different time. The results are helpful for the study of interaction mechanism of laser and silica, as well as laser etching monocrystalline silicon.
In order to study ultrafast dynamics of high power laser ablation of silica, the dynamic process of monocrystalline silicon ablated by nanosecond (ns) and femtosecond (fs) laser was investigated by the technology of ultrafast time-resolved optical diagnosis. The time-resolved shadowgraphs of the formation and evolution process of plasma expansion, material ejection and shock waves were obtained. For ns laser, material ejection occurs at 200ns ~300ns of delay time with gas-liquid mixture and at 1060ns of delay time with droplet ejection. For fs laser, material ejection occurs at 1ns~2ns of delay time with plasma. The result shows that the dynamic process of laser ablation is significantly different between by fs laser and by ns laser, especially the time of material ejection and the state and size of ejection particles. The results indicate that the process of material ejection induced by ns and fs laser is discontinuous and show that the material ejection is caused by different ablation mechanisms in different time. The results are helpful for the study of interaction mechanism of laser and silica, as well as laser etching monocrystalline silicon.
2015, 39(6): 769-775.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.008
Abstract:
In order to investigate effect of electric field interference on the properties of an optical voltage transducer with longitudinal modulation structure, using tensor analysis method and based on the relative inverse dielectric tensor of the electro-optic crystal, simulation analysis and experimental verification were carried out. According to experimental result of light separation, an optical electric field sensor was designed. The magnitude error of sensor was within 2%. The results show that light separation will occur in two transmitting normal modes of electro-optical crystal while electric field interference exists, which makes that the two polarized beams can not interfere effectively in the analyzer and which leads to a smaller output signal. The error caused by interference efficiency of KDP crystal can reached 0.3% when interference voltage was 500V and spot radius was 0.2mm. When interference field intensity is less than 105V/m, interference efficiency of Bi4Ge3O12(BGO) crystal is close to 1. The transducer error caused by electric field interference has the relationship not only with the magnitude of electric interference but also with the beam radius and the length of sensing crystal. The influence of interference electric field can be reduced effectively by selecting the light source with larger beam radius and the sensing crystal with smaller length. The research can provide the guidance for the design of optical voltage transducers.
In order to investigate effect of electric field interference on the properties of an optical voltage transducer with longitudinal modulation structure, using tensor analysis method and based on the relative inverse dielectric tensor of the electro-optic crystal, simulation analysis and experimental verification were carried out. According to experimental result of light separation, an optical electric field sensor was designed. The magnitude error of sensor was within 2%. The results show that light separation will occur in two transmitting normal modes of electro-optical crystal while electric field interference exists, which makes that the two polarized beams can not interfere effectively in the analyzer and which leads to a smaller output signal. The error caused by interference efficiency of KDP crystal can reached 0.3% when interference voltage was 500V and spot radius was 0.2mm. When interference field intensity is less than 105V/m, interference efficiency of Bi4Ge3O12(BGO) crystal is close to 1. The transducer error caused by electric field interference has the relationship not only with the magnitude of electric interference but also with the beam radius and the length of sensing crystal. The influence of interference electric field can be reduced effectively by selecting the light source with larger beam radius and the sensing crystal with smaller length. The research can provide the guidance for the design of optical voltage transducers.
2015, 39(6): 776-779.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.009
Abstract:
In order to obtain optical constants of TiO2 thin film, single-layer TiO2 film deposited on K9 glass with an optical automatic vacuum coating machine was measured and analyzed with a SE850 broadband ellipsometer produced by SENTECH, Germany, and the optical constant curve and thickness of TiO2 thin film in 300nm~2500nm spectrum were obtained. Based on the film characteristics and film forming characteristics of TiO2 film, taking the influence of the intermix layer and rough surface layer into account, models were set up with Cauchy index model and Tauc-Lorentz model and the measurement data were analyzed and compared. The smallest mean square error of 0.5544 was obtained with a so called model of substrate/Tauc-Lorentz model/rough surface layer. The measured TiO2 thickness was closest to calculation value of TFCalc software. The results have certain reference value for the design and preparation of TiO2 thin multilayer film.
In order to obtain optical constants of TiO2 thin film, single-layer TiO2 film deposited on K9 glass with an optical automatic vacuum coating machine was measured and analyzed with a SE850 broadband ellipsometer produced by SENTECH, Germany, and the optical constant curve and thickness of TiO2 thin film in 300nm~2500nm spectrum were obtained. Based on the film characteristics and film forming characteristics of TiO2 film, taking the influence of the intermix layer and rough surface layer into account, models were set up with Cauchy index model and Tauc-Lorentz model and the measurement data were analyzed and compared. The smallest mean square error of 0.5544 was obtained with a so called model of substrate/Tauc-Lorentz model/rough surface layer. The measured TiO2 thickness was closest to calculation value of TFCalc software. The results have certain reference value for the design and preparation of TiO2 thin multilayer film.
2015, 39(6): 780-784.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.010
Abstract:
In order to obtain the air cooling high repetition fiber laser with stable power, an acoustic-optical Q-switched all-fiber laser with master oscillator power amplifier structure was studied. The oscillator used the scheme of acousto-optic Q-switched with a pair of fiber Bragg grating as laser cavity mirrors. Pumped by 915nm laser diodes, 1064nm laser pulse output was acquired with adjustable repetition rates from 10kHz to 130kHz. Through two-stage double clad large mode area fiber amplifier, 101W output power was obtained with 328.1ns pulse width. The 3dB optical spectrum width of fiber laser was 0.6nm. Optical-optical efficiency of the second amplifier stage was 69%. The total optical-optical efficiency of laser was 62.7%. The distortion cause of long width seed pulse created by acousto-optic Q-switched through the amplification was studied. The experimental results show that pumped by 915nm laser diodes, the long-term stability of output power is proved to less than 2% under air cooling.
In order to obtain the air cooling high repetition fiber laser with stable power, an acoustic-optical Q-switched all-fiber laser with master oscillator power amplifier structure was studied. The oscillator used the scheme of acousto-optic Q-switched with a pair of fiber Bragg grating as laser cavity mirrors. Pumped by 915nm laser diodes, 1064nm laser pulse output was acquired with adjustable repetition rates from 10kHz to 130kHz. Through two-stage double clad large mode area fiber amplifier, 101W output power was obtained with 328.1ns pulse width. The 3dB optical spectrum width of fiber laser was 0.6nm. Optical-optical efficiency of the second amplifier stage was 69%. The total optical-optical efficiency of laser was 62.7%. The distortion cause of long width seed pulse created by acousto-optic Q-switched through the amplification was studied. The experimental results show that pumped by 915nm laser diodes, the long-term stability of output power is proved to less than 2% under air cooling.
2015, 39(6): 785-788.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.011
Abstract:
Thin film deposited by physical vapor deposition usually has stress. In order to prevent high-refractive (HR) coating stress from destroying the surface of the substrate, the stress of the film prepared by electron beam evaporation was measured with a digital wavefront interferometer. The affecting factors of stress of optical dielectric coating were discussed. HfO2 and SiO2 were alternatively deposited on the substrate surface. As high refractive material, HfO2 layers were in tensile stress. As lower refractive material, SiO2 layers were in compressed stress. The results show that the stress is balanced by adjusting the oxygen pressure and the evaporation rate of coating material under stable experimental conditions. HfO2/SiO2 HR coatings have high damage thresholds.
Thin film deposited by physical vapor deposition usually has stress. In order to prevent high-refractive (HR) coating stress from destroying the surface of the substrate, the stress of the film prepared by electron beam evaporation was measured with a digital wavefront interferometer. The affecting factors of stress of optical dielectric coating were discussed. HfO2 and SiO2 were alternatively deposited on the substrate surface. As high refractive material, HfO2 layers were in tensile stress. As lower refractive material, SiO2 layers were in compressed stress. The results show that the stress is balanced by adjusting the oxygen pressure and the evaporation rate of coating material under stable experimental conditions. HfO2/SiO2 HR coatings have high damage thresholds.
2015, 39(6): 789-793.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.012
Abstract:
In order to achieve high precision temperature control of a semiconductor laser, an experimental temperature control system was designed by using a thermoelectric cooler, a temperature sensor and corresponding radiators. Firstly, the mathematical model and the corresponding transfer function of temperature control were established by utilizing thermodynamic analysis method after theoretical analysis. Secondly, after obtaining the temperature data of the semiconductor laser, according to the characteristics of model parameters, an empirical curve of step response was presented and model parameters were identified by nonlinear curve least square fitting. Finally, the system was simulated based on the model parameters and experimental verification was carried out. The results show that the fitting curve and emulation curve is consistent with experimental curve and the fitting model parameters have better prediction accuracy. The result is helpful for optimizing temperature control.
In order to achieve high precision temperature control of a semiconductor laser, an experimental temperature control system was designed by using a thermoelectric cooler, a temperature sensor and corresponding radiators. Firstly, the mathematical model and the corresponding transfer function of temperature control were established by utilizing thermodynamic analysis method after theoretical analysis. Secondly, after obtaining the temperature data of the semiconductor laser, according to the characteristics of model parameters, an empirical curve of step response was presented and model parameters were identified by nonlinear curve least square fitting. Finally, the system was simulated based on the model parameters and experimental verification was carried out. The results show that the fitting curve and emulation curve is consistent with experimental curve and the fitting model parameters have better prediction accuracy. The result is helpful for optimizing temperature control.
