Map
WeChat
Email alert
RSS2016 Vol. 40, No. 2
Display Method:
2016, 40(2): 153-156.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.001
[Abstract]
[PDF 1481KB]
Abstract:
To avoid the influences of unseeded laser pulses on wind speed measurement of incoherent Doppler wind lidar, a detector of pulse laser injection seeded state was designed and implemented based on the principle of different laser pulse building time of the injection seeded and unseeded state. The time measurement accuracy of the detector was 45ps, time measurement range was from 3.5ns to 2500ns, and the highest pulse repetition rate was up to 1kHz. The experiment of injection seeded state detection was conducted with the detector. The results show that laser pulse building time of the injection seeded state is 123.27ns, less than 134.44ns of the unseeded state. The proportion of injection unseeded laser pulses to total laser pulses is 8.54% within 1.35h. The pulse laser injection seeded state detector can effectively detect and discriminate the injection seeded and unseeded laser pulses. The detector has a potential value to improve wind speed measurement reliability of Doppler wind lidar.
To avoid the influences of unseeded laser pulses on wind speed measurement of incoherent Doppler wind lidar, a detector of pulse laser injection seeded state was designed and implemented based on the principle of different laser pulse building time of the injection seeded and unseeded state. The time measurement accuracy of the detector was 45ps, time measurement range was from 3.5ns to 2500ns, and the highest pulse repetition rate was up to 1kHz. The experiment of injection seeded state detection was conducted with the detector. The results show that laser pulse building time of the injection seeded state is 123.27ns, less than 134.44ns of the unseeded state. The proportion of injection unseeded laser pulses to total laser pulses is 8.54% within 1.35h. The pulse laser injection seeded state detector can effectively detect and discriminate the injection seeded and unseeded laser pulses. The detector has a potential value to improve wind speed measurement reliability of Doppler wind lidar.
2016, 40(2): 161-165.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.003
Abstract:
To reduce the circuit's power and size of frequency domain equalization (FDE) system, and meet the requirements of FDE in long-distance few-mode fiber communication, the circuit for fast Fourier transformation (FFT), the key of FDE, was studied. The long point FFT operation was converted to short FFT by means of 2-D decomposition algorithm, and the hardware complexity was reduced. High-speed butterfly core based on field-programmable gate array(FPGA) was designed to implement 2-D R22SDF structure of 16384 point FFT, improve the resource utilization of memory and reduce the usage of complex multipliers. Through theoretical analysis and experiments, resource consumption information of the circuit under different clock frequencies was collected. The result show that the designed FFT can satisfy the optimization requirement of FDE circuit structure in few-mode fiber communication and realize real-time processing of 200MHz data speed in FDE.
To reduce the circuit's power and size of frequency domain equalization (FDE) system, and meet the requirements of FDE in long-distance few-mode fiber communication, the circuit for fast Fourier transformation (FFT), the key of FDE, was studied. The long point FFT operation was converted to short FFT by means of 2-D decomposition algorithm, and the hardware complexity was reduced. High-speed butterfly core based on field-programmable gate array(FPGA) was designed to implement 2-D R22SDF structure of 16384 point FFT, improve the resource utilization of memory and reduce the usage of complex multipliers. Through theoretical analysis and experiments, resource consumption information of the circuit under different clock frequencies was collected. The result show that the designed FFT can satisfy the optimization requirement of FDE circuit structure in few-mode fiber communication and realize real-time processing of 200MHz data speed in FDE.
2016, 40(2): 166-170.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.004
Abstract:
To improve the wear resistance of extruder screws, self-lubricating wear-resistant NiCr-MoS2-M coating was fabricated on 38CrMoAl substrates by laser cladding. Phase composition and microstructures were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Microhardness was measured with a microhardness tester. Tribological properties of the fabricated composite coatings were evaluated under dry sliding condition at room-temperature. The related data were obtained through theoretical analysis and experimental verification. XRD results show that the reinforced layer is composed of FeNi,Ni3Fe and Cr-Ni-Fe-C solid solution. According to SEM observation, the reinforced layer consists of solid solution dendrites, eutectic rich in Cr and undissolved MoS2 particles. The microhardness of the coating is about 313.7HV, about 94.32% of the matrix (332.6HV). Friction coefficient is about 0.513, about 1.63 times of the matrix (0.315). Wear loss of coatings is about 58.56110-3mm3, about 11.9 times of the matrix (4.9110-3mm3). This result is helpful for the further optimization of process parameters to improve the comprehensive mechanical properties of the reinforced layers.
To improve the wear resistance of extruder screws, self-lubricating wear-resistant NiCr-MoS2-M coating was fabricated on 38CrMoAl substrates by laser cladding. Phase composition and microstructures were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Microhardness was measured with a microhardness tester. Tribological properties of the fabricated composite coatings were evaluated under dry sliding condition at room-temperature. The related data were obtained through theoretical analysis and experimental verification. XRD results show that the reinforced layer is composed of FeNi,Ni3Fe and Cr-Ni-Fe-C solid solution. According to SEM observation, the reinforced layer consists of solid solution dendrites, eutectic rich in Cr and undissolved MoS2 particles. The microhardness of the coating is about 313.7HV, about 94.32% of the matrix (332.6HV). Friction coefficient is about 0.513, about 1.63 times of the matrix (0.315). Wear loss of coatings is about 58.56110-3mm3, about 11.9 times of the matrix (4.9110-3mm3). This result is helpful for the further optimization of process parameters to improve the comprehensive mechanical properties of the reinforced layers.
2016, 40(2): 171-177.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.005
Abstract:
To detect cloud boundaries accurately, millimeter wavelength cloud radar (MMCR) and micropulse lidar (MPL) were combined and used to detect stratocumulus, altostratus, altocumulus and cirrocumulus. Differences of cloud boundaries detected by two radars were analyzed comparatively. The results show that the cloud base height detected by MPL is usually higher than MMCR. The difference is large for altostratus but is small for other cases. The differences are mainly due to the different scattering mechanisms of cloud particle for light beam and microwave electromagnetic wave, and the different identification methods of cloud boundaries by MPL and MMCR. For small particles at the top of cloud and small ice crystals in the cloud, the detection ability of MPL is more powerful than MMCR. But for deep cloud, MPL can't detect the real top of cloud because of attenuation effect. Under the same situation, MMCR can completely penetrate the clouds.
