Study On Polarization-selective Diffractive Optical Elements And Radially Vector Beams

Polarization-selective diffractive optical elements (PSDOEs) can generate different outputs for different input or output polarization states. This polarization-sensitive property of the PSDOEs has brought a wide range of applications. PSDOEs can be realized with surface-etched birefringent crystal materials, subwavelength structures in isotropic substrates and induced birefringent components . However, these methods rely on high-resolution lithography and cannot realize dynamic mapping of output polarization states. Programmable liquid-crystal display (LCD) with high resolution provides a possible approach to dynamical control of the output of the PSDOEs. PSDOEs are also important elements for generating various vector beams that have attracted significant interests because of the unique feature compared with homogeneously polarized beams. A spatial light modulator (SLM) could provide the unique opportunity to design the arbitrary spatial (phase or amplitude) modulation patterns to generate the desired optical modes. Cylindrical vector beam has gained much interest recently due to its novel radially symmetry property, focusing property and potential applications. By annlysis above problems, important research results are obtained. In this paper, the main researches are as follows1. A method for realizing a PSDOE based on one single LCD is proposed. We demonstrated that there exist two orthogonal encoding channels when a twisted-nematic liquid-crystal display (TN-LCD) operates under some special conditions. Using the two orthogonal encoding channels, the complex amplitudes of two orthogonal polarized components of a field can be holographically encoded and reconstructed respectively, and hence different output images with different polarization states could be obtained or a vector beam with spatially inhomogeneous polarization distributions could be combined.2. Radially polarized beam has gained much interest recently due to its properties and applications. In this article, the focusing properties of radially polarized beam with radial cosine phase wavefront are investigated theoretically. Results show that when the radially polarized beam with radial cosine wavefront phase is focused, the focal pattern differs considerably with frequency parameter in the cosine function term. In the high numerical aperture focusing system, focal shift occurs, and novel focal patterns evolve considerably, for instance, from only one peak to two or multiple overlapping peaks. In addition, peak intensity ratio of radially polarized component to longitudinal polarized component in the focal region fluctuates smoothly for low-frequency parameter, then drops sharply, and comes back remarkably with increasing frequency parameter. Simultaneously focal shift increases slowly, and then decreases, suddenly, focal shift sign changes that results from focal switch phenomenon, and then fluctuates.