Fabrication and analysis of a directional coupler written in glass by nanojoule femtosecond laser pulses

Abstract

A directional coupler written in a glass sample by the focused 400-nm output from a 25-fs oscillator is reported. The coupler is single mode; the splitting ratio is 1.9 dB at 633 nm. A refractive-index profile of the waveguide with a magnitude of $\mathrm{\Delta }n=4.5\times {10}^{-3}$ was retrieved from a near-field mode pattern.