Small bend structures using trenches filled with low-refractive index material for miniaturizing silica planar lightwave circuits

We have proposed the fabrication of small bend structures using trenches along both sides of the core, filled with low-refractive index material, in order to miniaturise silica planar lightwave circuits. The minimum bending radius of a silica waveguide was reduced from 2 mm to 200 μm by filling the trenches with low-refractive index material. The local lateral relative refractive index difference (Δ) was increased to 8.64%. We fabricated cascade S-shaped waveguides to estimate a bend loss of the proposed structure. Moreover, we applied those structures to arrayed-waveguide gratings (AWG)s. Both 8-channel, 100-GHz channel-spacing and 8-channel, 12.5-GHz channel-spacing AWGs were successfully fabricated. Compared with conventional AWGs, sizes of these devices were reduced by factors of about 2 and 4, respectively.