Subwavelength waveguide grating for mode conversion and light coupling in integrated optics.

We propose a new method for mode conversion and coupling between an optical fiber and a sub-micrometer waveguide using a subwavelength grating (SWG) with a period less than the 1st order Bragg period. The coupler principle is based on gradual modification of the waveguide mode effective index by the SWG effect that at the same time frustrates diffraction and minimizes reflection loss. We demonstrate the proposed principle by two-dimensional …