Patent ID: 7113676

Claim:
A planar optical isolator formed within a sub-micron thick surface silicon layer of a silicon-on-insulator (SOI) structure, the planar optical isolator comprising: an input waveguiding region formed, at least in part, within the sub-micron thick surface silicon layer and defined as including an input port for coupling an input single mode optical signal into the input waveguiding region; an output waveguiding region formed, at least in part, within the sub-micron thick surface silicon layer and defined as including an output port for permitting a propagating single mode optical signal to exit the planar optical isolator; and a non-reciprocal, highly directional optical coupling regions disposed between the input and output waveguiding regions from transmitting a forward-directed, transmitted single mode optical signal from the input waveguiding region to the output waveguiding region and dissipating a rearward-directed, reflected optical signal such that only a relatively small portion of the reflected signal is coupled into the input waveguiding regions, thus providing a substantial degree of optical isolation for signals propagating in the reverse direction, wherein the non-reciprocal, highly directional optical coupling region comprises an N-way optical waveguide splitter/combiner including: a plurality of N input waveguiding sections and a single output waveguiding section, with a single one of the N input waveguiding sections coupled to the isolator input waveguiding region, the remaining N−1 input waveguiding sections defined as isolating waveguiding sections, and the output waveguiding section coupled to the isolator output waveguiding region; and a plurality of N−1 optical isolating elements, each optical isolating element disposed along a portion of an associated one of the N−1 isolating waveguiding sections such that a rearward-directed, reflected optical signal is coupled into each one of the plurality of N input waveguiding sections and is dissipated along the plurality of N−1 isolating waveguiding sections by its associated optical isolating element such that only a relatively small portion propagating along the input optical waveguiding region remains, wherein each isolating element comprises an optically radiative element formed within its associated isolating waveguiding region, the optically radiative element comprising a waveguide-based diffraction grating structure wherein the properties of the diffraction grating structure are configured to introduce an adiabatic change in effective index between the isolating waveguiding section and its associated isolating element.