Research On Vortex Photonic Devices Based On Surface Plasmon Polaritons

Optical vortex is a structured light field.Its transmission wavefront is spirally distributed and has orbital angular momentum(OAM).The OAM carried by optical vortex has mode orthogonality and can be transformed into mechanical torque when acting on tiny particles,so it can be applied in optical communication and optical manipulation.In addition,the rotational Doppler effect and annular intensity distribution of optical vortex can be applied in rotating body detection,optical switching,and super-resolution microscopy imaging.However,optical vortex related photonic devices usually rely on complex experimental optical paths and bulky optical components,which are not conducive to the development of integration.As an emerging technology,surface plasmon polaritons(SPPs)provide an effective way for researchers to design highly integrated photonic devices at the micro-nano scale.SPPs are evanescent waves formed by the coupled oscillation of photons and free electrons on the metal surface,which can realize local field enhancement effects and light field manipulation beyond diffraction limit.In this thesis,the SPPs vortex field excited by the coupling of optical vortex and nano slit is studied,and the vortex photonic devices based on SPPs are designed.The details are as follows:1.A vortex beam encoding universal all-optical logic gate based on nano-ring slits is proposed.The input signals are encoded through binary phase shift as the input logic state.The intensity of the excited SPPs at the center point of the nanoring plasmonic lens is encoded as the output logic state.The intensity contrast between output logic "1" and "0" is infinite on OR,NAND,XNOR and NOT gates,and 4:1 on AND,NOR and XOR gates.The output intensity of the same output logic state remains the same.This high-performance and integrated all-optical logic gate scheme will show good application potential in the design of all-optical computing equipment in the future.2.A scheme for continuously controlling the position of phase singularities at the nanoscale is proposed.The nanoscale continuous control of the phase singularity is achieved by changing the offset distance and angle between the incident optical axis and the center of the nanoring plasmonic lens.This scheme can not only be used in parallel with other schemes in practical applications,but also provides the theoretical basis for the study of non-aligned coupling of vortex beams and nanoring plasmonic lens,which will help and provide reference value for the design of future on-chip SPPs vortex devices.3.An on-chip absolute measurement detector of photon angular momentum is proposed.When the detected light is incident on the detector,two SPPs intensity points will be generated on the detector surface.The spin quantum number of the detected light can be determined by the quadrant generated by the focus point,and the topological charge can be determined by the angle between the line connecting the focal points and the horizontal axis of the detector coordinate system.This scheme is independent of the magnification in the imaging system and does not rely on any reference OAM beam,which provides a completely new way for the absolute measurement of photon angular momentum.It is expected to have potential applications in integrated photonic devices.