Femtosecond-Laser Microstructuring of Ribs on Active (Yb,Nb):RTP/RTP Planar Waveguides

We have produced rib waveguides by femtosecond-laser structuring of active (Yb,Nb):RbTiOPO
₄
/RbTiOPO
₄
epitaxial layers. The ribs were produced by the approximation scanning technique combined with beam multiplexing. The so-obtained waveguides are trapezoidal in shape and show propagation losses with an upper bound of ~4 dB/cm. A simulation of the rib waveguides with real geometry parameters reveals high levels of light confinement at 632 and 972 nm. The near-field patterns of the fundamental modes have been obtained by exciting the waveguides at wavelengths of 632 and 972 nm. Micro-Raman spectroscopy study reveals that the damage to the crystalline structure in the rib boundaries, showing no amorphization traces, is around 3 μm in length and depth, which is significantly shorter than the total width of the ribs.