US Patent 10302870 Optical coupling device for a photonic circuit

A coupling device including, integrated in or on a substrate, a waveguide capable of guiding a light beam centered on a central wavelength λ0 and an optical coupler. The waveguide and the optical coupler extend in two superposed stages of the coupling device. The optical coupler is composed of at least one index gradient structure. The average optical index in the index gradient structure varies monotonously, decreasing with increasing distance from the waveguide, the average optical index being an average value of the optical index in a cubic volume with a side dimension equal to: