, Volume 84, Issue 3, pp 257-260

Influence of focusing depth on the microfabrication of waveguides inside silica glass by femtosecond laser direct writing

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Abstract

We studied the influence of focusing depth on the index change threshold and damage threshold of silica glass irradiated by a focused 120 fs laser beam. Both thresholds increased with the focusing depth. The aspect ratio of the waveguide cross section can be selected by changing the focusing depth. A 5 mm long waveguide was written at the depth of 2100 μm, which was single mode at 632.8 nm and exhibited propagation loss of 0.56 dB/cm. The refractive index change was calculated to be ∼2.47×10-3. The influence of the focusing depth should be considered in multi-layer devices as shown in the fabrication of a 3×3 waveguide array.

PACS

42.62.-b; 42.82.Et; 81.05.Kf