Small V-bend silica waveguide using an elliptic mirror for miniaturization of planar lightwave circuits

A small v-bend optical waveguide using an elliptic mirror to miniaturize planar lightwave circuits has been proposed and fabricated. The v-bend waveguide is composed of a succession of single-mode curved waveguides, straight waveguides, a slab waveguide, and an elliptic Ag mirror. The design of the v-bend structure has been optimized to reduce the bending area. For example, the area of the 180° v-bend structure with a refractive index difference of 0.75% is approximately 0.25 mm × 1.1 mm, much smaller than that of a curved waveguide (10 mm × 5 mm). The detailed structure has been designed, with fabrication tolerances being investigated using a finite difference time domain (FDTD) method and a beam propagation method (BPM). The v-bend waveguides were fabricated with the usual silica waveguide processes: Ag metal was deposited on the etched surface using sputtering, electron beam deposition, or silver mirror reaction. The average total, polarization-dependent, and wavelength-dependent loss are about 1.9, 0.01, and 0.1 dB, respectively, in the wavelength range 1540-1600 nm. The origins of the v-bend waveguide loss have been studied and are attributed to the mirror position misalignment, the mirror facet tilt, the mirror surface roughness, and the mirror absorption.