| The structured beams with complex spatial amplitude,phase,polarization and even coherence characteristics produce new phenomena and effects when transmitting,transforming and interacting with matter,and have gradually developed into an independent optical branch that has attracted much attention.As a type of typical structured beam,the vector vortex beams(vortex beams and vector beams are two special types of vector vortex beams)with spatial inhomogeneous polarization state and spiral phase distribution play an increasingly important role in laser communication,optical micromanipulation,laser processing and other fields by virtue of their unique physical characteristics.The rapidly growing application demand also puts forward higher requirements for the generation and control technology of the vector vortex beams.With the continuous expansion of application fields,it is difficult to adapt to the growing application demand in the future by relying on a single device to achieve a single function.The development direction of the new generation and modulation technology of the vector vortex beams must be high power,multi-function and active.Coherent beam combining(CBC)provides a promising solution for greatly scaling up the output power.More importantly,taking the advantage of flexible and independent regulation of amplitude,phase,and polarization of each beamlet in the laser array,and benefiting from the high bandwidth of electro-optic modulators and controllers offers an efficient technical pathway for realizing high-power,fast switchable vector vortex optical beams by employing CBC.Therefore,taking CBC as the technical means and taking various vector vortex beams as the research objectives,this dissertation systematically studies the generation of the perfect vector vortex beams based on CBC,phase control technology,atmospheric propagation characteristics,and the spatiotemporal coherence tunable optical fiber laser source developed for CBC system.The main contents and results are as follows:(1)The generation method of single and double-ring perfect vector vortex beams are proposed by employing the characteristics of the flexible adjustment of the phase,polarization and amplitude of each beamlet in a CBC system,and the theoretical and simulation verification are carried out;The free space propagation characteristics of the generated perfect vector vortex beams are investigated,and it is proved that they could be stable for a certain distance;Based on the vector diffraction theory,the tightly focused characteristics of the coherently synthesized perfect radially polarized beams are analyzed.Compared with the traditional ring radially polarized beam,the size of the focal spot can be further compressed,which provides a new technical way to realize the extremely strong longitudinal light field.(2)Based on the Dammann vortex grating and adaptive gain random parallel gradient descent algorithm,the phase control technology scheme of the CBC system for generating perfect vector vortex beams is proposed,and the discrete phase locking of perfect vortex,vector and vectorial vortex beams is realized.The influence of laser dynamic phase noise and power variation on the optimization algorithm is quantitatively analyzed.The results show that both of them can bring about fluctuations of convergence curve.The dynamic phase noise can simultaneously slow down the convergence speed and worsen the convergence effect,while power variation can only lead to poor convergence effect,with almost no impact on the convergence speed.(3)With the generalized Huygens-Fresnel diffraction integral method,the probability density analytical formulas for coherently synthesized perfect vector vortex beams are analyzed,and the analytical formula of probability density are derived,and the physical mechanism of mode crosstalk induced by atmospheric turbulence are revealed.The theoretical results show that compared with perfect vortex beam,perfect vector and vectorial vortex beams can’t effectively mitigate the mode crosstalk;The mode crosstalk of coherently synthesized perfect vortex beam in atmospheric turbulence is simulated and compared with that of Gaussian vortex beam.The results demonstrate that coherently synthesized perfect vortex beam shows good performance on crosstalk mitigation for long distance and strong atmospheric turbulence;On this basis,with a vortex beams’generation and multiplexing device composed of two groups of laser arrays with orthogonal polarization and different spiral phase distribution,a scheme of optical communication system possessing simultaneously polarization-division multiplexing and orbital angular momentum multiplexing is proposed,and simulation verification of an 8-bit grayscale image is successfully realized.(4)Taking into consideration the laser coherence,the influence of temporal and spatial coherence on the atmospheric propagation characteristics of the vector vortex beams based on laser array is theoretically analyzed.The conclusion shows that the atmospheric propagation characteristics of the vector vortex beams based on laser array are closely to spatial coherence but not to the temporal coherence.The analytical expressions for spectral intensity,spectral degree of coherence,and spectral degree of polarization of spatially partially coherent vortex and vector beams based on laser array are derived.And also,based on numerical simulation,the influence of atmospheric and laser parameters on the propagation properties is numerically investigated.The simulation results show the beam profile presents an evolution trend of hollow-flat-top-Gaussian-like,and the spectral degree of coherence exhibits decaying oscillation analogous to under-damping vibration for both type of beams.For the spatially partially coherent vector beams based on laser array,although a dip appears in the distribution of the spectral degree of polarization,but the initial polarization distributions still show similar performance regardless of propagation distance.In addition,the communication performance of spatially partially coherent vortex and vector beams based on laser array is discussed and compared with Gaussian Schell mode.The results indicate that the communication capacity of the former two is close,but higher than that of Gauss-Schell mode.The ratio of communication capacity increases from 1.05 times at 2km to about5.1 times at 10km.(5)Taking advantage of characteristics of low temporal coherence and high spatial coherence of amplified spontaneous emission(ASE)single-mode fiber laser source,a fiber laser source with adjustable temporal and spatial coherence is experimentally studied.A broadband ASE ytterbium-doped fiber laser source with low temporal coherence(L_c=54.50?m)and high spatial coherence(single mode output)is obtained by using temperature-control method.Using the spectral filtering method based on the principle of grating monochromator,a narrowband ASE ytterbium doped fiber laser source with high temporal coherence(L_c=17027.35?m)and high spatial coherence(single mode output)is realized with parameter optimization;Adopting an optimized three-stage fiber amplifier chain,a narrowband ASE light source with an output power of 300 W and a wavelength tuning range of nearly 20 nm is obtained;Finally,for the designed the ASE fiber laser sources,the regulation mechanism of temporal and spatial coherence is discussed,and the specific control method is given. |
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