Generation And Propagation Characteristics Of Caustic Phase On Vector Optical Field

The phase and polarization are very important properties of the optical field,which are two independent freedom degrees and difficult to realize flexible control simultaneously.The structured light field,which requires the optical degrees of freedom including phase,polarization and amplitude,should be regulated completely in the spatial distribution of the cross section of the optical field,such as the novel light fields(e.g.the vortex light field and the vector light field).The structured light field are widely used in super-resolution microscope,optical tweezers,laser micromachining,information transmission and optical imaging et.al,which require local accurate control of all properties of light field,including phase,amplitude and polarization.In recent years,multiple caustic beams,such as Airy beams and Pearcey beams,have been generated in theory and experiment.However,most of the works focused on scalar light field,rarely on the effect of caustic phase on the vector light field with non-uniform polarization distribution,especially on the manipulation of optical angular momentum in the vortex vector light field.Studying the caustic vector optical field and caustic vortex optical field,as well as the dynamic operation and flexible transformation of the polarization state of the caustic vortex optical field,has important theoretical significance and practical value.The main contents of this paper are as follows:1.We introduce the basic concepts of vector optical field and vortex optical field as well as the active and passive generation methods of vector optical field,focusing on the generation method of vector optical field based on optical 4f systems.The radial,angular and hybrid polarization vector optical fields are generated using this approach,and the corresponding generation method of caustic vector optical field is discussed in this part.In addition,the basic theory,development status and the basic design method of caustic phase are introduced.2.We study the focal field distribution characteristics of the caustic vector optical field in the state of weak focus.Based on the theory of Rayleigh-Sommerfeld vector diffraction,the expression of focal field after weak focusing of the vector optical field with different phase parameters are derived and simplified,and the incident intensity,polarization distribution,propagation characteristics,focal intensity and polarization distribution after weak focusing are calculated.The caustic phase can make the light field having the self-accelerating track when it propagates in the free space.The self-focusing of the light field can be controlled to form the two foci distribution in the weak focusing state by further applying the vortex topological charge,showing the novel characteristics of the focal field.3.The spatial polarization conversion and angular momentum evolution of the caustic vector optical field are studied.Due to the effect of caustics phase,two foci with orthogonal polarizations can be generated when the caustic vector optical field propagates in free space.In addition,two foci are transformed into scalar polarization distribution that are orthogonal to each other.By adjusting the caustic phase distribution in initial incident optical field,the caustic vortex vector optical field with optical orbital angular momentum can be generated.In addition,through the reasonable design of the caustic phase and the initial parameters of the light field,the spatial polarization conversion and the flexible regulation of the vortex order of the light field in the weak focusing state can be realized.Finally,it can be realized that in the structured light field with the joint action of polarization and phase,forming a multi-dimensional joint regulation of the optical field.