To detect cloud boundaries accurately, millimeter wavelength cloud radar (MMCR) and micropulse lidar (MPL) were combined and used to detect stratocumulus, altostratus, altocumulus and cirrocumulus. Differences of cloud boundaries detected by two radars were analyzed comparatively. The results show that the cloud base height detected by MPL is usually higher than MMCR. The difference is large for altostratus but is small for other cases. The differences are mainly due to the different scattering mechanisms of cloud particle for light beam and microwave electromagnetic wave, and the different identification methods of cloud boundaries by MPL and MMCR. For small particles at the top of cloud and small ice crystals in the cloud, the detection ability of MPL is more powerful than MMCR. But for deep cloud, MPL can't detect the real top of cloud because of attenuation effect. Under the same situation, MMCR can completely penetrate the clouds.
2016, 40(2): 178-182.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.006
Abstract:
In order to achieve lithographic pattern with sub-diffraction resolution, a phase-change lithography system was designed. By using a pulse delay technology, digital signal with resolution of 1ns and adjustable pulse width was generated to drive the laser and obtain laser pulse with the corresponding width. With the aid of LabVIEW software and single chip microcomputer, communication between parts of system and computer and all system auto-lithography processing were obtained. By using Ge2Sb2Te5 thin film as base material and its optical properties, an innovative and fast autofocusing method to phase-change material was proposed. In the experiment, Ge2Sb2Te5 crystallization pattern with line width of 0.69m was obtained by phase-change lithographic system. The dimension of crystallization pattern is less than laser focus spot. The results show that the system has the advantages of high-precision, easy operation and low cost. The study has significance for simple phase-change lithography systems.
In order to achieve lithographic pattern with sub-diffraction resolution, a phase-change lithography system was designed. By using a pulse delay technology, digital signal with resolution of 1ns and adjustable pulse width was generated to drive the laser and obtain laser pulse with the corresponding width. With the aid of LabVIEW software and single chip microcomputer, communication between parts of system and computer and all system auto-lithography processing were obtained. By using Ge2Sb2Te5 thin film as base material and its optical properties, an innovative and fast autofocusing method to phase-change material was proposed. In the experiment, Ge2Sb2Te5 crystallization pattern with line width of 0.69m was obtained by phase-change lithographic system. The dimension of crystallization pattern is less than laser focus spot. The results show that the system has the advantages of high-precision, easy operation and low cost. The study has significance for simple phase-change lithography systems.
2016, 40(2): 183-188.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.007
Abstract:
In order to achieve optical packet switching system with high bandwidth utilization and large-capacity, based on theoretical analysis of carrier suppression principle, a scheme of optical label modulation was proposed. Simulation and experiment of the system were conducted. The results show that the center carrier suppression ratio of the carrier suppression light label is 21.3dB. Under label modulation rates of 622Mbit/s and 1.25Gbit/s, bit error rate (BER) of the system is lower than 10-10 when transmission distance is over 40km. In the standard of BER 10-10, power penalty of two label modulation rates is 1.7dB and 1.9dB when transmission distance is 40km. Carrier suppression light label in optical packet switching system has high extinction ratio and low power penalty, therefore it is suitable for long distance transmission.
In order to achieve optical packet switching system with high bandwidth utilization and large-capacity, based on theoretical analysis of carrier suppression principle, a scheme of optical label modulation was proposed. Simulation and experiment of the system were conducted. The results show that the center carrier suppression ratio of the carrier suppression light label is 21.3dB. Under label modulation rates of 622Mbit/s and 1.25Gbit/s, bit error rate (BER) of the system is lower than 10-10 when transmission distance is over 40km. In the standard of BER 10-10, power penalty of two label modulation rates is 1.7dB and 1.9dB when transmission distance is 40km. Carrier suppression light label in optical packet switching system has high extinction ratio and low power penalty, therefore it is suitable for long distance transmission.
2016, 40(2): 189-194.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.008
Abstract:
In order to repair dies automatically with low-power laser, crack images were taken by a coaxial vision acquisition system. Crack position information was acquired combining with digital image morphological thinning processing technology. Digital images processing were established and crack trajectory information was obtained. And then, dies were repaired by computer numerical control (CNC) system from numerical control (NC) code generated from curve fitting vector image. Crack center line was effectively obtained after image denoising, enhancement and morphological thinning treatments. NC codes were generated with the help of CAM software after crack bitmaps were converted to DXF file format. The results show that repair precision of dies can reach 0.0368mm and meet the repair demands of dies. Dies can be repaired automatically by means of image morphological thinning processing. It is theoretical support and technical foundation for automation and intelligence of laser processing equipment.
In order to repair dies automatically with low-power laser, crack images were taken by a coaxial vision acquisition system. Crack position information was acquired combining with digital image morphological thinning processing technology. Digital images processing were established and crack trajectory information was obtained. And then, dies were repaired by computer numerical control (CNC) system from numerical control (NC) code generated from curve fitting vector image. Crack center line was effectively obtained after image denoising, enhancement and morphological thinning treatments. NC codes were generated with the help of CAM software after crack bitmaps were converted to DXF file format. The results show that repair precision of dies can reach 0.0368mm and meet the repair demands of dies. Dies can be repaired automatically by means of image morphological thinning processing. It is theoretical support and technical foundation for automation and intelligence of laser processing equipment.
2016, 40(2): 195-198.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.009
Abstract:
Reflective enhancement has been proved to be an efficient way to raise the transfer efficiency of 266nm laser generation by the fourth harmonic generation (FHG). However, the reported enhancement cavities have some disadvantages, such as, the light beams reflected by different times are not overlapped well and the beam quality of violet light is poor. In order to obtain better beam quality, a new reflective cavity was described to realize the well overlap of the beams reflected by different times. The beam profile and transfer efficiency were calculated. The results show that a good beam quality of FHG violet light can be achieved and the efficiency of FHG can be further improved.
