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

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 Deltan = 4.5 x 10(-3) was retrieved from a near-field mode pattern. (C) 2001 Optical Society of America OCIS codes: 220.4000, 320.7130, 320.7160, 230.7370.