2015, 39(6): 794-797.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.013
Abstract:
Auto-focusing was an important part of imaging automation. In order to improve the focus accuracy and reduce the time of auto-focusing, an auto-focusing algorithm combining image ambiguity and image clarity was presented. At first, in the severe defocused state, the correct search direction of focus-motor was determined by the value of image ambiguity. And then, the correct focus position was determined by the value of image clarity and the optimized mountain climbing servo.The results show that this method could reduce focus time and obtain the high focus accuracy.
Auto-focusing was an important part of imaging automation. In order to improve the focus accuracy and reduce the time of auto-focusing, an auto-focusing algorithm combining image ambiguity and image clarity was presented. At first, in the severe defocused state, the correct search direction of focus-motor was determined by the value of image ambiguity. And then, the correct focus position was determined by the value of image clarity and the optimized mountain climbing servo.The results show that this method could reduce focus time and obtain the high focus accuracy.
2015, 39(6): 798-801.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.014
Abstract:
In order to measure and image cloud droplets ranging from 25m to 1550m, an airborne cloud particle imaging probe was designed based on the established optical imaging techniques. The images of particles passing through a collimated laser beam were projected onto a linear array of 64-element photo detectors and were reconstructed from the individual image slices. The function of each component and the quantitative standard of each detection unit were introduced. The method of data acquisition and the factors affecting the accuracy of cloud particle imaging were discussed. A calibration setup of particle size was constructed where seven kinds of standard dots were used to calibrate cloud imaging probe. The calibration experiment results show that cloud imaging probe can accurately achieve particle size distribution and display 2-D images. The airborne experiment data shows that cloud imaging probe is able to detect cloud droplets and acquire their images.
In order to measure and image cloud droplets ranging from 25m to 1550m, an airborne cloud particle imaging probe was designed based on the established optical imaging techniques. The images of particles passing through a collimated laser beam were projected onto a linear array of 64-element photo detectors and were reconstructed from the individual image slices. The function of each component and the quantitative standard of each detection unit were introduced. The method of data acquisition and the factors affecting the accuracy of cloud particle imaging were discussed. A calibration setup of particle size was constructed where seven kinds of standard dots were used to calibrate cloud imaging probe. The calibration experiment results show that cloud imaging probe can accurately achieve particle size distribution and display 2-D images. The airborne experiment data shows that cloud imaging probe is able to detect cloud droplets and acquire their images.
2015, 39(6): 802-805.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.015
Abstract:
Avalanche photodiode (APD) have been widely applied in laser ranging systems for high sensitivity and broad bandwidth. Based on the avalanche effect of an APD, adding a local oscillator signal to the APD bias voltage, optoelectronic heterodyne mixing is to make down converter of signal into realization. In order to analyze the effect of APD optoelectronic heterodyne mixing on signal-to-noise ratio (SNR) of a system, the mathematical model of an APD was built. The relationship between direct-current component of the bias voltage and SNR and the effect of APD breakdown voltage change on SNR were analyzed by simulation. The results show that SNR of the APD output signal is reduced by optoelectronic heterodyne mixing, however, the bandwidth of subsequent circuit is reduced too, which can improve SNR of the whole system. When the input signal of an APD is weak, optoelectronic heterodyne mixing of the APD can improve the SNR of the system.
Avalanche photodiode (APD) have been widely applied in laser ranging systems for high sensitivity and broad bandwidth. Based on the avalanche effect of an APD, adding a local oscillator signal to the APD bias voltage, optoelectronic heterodyne mixing is to make down converter of signal into realization. In order to analyze the effect of APD optoelectronic heterodyne mixing on signal-to-noise ratio (SNR) of a system, the mathematical model of an APD was built. The relationship between direct-current component of the bias voltage and SNR and the effect of APD breakdown voltage change on SNR were analyzed by simulation. The results show that SNR of the APD output signal is reduced by optoelectronic heterodyne mixing, however, the bandwidth of subsequent circuit is reduced too, which can improve SNR of the whole system. When the input signal of an APD is weak, optoelectronic heterodyne mixing of the APD can improve the SNR of the system.
2015, 39(6): 806-810.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.016
Abstract:
In order to solve the problems of huge amount of data and slow transmission speed after image encryption, a new image compression encryption algorithm combined discrete cosine transform (DCT) with deoxyribonucleic acid (DNA) operation was presented. At first, the original image was compressed by means of DCT and encoded according to DNA sequence. Finally, based on DNA operation, DNA addition operation was implemented to the original image by Chen chaotic system and an encrypted image was obtained. Simulation results show that the algorithm not only improves the speed of image transmission and reduces the storage space, but also has good encryption effect and high security.
In order to solve the problems of huge amount of data and slow transmission speed after image encryption, a new image compression encryption algorithm combined discrete cosine transform (DCT) with deoxyribonucleic acid (DNA) operation was presented. At first, the original image was compressed by means of DCT and encoded according to DNA sequence. Finally, based on DNA operation, DNA addition operation was implemented to the original image by Chen chaotic system and an encrypted image was obtained. Simulation results show that the algorithm not only improves the speed of image transmission and reduces the storage space, but also has good encryption effect and high security.
2015, 39(6): 811-814.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.017
Abstract:
Difficulties of underwater image restoration lies in lack of enough information about the point spread function of sea water which induces the ill-posed problem consequently. In order to improve the imaging quality of underwater laser imaging system, a blind image restoration algorithm based on particle swarm optimization regularization parameter was proposed. This method integrated the technique characteristics of Tikhonov regularization and the improved total variation(TV) regularization. An alternating iterative method was adopted to estimate point spread function and restored image respectively. Meanwhile, the regularization parameter was optimized by using particle swarm algorithm. After dealing with the simulation images and the actual underwater images, the results of underwater image restoration show that this method has good robustness for underwater image restoration and the algorithm is convergent and stable.
Difficulties of underwater image restoration lies in lack of enough information about the point spread function of sea water which induces the ill-posed problem consequently. In order to improve the imaging quality of underwater laser imaging system, a blind image restoration algorithm based on particle swarm optimization regularization parameter was proposed. This method integrated the technique characteristics of Tikhonov regularization and the improved total variation(TV) regularization. An alternating iterative method was adopted to estimate point spread function and restored image respectively. Meanwhile, the regularization parameter was optimized by using particle swarm algorithm. After dealing with the simulation images and the actual underwater images, the results of underwater image restoration show that this method has good robustness for underwater image restoration and the algorithm is convergent and stable.
2015, 39(6): 815-819.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.018
Abstract:
In order to investigate gain transient performance of burst-mode high-power Er/Yb co-doped fiber amplifier (EYDFA) in optical packet and circuit integrated network, comparison mode of gain transient performance of EYDFA with different doping area was proposed by adopting iterative algorithm of nonlinear rate-equations based on function limit. Gain transient performance of optical packet switching and optical circuit switching output signals with/without optical feedback , are analyzed and compared in detail. The results show that the maximum improvements of gain excursion for EYDFAs without optical feedback are about 12% when the core diameter of double-clad fiber changes from 3.6m to 4.6m. The gain fluctuation of EYDFAs with optical feedback caused by relaxation oscillation decreases with the increase of core diameter. The analysis suggests that relaxation oscillation of EYDFA feedback loop will be suppressed by enlarging active core diameter of doped fiber.
In order to investigate gain transient performance of burst-mode high-power Er/Yb co-doped fiber amplifier (EYDFA) in optical packet and circuit integrated network, comparison mode of gain transient performance of EYDFA with different doping area was proposed by adopting iterative algorithm of nonlinear rate-equations based on function limit. Gain transient performance of optical packet switching and optical circuit switching output signals with/without optical feedback , are analyzed and compared in detail. The results show that the maximum improvements of gain excursion for EYDFAs without optical feedback are about 12% when the core diameter of double-clad fiber changes from 3.6m to 4.6m. The gain fluctuation of EYDFAs with optical feedback caused by relaxation oscillation decreases with the increase of core diameter. The analysis suggests that relaxation oscillation of EYDFA feedback loop will be suppressed by enlarging active core diameter of doped fiber.
2015, 39(6): 820-823.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.019
Abstract:
In order to extract the layer for space-borne cloud/aerosol lidar reliably, a layer classification method based on histogram statistics was proposed. This method was analyzed theoretically. The experimental results show that the cloud/aerosol layer can be extracted reliably in different situations with this method. Compared with the current layer detection method, the new method can avoid the constraint for data feature. It is a highly-reliable and widely-applicable layer detection method.
In order to extract the layer for space-borne cloud/aerosol lidar reliably, a layer classification method based on histogram statistics was proposed. This method was analyzed theoretically. The experimental results show that the cloud/aerosol layer can be extracted reliably in different situations with this method. Compared with the current layer detection method, the new method can avoid the constraint for data feature. It is a highly-reliable and widely-applicable layer detection method.
2015, 39(6): 824-828.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.020
Abstract:
Combining the optical properties of tapered fiber with the filtering characteristics of fiber loop mirrors, an optical loop mirror filter structure was put forward based on tapered fiber optimization. The study shows that after adding tapered fiber into cascaded second-order high-birefringence fiber (HBF) loop mirrors, 3dB bandwidth of main peak of filter output spectrum is significantly compressed. Quality factor is further improved and can reach about 5.2 easily. The study also shows that after adding tapered fiber into cascaded second-order HBF loop mirrors, tuning is more flexible in the modulation depth range from 10dB to 35dB and the output waveform becomes more stable. The filtering characteristics of HBF loop mirror were improved, and the filter is tunable more flexibly.