Reflective enhancement has been proved to be an efficient way to raise the transfer efficiency of 266nm laser generation by the fourth harmonic generation (FHG). However, the reported enhancement cavities have some disadvantages, such as, the light beams reflected by different times are not overlapped well and the beam quality of violet light is poor. In order to obtain better beam quality, a new reflective cavity was described to realize the well overlap of the beams reflected by different times. The beam profile and transfer efficiency were calculated. The results show that a good beam quality of FHG violet light can be achieved and the efficiency of FHG can be further improved.
2016, 40(2): 199-204.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.010
Abstract:
In order to reduce discharge delay jitter of all solid state magnetic pulse compression discharge circuit for pulsed gas laser, the circuit was simulated with the pspice software including the full process of charging, magnetic switch resetting and discharging. The simulation results show that 1V jitter of initial storage capacitor voltage causes 5ns~10ns jitter of discharge time and the discharge jitter decreases with the increase of the charging voltage. It was found in experiments that the discharge jitter can be reduced from s level to ns level by applying a special two-stage coupled resetting circuit. The results show that the key to reduce the jitter is that the magnetic cores can be reset to a steady state with high frequency alternating current (AC) ripple in the process of charging through the resetting circuit so that the magnetic switches and saturable transformer can work more steady. The simulation model can provide a reference to the design of low jitter pulsed discharge circuits.
In order to reduce discharge delay jitter of all solid state magnetic pulse compression discharge circuit for pulsed gas laser, the circuit was simulated with the pspice software including the full process of charging, magnetic switch resetting and discharging. The simulation results show that 1V jitter of initial storage capacitor voltage causes 5ns~10ns jitter of discharge time and the discharge jitter decreases with the increase of the charging voltage. It was found in experiments that the discharge jitter can be reduced from s level to ns level by applying a special two-stage coupled resetting circuit. The results show that the key to reduce the jitter is that the magnetic cores can be reset to a steady state with high frequency alternating current (AC) ripple in the process of charging through the resetting circuit so that the magnetic switches and saturable transformer can work more steady. The simulation model can provide a reference to the design of low jitter pulsed discharge circuits.
2016, 40(2): 205-208.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.011
Abstract:
In order to prepare Si with supersaturated transition metal, a self-designed linear high power Nd:YAG continuous wave laser was used to irradiate a Si wafer sputtered a layer of Ti. Then the sample was measured by Auger electron spectroscopy and the thermal field was simulated based on the 2-D thermodynamic model. The experimental results indicate that the concentration of Ti in Si is much larger than the solid solubility of Ti in Si and the position of the maximum concentration of the Ti is below the surface of the sample. The maximum temperature is not at the top surface of the sample. Temperature distribution directly leads to the maximum temperature of Si wafer below the top surface of the sample. The simulation results are in good agreement with the experiment results. The saturated transition metal can be supersaturated by irradiating and scanning the material surface with a linear continuous wave laser.
In order to prepare Si with supersaturated transition metal, a self-designed linear high power Nd:YAG continuous wave laser was used to irradiate a Si wafer sputtered a layer of Ti. Then the sample was measured by Auger electron spectroscopy and the thermal field was simulated based on the 2-D thermodynamic model. The experimental results indicate that the concentration of Ti in Si is much larger than the solid solubility of Ti in Si and the position of the maximum concentration of the Ti is below the surface of the sample. The maximum temperature is not at the top surface of the sample. Temperature distribution directly leads to the maximum temperature of Si wafer below the top surface of the sample. The simulation results are in good agreement with the experiment results. The saturated transition metal can be supersaturated by irradiating and scanning the material surface with a linear continuous wave laser.
2016, 40(2): 209-212.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.012
Abstract:
For solving the problems of low surface intensity enhancement and slow response speed of fiber surface plasma resonance (SPR) sensors, a new type of optical fiber SPR-induced surface enhancement chip structure was proposed by using the mechanism of surface plasma resonance to improve the surface field enhancement degree. The characteristics of the proposed chip structure were analyzed based on the finite element method. When Au film layer thickness was near 40nm~50nm, a stronger field enhancement appeared. The degree of field enhancement was closely related with the transmitting wavelength. Reduction of cladding thickness, core diameter and refractive index contrast could increase the degree of field intensity enhancement, but radius and thickness of cladding had almost no effect on penetration depth. The results show that a good surface enhancement effort is feasible after optimization. The study could be beneficial for the application of fluid testing with high sensitivity and rapidity.
For solving the problems of low surface intensity enhancement and slow response speed of fiber surface plasma resonance (SPR) sensors, a new type of optical fiber SPR-induced surface enhancement chip structure was proposed by using the mechanism of surface plasma resonance to improve the surface field enhancement degree. The characteristics of the proposed chip structure were analyzed based on the finite element method. When Au film layer thickness was near 40nm~50nm, a stronger field enhancement appeared. The degree of field enhancement was closely related with the transmitting wavelength. Reduction of cladding thickness, core diameter and refractive index contrast could increase the degree of field intensity enhancement, but radius and thickness of cladding had almost no effect on penetration depth. The results show that a good surface enhancement effort is feasible after optimization. The study could be beneficial for the application of fluid testing with high sensitivity and rapidity.
2016, 40(2): 213-218.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.013
Abstract:
In order to detect the gas signals in complex environments of coal mine and solve the problem of the buried weal signal and the abnormal data because of surrounding noise interference on gas signal, a detection method for weak gas signal was introduced based on stochastic resonance. Sub-sampling method was used to transform large frequency signal scale and particle swarm optimization algorithm was used to optimize structural parameters. The resonance effect of large-parameter weak signal in a stochastic resonance system was analyzed. The results show that optimum matching between the nonlinear system, the input signal and the noise could be achieved adaptively with lower sampling frequency. The large-parameter multi-frequency weak signal can be distinguished from strong background noise effectively, and the detection sensitivity and dynamic range are enhanced. The research provides theory basic for early identification of gas outburst information.
