An optical apparatus comprises an optical interconnect structure defining one or more optical source and receiver ports and one or more interconnect optical signal pathways connecting corresponding optical signal source and receiver ports. The optical interconnect structure comprises an optical waveguide defining a portion of each interconnect optical signal pathway. Each interconnect pathway includes a wavefront diffractive transformation region and a corresponding set of diffractive elements thereof. Each diffractive element set diffractively transforms a corresponding diffracted portion of an incident signal with a corresponding design input signal wavefront into an emergent signal with a corresponding design output signal wavefront. For at least one diffractive element set, only one of the corresponding design input or output signal wavefronts is confined in at least one transverse dimension by the optical waveguide, while the other design wavefront propagates without confinement by the optical waveguide.