Influence of focusing depth on the microfabrication of waveguides inside silica glass by femtosecond laser direct writing
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- Liu, D., Li, Y., An, R. et al. Appl. Phys. A (2006) 84: 257. doi:10.1007/s00339-006-3610-4
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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.