Low-loss curved waveguides in polymers written with a femtosecond laser.

We present straight and s-curve waveguides in polymers fabricated by femtosecond laser writing. A number of parallel tracks are written inside the bulk material with a well-defined gap in the middle that forms the waveguide core. This approach offers the flexibility to tailor the mode-field diameter of the waveguide by adjusting the size of the gap. The waveguides exhibit very low propagation losses of 0.3 dB/cm and no significant bend losses for curve radii of R ≥ 20 mm. This fabrication process will allow for the realization of complex waveguide networks in a compact footprint chip.