Synthesis of sub-wavelength diffractive optical elements by 3D full-vectorial beam propagation method

The design method for nonperiodic sub-wavelength grating structure diffractive optical elements (DOEs) to be fabricated by direct-writing electron beam lithography in the polymer layer is described. The design is based on the application of 3D full-vectorial beam propagation method which is faster than the finite difference time domain method (FDTD) usually used for simulation of sub-wavelength vectorial DOEs. It were designed DOEs with one, two and four focal spots (focusing beam splitters) having 25 mum DOE width, 50 mum focal length, 0.1 mum width of pixels, grating profile with four levels of grey and total height of 1.29 mum for operation at the 0.6328 mum wavelength.