In order to detect the gas signals in complex environments of coal mine and solve the problem of the buried weal signal and the abnormal data because of surrounding noise interference on gas signal, a detection method for weak gas signal was introduced based on stochastic resonance. Sub-sampling method was used to transform large frequency signal scale and particle swarm optimization algorithm was used to optimize structural parameters. The resonance effect of large-parameter weak signal in a stochastic resonance system was analyzed. The results show that optimum matching between the nonlinear system, the input signal and the noise could be achieved adaptively with lower sampling frequency. The large-parameter multi-frequency weak signal can be distinguished from strong background noise effectively, and the detection sensitivity and dynamic range are enhanced. The research provides theory basic for early identification of gas outburst information.
2016, 40(2): 219-222.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.014
Abstract:
To get Al-Si alloy parts with high performance, the formation and cracking behaviors of Al-Si alloy parts fabricated by selective laser melting were studied. The relationship between process parameters and fabrication densification, and the mechanism of crack formation were revealed. The results show that the density of the fabricated samples increases at first and then decreases with the increase of laser power density. The cold cracks are formed in most of the samples which expand along the cladding layer. Its formation mechanism is that a large number of eutectic Si is formed during the process and eutectic Si reduces crack resistance strength of Al-Si aluminum alloy, and crack resistance cannot be enough to resist the high temperature gradient during the forming process, and the generated residual stress is the cause of cold cracks. By improving the process parameters, Al-Si alloy parts with high performance and without cracks could be formed.
To get Al-Si alloy parts with high performance, the formation and cracking behaviors of Al-Si alloy parts fabricated by selective laser melting were studied. The relationship between process parameters and fabrication densification, and the mechanism of crack formation were revealed. The results show that the density of the fabricated samples increases at first and then decreases with the increase of laser power density. The cold cracks are formed in most of the samples which expand along the cladding layer. Its formation mechanism is that a large number of eutectic Si is formed during the process and eutectic Si reduces crack resistance strength of Al-Si aluminum alloy, and crack resistance cannot be enough to resist the high temperature gradient during the forming process, and the generated residual stress is the cause of cold cracks. By improving the process parameters, Al-Si alloy parts with high performance and without cracks could be formed.
2016, 40(2): 223-226.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.015
Abstract:
In order to study effect of laser on extreme ultraviolet (EUV) plasma debris, CO2 and Nd:YAG pulsed laser was used to produced Sn plasma. Based on direct imaging method, expansion characteristics of plasma plume at low pressure were studied. 2-D pictures of Sn plume were taken directly by intensified charge coupled device (ICCD) and plasma boundary was determined. The time-dependant variation of plasma plume expansion boundary at different angles and the variation of kinetic energy with the change of motion path were calculated. The results show that under the same laser energy density of 2.5106 mJ/cm2 and the atmosphere pressure of 10Pa, EUV Sn plasma kinetic energy produced by Nd:YAG laser is greater than that produced by CO2 laser. CO2 laser is superior to Nd:YAG laser for decreasing plasma debris. This result is helpful for the application of laser plasma.
In order to study effect of laser on extreme ultraviolet (EUV) plasma debris, CO2 and Nd:YAG pulsed laser was used to produced Sn plasma. Based on direct imaging method, expansion characteristics of plasma plume at low pressure were studied. 2-D pictures of Sn plume were taken directly by intensified charge coupled device (ICCD) and plasma boundary was determined. The time-dependant variation of plasma plume expansion boundary at different angles and the variation of kinetic energy with the change of motion path were calculated. The results show that under the same laser energy density of 2.5106 mJ/cm2 and the atmosphere pressure of 10Pa, EUV Sn plasma kinetic energy produced by Nd:YAG laser is greater than that produced by CO2 laser. CO2 laser is superior to Nd:YAG laser for decreasing plasma debris. This result is helpful for the application of laser plasma.
2016, 40(2): 227-231.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.016
Abstract:
In order to improve the image quality and recognition of an artificial target hidden in the natural background, an enhancement method of the visible light image based on the polarization imaging was put forward to highlight the artificial target and provide more details and texture information. Firstly, the degree of polarization, polarization angle and ellipticity angle of the image were obtained based on polarization imaging. Secondly, the polarization characteristics were obtained after the pixels in the multidimensional image clustered in the Poincare sphere. Fianlly, the intensity image and the polarization characteristic image was decomposed by means of the dual tree complex wavelet transform. The principal component analysis was used in the low frequency sub-band and the feature fusion strategy based on the region variance was used in the high frequency sub-band, then the enhancement image was obtained. The outdoor experiment was performed to test the effectiveness of the algorithm proposed in the paper. After the theoretical analysis, the performance index of each image was obtained. The results of the subjective and objective evaluation both show that the enhancement image has more details and polarization information, which are important for target recognition and detection.
In order to improve the image quality and recognition of an artificial target hidden in the natural background, an enhancement method of the visible light image based on the polarization imaging was put forward to highlight the artificial target and provide more details and texture information. Firstly, the degree of polarization, polarization angle and ellipticity angle of the image were obtained based on polarization imaging. Secondly, the polarization characteristics were obtained after the pixels in the multidimensional image clustered in the Poincare sphere. Fianlly, the intensity image and the polarization characteristic image was decomposed by means of the dual tree complex wavelet transform. The principal component analysis was used in the low frequency sub-band and the feature fusion strategy based on the region variance was used in the high frequency sub-band, then the enhancement image was obtained. The outdoor experiment was performed to test the effectiveness of the algorithm proposed in the paper. After the theoretical analysis, the performance index of each image was obtained. The results of the subjective and objective evaluation both show that the enhancement image has more details and polarization information, which are important for target recognition and detection.
