Fabrication of photonic devices directly written in glass using ultrafast Bessel beams

Optical waveguides have been inscribed in fused silica by focusing femtosecond laser pulses with an axicon. The axicon is a conical lens that allows obtaining an optical beam with a transverse intensity profile that follows a zero-order Bessel function. This profile is invariant along a certain distance (>1 cm). The advantage of using axicon is that the beam is focused along a narrow focal line of a few micron width. Therefore the inscription of waveguides can be done without moving the glass sample. The waveguides so fabricated exhibit low losses and no detectable birefringence due their excellent circular symmetry. By translating the glass sample during the inscription process, we have induced a refractive index change along a thin plane in order to fabricate planar waveguides.