Combining the optical properties of tapered fiber with the filtering characteristics of fiber loop mirrors, an optical loop mirror filter structure was put forward based on tapered fiber optimization. The study shows that after adding tapered fiber into cascaded second-order high-birefringence fiber (HBF) loop mirrors, 3dB bandwidth of main peak of filter output spectrum is significantly compressed. Quality factor is further improved and can reach about 5.2 easily. The study also shows that after adding tapered fiber into cascaded second-order HBF loop mirrors, tuning is more flexible in the modulation depth range from 10dB to 35dB and the output waveform becomes more stable. The filtering characteristics of HBF loop mirror were improved, and the filter is tunable more flexibly.
2015, 39(6): 829-833.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.021
Abstract:
An active laser detection system could detect and recognize cat's eye targets at long distance. Detection capability analysis was the basis of system design. To assess the detection capability, a mathematical model of the system's signal-to-noise ratio(SNR) was established based on laser echo power. The dependence of SNR on several factors, such as receiving optical lens diameter, laser peak power, laser divergence angle, defocusing distance was quantitively analyzed. The results show that at a certain distance, the detector noise comes mainly from shot noise and background noise which surpass dark current noise and thermal noise at least 2 magnitudes. The most effective way to improve detection capability is to use lasers with small divergence angles. The result is helpful for the design of active laser detection systems.
An active laser detection system could detect and recognize cat's eye targets at long distance. Detection capability analysis was the basis of system design. To assess the detection capability, a mathematical model of the system's signal-to-noise ratio(SNR) was established based on laser echo power. The dependence of SNR on several factors, such as receiving optical lens diameter, laser peak power, laser divergence angle, defocusing distance was quantitively analyzed. The results show that at a certain distance, the detector noise comes mainly from shot noise and background noise which surpass dark current noise and thermal noise at least 2 magnitudes. The most effective way to improve detection capability is to use lasers with small divergence angles. The result is helpful for the design of active laser detection systems.
2015, 39(6): 834-839.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.022
Abstract:
As the first navy demonstrator of high energy solid-state laser weapon, the laser weapons system (LaWS) of US Navy was deployed on US Ponce warship. Firstly, application goal, development team and system configuration of LaWS were introduced. Laser, transmitting telescope and control system were analyzed in detail. Fighting capability of LaWS was deduced from its system parameters. A series of demonstration tests of LaWS were reviewed. Technical issues exposed in tests and the corresponding solutions were summarized. The analyses show that common aperture design was used in the transmitting telescope of LaWS system; incoherent synthesis of fiber laser was used as light source of combat. In system integration, apart from a small amount of custom parts, a large number of commercial off-the-shelf (COTS) were used widely, such as industrial lasers, inertial measurement unit, sensor and video trackers. LaWS system used the progressive improvement in the development to reduce systemic risk and development costs to some extent. Technical development trends of LaWS in the future were analyzed in the end.
As the first navy demonstrator of high energy solid-state laser weapon, the laser weapons system (LaWS) of US Navy was deployed on US Ponce warship. Firstly, application goal, development team and system configuration of LaWS were introduced. Laser, transmitting telescope and control system were analyzed in detail. Fighting capability of LaWS was deduced from its system parameters. A series of demonstration tests of LaWS were reviewed. Technical issues exposed in tests and the corresponding solutions were summarized. The analyses show that common aperture design was used in the transmitting telescope of LaWS system; incoherent synthesis of fiber laser was used as light source of combat. In system integration, apart from a small amount of custom parts, a large number of commercial off-the-shelf (COTS) were used widely, such as industrial lasers, inertial measurement unit, sensor and video trackers. LaWS system used the progressive improvement in the development to reduce systemic risk and development costs to some extent. Technical development trends of LaWS in the future were analyzed in the end.
2015, 39(6): 840-844.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.023
Abstract:
Infrared images are usually interfered by random noise seriously. Infrared targets detected by the traditional detection algorithm based on Gaussian mixture model are difficult to be identified because of false contour. In order to identify the infrared target accurately, an infrared target detection algorithm based on pulse coupled neural network(PCNN) and Gaussian mixture model was proposed. Firstly, Gaussian mixture model was used to locate the approximate location of moving targets. And then, a closed region was obtained by using watershed algorithm based on spatial information. Segmentation algorithm based on PCNN was used to shear the pseudo-target and the complete moving target was detected. The experimental results show that this method can eliminate the pseudo target of the traditional methods and detect the infrared moving targets accurately. The new algorithm is superior to the other conventional algorithms.
Infrared images are usually interfered by random noise seriously. Infrared targets detected by the traditional detection algorithm based on Gaussian mixture model are difficult to be identified because of false contour. In order to identify the infrared target accurately, an infrared target detection algorithm based on pulse coupled neural network(PCNN) and Gaussian mixture model was proposed. Firstly, Gaussian mixture model was used to locate the approximate location of moving targets. And then, a closed region was obtained by using watershed algorithm based on spatial information. Segmentation algorithm based on PCNN was used to shear the pseudo-target and the complete moving target was detected. The experimental results show that this method can eliminate the pseudo target of the traditional methods and detect the infrared moving targets accurately. The new algorithm is superior to the other conventional algorithms.
