Image Number 6 for United States Patent #7194164.
An optical apparatus comprises a planar optical waveguide having at least one set of diffractive elements and confining in at least one transverse spatial dimension optical signals propagating therein. Each diffractive element set routes, between corresponding input and output optical ports, a corresponding diffracted portion of an input optical signal propagating in the waveguide that is successively incident on the diffractive elements and is diffracted by the diffractive element set. The optical signals propagate in the waveguide in corresponding diffractive-region optical transverse modes in regions where the diffractive elements are present, and in corresponding non-diffractive-region optical transverse modes in regions where the diffractive elements are absent. The diffractive element set is adapted so as to yield an operationally acceptable level of either or both of i) optical coupling between corresponding diffractive-region and non-diffractive-region optical transverse modes, and ii) diffraction efficiency of the diffractive element set.