Birefringence control and dimension monitoring of silica-based ridge waveguides using Bragg gratings and ultraviolet irradiation

Abstract

A simple numerical method is developed to analyze how the intrinsic birefringence of silica-based ridge waveguides changes with waveguide dimensions and UV irradiation. Identical Bragg gratings were induced on waveguides with different widths which varied from 5 µm×6 µm to 9 µm×6 µm with ArF excimer irradiation and a phase mask. The variation of the waveguide effective index and birefringence as a function of the waveguide dimensions and UV processing are observed and quantified by monitoring the shifts in Bragg wavelength with UV irradiation. With UV irradiation, zero birefringence was easily realized in the waveguides, having an initial birefringence of <2.5×10–4. The mechanism for controlling the waveguide birefringence with UV irradiation is verified both in the theoretical analysis and experimentally. Additionally, the ±0.1-nm variation in Bragg wavelength for waveguides with the same nominal width corresponds to a ±0.1-µm dimensional change in the actual waveguides geometry. This result is used as a way for improving quality control over the waveguide dimensions obtained from the photolithographic and RIE processes.