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RSS2009 Vol. 33, No. 5
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2009, 33(5): 449-451,458.
doi: 10.3969/j.issn.1001-3806.2009.05.001
[Abstract]
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Abstract:
In order to study the key technology of distributed fiber Raman amplifier,combining the numerical simulation and the experiment,the power coupling equation group was analyzed in theory,and the reciprocity of the pumps and signal was calculated,then the number of pump source,wavelength and power satisfying the gain were obtained.The on-off gain of signals in C+L band up to 10dB,gain flatness less than 1.6dB,gain of polarization relativity less than 0.4dB,polarization mode dispersion less than 0.16ps were obtained by adjusting the pump power.The experiment results indicate that the pumps parameters fully satisfy Raman gain of the system,the technique parameters of the system meet communication standard.
In order to study the key technology of distributed fiber Raman amplifier,combining the numerical simulation and the experiment,the power coupling equation group was analyzed in theory,and the reciprocity of the pumps and signal was calculated,then the number of pump source,wavelength and power satisfying the gain were obtained.The on-off gain of signals in C+L band up to 10dB,gain flatness less than 1.6dB,gain of polarization relativity less than 0.4dB,polarization mode dispersion less than 0.16ps were obtained by adjusting the pump power.The experiment results indicate that the pumps parameters fully satisfy Raman gain of the system,the technique parameters of the system meet communication standard.
2009, 33(5): 452-454,469.
doi: 10.3969/j.issn.1001-3806.2009.05.002
Abstract:
In order to study the characteristics of pulse amplification in multi-stage cascade ytterbium-doped fiber amplifiers,the three-stage high-gain pulse fiber amplifier with all-fiber structure was experimentally studied based on the master oscillator power amplifier(MOPA)technology.The length of the gain fibers and the pump powers in every stage were optimized experimentally to obtain high signal gain,and the spurious lasing of the amplification stimulation emission light was suppressed at the same time.The stable output was obtained with a peak wavelength of 1064nm,pulse duration of 19ns,repetition frequency of 5kHz,the peak power of 3.8kW,and the total gain of 43.8dB.The compact prototype of an all-fiber pulse fiber amplifier was developed and used to amplify a pulse signal at 1Hz repetition frequency,a signal gain of 43.2dB was obtained.The results show that this amplifier has a good amplification effect on the pulse signal at a low repetition frequency.
In order to study the characteristics of pulse amplification in multi-stage cascade ytterbium-doped fiber amplifiers,the three-stage high-gain pulse fiber amplifier with all-fiber structure was experimentally studied based on the master oscillator power amplifier(MOPA)technology.The length of the gain fibers and the pump powers in every stage were optimized experimentally to obtain high signal gain,and the spurious lasing of the amplification stimulation emission light was suppressed at the same time.The stable output was obtained with a peak wavelength of 1064nm,pulse duration of 19ns,repetition frequency of 5kHz,the peak power of 3.8kW,and the total gain of 43.8dB.The compact prototype of an all-fiber pulse fiber amplifier was developed and used to amplify a pulse signal at 1Hz repetition frequency,a signal gain of 43.2dB was obtained.The results show that this amplifier has a good amplification effect on the pulse signal at a low repetition frequency.
2009, 33(5): 455-458.
doi: 10.3969/j.issn.1001-3806.2009.05.022
Abstract:
In order to study the methods of determining the height of the mixing layer,some important methods,such as visual inspection and gradient method,were analyzed.A novel method,namely the Steyn method,was put forward.After describing its basic principle,its ideal model was given out.It was emphasized how the initial value affected the fit result.Then the signals(the profile of aerosol backscatter coefficient and height)obtained from the ceilomter Vaisala CL31 were fitted and the height of the mixing layer was obtained.The results show that with the Steyn method,some information,such as the mixing layer height and the entrainment depth,can be obtained accurately no matter the backscatter vertical distribution varies greatly or the mixing layer is very shallow.The spatial and time distribution of the mixing layer height agrees with the theoretical prediction very well.
In order to study the methods of determining the height of the mixing layer,some important methods,such as visual inspection and gradient method,were analyzed.A novel method,namely the Steyn method,was put forward.After describing its basic principle,its ideal model was given out.It was emphasized how the initial value affected the fit result.Then the signals(the profile of aerosol backscatter coefficient and height)obtained from the ceilomter Vaisala CL31 were fitted and the height of the mixing layer was obtained.The results show that with the Steyn method,some information,such as the mixing layer height and the entrainment depth,can be obtained accurately no matter the backscatter vertical distribution varies greatly or the mixing layer is very shallow.The spatial and time distribution of the mixing layer height agrees with the theoretical prediction very well.
2009, 33(5): 459-461,465.
doi: 10.3969/j.issn.1001-3806.2009.05.023
Abstract:
In order to improve the measurement accuracy of the transmission characteristics of the parts in high power fiber laser,an automated measurement system of power ratio was designed by means of the dual optical path measuring system with full consideration of the standard transmission measuring methods.The dual optical path measuring system was analyzed.With the measuring system equipped with a microchip solid laser and a unique refractive index matching cladding mode filter,the transmission loss of a double clad fiber laser was measured.In experiment,for a 35m of Yb-doped double cladding fiber its insert loss was 2.645dB at 1064nm and standard deviation is 0.026dB for 100 test data.Moreover,the repeated measurement error was less than 0.07dB proven by the experiments under different conditions.The result is useful to improve the measurement accuracy.
