Numerical analysis of the whispering gallery regime in open waveguide micro-bends

We analyse the transition from single mode waveguiding through to the whispering gallery regime in open waveguide micro-bends. 2D FDTD simulations reveal a critical sensitivity of bend loss and waveguiding properties to waveguide width. Vectorial mode-solver analysis identifies a regime of significant and deleterious mode mixing, even for structures operating within the whispering gallery caustic radius. Careful choice in dimensions can however lead to highly fabrication tolerant microbends with a loss variation of order ±0.01dB for a waveguide variation of ±100 nm.