Optical device positioning by using Becke lines

摘要

A new passive-alignment technique using Becke lines is proposed for assembling optical devices. Optical devices with a waveguide structure, such as planar lightwave circuits and laser diodes, have a core or active layer whose refractive index is slightly higher than that of the surrounding area. The Becke lines are diffractive stripes appearing at the boundary between materials having different refractive indices such as cores and the surroundings. For low-loss optical connection between the devices, their cores must be precisely aligned with each other. In our technique, the optical devices are aligned by observing the Becke lines located on both edges of the core, which make it possible to determine the exact core position. With this technique, optical devices can be precisely aligned without using the thin metal-film markers used for conventional passive alignment. The position of an optical waveguide was experimentally aligned by illuminating it with infrared (IR) light, obseving the Becke lines with video system and moving it with motor-driven stages. The positioning uncertainty was less than 0.2 μm, which is the same as the resolution of the video system used. This technique is thus practical for precisely assembling optical devices.