Integrated diffractive optical mode converter for fiber-to-waveguide coupling

An integrated diffractive optical mode converter, which can be integrated into planar lightwave circuits (PLCs), consisting of a diffractive optical element (DOE) and a slab waveguide is presented for fiber-to-waveguide coupling. The DOE is designed using iterative phase retrieval algorithm. In the iterative algorithm, we introduce a new modification of far-field amplitude constraint to provide very high mode conversion quality. Compared with previously published mode converters, the scheme is more universal because it is applicable for any waveguide structure. In simulation, coupling losses lower than 0.12 dB have been reached for all the discussed waveguides. The converter is shown to be polarization-insensitive and applicable in multi-wavelength PLCs. And the tolerance on axis misalignment has been investigated.