Research On The High-order Poincare Sphere Beams

Traditional Poincaré sphere unifies the geometric representation of arbitrary basic state of polarization on the sphere,which is not only helpful to deepen the understanding of the state of polarization,but also tremendously facilitate the handling of complex polarization problems,whereby this notation is still applied nowadays.In recent decades,vortex beams(VBs)have been widely researched and used due to their unique polarization or phase distributions.High-order Poincare sphere(HOPS)is demonstrated for its ability to represent VBs,which greatly expands the practicability of the Poincare sphere.HOPS beams have shown remarkable application value and been exploited in fields like optical communication,optical sensing,quantum information processing,surface plasmon excitation,optical trapping,material processing,microscopic imaging,etc.Therefore,it is of great and far-reaching significance to study the generation,evolution and detection of HOPS beams.Currently,methods for generating HOPS beams mainly include holography,metasurface and optical vortex retarder based methods.By using these approaches,the structures are complex or HOPS beams with only one order can be generated.Therefore,it is urgent and necessary to find a simpler method for switchable generation of multiple different HOPS beams.In the field of optical communication,mode multiplexing and demultiplexing are involved,so the beam mode needs to be detected.In addition,the devices generating HOPS beam also need to be detected and characterized.Therefore,the detection of HOPS beams is also a research hotspot in recent years.Methods have been proposed to detect the HOPS beams including point-by-point detection method,machine learning method and digital holography method.These methods realize the characterization and demultiplexing of HOPS beams,but relatively more simple and efficient detection methods are also need to be proposed.On top of this,HOPS beams are also expected to be generated at the source from lasers.The main research works of this thesis are as follows:1.We propose a cascaded mode converter.The cascaded mode converter consists of two substructures,the first is the cascaded addition structure of vortex plate,namely VP-HP-VP type structure,and the second is the cascaded subtraction structure,namely VP-VP-HP type structure.We theoretically analyze the one-to-one correspondence between the input beam of the fundamental mode and the output beam after passing through the proposed cascaded mode converter.In addition,we realize the exponential growth of the available number of HOPS beams by utilizing the cascaded mode converter.Finally,-7th order to 7th order Poincaré sphere beams are experimentally generated with the combination of a first order,a second order and a fourth order vortex plates.The order and polarization state of the beam can encode two bits of information as two degrees of freedom.2.We study the polarization evolution of HOPS beams on the sphere.we represent the vortex plate on the HOPS by a diameter on the equatorial plane,and the distribution of the fast and slow axes are represented by two ends of the diameter respectively.If a m-order HOPS beam is input onto the 2m-order vortex plate,the polarization state of the output light can be obtained by rotating the input state around the diameter by an angle,the rotation angle is numerically equal to the phase retardance introduced by the vortex wave plate.This evolution rule can make full use of the geometric representation of HOPS,deepen the understanding of HOPS beams and make it easy to design various polarization elements.3.We propose a quantitative measurement method for the polarization state on the HOPS.Three sets of nonuniform polarization bases are introduced in the high-order Stokes parameters.By using the inverse convention of the vortex plate,we realize the direct measurement of the higher-order Stokes vector.In the experiment,we take the first HOPS beams as an example,and the measurement accuracy is greater than 91%.4.Fiber lasers for generating traditional Poincare sphere beams and HOPS beams are also proposed.The main innovations of this thesis are as follows:1.We propose a cascaded mode converter to realize the switchable generation of multiple different HOPS beams,exponential growth of the available number of HOPS beams of different orders is achieved compared with the number of vortex plates.The order and polarization state of the beam can encode two bits of information as two degrees of freedom.2.The evolution of HOPS beams on the HOPS is proposed.For the first time,we represent the vortex plate on the HOPS by a diameter on the equatorial plane,and the distribution of the fast and slow axes is represented by the ends of the diameter respectively.If a m-order HOPS beam is input onto the 2m-order vortex plate,the polarization state of the output light can be obtained by rotating the input state around the diameter by an angle,the rotation angle is numerically equal to the phase retardance introduced by the vortex wave plate.This evolution rule can make full use of the geometric representation of HOPS,deepen the understanding of HOPS beams and make it easy to design various polarization elements.3.We propose a quantitative measurement method for the polarization state on the HOPS.Three sets of nonuniform polarization bases are introduced in the high-order Stokes parameters.By using the inverse convention of the vortex plate,we realize the direct measurement of the higher-order Stokes vector.