In order to improve the measurement accuracy of the transmission characteristics of the parts in high power fiber laser,an automated measurement system of power ratio was designed by means of the dual optical path measuring system with full consideration of the standard transmission measuring methods.The dual optical path measuring system was analyzed.With the measuring system equipped with a microchip solid laser and a unique refractive index matching cladding mode filter,the transmission loss of a double clad fiber laser was measured.In experiment,for a 35m of Yb-doped double cladding fiber its insert loss was 2.645dB at 1064nm and standard deviation is 0.026dB for 100 test data.Moreover,the repeated measurement error was less than 0.07dB proven by the experiments under different conditions.The result is useful to improve the measurement accuracy.
2009, 33(5): 462-465.
doi: 10.3969/j.issn.1001-3806.2009.05.032
Abstract:
In order to retrieve the nature phase of the tested objects in optical three dimensional sensing based on phase measuring profilometry,a new phase unwrapping method,which connects the residue pairs by branch cuts based on the outline of modulation of the measured object,was presented.The new algorithm employs Laplacian edge detection to extract the outline of modulation,used to guide the branch cuts setting.Then,adopting diamond phase-unwrapping algorithm,the wrapped phase of the measured object can be retrieved accurately.The experimental results show that this new method,combining with the advantages of the reliability of modulation and the rapidity of branch cut algorithm,can effectively remain the accuracy of the measurement and fast retrieve the nature phase of the tested objects under the condition of a steep-shape.It is three times faster than the reliabilityguided phase unwrapping algorithm.
In order to retrieve the nature phase of the tested objects in optical three dimensional sensing based on phase measuring profilometry,a new phase unwrapping method,which connects the residue pairs by branch cuts based on the outline of modulation of the measured object,was presented.The new algorithm employs Laplacian edge detection to extract the outline of modulation,used to guide the branch cuts setting.Then,adopting diamond phase-unwrapping algorithm,the wrapped phase of the measured object can be retrieved accurately.The experimental results show that this new method,combining with the advantages of the reliability of modulation and the rapidity of branch cut algorithm,can effectively remain the accuracy of the measurement and fast retrieve the nature phase of the tested objects under the condition of a steep-shape.It is three times faster than the reliabilityguided phase unwrapping algorithm.
2009, 33(5): 466-469.
doi: 10.3969/j.issn.1001-3806.2009.05.006
Abstract:
In order to obtain the noncritical phase-matched property of BiB3O6(BIBO)crystal and improve its application,based on its thermo-optical dispersion formula,with the green light at 532nm as the pump light,the temperature tuning range,efficient nonlinear coefficient and acceptance parameter of BIBO in noncritical phase-matching are calculated accurately by means of MATLAB programs.When the matched angle θ=90°,the signal light can tunes within 0.65μm~3.0μm.When the signal light is at 670nm,the optimal phase-matched condition of difference frequency type Ⅱ(B)phase-matching is obtained:Tm=22.3℃,φ=35°,deff=1.904pm/V.The result is promising to be applied in the laser product in visible waveband,such as laser TV.
In order to obtain the noncritical phase-matched property of BiB3O6(BIBO)crystal and improve its application,based on its thermo-optical dispersion formula,with the green light at 532nm as the pump light,the temperature tuning range,efficient nonlinear coefficient and acceptance parameter of BIBO in noncritical phase-matching are calculated accurately by means of MATLAB programs.When the matched angle θ=90°,the signal light can tunes within 0.65μm~3.0μm.When the signal light is at 670nm,the optimal phase-matched condition of difference frequency type Ⅱ(B)phase-matching is obtained:Tm=22.3℃,φ=35°,deff=1.904pm/V.The result is promising to be applied in the laser product in visible waveband,such as laser TV.
2009, 33(5): 470-472.
doi: 10.3969/j.issn.1001-3806.2009.05.007
Abstract:
In order to reduce coupling loss between different fibers in a fiber laser or amplifier,fused taper technique was applied to couple fibers.Based on theoretical analysis,when the laser signal transmitted from a large numerical aperture(NA)fiber into a small NA fiber,the transmitted power can be improved effectively with fused taper technique.In experiment,largemode fiber fusion splicer was applied to taper fibers.Different tapered fibers can be achieved with precise control of arc-discharged time and power,stepped size and velocity.The transmitted efficiency was improved from 50% to 85% with much lower coupling loss for the coupling between a standard single-mode fiber and a large-mode fiber based on fused taper technique.Fused taper technique offers a simple and practical method to couple different fibers.
In order to reduce coupling loss between different fibers in a fiber laser or amplifier,fused taper technique was applied to couple fibers.Based on theoretical analysis,when the laser signal transmitted from a large numerical aperture(NA)fiber into a small NA fiber,the transmitted power can be improved effectively with fused taper technique.In experiment,largemode fiber fusion splicer was applied to taper fibers.Different tapered fibers can be achieved with precise control of arc-discharged time and power,stepped size and velocity.The transmitted efficiency was improved from 50% to 85% with much lower coupling loss for the coupling between a standard single-mode fiber and a large-mode fiber based on fused taper technique.Fused taper technique offers a simple and practical method to couple different fibers.
2009, 33(5): 473-477,481.
doi: 10.3969/j.issn.1001-3806.2009.05.008
Abstract:
The development of distributed optic fiber sensors based on Brillouin scattering was reviewed.After introducing the measurement principles of this technique,several research hot spots in this field were introduced,such as spatial resolution improvement,cross sensitivity for several parameters measurement,elimination of polarization fading for higher precision.Both advantages and disadvantages of each solution were pointed out.Finally some predictions of its future development were also presented.
The development of distributed optic fiber sensors based on Brillouin scattering was reviewed.After introducing the measurement principles of this technique,several research hot spots in this field were introduced,such as spatial resolution improvement,cross sensitivity for several parameters measurement,elimination of polarization fading for higher precision.Both advantages and disadvantages of each solution were pointed out.Finally some predictions of its future development were also presented.