2016, 40(2): 232-236.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.017
Abstract:
In order to optimize pump pulse formats of Brillouin optical time-domain analysis based on optical differential parametric amplification (ODPA-BOTDA) and pulse-width difference between Stokes pulse and anti-Stokes pulse, by using perturbation method and small signal approximation, pulse response of probe light with Stokes and anti-Stokes pulses in the small region was obtained. After theoretical analysis and numerical verification of the performances, the results show that Stokes pulse with -phase can effectively compress Brillouin gain spectrum width and increase Brillouin signal-to-noise ratio. Meanwhile, the maximum Brillouin gain is achieved when an optimized pulse-width is 8ns. The study would be helpful for the investigation of ODPA-BOTDA in the subsequent research.
In order to optimize pump pulse formats of Brillouin optical time-domain analysis based on optical differential parametric amplification (ODPA-BOTDA) and pulse-width difference between Stokes pulse and anti-Stokes pulse, by using perturbation method and small signal approximation, pulse response of probe light with Stokes and anti-Stokes pulses in the small region was obtained. After theoretical analysis and numerical verification of the performances, the results show that Stokes pulse with -phase can effectively compress Brillouin gain spectrum width and increase Brillouin signal-to-noise ratio. Meanwhile, the maximum Brillouin gain is achieved when an optimized pulse-width is 8ns. The study would be helpful for the investigation of ODPA-BOTDA in the subsequent research.
2016, 40(2): 237-240.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.018
Abstract:
In order to design high performance filters based on photonic crystal waveguide, new band-stop filter was proposed by introducing a series of tooth-shaped defects into 2-D photonic crystal waveguide. Transmission characteristics of tooth-shaped photonic crystal waveguide were studied by finite element method. The results show that, for single tooth-shaped defect, resonance frequency generated by defect leads to a band-stop structure and good narrowband filter is achieved. Resonance frequency can be modulated by changing the depth of defect. For multiple tooth-shaped defects, due to the coupling effect, a series of defects form a wide band stop of photonic crystal waveguide with relatively wider bandwidth. Photonic crystal waveguide filters can be simple and fiexible adjustment by introducing tooth-shaped defects to achieve narrow/broadband filters. The study has potential value in the design of photonic filter devices based on photonic crystal waveguides.
In order to design high performance filters based on photonic crystal waveguide, new band-stop filter was proposed by introducing a series of tooth-shaped defects into 2-D photonic crystal waveguide. Transmission characteristics of tooth-shaped photonic crystal waveguide were studied by finite element method. The results show that, for single tooth-shaped defect, resonance frequency generated by defect leads to a band-stop structure and good narrowband filter is achieved. Resonance frequency can be modulated by changing the depth of defect. For multiple tooth-shaped defects, due to the coupling effect, a series of defects form a wide band stop of photonic crystal waveguide with relatively wider bandwidth. Photonic crystal waveguide filters can be simple and fiexible adjustment by introducing tooth-shaped defects to achieve narrow/broadband filters. The study has potential value in the design of photonic filter devices based on photonic crystal waveguides.
2016, 40(2): 241-244.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.019
Abstract:
In order to measure aerosol extinction coefficients with higher sensitivity, a system for measuring aerosol extinction coefficients was set up based on high-reflectivity cavity mirrors and pulse cavity ring-down technology. The actual atmosphere under different conditions was measured. The experimental results were analyzed and studied, and compared with the research results at home and abroad. The results of the experiment show that cavity ring-down time is greater than 40s, stability is better than 0.3% and detection sensitivity is greater than 1.810-7m-1. Cavity mirrors with high reflectivity and pulse cavity ring-down technology are quite feasible in development of detection systems of aerosol extinction coefficients with high sensitivity.
In order to measure aerosol extinction coefficients with higher sensitivity, a system for measuring aerosol extinction coefficients was set up based on high-reflectivity cavity mirrors and pulse cavity ring-down technology. The actual atmosphere under different conditions was measured. The experimental results were analyzed and studied, and compared with the research results at home and abroad. The results of the experiment show that cavity ring-down time is greater than 40s, stability is better than 0.3% and detection sensitivity is greater than 1.810-7m-1. Cavity mirrors with high reflectivity and pulse cavity ring-down technology are quite feasible in development of detection systems of aerosol extinction coefficients with high sensitivity.
2016, 40(2): 245-249.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.020
Abstract:
In order to explore effect of incident light polarization on optimum incident angle to Faraday wedge of multi-oscillator ring laser gyroscope, the Jones matrix for Faraday wedge was established. The circularly polarization and the elliptically polarization were numerically simulated by using MATLAB. The optimum incident angle was obtained by searching for the minimum amplitude of magnetic circular dichroic loss at different incident angles and different temperatures in the range of -40℃~80℃. The results show the optimum incident angles to Faraday wedge for circularly polarization and elliptically polarization are different. This difference is enough to affect measurement accuracy of multi-oscillator ring laser gyroscope. The impact of incident polarization on the optimum incident angle should be taken into consideration when placing Faraday wedge. Phase shifts of p(perpendicular to incident plane) and s (parallel with incident plane) polarizations, reflecting coefficients of four reflecting mirrors of multi-oscillator ring laser gyroscope have the influence on the optimum incident angle.
In order to explore effect of incident light polarization on optimum incident angle to Faraday wedge of multi-oscillator ring laser gyroscope, the Jones matrix for Faraday wedge was established. The circularly polarization and the elliptically polarization were numerically simulated by using MATLAB. The optimum incident angle was obtained by searching for the minimum amplitude of magnetic circular dichroic loss at different incident angles and different temperatures in the range of -40℃~80℃. The results show the optimum incident angles to Faraday wedge for circularly polarization and elliptically polarization are different. This difference is enough to affect measurement accuracy of multi-oscillator ring laser gyroscope. The impact of incident polarization on the optimum incident angle should be taken into consideration when placing Faraday wedge. Phase shifts of p(perpendicular to incident plane) and s (parallel with incident plane) polarizations, reflecting coefficients of four reflecting mirrors of multi-oscillator ring laser gyroscope have the influence on the optimum incident angle.
