Abstract
The wafer fusion technique for realization of compact waveguide switches, filters and 3D photonic integrated circuits is investigated theoretically and experimentally. Calculations based on the beam propagation method show that very short vertical directional couplers with 40-220 μm coupling lengths and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface was investigated by comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region. This reveals an excess loss of 1.1 dB/cm at 1.55 μm wavelength due to the fused interface. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 μm gap layer exhibit a coupling length of 62 μm and a switching voltage of about 12 volts. Since GaAs and InP have different material dispersion at 1.55 μm wavelength, a combination of InP and GaAs couplers is used to demonstrate an inherent polarization independent and narrowband filter.
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