Optimization of photonic waveguide bends for low index contrast material platforms

Compact and low loss waveguide bends are vital for enhancing the integration density of on chip photonic devices. The bend loss becomes extremely critical, particularly for compact bends in low index contrast platforms such as Indium Phosphide. To address this issue, we introduce an elliptical width modulated bend, which exhibits low loss. For example, at 6 micrometers radius bend loss for elliptical width modulated bend is 0.22 decibels per 90 degrees, resulting in about 40 percent and 27 per cent reduction compared to conventional circular bends and circular width modulated bends, respectively with only a 15 per cent increase in footprint providing a better loss area trade off. Additionally, conventional effective index based analytical models do not account for the impact of width modulation. In this work, we develop an enhanced analytical bend loss formulation that incorporates these effects and validates its accuracy through close agreement with full three dimensional Finite Difference Time Domain simulations.