In-volume waveguides by fs-laser direct writing in rare-earth-doped Fluoride glass and Phosphate glass

D. Esser, D. Wortmann, J. Gottmann
Proc. SPIE Vol. 7205, p. 720510

FCPA µJewel D-1000

Refractive index modifications are fabricated in the volume of rare-earth-doped glass materials namely Er- and Pr-doped ZBLAN (a flouride glass consisting of ZrF4, BaF2, LaF3, AlF3, NaF), and Er-doped nano-crystalline glass ceramic and Yb- and Er-doped Phosphate glass IOG. Femotosecond laser radation (τ = 500 fs, λ = 1045 nm, f = 0.1 – 5 MHz) from an Yb-fiber laser is focused with a microscope objective in the volume of the glass materials and scanned below the surface with different scan velocities and pulse energies. Non-linear absorption processes like multi-photon- and avalanche absorption lead to localized density changes and the formation of color centers. The refractive index change is localized to the focal volume of the laser radiation and therefore, a precise control of the modified volume is possible. The width of the written structures is analyzed by transmission light microscopy and additionally with the quantitative phase microscopy (QPm) software to determine the refractive index distribution perpendicular to the waveguide. Structures larger than 50 µm in width are generated at high repetition rates due to heat accummulation effects. In addition, the fabricated waveguides are investigated by far-field measurements of the guided light to determine their numerical apertures. Using interference microscopy the refractive index distribution of waveguide cross-sections in phosphate glass IOG is determined. Several regions with an alternating refractive index change are observed whose size depend on the applied pulse energies and scan velocities.

View Full Paper