Microspectroscopy of ultrafast laser inscribed channel waveguides in Yb: tungstate crystals

We report microspectroscopy measurements of crystalline channel waveguides fabricated in Yb:KGd (WO₄)₂ and Yb:KY (WO ₄)₂ using the ultrafast laser inscription technique. From these measurements we find that densification of the WO₂ W bridge in the double tungstate crystal lattice is responsible for the refractive index increase, which creates the waveguide confinement. We identified that shifts toward lower energies in the ~760 cm^-1 Raman mode indicate regions, which guide light polarized along the crystallographic b axis, while higher energy shifts in the 682 and 898 cm^-1 Raman lines correspond to guiding regions for light polarized along the crystallographic a axis. © 2011 American Institute of Physics.