Basic Study of Coupling on Three-Dimensional Crossing of Si Photonic Wire Waveguide for Optical Interconnection on Inter or Inner Chip

For speeding up of transmission and energy saving on inter or inner chips of semiconductors, hydrogenated amorphous silicon (a-Si:H), unlike conventional crystal Si (c-Si), promises optical multilevel wiring on a Si IC. For three-dimensional (3D) crossing of Si/a-Si:H photonic wire waveguides, the loss and crosstalk as S-parameters of the two propagation modes are evaluated by numerical analysis at the C-band when the waveguide core is 200 ×400 nm2. Whether the crosstalk can be suppressed to -50 dB or less is to be a criterion. Even at the crossing angle of 30°, when the distance between the waveguides of the crossing is 1 µm or less, the crosstalk is suppressed sufficiently, while the radiation loss is also small if a TE-like mode propagates. These quantitative results are derived for the first time and show that the photonic 3D crossing can rival the present electric multilevel wiring from the viewpoint of device height. An important index for the 3D waveguide crossing fabrication is obtained.