2009, 33(5): 478-481.
doi: 10.3969/j.issn.1001-3806.2009.05.009
Abstract:
In order to measure the infrared spectra,photo refractive threshold,phase conjugation and associative storage properties of Zr:Fe:LiNbO3 crystals,the crystals were firstly grown by means of the Czochralski technique.The experiment showed that the OH-vibrational peak corresponding to Zr:Fe:LiNbO3 crystal red-shifted to 3488cm-1.The optical damage resistance ability of Zr:Fe:LiNbO3 crystal was enhanced with the increase of Zr4+ion concentration.The optical damage resistance ability of Zr(mole fraction XZr=0.06):Fe:LiNbO3 crystal was one order magnitude higher than that of Fe:LiNbO3 crystal.With the increase of doping Zr4+ ions concentration,the response speed of phase conjugation of crystals was improved,and the reflection index of phase conjugation of crystals was weakly decreased,i.e.,the speed of Zr(xZr=0.02):Fe:LiNbO3 crystal was one order magnitude higher than that of Fe:LiNbO3 crystal.Otherwise,when Zr(xZr=0.04):Fe(mass fraction wFe=0.0003):LiNbO3 crystal was as the storage media and Zr(xZr=0.06):Fe(wFe=0.0003):LiNbO3 crystal was as phase conjugation mirror,the better quality storage image was received by the output plane.The above results show that Zr:Fe:LiNbO3 crystals have strong photorefractive damage ability and excellent associative storage properties.
In order to measure the infrared spectra,photo refractive threshold,phase conjugation and associative storage properties of Zr:Fe:LiNbO3 crystals,the crystals were firstly grown by means of the Czochralski technique.The experiment showed that the OH-vibrational peak corresponding to Zr:Fe:LiNbO3 crystal red-shifted to 3488cm-1.The optical damage resistance ability of Zr:Fe:LiNbO3 crystal was enhanced with the increase of Zr4+ion concentration.The optical damage resistance ability of Zr(mole fraction XZr=0.06):Fe:LiNbO3 crystal was one order magnitude higher than that of Fe:LiNbO3 crystal.With the increase of doping Zr4+ ions concentration,the response speed of phase conjugation of crystals was improved,and the reflection index of phase conjugation of crystals was weakly decreased,i.e.,the speed of Zr(xZr=0.02):Fe:LiNbO3 crystal was one order magnitude higher than that of Fe:LiNbO3 crystal.Otherwise,when Zr(xZr=0.04):Fe(mass fraction wFe=0.0003):LiNbO3 crystal was as the storage media and Zr(xZr=0.06):Fe(wFe=0.0003):LiNbO3 crystal was as phase conjugation mirror,the better quality storage image was received by the output plane.The above results show that Zr:Fe:LiNbO3 crystals have strong photorefractive damage ability and excellent associative storage properties.
2009, 33(5): 482-485.
doi: 10.3969/j.issn.1001-3806.2009.05.010
Abstract:
In order to simulate the stimulated Brillouin scattering(SBS)in a pulse amplifier,its transient model was modified based on the time dependent rate equation in an Er/Yb co-doped fiber,including both gain-increasing processes of signal light transfer and dissipation of inverse populations.The influence of SBS on the single pulse energy,peak power,spectrum and time domain waveform in a fiber laser with high power,low repetition rate,narrow pulse width was analyzed.A two-stage master oscillator power amplifier(MOPA)experimental setup was built based on a 156kHz,Q-switched pulse signal.In the experiment,average output power of 1.32W was obtained and the frequency spectra and time domain waveform of serial SBS was observed. The experimental results are conformal to the theoretical results,which proves the validity of the modified model.
In order to simulate the stimulated Brillouin scattering(SBS)in a pulse amplifier,its transient model was modified based on the time dependent rate equation in an Er/Yb co-doped fiber,including both gain-increasing processes of signal light transfer and dissipation of inverse populations.The influence of SBS on the single pulse energy,peak power,spectrum and time domain waveform in a fiber laser with high power,low repetition rate,narrow pulse width was analyzed.A two-stage master oscillator power amplifier(MOPA)experimental setup was built based on a 156kHz,Q-switched pulse signal.In the experiment,average output power of 1.32W was obtained and the frequency spectra and time domain waveform of serial SBS was observed. The experimental results are conformal to the theoretical results,which proves the validity of the modified model.
2009, 33(5): 486-489.
doi: 10.3969/j.issn.1001-3806.2009.05.024
Abstract:
In order to study the application of fiber laser in direct manufacturing of 316L stainless steel fine part by selective laser melting(SLM),a fiber laser was focused to a minimal fine spot size of 30μm~50μm on the work plane of the SLM system by means of a beam expander and f-θ lens.After analyzing some SLM experiment results under different conditions of defocus,laser power,scanning speed and path,the effect of the above parameters on the part prototyping accuracy was found.The analysis result shows that a stainless 316L part with minimal thin wall of 0.1 mm can be built through optimization of processing parameters and scanning path.
In order to study the application of fiber laser in direct manufacturing of 316L stainless steel fine part by selective laser melting(SLM),a fiber laser was focused to a minimal fine spot size of 30μm~50μm on the work plane of the SLM system by means of a beam expander and f-θ lens.After analyzing some SLM experiment results under different conditions of defocus,laser power,scanning speed and path,the effect of the above parameters on the part prototyping accuracy was found.The analysis result shows that a stainless 316L part with minimal thin wall of 0.1 mm can be built through optimization of processing parameters and scanning path.
