Hollow waveguide array with subwavelength dimensions as a space-variant polarization converter

A hollow waveguide array with subwavelength dimensions is demonstrated as a polarization converter. An individual waveguide in the array has a rectangular cross-section, which leads to an anisotropy of propagation constants and therefore to a phase shift between vertical and horizontal field components upon propagation. The hollow waveguide array was fabricated by a two-photon polymerization process followed by electrochemical deposition of gold. The fabricated array consists of about 2000 x 2500 hollow waveguide cells, each with dimensions of 1150 nm x 930 nm and height of 2 mu m. With these dimensions, the structure can, for example, be used at a wavelength of 1550 nm. Other wavelengths and phase shifts are accessible by changing the dimensions of the cross- section and the height. Since the widths of individual waveguides are variable, space-variant operation can be implemented. (C) 2019 Optical Society of America