2015, 39(6): 845-849.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.024
Abstract:
Available measurement methods of laser beam quality can't reach the demands of speed and accuracy simultaneously. In order to take speed and precision into account, a double-slit scanning method was proposed. The complexity of data analysis reduced because attenuator was not used in the optical path. Embedded technology was selected to control and process the data, and real time data processing can be realized while the whole system was easy to carry. After theoretical analysis and experimental verification, the results show that this method can get fast synchronous measurement of dual axis shaft power distribution. Dynamic range can reach 70dB and scan rate is from 2Hz to 18Hz. This method can be used for the analysis of continuous or pulsed laser beam and is helpful for reaching the demands of both measurement speed and accuracy.
Available measurement methods of laser beam quality can't reach the demands of speed and accuracy simultaneously. In order to take speed and precision into account, a double-slit scanning method was proposed. The complexity of data analysis reduced because attenuator was not used in the optical path. Embedded technology was selected to control and process the data, and real time data processing can be realized while the whole system was easy to carry. After theoretical analysis and experimental verification, the results show that this method can get fast synchronous measurement of dual axis shaft power distribution. Dynamic range can reach 70dB and scan rate is from 2Hz to 18Hz. This method can be used for the analysis of continuous or pulsed laser beam and is helpful for reaching the demands of both measurement speed and accuracy.
2015, 39(6): 850-853.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.025
Abstract:
In order to study the influence of heat input on laser welding quality of 304 austenitic stainless steel, experiments were carried out by using high power Nd:YAG laser and welding robots. Weld appearance, microhardness and mechanical properties were analyzed with an optical microscope, a microhardness tester and a tensile testing machine. Experimental results show that heat input has great influence on weld appearance, microhardness and mechanical properties. Furthermore microhardness is different in different areas. The lowest tensile strength values of laser welding are 671.67MPa at low laser power and 780MPa at high laser power.
In order to study the influence of heat input on laser welding quality of 304 austenitic stainless steel, experiments were carried out by using high power Nd:YAG laser and welding robots. Weld appearance, microhardness and mechanical properties were analyzed with an optical microscope, a microhardness tester and a tensile testing machine. Experimental results show that heat input has great influence on weld appearance, microhardness and mechanical properties. Furthermore microhardness is different in different areas. The lowest tensile strength values of laser welding are 671.67MPa at low laser power and 780MPa at high laser power.
2015, 39(6): 854-857.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.026
Abstract:
To solve the problem that it is difficult to position the perturbation point and judge the perturbation time under multiple simultaneous perturbations in a distributed optical fiber vibration sensing system, signal processing method was carried out and clustering analysis technology was applied. Firstly, hotspot map gathered by the system was processed above a threshold, and then the target objects were extracted. According to the results of clustering analysis, perturbation points are positioned and perturbation time is confirmed. The results show that the method makes an accurate and reasonable judgment for positioning the perturbation behavior and perturbation duration and the noise interference is eliminated at the same time. This is one step of event classification. The study provides the basis for the final system alarm strategy.
To solve the problem that it is difficult to position the perturbation point and judge the perturbation time under multiple simultaneous perturbations in a distributed optical fiber vibration sensing system, signal processing method was carried out and clustering analysis technology was applied. Firstly, hotspot map gathered by the system was processed above a threshold, and then the target objects were extracted. According to the results of clustering analysis, perturbation points are positioned and perturbation time is confirmed. The results show that the method makes an accurate and reasonable judgment for positioning the perturbation behavior and perturbation duration and the noise interference is eliminated at the same time. This is one step of event classification. The study provides the basis for the final system alarm strategy.
2015, 39(6): 858-862.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.027
Abstract:
In order to obtain divergence feature of light spot of a circular light emitting diode(LED) array, illumination formula, and light spot radius formula and divergence angle formula of a circular LED array were deduced by using single LED illumination formula. The dependence of the divergence angle of a circular LED array on the m value, array radius and target distance were analyzed theoretically by using numerical methods. The change data of divergence angle under three conditions were obtained. The results show that the divergence angle decreases with the increase of m value and array radius. However, the divergence angle increases with the increase of target distance. The results are helpful for the illumination source design with circular LED arrays.
In order to obtain divergence feature of light spot of a circular light emitting diode(LED) array, illumination formula, and light spot radius formula and divergence angle formula of a circular LED array were deduced by using single LED illumination formula. The dependence of the divergence angle of a circular LED array on the m value, array radius and target distance were analyzed theoretically by using numerical methods. The change data of divergence angle under three conditions were obtained. The results show that the divergence angle decreases with the increase of m value and array radius. However, the divergence angle increases with the increase of target distance. The results are helpful for the illumination source design with circular LED arrays.
