Space-variant polarization state manipulation using subwavelength metal grating

Summary form only given. Subwavelength metal stripe gratings are usually used as homogenous space-variant polarizers. Sometimes, however, a different polarization state is required at each location. Such nonuniform space-variant polarization state is useful for polarization coding of data in optical communication, optical computers and neural networks, optical encryption, tight focusing, imaging polarimetry and for particle trapping and acceleration. Here, we demonstrate a novel method for designing, analyzing and realizing computer generated space-variant metal stripe polarization elements. The design method is based on determining the local direction and period of subwavelength metal stripe grating using vectorial optics to obtain any desired continuous polarization change, hence, completely suppressing any diffraction arising from polarization discontinuity. Analysis of the element can then be performed using an original method combining coupled wave analysis (RCWA) and Jones calculus, in which the element is represented as a space-varying Jones matrix, defined by the local period and orientation of the grating.