Waveguide fabrication with an ultrafast laser system and the mechanism of index modification have been investigated in Corning Gorilla glass. Type I waveguides were obtained when the pulse duration was in the range of  250 fs to 15 ps. With the increase of pulse energy, single-mode waveguides converted to ring-mode waveguides. The variation tendency of Raman peak at 580cm580cm？1 band is nonmonotonic with the increase of pulse energy, and the negative index change appears finally in the waveguide core. The alkali ions migrated towards the outside with different diffusivities after the laser irradiation. Finally, bend waveguides and hexagon-link waveguide connectors were produced. 

Experimental setup of the femtosecond laser waveguide writing arrangement indicating the irradiation geometry and the orientation of the microscopic observation. 

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