LED-Based Orbital Angular Momentum Beam Manipulation And Application In Optical Communication

Due to the rapid development of internet and multimedia equipment,the communication network is becoming crowded.In the optical communication system,the amplitude,phase,and polarization are utilizd for encoding the information,which aims at increasing the data incapacity.In the optical communication techniques,the data incapacity is enriched by multiplexing different data channels,which range from wavelength division multiplexing(WDM),the polarization division multiplexing(PDM),space division multiplexing(SDM).During the last few decades,the orbital angular momentum(OAM)for its high advantages in the security and high dimension characters has become a new solution for the crowded data capacity,multiplexing/demultiplexing of information-carrying OAM beams for free-space data transmission,achieving a capacity of Tbit per second magnitude.At present,OAM beam has been extensively employed in the laser communication systems,as the laser possessed good coherent,low divergence and concentrated their power at a great distance.In this thesis,we developed the OAM information encoding scheme to the LED light source.The researches of generation,manipulation,detection and the applications of the LED-based OAM vortex and its superposition are systematically investigated.The main contents and innovations are as follows:1.The propagation dynamics of various LED-based vortex have been generated and investigated.Based on the Gaussian-Shell mode and the DSI method,we developed and generalized the diffraction formulae of the paraxial ABCD system,which can be applied to negative and superposition OAM beams.Besides,we simulated the propagation dynamics of the vortex beams.Furthermore,we experimentally investigate various vortices and discuss the mergence and filling phenomena after propagation.These numerical are coincide well with the experimental results.The work shows us a new paradigm for shaping the partially coherent vortex and plays a theory fundamental role in the LED-based OAM communication system.2.Based on the investigation of the propagation dynamics of the LED vortex,the LED-based OAM beams communication link utilizing the vortex superposition for encoding and decoding information are proposed,which successfully transmit the chromatic image and audio with high fidelity.At the sender,we use LED as a light source and the RGB twisted light serve as three independent channels and the OAM superposition states are employed as the information carrier.At the receiver,the lenses groups are applied to demagnify and collected the beam,and then the supervised machine learning is employed to recognize each pattern and reconstruct the image and audio with high accuracy.Unlike the broadcasting style of Li-Fi,the transmission link is an indoor point-to-point model.Therefore,offering additional security,which might be a supplement for the traditional broadcasting visible light communication.3.In the research of laser beam manipulation,the propagation dynamics of non-standard vortex beam are investigated by modulating the phase structure when interplay with circular obstacle.Experimentally,via shaping the Poisson spot and the doughnut OAM beams the two seemly independent effects can be connected naturally,which indicate that the light can be conducted by the interaction of spiral phase modulation and the amplitude mask.Besides,the effect of spiral phase modulation on the formation of the Poisson spot is intuitively presented.Theoretically,the propagation behavior and the Poynting vectors of the non-standard OAM beams are investigated by digital spiral image(DSI)method.The azimuthal and radial component of the Poynting vector of the beam with variant phase steps have been simulated and then conclude that the light and the Poynting vectors can be conducted and manipulated by the spiral phase and the obstruction.