Classical Correlations And Information Encoding Based On Orbital Angular Momentum Of Light

In the last two decades,the light beams with orbital angular momentum(OAM),which have a composite light field structure,have gradually become the researchful hotspot.Especially at both the classical and quantum communications regimes,the light's OAM has shown great value of application.For example,using the existing multiplexing and demultiplexing techniques,the information capacity of classical communication can be greatly increased.Based on the high-dimensional entanglement of OAM,the security of the quantum key distribution protocol and the rate of the secret key distribution can be improved significantly.In order to study systematically the importance of OAM in the classical and quantum systems,this thesis explores the information encoding and the simulations of quantum correlation using OAM beams.Furthermore,we have studied the applications of such classical simulations.The main points of this thesis are listed as below.Firstly,using the modified Mach-Zehnder(MZ)interferometer,we first proposed and demonstrated experimentally a simple and efficient way to identify nondestructively unknown vortex beams,which include OAM beams with integer topological charges and generalized vortex beams with noninteger topological charges.Compared with the traditional identification methods,our scheme may have important application in optical communications using vortex beam as a carrier.Secondly,we present a multi-ary encoding/decoding protocol exploiting a vector beam consisting of OAM and polarization degree of freedom(Do F).Based on the nonseparability of such the two Do Fs,we find that N-ary encoding can be realized by manipulating only N/2different OAM modes,which is similar to the process for dence coding.It is equivalent to encodinglog₂^N bits of information.Compared with the encoding protocol using scalar OAM beams,fewer OAM modes are required to encode the same amount of information based on vector beams.Moreover,taking quaternary and hexadecimal encoding/decoding as examples,we have quantified the effect of crosstalk between OAM modes on information transmission.Thirdly,based on a post-selected method,we have realized the simulation of quantum hyperentangled states(multi-qubit)using two spatially separate beams.After measurement,the relationship of such two beams can be quantified by performing Bell's inequality of CHSH type.Based on such a classical correlation,we have realized the analogy of the process of quantum superdense coding.Compared with the simiulation of quantum entanglement using vector beams,our scheme enables the simulation of multi-qubit entangled states,and is beneficial for us to understand and explore quantum onformation process.Finally,based on the high-dimensional OAM Hilbert space,we study further the simulation of high-dimensional OAM entangled states(qudits)using classical light,and demonstrate the violations of the high-dimensional Bell inequalities.Moreover,due to the mathematical similarities between the classical correlated states we construct and the corresponding quantum entangled states,we also show theoretically that the state decay of the established high-dimensional correlation is equivalent to that of quantum entangled photons when one-side channel is perturbed by a turbulent atmosphere.The equivalence means that quantum channels with high-dimensional entangled states can be characterized robustly using classical light instead of multiple measurements on quantum states.Therefore,our scheme allows one to implement error correction of the data in real time in high-dimensional quantum information processes,and shows potential applications.