Manipulation Of Circularly Symmetric Structured Light Fields With Metasurface And All-optical Information Processing

Owing to the particular field profiles and optical properties,the circularly symmetric structured light beams have attracted much attention in diverse fields,such as optical tweezer,particle manipulation,optical imaging,super-resolution and quantum information,etc.Especially for optical communication,the spatial modes of circularly symmetric structured light beams show infinite orthogonal space,and different data sequences can be loaded into different mode channels,which can be used for mode-division multiplexing communication.Due to the spatial modes carried by the circularly symmetric structured light beams are constructed by phase and polarization manipulation of light,the multiplexing and demultiplexing of circularly symmetric structured light modes can be realized with phase-and polarization-type modulation devices.Meanwhile,the mode transformation can be also be performed with phase and polarization manipulation.It is expected to design passive optical devices for all-optical mode signals processing.As a new information multiplexing dimension,the spatial modes of circularly symmetric structured light beams are capable of improving capacity density and all-optical information processing,and achieving alloptical interconnect and all-optical networks.At present,lots of works have been reported on the generation and detection of single circularly symmetric structured light mode.However,in practical applications,it is always need to use a single system to achieve the flexible and controllable generation and detection of multiple circularly symmetric structured light beams.Therefore,how to realize the generation,manipulation and detection of circularly symmetric structured light beams are the key problems to be solved in the further study of the application of circularly symmetric structured light beams.In the application of optical interconnection,the core of spatial mode multiplexing and all-optical mode information processing lies in mode coupling and separation,mode transformation.However,the existing devices for mode multiplexing and demultiplexing of circularly symmetric structured light are hard to meet the requirements of small size,high bandwidth and arbitrary polarization response,and the study of vector mode multiplexer has not been carried out.Limited by the mode multiplexers,the efficiencies of the proposed circularly symmetric structured light communications are quite low,and the communications systems are complicated.Few works on all-optical mode transformation devices have been reported,and the all-optical mode processing technologies in optical domain are not mature,which greatly hinder the practical applications of circularly symmetric structured light beams in all-optical interconnection and photon integration.In this paper,the micro-nano optics is regarded as the research carrier,and starting from the basic research of circularly symmetric structured light beams.Aiming to solving the problems of lacking the generation,detection and flexible manipulation technologies of circularly symmetric structured light beams.Generation and conversion of circularly symmetric structured light beams are realized by properly using the spinorbit interaction mechanism of metasurface Q-plate.Then,by designing the phase retardance and q-value of the bilayer metasurface Q-plate,the weight and polarization directions of the dual polarization basis vectors of the circularly symmetric beam are manipulated.In order to detect circularly symmetric structured light beams,two orthogonal polarization separation techniques are proposed.One is to separate the linear polarization basis vector,and then obtain the complete information of structured light beams by interference detection;the other is to separate the circular polarization basis vector,and extracting the information of beam by astigmatic diffraction of "twisting" phase.Furthermore,the problems of small bandwidth,large size,polarization sensitivity and the lack of mode conversion devices in the all-optical interconnect of circularly symmetric structured light beams are further studied.Based on the Pancharatnam-Berry(P-B)phase mechanism,a kind of metasurface Dammann vortex grating is designed,which can realize the multiplexing and demultiplexing of orbital angular momentum modes with high bandwidth and insensitive polarization property.Then,the transmission phase and P-B phase are combined to realize the metasurface vector Dammann vortex grating,which can be used for the multiplexing and demultiplexing of vector modes.Finally,using the spin-orbit interaction mechanism of P-B phase metasurface Q-plate,the flexible transformations of two circularly symmetric structured light modes are realized,and the corresponding all-optical mode information processing technologies are proposed.The research results will provide theoretical and experimental basis for revealing the interaction mechanism between the circularly symmetric structured light fields and the micro-nano photonic devices,and further promote the applications of the circularly symmetric structured light in optical communications and all-optical interconnection.The main contents and innovations of this paper are listed as follow:1)In order to realize the flexible manipulation of the circularly symmetric structured light beams,a circularly symmetric structured light manipulation technology based on the bilayer metasurface Q-plate is proposed and experimentally verified.By adjusting the q-value and phase retardance of the bilayer metasurface Q-plate,we can realize the conjugate phase modulation of the forward and backward nonreciprocal orthogonally circular polarization basis vectors and the orthogonal linear polarization basis vectors.The design of bilayer metasurface Q-plate,on one hand,two layers of structure are integrated into single metasurface,which is good for system integration.On the other hand,by rotating the bilayer metasurface Q-plate,the weights of the circular polarization basis vectors and the polarization rotations of the linear polarization basis vectors can be adjusted,which can realizing the beam manipulation in the high-order Poincaré sphere.It provides a new method for the manipulation of circularly symmetric structured light beams.2)The traditional detection method of circularly symmetric structured light beams can only detect the single structured light and the functionality is limited.In order to realize the joint detection of multiple structured light beams,a kind of polarization sensitive blazed grating is designed for the separation of orthogonal linear polarization basis vectors after transforming.After interfering with planar wave,the complete modal information of circularly symmetric structured light beams can be calculated out.Then,in order to improve the practicability and flexibility of the detection method,the controllable spin Hall effect based on the phase function construction is proposed.With this working mechanism,on one hand,by changing the position shift of the incident light,the spin-dependent separation can be flexibly adjusted and used for the detection of the polarization ellipticity of the beam.On the other hand,under the modulation of the constructed phase,the applications of mode information detection of circularly symmetric structured light beams can be realized.This method shows better performance in simplicity and flexibility.3)A plasmonic metasurface Dammann vortex grating based on P-B phase is proposed and experimentally verified to solve the shortage of the existing mode multiplexer/demultiplexer in the size,bandwidth,polarization response.The theoretical working wavelength of the metasurface ranges from 1000-2000 nm,and shows the property of polarization insensitive.Based on the transmission phase and P-B phase,a plasmonic metasurface vector Dammann vortex grating is proposed and simulated.With the combination of P-B phase and transmission phase,the hybrid phase can be used for loading conjugate Dammann vortex grating phase on two spin components of the beam,which can be used for multiplexing and demultiplexing of vector modes.This device fills the gap of vector mode multiplexer in the vector mode multiplexing communications.4)In order to improve the compatibility of the existing all-optical mode processing devices and promote the fusion of circularly symmetric structured light beams and alloptical information processing,a circularly symmetric structured light beams' mode processing prototype device is demonstrated.It is P-B phase all dielectric metasurface Q-plate.The P-B phase involved with dispersion-free characteristic and spin-orbital interaction rewards the P-B phase-based metasurface a naturally broadband working wavelength ranging from telecom C-to L-band and is capable of converting orbital angular momentum(OAM)and vector modes simultaneously.By manipulating the order of OAM and vector modes via designing the q-value of P-B phase metasurface,the all-optical information processing(mode exchange,retrieving,and conversion)of the multiplexed OAM modes are successfully performed,and the all-optical information processing of vector modes are firstly performed.