3D photonic devices at telecom wavelengths fabricated by a femtosecond oscillator

Optical waveguide writing with femtosecond laser pulses represents a good alternative to traditional fabrication methods thanks to its simplicity, flexibility and possibility to realize 3D structures. The direct use of a laser oscillator allows a simpler setup, without amplification stages, greater processing speed, up to 1 cm/s, and intrinsically symmetric waveguide cross-sections due to isotropic heat diffusion. In this work we report on the fabrication and optical characterization of waveguides at telecom wavelengths by a stretched-cavity (26 MHz repetition rate) Ti:Sapphire oscillator. The best results have been obtained on Corning 0211 and the previously unexplored Schott IOG10. Operation at 1.55-micron is demonstrated and a comparison between optical properties of the waveguides on the two glasses is made. The refractive index profiles have been measured with two different techniques: the innovative Digital Holography Microscopy (DHM), applied for the first time to optical waveguides, and near-field refractive index profilometry (RNF). The shape of the refractive index profile was found to depend strongly on the glass type. We demonstrate passive photonic devices at 1.55-micron, exploiting the unique 3D capabilities of the technique. These devices include: (i) a 1x2 splitter, obtained by writing two straight waveguides at an angle and separated by a depth displacement; (ii) a 1x4 splitter, realized by combining 1x2 splitters on different planes in the depth; (iii) a WDM coupler, with a good rejection of the 980-nm signal with respect to the 1550-nm one. Perspectives of the technique will also be addressed.