Orbital Angular Momentum Modes Identification And Frequency Multiplier Of Optical Vortices

Optical vortice is a structured beam that can carry orbital angular momentum(OAM)and has a spiral phase wavefront.The vortex beam has unique dynamic characteristics,OAM characteristics and topological structure,it can greatly improve people's ability to control light,and has important application prospects in many fields,such as micro-manipulation,communication,optoelectronics,quantum information,and remote sensing.Especially in the field of optical communication,since the orbital angular momentum mode that the vortex beam can carry is theoretically infinitely orthogonal.If it is combined with the traditional multiplexing modulation dimension,it is expected to double the communication rate and capacity to meet the development needs of communication technology.The research of orbital angular momentum optical communication technology is mainly focused on two major pieces: one is the orbital angular momentum reuse technology using the orbital angular momentum mode as an information carrier,and the other is the orbital angular momentum modulation technology that maps the orbital angular momentum mode to a data sequence.It is worth noting that,whether it is orbital angular momentum modulation or orbital angular momentum multiplexing optical communication system,the key technology lies in the regulation and detection of orbital angular momentum mode.In terms of orbital angular momentum mode detection,researchers have proposed a variety of methods that can be used for topological charge detection.The most common methods are interference and diffraction.The interference method uses a plane wave or a spherical wave to interfere with a vortex beam.Plane or spherical waves can accurately identify orbital angular momentum modes,but usually involve complex interference settings or interference modes.Diffraction method recognizes vortex light through a pattern formed by a specific design aperture diffraction,and compared with the simulation results,it usually reduces the experimental results of the diffraction method,thereby reducing its efficiency in practical applications.In terms of orbital angular momentum control,linear optical methods are mainly used for up / down conversion of orbital angular momentum mode.Researchers have achieved the switching of orbital angular momentum by cascading multiple optical components,such as the liquid crystal spatial light modulator method and the metasurface method.But these methods not only have a single function,but can only switch between several modes,and cannot switch at high speed.Moreover,the cascading use of multiple components greatly increases the complexity of the optical system.Therefore,in view of the above problems,the detection and doubling research of angular momentum mode of vortex light field is proposed.The second-order nonlinear frequency doubling effect is used to realize orbital angular momentum mode conversion.By designing a binaural-circular aperture(BCA),the orbital angular momentum modes can be accurately detected.The main work and results are as follows:1.An orbital angular momentum mode frequency doubling scheme based on second-order nonlinearity is proposed.Based on the interaction mechanism of vortex light and nonlinear materials,the second-order nonlinearity is used to achieve the frequency doubling of the orbital angular momentum mode,thereby achieving variable mode switching,regulation,and higher-order modal generation.2.The traditional orbital angular momentum mode detection scheme is improved.The diffraction characteristics of vortex beams passing through a special aperture and the effects of changes in orbital angular momentum mode on the diffraction pattern are discussed.Based on this theory,an orbital angular momentum mode detection method based on binaural-circular aperture(BCA)diaphragm is proposed,and the accurate judgment of the orbital angular momentum mode of the vortex beam is experimentally verified.