2016, 40(2): 250-253.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.021
Abstract:
In order to study the forward measurement principle of scattering measurement, the diffraction model of 1-D periodic rectangular structure was made by rigorous coupled-wave analysis (RCWA) algorithm and programmed by MATLAB. Measurement characteristics of height, linewidth and duty cycle for 1-D periodic structure were thoroughly discussed. In theory, the measurement resolution of linewidth could achieve nanometer level. The results show that RCWA algorithm could achieve accurate and efficient purpose and its good measurement properties for 1-D periodic micro-and nano-structure provide a scientific and feasible basis for scattering measurement.
In order to study the forward measurement principle of scattering measurement, the diffraction model of 1-D periodic rectangular structure was made by rigorous coupled-wave analysis (RCWA) algorithm and programmed by MATLAB. Measurement characteristics of height, linewidth and duty cycle for 1-D periodic structure were thoroughly discussed. In theory, the measurement resolution of linewidth could achieve nanometer level. The results show that RCWA algorithm could achieve accurate and efficient purpose and its good measurement properties for 1-D periodic micro-and nano-structure provide a scientific and feasible basis for scattering measurement.
2016, 40(2): 254-258.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.022
Abstract:
In order to prepare high-performance and large-size tungsten alloy parts, the preliminary experiments were carried out by using the laser solid forming technique. Various proportions of W-Ni-Fe high-density alloy mechanical tensile test pieces were prepared under atmospheric conditions. By testing tensile strength and hardness, by analyzing the structure and the compents proportions, the differences between the traditional powder metallurgy sintering process and formability and mechanical properties were found. The results show that the maximum tensile strength reaches 717.5MPa under 0.6 of W atomicity fraction and it decreases significantly with the increase of W atomicity fraction. When atomicity fraction of W atom is more than 0.8, the strength is lower than 400MPa. Holes and oxidation phenomenon exist in the samples. A large number of W doesn't melt. The more Ni, Fe elements, the better microstructure uniformity, the smaller composition segregation. The results preesent that tungsten alloy can be formed by laser solid forming technique but experiment process parameters and experimental environment remain to be further improved. Samples can be obtained free from effect of atmosphere and process parameters limits based on this study. Furthemore, the study is helpful to obtain better performance of tungsten alloy laser solid forming parts.
In order to prepare high-performance and large-size tungsten alloy parts, the preliminary experiments were carried out by using the laser solid forming technique. Various proportions of W-Ni-Fe high-density alloy mechanical tensile test pieces were prepared under atmospheric conditions. By testing tensile strength and hardness, by analyzing the structure and the compents proportions, the differences between the traditional powder metallurgy sintering process and formability and mechanical properties were found. The results show that the maximum tensile strength reaches 717.5MPa under 0.6 of W atomicity fraction and it decreases significantly with the increase of W atomicity fraction. When atomicity fraction of W atom is more than 0.8, the strength is lower than 400MPa. Holes and oxidation phenomenon exist in the samples. A large number of W doesn't melt. The more Ni, Fe elements, the better microstructure uniformity, the smaller composition segregation. The results preesent that tungsten alloy can be formed by laser solid forming technique but experiment process parameters and experimental environment remain to be further improved. Samples can be obtained free from effect of atmosphere and process parameters limits based on this study. Furthemore, the study is helpful to obtain better performance of tungsten alloy laser solid forming parts.
2016, 40(2): 259-263.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.023
Abstract:
Graphene is a 2-D carbon nano material with very excellent optical properties. Passive Q switches, by using its saturated absorption characteristics, have such advantages as stability, wide responding wavelength from the visible to mid-infrared wavelength region, low nonsaturable loss, ultrafast recovery time (about 100fs), easy fabrication and low cost and have been used in passive Q-switched pulse laser widely. The research progress of graphene passively Q-switched Nd3+-doped lasers was reviewed and the future development of this filed was discussed. The excellent graphene saturable absorber is the key to its development.
Graphene is a 2-D carbon nano material with very excellent optical properties. Passive Q switches, by using its saturated absorption characteristics, have such advantages as stability, wide responding wavelength from the visible to mid-infrared wavelength region, low nonsaturable loss, ultrafast recovery time (about 100fs), easy fabrication and low cost and have been used in passive Q-switched pulse laser widely. The research progress of graphene passively Q-switched Nd3+-doped lasers was reviewed and the future development of this filed was discussed. The excellent graphene saturable absorber is the key to its development.
2016, 40(2): 264-269.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.024
Abstract:
The unsynchronization of optical satellite communication leads to error information and demodulation difficulty. And carrier frequency offset has effect on frame synchronization of sliding correlation algorithm. To solve the problem, frequency offset caused by satellite Doppler effects was analyzed by calculation simulation and difference relation algorithm was proposed for the realization of frame synchronization and frequency offset estimation. Implementation scheme of hardware was given. The performance of difference relation algorithm was analyzed. The results show that difference relation algorithm implements frame synchronization under the influence of high carrier frequency offset and has strong ability of frequency offset estimation. After using difference correlation algorithm, the error bit performance of the system increases nearly 3dB. It is useful to use difference relation algorithm to solve the synchronization problem of laser satellite link.
The unsynchronization of optical satellite communication leads to error information and demodulation difficulty. And carrier frequency offset has effect on frame synchronization of sliding correlation algorithm. To solve the problem, frequency offset caused by satellite Doppler effects was analyzed by calculation simulation and difference relation algorithm was proposed for the realization of frame synchronization and frequency offset estimation. Implementation scheme of hardware was given. The performance of difference relation algorithm was analyzed. The results show that difference relation algorithm implements frame synchronization under the influence of high carrier frequency offset and has strong ability of frequency offset estimation. After using difference correlation algorithm, the error bit performance of the system increases nearly 3dB. It is useful to use difference relation algorithm to solve the synchronization problem of laser satellite link.
