Wafer-fused optoelectronics for switching

Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 mu m 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 is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 mu m wavelength. Fused straight vertical directional couplers have been fabricated and characterized, 'Waveguides separated by 0.6 mu m gap layer exhibit a coupling length of 62 mu m and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed.