Hollow Waveguide Arrays as Quarter- and Half-Wave Plates

We present hollow waveguide arrays acting like quarter- and half-wave plates. Approximately 2000 × 2500 individual rectangular hollow waveguides filled with air and surrounded by a gold cladding form the basis of the wave plates. The hollow waveguides fabricated by combining femtosecond 3D direct laser writing with electroplating have sub-micron dimensions of less than 500 nm in the cladding area. Both wave plates show the characteristic properties of quarter- and half-wave plates converting a linear polarized input field into a circular (quarter-wave plate) and a linear 180
$^\circ$
phase shifted polarized output field (half-wave plate). This is confirmed experimentally by measuring the angle-dependent phase shift, the Stokes vectors and polarization ellipses for both wave plates.