Air trench waveguide bend for high density optical integration

Air trench structure for reduced-size bends in low ( n=0.01-0.1) and medium ( n=0.1-0.3) index contrast waveguides is proposed. Local high index contrast at bends is achieved by introducing air trenches. An air trench bend consists of cladding tapers to avoid junction loss, providing adiabatic mode shaping between low and high index contrast regions. Drastic reduction in effective bend radius is achieved. We present FDTD simulations of bends in representative silica index contrasts, fabrication scheme and waveguide loss measurement results using Fabry-Perot loss measurement technique. We employed CMOS compatible processes to realize air trench bends and T-splitters to achieve low production cost and high yield. A simple, compact waveguide and T-splitter are fabricated and evaluated. The loss measurement results show that losses are consistent with theoretical simulations. By using air trench waveguides, other applications such as BioMEMS (e.g. Evanescent-field sensor) or EDWA can be realized.