2009, 33(5): 490-492,496.
doi: 10.3969/j.issn.1001-3806.2009.05.025
Abstract:
In order to study the damage threshold of fiber end faces under pulsed laser condition,a pulsed Nd:YAG laser was adopted to measure the laser induced damage characteristics.The results showed that the process,the optical quality,the surface perfection of the fiber end face,the repetition frequency of pulsed laser had important effect on the damage threshold.
In order to study the damage threshold of fiber end faces under pulsed laser condition,a pulsed Nd:YAG laser was adopted to measure the laser induced damage characteristics.The results showed that the process,the optical quality,the surface perfection of the fiber end face,the repetition frequency of pulsed laser had important effect on the damage threshold.
2009, 33(5): 493-496.
doi: 10.3969/j.issn.1001-3806.2009.05.013
Abstract:
In order to study the effect of system jitter on the far field of coherently combined beam,based on a hexagonal laser array and Fourier optics,the expression of far-field energy distribution with phase difference induced by the jitter of the system was obtained.The expression describes the variation of the maximum intensity and the ratio of the energy of the central lobe to the total energy with the phase jitter of one light source.The effect of the random jitter of an optional light source in the array changing in different ranges was studied.It was found that not only the energy of central lobe and the maximum intensity were reduced due to the system jitter,but also the far-field symmetry was affected,and that far-field of the combined beam was affected only a little with the system jitter controlled within the range of 3π/8.
In order to study the effect of system jitter on the far field of coherently combined beam,based on a hexagonal laser array and Fourier optics,the expression of far-field energy distribution with phase difference induced by the jitter of the system was obtained.The expression describes the variation of the maximum intensity and the ratio of the energy of the central lobe to the total energy with the phase jitter of one light source.The effect of the random jitter of an optional light source in the array changing in different ranges was studied.It was found that not only the energy of central lobe and the maximum intensity were reduced due to the system jitter,but also the far-field symmetry was affected,and that far-field of the combined beam was affected only a little with the system jitter controlled within the range of 3π/8.
2009, 33(5): 497-499,502.
doi: 10.3969/j.issn.1001-3806.2009.05.011
Abstract:
In order to study guiding and far-field radiation characteristics of micro/nano optical fibers,the relation between core diameters and the mode field,z-direction Poynting vector,effective mode area and far-field intensity was simulated.Then experimental demonstration was carried out by means of tapered fibers.The results showed that the micro/nano fibers might have a large mode area evanescent field larger than 1O00μm2 for an appropriate design.Experimental results of tapered fibers verify that the micro/nano optical fiber can effectively guide the field and radiate it out.
In order to study guiding and far-field radiation characteristics of micro/nano optical fibers,the relation between core diameters and the mode field,z-direction Poynting vector,effective mode area and far-field intensity was simulated.Then experimental demonstration was carried out by means of tapered fibers.The results showed that the micro/nano fibers might have a large mode area evanescent field larger than 1O00μm2 for an appropriate design.Experimental results of tapered fibers verify that the micro/nano optical fiber can effectively guide the field and radiate it out.
2009, 33(5): 500-502.
doi: 10.3969/j.issn.1001-3806.2009.05.026
Abstract:
With the aim of reducing wear and prolonging working life of a mould die,laser texturing technology was applied to the surface of the mould die.In the experiment,a 200W lamp pumped Nd:YAG laser was adopted to process the mould die surface.Then the rule of the effect of laser parameters on the micro profile of the mould die was obtained after experiments.Finally,the expected profile was obtained.The surface hardness and metallographic structure were measured and analyzed.The results showed that the surface hardness of slight protuberance was improved 30%~40% compared with that of the substrate and the wear resistance of mould die was improved too.
With the aim of reducing wear and prolonging working life of a mould die,laser texturing technology was applied to the surface of the mould die.In the experiment,a 200W lamp pumped Nd:YAG laser was adopted to process the mould die surface.Then the rule of the effect of laser parameters on the micro profile of the mould die was obtained after experiments.Finally,the expected profile was obtained.The surface hardness and metallographic structure were measured and analyzed.The results showed that the surface hardness of slight protuberance was improved 30%~40% compared with that of the substrate and the wear resistance of mould die was improved too.
2009, 33(5): 503-505.
doi: 10.3969/j.issn.1001-3806.2009.05.012
Abstract:
In order to realize large mode area and single-mode fibers,a combining method of gain-guiding and indexantiguiding technique was adopted.Based on this method,the effect of the reflectivity of the resonator mirror on gain-guided and index-antiguided fiber lasers was analyzed in detail.Numerical simulation results show that the mode field distribution is varied with gain coefficient and negative index step,so the large mode area fiber with single mode operation can be realized by choosing optimal parameters,which is highly instructive for the design of large mode area fibers.
In order to realize large mode area and single-mode fibers,a combining method of gain-guiding and indexantiguiding technique was adopted.Based on this method,the effect of the reflectivity of the resonator mirror on gain-guided and index-antiguided fiber lasers was analyzed in detail.Numerical simulation results show that the mode field distribution is varied with gain coefficient and negative index step,so the large mode area fiber with single mode operation can be realized by choosing optimal parameters,which is highly instructive for the design of large mode area fibers.
2009, 33(5): 506-508.
doi: 10.3969/j.issn.1001-3806.2009.05.027
Abstract:
In order to denoise the optical feedback self-mixing interferometric signal,an improved threshold function is proposed according to the characteristics of the signal after analyzing wavelet threshold denoising method.The new threshold function overcomes the shortcomings of the hard threshold with discontinuous function and solves the problem of the permanent bias in soft threshold function,and it is more flexible than the soft threshold and hard threshold function.The optical self-mixing interferometric signal is denoised by means of three threshold functions.Denoising simulation and measured signals prove that the improved threshold method is better than traditional hard and soft methods not only in denoising effect,but also in mean square error performance and signal-to-noise ratio gain.
In order to denoise the optical feedback self-mixing interferometric signal,an improved threshold function is proposed according to the characteristics of the signal after analyzing wavelet threshold denoising method.The new threshold function overcomes the shortcomings of the hard threshold with discontinuous function and solves the problem of the permanent bias in soft threshold function,and it is more flexible than the soft threshold and hard threshold function.The optical self-mixing interferometric signal is denoised by means of three threshold functions.Denoising simulation and measured signals prove that the improved threshold method is better than traditional hard and soft methods not only in denoising effect,but also in mean square error performance and signal-to-noise ratio gain.
2009, 33(5): 509-511.
doi: 10.3969/j.issn.1001-3806.2009.05.013
Abstract:
To investigate the polarization property of a double-clad fiber(DCF),the polarization states of a home made D-shape DCF laser at different coiling radii and pump powers were measured under the condition of one end pump.Results show that when the laser operates at a single wavelength around the threshold level,the output laser shows clear evidence of polarization at a small coiling radius and that the polarization behavior of output laser is relatively weak at a large coiling radius.When the laser operates at multiwavelengths above threshold power,there is no sign of polarization for the output laser independent of the coiling radius.
To investigate the polarization property of a double-clad fiber(DCF),the polarization states of a home made D-shape DCF laser at different coiling radii and pump powers were measured under the condition of one end pump.Results show that when the laser operates at a single wavelength around the threshold level,the output laser shows clear evidence of polarization at a small coiling radius and that the polarization behavior of output laser is relatively weak at a large coiling radius.When the laser operates at multiwavelengths above threshold power,there is no sign of polarization for the output laser independent of the coiling radius.
2009, 33(5): 512-514,517.
doi: 10.3969/j.issn.1001-3806.2009.05.014
Abstract:
In order to improve the beam properties of fiber lasers,the fiber-end surface is processed similar to a convex spherical surface.The beam quality and the output power of the fiber lasers were studied experimentally.Based on the rate equation with transverse spatial hole burning taken into account,a theoretical model of mode selection with end face for the fiber lasers was set up and the effect was numerically simulated with the fiber convex output end.Numerical simulation and experimental results show that the output beam quality can be improved taking a convex face as the output end of a fiber laser.
In order to improve the beam properties of fiber lasers,the fiber-end surface is processed similar to a convex spherical surface.The beam quality and the output power of the fiber lasers were studied experimentally.Based on the rate equation with transverse spatial hole burning taken into account,a theoretical model of mode selection with end face for the fiber lasers was set up and the effect was numerically simulated with the fiber convex output end.Numerical simulation and experimental results show that the output beam quality can be improved taking a convex face as the output end of a fiber laser.
2009, 33(5): 515-517.
doi: 10.3969/j.issn.1001-3806.2009.05.028
Abstract:
There are several problems of the present laser pointing system of shipborne weapons,such as small imaging spot and its possibility deviating from the field of view under dynamic conditions.In order to overcome the disadvantages,a graded index optical waveguide was used to extend the imaging laser in one dimension perpendicular to the propagating direction.The laser beam was extended in only in one direction,keeping invariable in the other direction.Experiments on the modified system show that the point performance of the extended beam is good.
There are several problems of the present laser pointing system of shipborne weapons,such as small imaging spot and its possibility deviating from the field of view under dynamic conditions.In order to overcome the disadvantages,a graded index optical waveguide was used to extend the imaging laser in one dimension perpendicular to the propagating direction.The laser beam was extended in only in one direction,keeping invariable in the other direction.Experiments on the modified system show that the point performance of the extended beam is good.
2009, 33(5): 518-521.
doi: 10.3969/j.issn.1001-3806.2009.05.029
Abstract:
In order to study the effect of different zenith angles,propagation distances,coherence of source and outer scale of turbulence on the spatial coherence on the receiver,based on the extended Huygens-Fresnel principle and the quadratic approximation of phase structure function,the expression of the spatial coherence for partially coherent flat-topped beam propagating through slant turbulent atmosphere was derived with the help of tensor integral.Results show that the spatial coherence of the beam oscillates with the increase of distance between two observed points for shorter propagation distances in slant atmosphere path and the oscillating phenomenon disappears for longer propagation distances.When the propagation distance is fixed,the width of spatial coherence is shorter at larger zenith angles.In the slant atmosphere path,for the beam with shorter initial coherent lengths,the width of spatial coherence doesn't become shorter with the increase of propagation distance.The spatial coherence of the beam is not relevant to its initial coherence for longer propagation distances.
In order to study the effect of different zenith angles,propagation distances,coherence of source and outer scale of turbulence on the spatial coherence on the receiver,based on the extended Huygens-Fresnel principle and the quadratic approximation of phase structure function,the expression of the spatial coherence for partially coherent flat-topped beam propagating through slant turbulent atmosphere was derived with the help of tensor integral.Results show that the spatial coherence of the beam oscillates with the increase of distance between two observed points for shorter propagation distances in slant atmosphere path and the oscillating phenomenon disappears for longer propagation distances.When the propagation distance is fixed,the width of spatial coherence is shorter at larger zenith angles.In the slant atmosphere path,for the beam with shorter initial coherent lengths,the width of spatial coherence doesn't become shorter with the increase of propagation distance.The spatial coherence of the beam is not relevant to its initial coherence for longer propagation distances.
