Design of a binary chirped grating for near-field operation

An exact, analytic model for binary chirped gratings is presented together with a rigorous solution applicable in the electromagnetic regime. The solution employs a multiple scattering matrix formulation and boundary value problem techniques to determine the scattering coefficients of the diffracted fields in the fast polarization case, which in turn leads to an iterative algorithm for wavefront shaping and grating parameter design. Numerical examples on the design of a binary grating lens operating in the near field are presented with computer simulations. These show that under oblique plane wave illumination more than 90% of the diffracted power can be focused into a narrow beam of one wavelength of beamwidth over the image plane, which is located only 12 wavelengths away from the grating plane.