Experimental study of femtosecond laser written waveguide in Yb³⁺:phosphate glass and waveguide laser

Femtosecond laser with repetition rate of 1 kHz, central wavelength of 800 nm and pulse width of 120 fs is used to write waveguides in Yb³⁺:phosphate glass, then near-field modes of waveguide written by different laser parameters are measured. The refractive index changes in the written region and mode field diameter as functions of writing parameters (scanning speed and writing pulse energy) are obtained, which show the writing window of waveguide formation in Yb³⁺:phosphate glass. The fluorescence spectra of the waveguide and the bulk material are tested and compared. Experimental results show that there is no difference in the fluorescence spectra of the waveguide and the bulk material with 20× objective lens, scanning speed of 20 μm/s and pulse energy of 1.8 μJ, the mode field diameter is 20 μm injected at 976 nm, the refractive index change is 2.7×10^-4, and the fluorescence properities keep the same after femtoscecond laser effect. Stable and continuous wave (CW) Yb³⁺:doped waveguide laser is achieved in a Fabry-Perot cavity configuration by using dichronic mirror and 2% output coupler. An output with power of 2.9 mW at a central wavelength of 1031 nm is obtained.