2015, 39(6): 863-868.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.028
Abstract:
In order to study effect of aluminum surface state and welding processing on the properties of welding joints, the process of laser welding Al-Mg series aluminum alloy with Nd:YAG laser was analyzed in theory and verified in experiments. The experimental results of the characteristics of welding joints were obtained. The results show that welding process of untreated sample and alkali corrosion surface treatment sample are not stable while welding process of anodizing treatment sample is stable and hole effect is formed stably. Weld seam penetration and depth-to-width ratio are all improved effectively by the aid of anodizing, double welding and powder filling welding. The tensile strength of the weld seam of anodizing sample, double-sided welding sample and powder filling welding sample increases more than 1 times and powder filling welding sample of Al-0.05Si has the highest tensile strength. Hardness of all surface treatment samples is improved and the effect of phosphoric acid anodizing is the best. Hardness of weld seam and fusion zone is improved through double welding. Central hardness of powder filling weld is lower while hardness of fusion zone increases obviously. Hardness of heat affected zone of double welding and powder filling welding is lower than hardness of single side welding. The results show that anodic oxidation surface treatment and double-sided welding technology can improve the property of laser welding of Al-Mg series aluminum alloy effectively.
In order to study effect of aluminum surface state and welding processing on the properties of welding joints, the process of laser welding Al-Mg series aluminum alloy with Nd:YAG laser was analyzed in theory and verified in experiments. The experimental results of the characteristics of welding joints were obtained. The results show that welding process of untreated sample and alkali corrosion surface treatment sample are not stable while welding process of anodizing treatment sample is stable and hole effect is formed stably. Weld seam penetration and depth-to-width ratio are all improved effectively by the aid of anodizing, double welding and powder filling welding. The tensile strength of the weld seam of anodizing sample, double-sided welding sample and powder filling welding sample increases more than 1 times and powder filling welding sample of Al-0.05Si has the highest tensile strength. Hardness of all surface treatment samples is improved and the effect of phosphoric acid anodizing is the best. Hardness of weld seam and fusion zone is improved through double welding. Central hardness of powder filling weld is lower while hardness of fusion zone increases obviously. Hardness of heat affected zone of double welding and powder filling welding is lower than hardness of single side welding. The results show that anodic oxidation surface treatment and double-sided welding technology can improve the property of laser welding of Al-Mg series aluminum alloy effectively.
2015, 39(6): 869-872.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.029
Abstract:
In order to study thermal effect of femtosecond laser on the surface of LiNbO3 crystal, LiNbO3 crystal surface was etched by tightly-focused femtosecond laser pulses with repetition rate of 25MHz, pulse duration of 100fs and average output power of 500mW. A theoretical thermal diffusion model was built to simulate the temperature filed distribution of the area etched by laser pulses with repetition rate of 25MHz, and the morphology of the etched area was analyzed by a scanning electron microscope. There were three regions with different sizes and densities from the inside to the outside of the etched area, and the central region was ablated by high temperature and was accompanied with the appearance of cracks. Relative contents of Nb and O at the three regions were measured by using energy dispersive spectroscopy and were analyzed with temperature field distribution and morphology. The result shows that Nb and O elements spread out under the drive of temperature field, and relative contents of Nb and O have an important influence on surface structure of etch area. The results are useful for mechanism research of the interaction between high repetition rate femtosecond laser and LiNbO3 crystal.
In order to study thermal effect of femtosecond laser on the surface of LiNbO3 crystal, LiNbO3 crystal surface was etched by tightly-focused femtosecond laser pulses with repetition rate of 25MHz, pulse duration of 100fs and average output power of 500mW. A theoretical thermal diffusion model was built to simulate the temperature filed distribution of the area etched by laser pulses with repetition rate of 25MHz, and the morphology of the etched area was analyzed by a scanning electron microscope. There were three regions with different sizes and densities from the inside to the outside of the etched area, and the central region was ablated by high temperature and was accompanied with the appearance of cracks. Relative contents of Nb and O at the three regions were measured by using energy dispersive spectroscopy and were analyzed with temperature field distribution and morphology. The result shows that Nb and O elements spread out under the drive of temperature field, and relative contents of Nb and O have an important influence on surface structure of etch area. The results are useful for mechanism research of the interaction between high repetition rate femtosecond laser and LiNbO3 crystal.
2015, 39(6): 873-876.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.030
Abstract:
In order to study effect of incident angles on echo intensity distribution of a cat's eye photoelectric system, the model of intensity distribution of Gaussian beam passing through the cat's eye photoelectric system was built on the basis of generalized diffraction integral formula and the analytical expressions of transmission were deduced. The intensity distribution varying with the incident angle at two detection distances was simulated numerically. The results show that in the range of half the field of view of a cat's eye photoelectric system, when incident beam is Gaussian beam, the power of echo light beam becomes smaller with the increase of detection distance and incident angle and the distribution mode is close to Gaussian mode. Compared with the short distance detection, echo intensity distribution of the long distance detection which reaches the Gaussian mode has more stringent demands for incidence condition. This study provides theoretical basis for actual detection and has particular significance for selection of incidence angles.