2016, 40(2): 270-273.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.025
Abstract:
In order to restore the heat source in infrared images, Gaussian point spread function (PSF) was presented to improve the definition and contrast of infrared heat source. Firstly, the PSF of the heat source images was determined and the degradation model was established. Wiener filtering was used to restore the infrared radiation source and the color information of temperature field was restored by YIQ transform. Finally, the restoration image was evaluated quantitatively by edge acutance value (EAV) and standard deviation, and the restoration method was compared with blind restoration algorithm. The results show that EAV and standard deviation increase 0.502% and 0.124% respectively. The restoration method of heat source of infrared images based on Gaussian point spread function is effective obviously.
In order to restore the heat source in infrared images, Gaussian point spread function (PSF) was presented to improve the definition and contrast of infrared heat source. Firstly, the PSF of the heat source images was determined and the degradation model was established. Wiener filtering was used to restore the infrared radiation source and the color information of temperature field was restored by YIQ transform. Finally, the restoration image was evaluated quantitatively by edge acutance value (EAV) and standard deviation, and the restoration method was compared with blind restoration algorithm. The results show that EAV and standard deviation increase 0.502% and 0.124% respectively. The restoration method of heat source of infrared images based on Gaussian point spread function is effective obviously.
2016, 40(2): 274-279.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.026
Abstract:
In order to analyze the process of laser removal of paint on metal surface, the model was established by using finite element method (FEM). Temperature distribution on stainless steel surface with paint film irradiated by moving laser was simulated. The relative and comparative experiment was done. The results show that, temperature of paint film changes with the movement of laser source. Temperature distribution has a rendering tail like comet-shape. The peak temperature of paint film increases linearly with the increase of laser fluence and laser repetition rate, and decreases exponentially with the increase of scanning rate. The higher the laser fluence and repetition rate, the higher the paint removal efficiency. Cumulative effect of temperature can improve the efficiency of removing paint. The results can give references to select laser parameters in the process of laser paint removal.
In order to analyze the process of laser removal of paint on metal surface, the model was established by using finite element method (FEM). Temperature distribution on stainless steel surface with paint film irradiated by moving laser was simulated. The relative and comparative experiment was done. The results show that, temperature of paint film changes with the movement of laser source. Temperature distribution has a rendering tail like comet-shape. The peak temperature of paint film increases linearly with the increase of laser fluence and laser repetition rate, and decreases exponentially with the increase of scanning rate. The higher the laser fluence and repetition rate, the higher the paint removal efficiency. Cumulative effect of temperature can improve the efficiency of removing paint. The results can give references to select laser parameters in the process of laser paint removal.
2016, 40(2): 280-283.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.027
Abstract:
In order to reach demands of tunable lasers in the current optical fiber communication systems, a design concept for wavelength tunable lasers was proposed based on vernier effect. A three-section slotted Fabry-Perot tunable semiconductor laser with stable power and adjustable frequency was designed and its design principle of system structure was given. After theoretical analysis and experimental verification, the lasing spectrum overlay data of the three-section slotted Fabry-Perot tunable semiconductor laser was obtained. Its laser line width was measured by using fiber delay self-heterodyne method. Measurement curves of line widths of three different lasers were compared. The results show that the slotted Fabry-Perot tunable semiconductor laser based on vernier effect is simple and convenient. It has good single-mode performance and channel switching capability. In the future, it has some value and practical significance in the field of optical communication.
In order to reach demands of tunable lasers in the current optical fiber communication systems, a design concept for wavelength tunable lasers was proposed based on vernier effect. A three-section slotted Fabry-Perot tunable semiconductor laser with stable power and adjustable frequency was designed and its design principle of system structure was given. After theoretical analysis and experimental verification, the lasing spectrum overlay data of the three-section slotted Fabry-Perot tunable semiconductor laser was obtained. Its laser line width was measured by using fiber delay self-heterodyne method. Measurement curves of line widths of three different lasers were compared. The results show that the slotted Fabry-Perot tunable semiconductor laser based on vernier effect is simple and convenient. It has good single-mode performance and channel switching capability. In the future, it has some value and practical significance in the field of optical communication.
2016, 40(2): 284-287.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.028
Abstract:
In order to improve accuracy and precision of lidar echo decomposition, the theory combining particle swarm optimization algorithm with the least squares method was used and the principles of lidar echo decomposition and particle swarm optimization algorithm were analyzed. The application of particle swarm optimization algorithm in lidar echo decomposition was studied. After theoretical analysis and experimental verification, real data of decomposition experiment was gotten. The results show that lidar echo can be decomposed into a series of single waveform by the combining method. The fitting degree was improved to 0.989 by using the parameters of time delay, intensity and pulse width. It may reduce noise interference to some extent. The result shows this algorithm is effective and feasible.
In order to improve accuracy and precision of lidar echo decomposition, the theory combining particle swarm optimization algorithm with the least squares method was used and the principles of lidar echo decomposition and particle swarm optimization algorithm were analyzed. The application of particle swarm optimization algorithm in lidar echo decomposition was studied. After theoretical analysis and experimental verification, real data of decomposition experiment was gotten. The results show that lidar echo can be decomposed into a series of single waveform by the combining method. The fitting degree was improved to 0.989 by using the parameters of time delay, intensity and pulse width. It may reduce noise interference to some extent. The result shows this algorithm is effective and feasible.
2016, 40(2): 288-291.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.029
Abstract:
In order to study effect of laser shock processing (LSP) on surface integrity of Ti-6Al-4V titanium alloy at middle and high temperatures, a high power short pulse Nd:YAG laser was used to shock the surface of Ti-6Al-4V titanium alloy. And then, the specimens after LSP were held at 400℃, 500℃, 550℃ and 600℃ respectively for one hour. The influence of LSP on surface integrity of Ti-6Al-4V titanium alloy at middle and high temperatures were analyzed from surface morphology, surface roughness and surface residual stress. The results indicate that LSP increases the surface roughness of Ti-6Al-4V titanium alloy. The surface roughness increases with the increase of heat treatment temperature. The surface residual stress of Ti-6Al-4V titanium alloy increases obviously after LSP. The higher the temperature, the smaller the surface residual stress is. The research results are helpful for understanding the performance of Ti-6Al-4V titanium alloy.
