Planar monomode optical couplers based on multimode interference effects

The self-imaging property of a homogeneous multimoded planar optical waveguide has been applied in the design of passive planar monomode optical couplers based on multimode interference (MMI). Based on these designs, 3 dB and cross couplers were fabricated in SiO/sub 2//Al/sub 2/O/sub 3//SiO/sub 2/ channel waveguides on Si substrates. Theoretical predictions and experimental results at 1.52- mu m wavelength are presented which demonstrate that MMI couplers offer high performance: on-chip excess loss better than 0.5 dB, high reproducibility, low polarization dependence and small device size