In this century of continuous exponential growth of communications worldwide, traditional electrical interconnection is finding increasingly difficult to respond to the bandwidth pressure, and photonic interconnection will most likely be the future standard.
Planar lightwave circuit (PLC) technology is capable of high-throughput fabrication of low loss waveguides, but is in general limited to its 2D geometry.
On the other hand femtosecond direct writing (FDW) provides a solid tool for the fabrication of optical circuits with great flexibility, exploiting its truly 3D properties, but suffers from higher losses and lower throughput.
By combining with PLC technology, FDW could aid in the bridging of different layers of optical circuits, exponentially decreasing their footprint. We report in this work the fabrication of such optical vias.
The fabrication of vertical waveguides in fused silica, using a IR femtosecond fiber laser, with parameters optimised to induce the previously reported micro-explosions mechanism inside fused silica. By using a
long working distance water immersion objective, we reduced spherical aberrations due to a better phase matching with the glass. A helix path was applied to create a cone of damaged material, leaving a stress-induced central waveguide, with propagation losses lower than 1 dB/mm.
Finally, we analyse the possibility of tilting these waveguides and its effect on their optical properties. This feature adds to the flexibility of this method, that could for example accommodate input/output angles of common coupling strategies used with PLC technologies.