2009, 33(5): 522-525.
doi: 10.3969/j.issn.1001-3806.2009.05.030
Abstract:
A laser alignment system based on interference fringe was developed to test the alignment of a rail.After being collimated and broadened,a semiconductor laser was irradiated onto a wedge.Reflecting on the front and back surfaces of the wedge,the laser beam was divided into two cross beams at an angle of 2α,leading to interference fringes in the crossing zone.The interference beam was used to be the measuring reference,and a linear CCD was fixed on the receiving target.The offset distance between the measured point and the measure reference was obtained by detecting the interference position on the receiving target. The stability and repetition of the measuring system was tested.The test results were compared with those obtained with a photoelectricity autocollimator.The alignment error was 18.96μm when the test length was 842mm.The maximum test length was up to 14m.The results indicate that the performance of the sample device met the scheduled target.
A laser alignment system based on interference fringe was developed to test the alignment of a rail.After being collimated and broadened,a semiconductor laser was irradiated onto a wedge.Reflecting on the front and back surfaces of the wedge,the laser beam was divided into two cross beams at an angle of 2α,leading to interference fringes in the crossing zone.The interference beam was used to be the measuring reference,and a linear CCD was fixed on the receiving target.The offset distance between the measured point and the measure reference was obtained by detecting the interference position on the receiving target. The stability and repetition of the measuring system was tested.The test results were compared with those obtained with a photoelectricity autocollimator.The alignment error was 18.96μm when the test length was 842mm.The maximum test length was up to 14m.The results indicate that the performance of the sample device met the scheduled target.
2009, 33(5): 526-528.
doi: 10.3969/j.issn.1001-3806.2009.05.031
Abstract:
In order to obtain nanosecond high peak power optical pulses from a master oscillator power amplifier(MOPA),a semiconductor seed laser was designed in the MOPA system.It can be programmed and output various optical pulses and its output quality was improved with adaptive pulse shape control technology.In the experiment,a high-speed and high-current drive module and a programmable arbitrary modulating waveform generator and a 1064nm QW-DFB(quantum well distributed feedback)high-power diode laser were adopted.The experimental results show that this programmable semiconductor pulse seed laser which can output many shapes,while the peak power is more than 200mW,the dynamic range is better than 20dB,the pulse width is adjustable from 40ns to 1μs,and a pulse frequency is adjustable from 0MHz to 5MHz.
In order to obtain nanosecond high peak power optical pulses from a master oscillator power amplifier(MOPA),a semiconductor seed laser was designed in the MOPA system.It can be programmed and output various optical pulses and its output quality was improved with adaptive pulse shape control technology.In the experiment,a high-speed and high-current drive module and a programmable arbitrary modulating waveform generator and a 1064nm QW-DFB(quantum well distributed feedback)high-power diode laser were adopted.The experimental results show that this programmable semiconductor pulse seed laser which can output many shapes,while the peak power is more than 200mW,the dynamic range is better than 20dB,the pulse width is adjustable from 40ns to 1μs,and a pulse frequency is adjustable from 0MHz to 5MHz.
2009, 33(5): 529-531,534.
doi: 10.3969/j.issn.1001-3806.2009.05.015
Abstract:
In order to achieve high-power and high-brightness fiber laser beams,based on the strong coupling mechanism of evanescent field,the modal field characteristics of multicore fibers,including a bundle of multiple micro/nano fibers or a bundle of multiple micro/nano fibers and large core fibers,were numerically simulated and theoretically analyzed with finite difference time domain(FDTD)method.The result shows that good coupling among the fibers can be obtained in a micro/nano fiber array and that the modal field is flattened by the micro/nano fibers in the bundle of multiple micro/nano fibers and large core fibers.The result is useful to further development of high-power lasers and amplifiers.
In order to achieve high-power and high-brightness fiber laser beams,based on the strong coupling mechanism of evanescent field,the modal field characteristics of multicore fibers,including a bundle of multiple micro/nano fibers or a bundle of multiple micro/nano fibers and large core fibers,were numerically simulated and theoretically analyzed with finite difference time domain(FDTD)method.The result shows that good coupling among the fibers can be obtained in a micro/nano fiber array and that the modal field is flattened by the micro/nano fibers in the bundle of multiple micro/nano fibers and large core fibers.The result is useful to further development of high-power lasers and amplifiers.
2009, 33(5): 532-534.
doi: 10.3969/j.issn.1001-3806.2009.05.016
Abstract:
In order to study a two-stage Yb3+-doped fiber amplifier for low repetition frequency pulses,a pulse driven laser diode was used as the seed source to obtain rectangle optical pulses with repetition rate of 100Hz,full width at half maximum(FWHM)of 100ns and energy of 30nJ.In the first stage,8.2 μJ pulse energy was obtained by a single mode Yb3+-doped fiber amplifier,in which amplified spontaneous emission was restrained efficiently by means of the method of round-trip amplification. Pumped by 980nm high power multimode laser diodes,the second stage was a double clad Yb3+-doped fiber amplifier with 15 μm fiber core diameter.242μJ output pulse energy was obtained at 7.3W pump power.The FWHM was compressed to 29ns.A near diffraction limited beam was produced from the amplifier with quasi-single mode output.The results shows that the high pulse energy fiber laser has advantage of simple all fiber structure.
In order to study a two-stage Yb3+-doped fiber amplifier for low repetition frequency pulses,a pulse driven laser diode was used as the seed source to obtain rectangle optical pulses with repetition rate of 100Hz,full width at half maximum(FWHM)of 100ns and energy of 30nJ.In the first stage,8.2 μJ pulse energy was obtained by a single mode Yb3+-doped fiber amplifier,in which amplified spontaneous emission was restrained efficiently by means of the method of round-trip amplification. Pumped by 980nm high power multimode laser diodes,the second stage was a double clad Yb3+-doped fiber amplifier with 15 μm fiber core diameter.242μJ output pulse energy was obtained at 7.3W pump power.The FWHM was compressed to 29ns.A near diffraction limited beam was produced from the amplifier with quasi-single mode output.The results shows that the high pulse energy fiber laser has advantage of simple all fiber structure.
