Research On High-Efficiency Orbital Angular Momentum Modes Detecting Systems

With the rapid development of communication technology,people have higher and higher requirements on the capacity and speed of information transmission,and achieving higher data transmission capacity is one of the main directions of optical free-space communications.A typical way to increase the transmission capacity of optical communication system is to multiplex multiple independent data channels,such as wavelength division multiplexing(WDM),polarization multiplexing(PDM)and space division multiplexing(SDM).Recently,optical orbital angular momentum(OAM)multiplexing technique has been attracted many researchers' attentions by.This dissertation focuses on the dilemma of OAM mode analysis in OAM optical communication system,and proposes two efficient mode analysis methods,and two highly effective mode analytical methods are given.The main content of this dissertation are as follows:(1)Established a high-efficiency sorting and measurement of orbital angular momentum modes based on the modified March-Zehnder Interferometer(MZI)and Complex Phase Gratings(CPG).Based on the orthogonality between the vortex beams,we propose a novel OAM de/multiplexing method based on the combination of the MZI implanted pair of dove prisms(DP)(MZI-DP)and a CPG,which can be used to sort and detect multiple OAM modes simultaneously.The MZI-DP system can sort different OAM modes into odd and even values of topological charges.And then,the designed CPGs perform the concrete measurements of different sorted OAM modes.With this designed system,we can measure the high-density OAM modes without any overlapping between adjacent modes.Furthermore,we simulated the simultaneous measurement of multiplexed OAM beams with 50 OAM states.The results show that our proposed scheme has superior performance with high recognition rate.(2)Established a large range detection system of Perfect Optical Vortex based on modified mode transformer.Here,we propose an improved mode converter to achieve a wider detection range of perfect optical vortex(POV).The proposed improved mode convert a POV beam to a rectangular beam array by the phase plate(P1),a phase corrector(P2)and the Fourier lens array.The composite phase loaded by the phase plate P1 includes spiral phase,linear phase,and fan-out phase.Through phase P1,the POV will be mapped to the rectangular beam array,P2 is the phase corrector element that corrects the phase distortion arise from the mapping transformation.Finally,we use the Fourier lens array to perform Fourier transform on the rectangular beam array to obtain the array of light spots needed for detection,so that a wider detection range of POV can be achieved.Furthermore,in order to verify the reliability of the scheme,we use the proposed method for grayscale image transmission,and the results show that the proposed system can achieve error-free bit rate transmission.