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Direct writing of optical waveguides in fused silica by the fundamental beam of an Yb:KGW femtosecond laser

We report the fabrication of an optical waveguide with a propagation loss below 1 dB/cm in fused silica using the fundamental beam of an Yb:KGW femtosecond laser. By selecting the pulse energy and pulse duration, we obtained a propagation loss comparable with that of a waveguide made using a Ti:Sapphire laser. We demonstrate that the nano-wrinkles and nano-pores, which dominate the losses, are not formed in the modified silica if the pulse energy is below 0.80 μJ and the pulses are shorter than 300 fs.