Patent ID: 7194164
Filing Date: 2007-03-20
Classification: G02B,G03H

Abstract:
1. An optical apparatus, comprising a planar optical waveguide having at least one set of diffractive elements, the planar optical waveguide substantially confining in at least one transverse spatial dimension optical signals propagating therein, wherein: each diffractive element set routes, between corresponding input and output optical ports, a corresponding diffracted portion of an input optical signal propagating in the planar waveguide that is diffracted by the diffractive element set; the input optical signal is successively incident on the diffractive elements; the optical signals propagate in the planar waveguide in corresponding diffractive-region optical transverse modes in regions of the planar waveguide where the diffractive elements are present; the optical signals propagate in the planar waveguide in corresponding non-diffractive-region optical transverse modes in regions of the planar waveguide where the diffractive elements are absent; and the diffractive element set or the planar optical waveguide is adapted so as to yield an operationally acceptable level of (i) optical coupling between corresponding diffractive-region and non-diffractive-region optical transverse modes, or (ii) diffraction efficiency of the diffractive element set, and wherein the adaptation of the diffractive element set or the planar optical waveguide comprises: diffractive elements having sufficiently large transverse extent in the confined dimension so as to substantially suppress optical coupling between diffractive-region optical modes and non-confined optical modes; diffractive elements positioned in the confined dimension so as to spatially overlap the diffracting-region optical mode at or near a spatial maximum of the amplitude thereof; diffractive elements having sufficiently large refractive index and sufficiently large transverse extent in the confined dimension so as to yield diffractive-region optical modes that substantially spatially overlap the diffractive elements; a planar waveguide core in a non-diffracting region of the planar waveguide that is offset in the confined dimension relative to a planar waveguide core in a diffracting region of the planar waveguide; a planar waveguide core in a non-diffracting region of the planar waveguide that differs in transverse extent, in the confined dimension, from a planar waveguide core in a diffracting region of the planar waveguide; a planar waveguide core in the non-diffracting region with a refractive index higher than a refractive index of a planar waveguide core in the diffracting region and lower than a refractive index of the diffractive elements; a transition region of the planar waveguide between the diffracting region and the non-diffracting region wherein a less-than-unity fill factor for the diffractive elements increases from the non-diffracting region toward the diffracting region; a transition region of the planar waveguide between the diffracting region and the non-diffracting region wherein number density of the diffractive elements increases from the non-diffracting region toward the diffracting region; a transition region of the planar waveguide between the diffracting region and the non-diffracting region wherein longitudinal extent of the diffractive elements increases from the non-diffracting region toward the diffracting region; a transition region of the planar waveguide between the diffracting region and the non-diffracting region wherein transverse extent in the confined dimension of the diffractive elements increases from the non-diffracting region toward the diffracting region; or a transition region of the planar waveguide between the diffracting region and the non-diffracting region wherein refractive index of the diffractive elements increases from the non-diffracting region to the diffracting region.