In order to study effect of incident angles on echo intensity distribution of a cat's eye photoelectric system, the model of intensity distribution of Gaussian beam passing through the cat's eye photoelectric system was built on the basis of generalized diffraction integral formula and the analytical expressions of transmission were deduced. The intensity distribution varying with the incident angle at two detection distances was simulated numerically. The results show that in the range of half the field of view of a cat's eye photoelectric system, when incident beam is Gaussian beam, the power of echo light beam becomes smaller with the increase of detection distance and incident angle and the distribution mode is close to Gaussian mode. Compared with the short distance detection, echo intensity distribution of the long distance detection which reaches the Gaussian mode has more stringent demands for incidence condition. This study provides theoretical basis for actual detection and has particular significance for selection of incidence angles.
2015, 39(6): 877-884.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.031
Abstract:
In order to study propagation properties of partially coherent flat-topped beam array(PCFT) in the oceanic turbulence, based on the extended Huygens-Fresnel principle and Wigner distribution function, combined with the spatial power spectrum of oceanic turbulence, analytical formulas of M2 factor,effective radius of curvature and Rayleigh range of PCFT beam array in oceanic turbulence were obtained and the relationship between M2 factor,effective radius of curvature and Rayleigh range of PCFT beam array in oceanic turbulence and the coherent width, temperature change, salinity change, dissipation rate of turbulent kinetic energy, dissipation rate of mean-squared temperature were analyzed and discussed. The results show that, under the same condition, when the propagation distance is more than 400m, compared with the partially coherent Gaussian beam, the partially coherent flat-topped beam and the partially coherent Gaussian beam array, PCFT beam array is less affected by the oceanic turbulence and the propagation characteristic is more stable. The results have certain reference value for selecting the suitable beams propagating in oceanic turbulence.
In order to study propagation properties of partially coherent flat-topped beam array(PCFT) in the oceanic turbulence, based on the extended Huygens-Fresnel principle and Wigner distribution function, combined with the spatial power spectrum of oceanic turbulence, analytical formulas of M2 factor,effective radius of curvature and Rayleigh range of PCFT beam array in oceanic turbulence were obtained and the relationship between M2 factor,effective radius of curvature and Rayleigh range of PCFT beam array in oceanic turbulence and the coherent width, temperature change, salinity change, dissipation rate of turbulent kinetic energy, dissipation rate of mean-squared temperature were analyzed and discussed. The results show that, under the same condition, when the propagation distance is more than 400m, compared with the partially coherent Gaussian beam, the partially coherent flat-topped beam and the partially coherent Gaussian beam array, PCFT beam array is less affected by the oceanic turbulence and the propagation characteristic is more stable. The results have certain reference value for selecting the suitable beams propagating in oceanic turbulence.
2015, 39(6): 885-888.
doi: 10.7510/jgjs.issn.1001-3806.2015.06.032
Abstract:
For the purpose of improving the structure of adiabatic micro-ring resonator and reducing the resonator cavity loss, a new carrier injection/extraction structure was proposed based on adiabatic transition curve. After theoretical analysis and experimental verification, the data of resonant full wave at half maximum(FWHM) of the adiabatic micro-ring resonator, extinction ratio and frequency response parameters were obtained and compared with the loss of a traditional micro-ring resonator. The results show that FWHM of the adiabatic ring with outer radius of 2m is only 29.5% of that of a traditional micro-ring, the constrained bandwidth of resistance and capacitance increases 4 times, extinction ratio is 13.5dB and energy consumption is 5.1fJ/bit under modulation speed of 10Gbit/s. This research is helpful to improve the frequency response and reduce the power consumption of an adiabatic micro-ring resonator significantly. The study on adiabatic transition and carrier injection/extraction structure can further improve the performance of the adiabatic micro-ring, and push the development of low energy consumption research.
For the purpose of improving the structure of adiabatic micro-ring resonator and reducing the resonator cavity loss, a new carrier injection/extraction structure was proposed based on adiabatic transition curve. After theoretical analysis and experimental verification, the data of resonant full wave at half maximum(FWHM) of the adiabatic micro-ring resonator, extinction ratio and frequency response parameters were obtained and compared with the loss of a traditional micro-ring resonator. The results show that FWHM of the adiabatic ring with outer radius of 2m is only 29.5% of that of a traditional micro-ring, the constrained bandwidth of resistance and capacitance increases 4 times, extinction ratio is 13.5dB and energy consumption is 5.1fJ/bit under modulation speed of 10Gbit/s. This research is helpful to improve the frequency response and reduce the power consumption of an adiabatic micro-ring resonator significantly. The study on adiabatic transition and carrier injection/extraction structure can further improve the performance of the adiabatic micro-ring, and push the development of low energy consumption research.