In order to study effect of laser shock processing (LSP) on surface integrity of Ti-6Al-4V titanium alloy at middle and high temperatures, a high power short pulse Nd:YAG laser was used to shock the surface of Ti-6Al-4V titanium alloy. And then, the specimens after LSP were held at 400℃, 500℃, 550℃ and 600℃ respectively for one hour. The influence of LSP on surface integrity of Ti-6Al-4V titanium alloy at middle and high temperatures were analyzed from surface morphology, surface roughness and surface residual stress. The results indicate that LSP increases the surface roughness of Ti-6Al-4V titanium alloy. The surface roughness increases with the increase of heat treatment temperature. The surface residual stress of Ti-6Al-4V titanium alloy increases obviously after LSP. The higher the temperature, the smaller the surface residual stress is. The research results are helpful for understanding the performance of Ti-6Al-4V titanium alloy.
2016, 40(2): 292-295.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.030
Abstract:
Chirp characteristics of signal light can largely affect the performance of quantum-dot semiconductor optical amplifiers (QD-SOA), cause the walk-off effect of transmitted signal and increase the bit error rate. To improve this situation, chirp characteristics of QD-SOA all-optical wavelength converters were analyzed. Based on all-optical wavelength conversion principle of QD-SOA's cross-gain modulation (XGM), using Newton's method and 4-order Runge-Kutta method, rate equations and light field transmission equation were solved, chirp values of converted light of a QD-SOA all-optical wavelength converter were calculated with the change of injection current, pumping light pulse width and extinction ratio of pumping light. The results show that increasing pulse width of pumping light, reducing injection current and extinction ratio of pumping light can reduce the chirp value of converted light. The impact of chirp can be reduced by optimizing these parameters. But during the design of QD-SOA all-optical wavelength converters, the balance between extinction ratio of pump light and chirp of conversion light should be considered.
Chirp characteristics of signal light can largely affect the performance of quantum-dot semiconductor optical amplifiers (QD-SOA), cause the walk-off effect of transmitted signal and increase the bit error rate. To improve this situation, chirp characteristics of QD-SOA all-optical wavelength converters were analyzed. Based on all-optical wavelength conversion principle of QD-SOA's cross-gain modulation (XGM), using Newton's method and 4-order Runge-Kutta method, rate equations and light field transmission equation were solved, chirp values of converted light of a QD-SOA all-optical wavelength converter were calculated with the change of injection current, pumping light pulse width and extinction ratio of pumping light. The results show that increasing pulse width of pumping light, reducing injection current and extinction ratio of pumping light can reduce the chirp value of converted light. The impact of chirp can be reduced by optimizing these parameters. But during the design of QD-SOA all-optical wavelength converters, the balance between extinction ratio of pump light and chirp of conversion light should be considered.
2016, 40(2): 296-302.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.031
Abstract:
In order to realize rapid and accurate segmentation of nodular tissue in thyroid ultrasound images and overcome the effects of uneven gray distribution and fuzzy boundary of images on segmentation results, an improved active contour segmentation model based on phase congruency was proposed. First, a new speed function was constructed by means of the principle of phase congruency edge detection. It not only made up the defect of edge damage due to filter processing during gradient operator edge detection but also controlled curve evolution rate flexibly. After that, the speed function was introduced to the energy term of active contour model without edge to avoid the problem of weight distribution in the linear combination and have global segmentation ability. Through theoretical analysis and experimental verification,the relative difference of the improved model is less than 1% and the running time is less than that of the comparison models. The results show that the new model achieves accurate segmentation of image with uneven gray distribution and the efficiency of segmentation is improved.
In order to realize rapid and accurate segmentation of nodular tissue in thyroid ultrasound images and overcome the effects of uneven gray distribution and fuzzy boundary of images on segmentation results, an improved active contour segmentation model based on phase congruency was proposed. First, a new speed function was constructed by means of the principle of phase congruency edge detection. It not only made up the defect of edge damage due to filter processing during gradient operator edge detection but also controlled curve evolution rate flexibly. After that, the speed function was introduced to the energy term of active contour model without edge to avoid the problem of weight distribution in the linear combination and have global segmentation ability. Through theoretical analysis and experimental verification,the relative difference of the improved model is less than 1% and the running time is less than that of the comparison models. The results show that the new model achieves accurate segmentation of image with uneven gray distribution and the efficiency of segmentation is improved.
2016, 40(2): 303-306.
doi: 10.7510/jgjs.issn.1001-3806.2016.02.032
Abstract:
In order to output high beam quality laser from a side-pumped all-solid-state 355nm ultraviolet laser, resonant cavity structure was optimized and intra-cavity double frequency and triple frequency was designed by using the method of intra-cavity beam propagation matrix simulation. Theoretical analysis and experimental verification show that under pump power of 280W and acousto-optic modulation frequency of 40kHz,output power of 355nm ultraviolet laser is 10.58W, pulse width is 20ns and quality factor M2 is 1.3. The results show that side pump intra-cavity double frequency and triple frequency can realize the output of high power ultraviolet laser of approximate fundamental mode. The study has guidance for the engineering of ultraviolet laser.
In order to output high beam quality laser from a side-pumped all-solid-state 355nm ultraviolet laser, resonant cavity structure was optimized and intra-cavity double frequency and triple frequency was designed by using the method of intra-cavity beam propagation matrix simulation. Theoretical analysis and experimental verification show that under pump power of 280W and acousto-optic modulation frequency of 40kHz,output power of 355nm ultraviolet laser is 10.58W, pulse width is 20ns and quality factor M2 is 1.3. The results show that side pump intra-cavity double frequency and triple frequency can realize the output of high power ultraviolet laser of approximate fundamental mode. The study has guidance for the engineering of ultraviolet laser.
