Study Of Circularly Polarized OAM Beam Emitters

Internet data traffic is experiencing explosive growth as new data services such as interactive multimedia,Io T,driverless and others step into people's lives.However,the transmission capacity of fiber optic communication systems and networks,the cornerstone of the Internet,has grown sluggishly after several technological innovations and breakthroughs,and is approaching the theoretical nonlinear Shannon limit.Orbital angular momentum(OAM)is the only unexplored dimensional resource of electromagnetic waves(light waves)other than amplitude,phase,frequency,polarization(spin angular momentum),and time,and has received a lot of attention.OAM-based multiplexing technology is considered to be one of the ways to effectively solve the transmission capacity and spectral efficiency that has became to a top topic in the field of fiber optic communication,and has achieved breakthroughs in OAM chip and fiber technology.However,the mode field matching problems such as spot mismatch,polarization mismatch and phase mismatch in the coupling of OAM chip and OAM fiber have not been given enough attention.In this paper,an in-depth study of on-chip polarization modulation is carried out to address the polarization mismatch problem,and two new circularly polarized beam emitter implementation are proposed based on silicon-based micro-ring OAM beam emitters.The main research works are as follows.1.A design scheme of circularly polarized beam emitter based on a single-mode micro-ring is proposed.Based on the Jones vector of the vector beam,the idea of generating a circularly polarized beam by superimposing a radially polarized beam with an angularly polarized beam is demonstrated.When perturbation exists in the resonant cavity of the micro-ring,mode splitting occurs,forming antisymmetric mode(ASM)and symmetric mode(SM)modes.The electric field distribution of the two modes in the micro-ring is analyzed,and it is found that the ASM mode radiates a radially polarized beam and the SM mode radiates an angularly polarized beam.The relationship between perturbation and mode splitting is analyzed,and the results show that the resonant wavelengths of ASM and SM modes increase with the enhancement of perturbation,and there is an intersection point between the two modes.Based on this,a circularly polarized beam emitter is designed and the device is simulated and verified,and the experimental results show that the device can produce circularly polarized light with high purity.2.A design scheme of circularly polarized OAM beam emitter based on few-mode micro-ring is proposed.Based on the dipole model,the device scheme is demonstrated,and the results show that the device can realize the modulation of radial and angular OAM beams and can superimpose to generate circularly polarized OAM beams.In the design of the device,the design of the microring resonant cavity and the diffraction grating are focused.The design requirements for the microring resonant cavity are that there are two modes with the same effective refractive index,and the two modes are concatenated so that they resonate at the same wavelength in the micro-ring;the design requirements for the diffraction grating are that the radial and angular components of the waveguide can be modulated simultaneously,and the device can emit both radial and angular OAM beams.After determining the parameters of the device,the device is simulated and verified,and the experimental results show that the device is able to produce a high-purity and energy-concentrated circularly polarized OAM beam.