2009, 33(5): 535-537,540.
doi: 10.3969/j.issn.1001-3806.2009.05.017
Abstract:
With the purpose of further discussion on the property of amplification of gain-guided and index-antiguided Yb-doped fiber amplifiers,with a negative refractive index step from the cladding to the core,the gain characteristics of a Yb3+-doped fiber in a diameter of 100μm were obtained after solving propagation rate equations by means of signal saturation S method.The relationship between the signal gain and the fiber length was obtained under a certain condition of doping concentration and pumping power and the curve was drawn.Comparing with a common fiber amplifier,the amplification property of this gain-guided and index-antiguided fiber was highly improved.
With the purpose of further discussion on the property of amplification of gain-guided and index-antiguided Yb-doped fiber amplifiers,with a negative refractive index step from the cladding to the core,the gain characteristics of a Yb3+-doped fiber in a diameter of 100μm were obtained after solving propagation rate equations by means of signal saturation S method.The relationship between the signal gain and the fiber length was obtained under a certain condition of doping concentration and pumping power and the curve was drawn.Comparing with a common fiber amplifier,the amplification property of this gain-guided and index-antiguided fiber was highly improved.
2009, 33(5): 538-540.
doi: 10.3969/j.issn.1001-3806.2009.05.027
Abstract:
In order to measure the variation of polarization parameter of mica wave-plate varying with temperature,the polarization interference spectrum of mica wave-plate at different temperature was measured with Daojing UV-3101PC spectrophotometer,in whose sample chamber,a temperature control device was set up to change the temperature of the wave-plate. After measuring the polarization interference spectrum of four mica wave-plates in 80μm,227.5μm,300μm and 813.5μm thick respectively,it was found that the spectrum drifted to shorter wavelength.Moreover,the drift was more obvious when the variation of temperature was larger because of the variation of thickness and birefringence of the wave-plate varying with temperature.The drifted polarization interference spectrum is accurate and visual and simple,which offers an effective method for measuring the variation of polarization parameter of mica wave-plate varying with temperature.
In order to measure the variation of polarization parameter of mica wave-plate varying with temperature,the polarization interference spectrum of mica wave-plate at different temperature was measured with Daojing UV-3101PC spectrophotometer,in whose sample chamber,a temperature control device was set up to change the temperature of the wave-plate. After measuring the polarization interference spectrum of four mica wave-plates in 80μm,227.5μm,300μm and 813.5μm thick respectively,it was found that the spectrum drifted to shorter wavelength.Moreover,the drift was more obvious when the variation of temperature was larger because of the variation of thickness and birefringence of the wave-plate varying with temperature.The drifted polarization interference spectrum is accurate and visual and simple,which offers an effective method for measuring the variation of polarization parameter of mica wave-plate varying with temperature.
2009, 33(5): 541-544.
doi: 10.3969/j.issn.1001-3806.2009.05.018
Abstract:
In order to study the impact of amplified spontaneous emission(ASE)generation on the performance of high power Er/Yb co-doped fiber pulse amplifiers,based on the rate equation,the theoretical models for several amplifiers with different pump,signal and configure parameters were solved with finite difference method.The results show that because of the ASE self-saturation,there is an optimal repetition rate for the input signal in order to achieve the highest peak power and maximum pulse energy and the repetition rate is linear with the pump power and inverse to the pulse duration.The results are important for the design and experimental research of high power Er/Yb co-doped fiber pulse amplifiers.
In order to study the impact of amplified spontaneous emission(ASE)generation on the performance of high power Er/Yb co-doped fiber pulse amplifiers,based on the rate equation,the theoretical models for several amplifiers with different pump,signal and configure parameters were solved with finite difference method.The results show that because of the ASE self-saturation,there is an optimal repetition rate for the input signal in order to achieve the highest peak power and maximum pulse energy and the repetition rate is linear with the pump power and inverse to the pulse duration.The results are important for the design and experimental research of high power Er/Yb co-doped fiber pulse amplifiers.
2009, 33(5): 545-547.
doi: 10.3969/j.issn.1001-3806.2009.05.019
Abstract:
In order to study the condition and gain spectra of perturbation frequency related modulation instability induced by cross-phase modulation in optical fibers with high order effects,starting from the coupled nonlinear Schrödinger equations including quintic nonlinearity and fourth-order dispersion effect and utilizing the linear-stability analysis,the condition and gain spectra are analyzed and calculated when the perturbation frequencies of the two optical waves are not equal.The results show that,when the second-order and the fourth-order dispersions are of the same sign,there are two possible kinds of gain spectra for modulation instability,and one spectrum includes the other.Moreover,the spectrum which is included by the other one has different condition of modulation instability from the ordinary case,and is scarcely affected by the sign of dispersion and parameter of quintic nonlinearity.With increase of one of the perturbation frequencies,the number of the spectral regions and its variation will be different for different dispersion regimes.The positive(negative)quintic nonlinearity can make the peak value of gain spectrum increase(decrease)and the spectral width wider(narrower).This study is significant for generation of ultra-short optical pulse chain at high repetition rate.
