Anatomy of a femtosecond laser processed silica waveguide [Invited]

Waveguides are inscribed through densification of the surrounding region of a damage induced channel created by femtosecond irradiation within silica. Single mode propagation at 1.5 μm is obtained below the damage region whilst at shorter wavelengths guidance is only observed away on either side of the region. The quasi-periodic nanostructure that is induced can explain the mode profile elongation observed with polarised light at 45°. The origin of this guidance area is explored using SEM analysis, which reveals nanoporous regions within laser track structure above and below the densified region where 1.5 μm propagates. Shorter wavelength light is not supported in this area.