Input waveguide grating couplers designed for a desired wavelength and polarization response

Input grating couplers are used to couple light from free space into a waveguide and can provide additional functions such as focusing and beam splitting of the light into arbitrary desired positions in the waveguide. We show that it is possible to design the couplers so that they perform different desired functions depending on the polarization or wavelength of the incident light. We demonstrate experimentally a number of couplers that may be of interest, e.g., in optical fiber communications. Examples are polarization-independent couplers, designed to have the same response for two orthogonal polarizations of the incident light, and couplers for demultiplexing in wavelength division multiplexing applications, designed to separate and focus different input wavelengths to different positions in the waveguide.