Fabrication of buried waveguides in planar silica films using a direct CW laser writing technique

A CW CO2 laser ablation technique is used to form buried waveguides in planar silica films. It is shown that the refractive index of a silica thin film is reduced sufficiently adjacent to the laser processed region to allow the fabrication of low loss waveguides. The refractive index distribution of these structures is measured using the reflectance of a focussed spot from the surface of the films. The change in refractive index is measured to be of the order of the core cladding refractive index difference of typical single mode waveguides. The spatial resolution of the reflectance technique is 1.3 μm with a refractive index resolution of ±5 × 10−4. Devices such as 1 × 2 and 1 × 4 multi-mode interference (MMI) splitters have also been demonstrated and shown to exhibit low transmission losses.