In order to study the condition and gain spectra of perturbation frequency related modulation instability induced by cross-phase modulation in optical fibers with high order effects,starting from the coupled nonlinear Schrödinger equations including quintic nonlinearity and fourth-order dispersion effect and utilizing the linear-stability analysis,the condition and gain spectra are analyzed and calculated when the perturbation frequencies of the two optical waves are not equal.The results show that,when the second-order and the fourth-order dispersions are of the same sign,there are two possible kinds of gain spectra for modulation instability,and one spectrum includes the other.Moreover,the spectrum which is included by the other one has different condition of modulation instability from the ordinary case,and is scarcely affected by the sign of dispersion and parameter of quintic nonlinearity.With increase of one of the perturbation frequencies,the number of the spectral regions and its variation will be different for different dispersion regimes.The positive(negative)quintic nonlinearity can make the peak value of gain spectrum increase(decrease)and the spectral width wider(narrower).This study is significant for generation of ultra-short optical pulse chain at high repetition rate.
2009, 33(5): 548-550,554.
doi: 10.3969/j.issn.1001-3806.2009.05.020
Abstract:
It is effective to produce super short pulses from passive mode-locked fiber lasers based on nonlinear polarization rotation due to their simple and compact all-fiber configurations.In order to study the operation states in a passive mode-locked fiber laser,the effect of normal solitons,bound solitons and noise-like pulse state was investigated in experiments.Experiment results show that there are multiple output states from a passive mode-locked fiber laser.
It is effective to produce super short pulses from passive mode-locked fiber lasers based on nonlinear polarization rotation due to their simple and compact all-fiber configurations.In order to study the operation states in a passive mode-locked fiber laser,the effect of normal solitons,bound solitons and noise-like pulse state was investigated in experiments.Experiment results show that there are multiple output states from a passive mode-locked fiber laser.
2009, 33(5): 551-554.
doi: 10.3969/j.issn.1001-3806.2009.05.033
Abstract:
In order to overcome the applicable limitation of single-scattering propagation model in UV communication in low visibility,non-line-of-sight(NLOS)single-scattering propagation model proposed by Luegtten was improved based on 1st order multi-scattering theory.In the amended model,the Rayleigh scattering of atmosphere molecule and the Mie scattering of aerosol were involved,the effect of multi-scattering was taken into account and it was simulated with Matlab.The results show that compared with former model,the amended one accords with experiment results better in low visibility,and that due to the applicable limitation of 1st order multi-scattering theory,the amended model differs from actual fact to a certain extent.It could provide reference for UV communication experiments in low visibility.
In order to overcome the applicable limitation of single-scattering propagation model in UV communication in low visibility,non-line-of-sight(NLOS)single-scattering propagation model proposed by Luegtten was improved based on 1st order multi-scattering theory.In the amended model,the Rayleigh scattering of atmosphere molecule and the Mie scattering of aerosol were involved,the effect of multi-scattering was taken into account and it was simulated with Matlab.The results show that compared with former model,the amended one accords with experiment results better in low visibility,and that due to the applicable limitation of 1st order multi-scattering theory,the amended model differs from actual fact to a certain extent.It could provide reference for UV communication experiments in low visibility.
2009, 33(5): 555-557,560.
doi: 10.3969/j.issn.1001-3806.2009.05.021
Abstract:
In order to study the effect of higher order modes of a fiber laser on the characteristics of coherent combination,the fundamental mode and higher order modes in a double-clad fiber laser were approximated to a linear combination of Laguerre-Gaussian beams.Based on its propagation law,the far field distribution of fiber laser array was obtained with consideration of higher order modes.The peak intensity and fringe visibility of a fiber laser array mixing with higher modes of LP01 and LP11and mixing with higher modes of LP01and LP02 were analyzed respectively.The numerical results show that the peak intensity decreases linearly with LP11 increasing and that the fringe visibility decreases linearly with LP02 increasing.
In order to study the effect of higher order modes of a fiber laser on the characteristics of coherent combination,the fundamental mode and higher order modes in a double-clad fiber laser were approximated to a linear combination of Laguerre-Gaussian beams.Based on its propagation law,the far field distribution of fiber laser array was obtained with consideration of higher order modes.The peak intensity and fringe visibility of a fiber laser array mixing with higher modes of LP01 and LP11and mixing with higher modes of LP01and LP02 were analyzed respectively.The numerical results show that the peak intensity decreases linearly with LP11 increasing and that the fringe visibility decreases linearly with LP02 increasing.
2009, 33(5): 558-560.
doi: 10.3969/j.issn.1001-3806.2009.05.033
Abstract:
In order to increase output power of a single fiber amplifier,a double clad Yb-doped fiber in a new refractive index profile was designed with a core diameter of 30μm and a cladding diameter of 125μm.The fiber,prepared with modified chemical vapor deposition(MCVD)process and improved high temperature vapor deposition,has a hollow refractive index profile with lower refractive index in the doped area.The fluorescence,mode field and amplification characteristics of the fiber were tested.The test results show that the pump power can be absorbed effectively and fluorescent spectrum curve becomes smooth for this new kind fiber.It is realized that smooth mode field energy can output by bending the fiber.40dB high power fs signal light was amplified in a 5m fiber with output power up to 30kW.
In order to increase output power of a single fiber amplifier,a double clad Yb-doped fiber in a new refractive index profile was designed with a core diameter of 30μm and a cladding diameter of 125μm.The fiber,prepared with modified chemical vapor deposition(MCVD)process and improved high temperature vapor deposition,has a hollow refractive index profile with lower refractive index in the doped area.The fluorescence,mode field and amplification characteristics of the fiber were tested.The test results show that the pump power can be absorbed effectively and fluorescent spectrum curve becomes smooth for this new kind fiber.It is realized that smooth mode field energy can output by bending the fiber.40dB high power fs signal light was amplified in a 5m fiber with output power up to 30kW.
