Curved Yb:YAG waveguide lasers, fabricated by femtosecond laser inscription

Abstract

Straight and s-curve Yb(7%):YAG waveguides have been fabricated with the femtosecond laser writing technique. By employing a novel writing scheme an increase of the refractive index change could be achieved in comparison to waveguides written with the standard procedure. Straight waveguides, fabricated with this scheme, enabled highly efficient Ti:sapphire laser pumped waveguide lasers with slope efficiencies of 79% and output powers of more than 1 W. With slope efficiencies from 50% to 60% for the curved waveguide lasers with radii of curvature of R ≥ 20 mm the possibility of fs-laser written complex optical devices is demonstrated.

Crystalline Waveguide Lasers in the Visible and Near-Infrared Spectral Range

“…Considering the microscopy results this is an additional hint for a larger refractive index change Δn achievable with scheme B waveguides, since a larger Δn results in a stronger confinement. This is confirmed by a rough estimation of Δn from the numerical aperture (NA) of the waveguides [26], [55]. The refractive index difference is in the order a few times 10 −4 and for the scheme B waveguides twice as large as for scheme A waveguides.…”

“…For radii of curvatures larger or equal to 20 mm high slope efficiencies of more than 50% were demonstrated. Also nearly 900 mW output power were achieved with these devices at an incident pump of 1.6 W [26]. An exemplary input-output curve for an S-curved waveguide laser with a radius of 20 mm is displayed in Fig.…”

“…1(b) with a sine oscillation in x-direction so that a larger volume is modified (scheme B in Fig. 1(b) [26].…”

“…This effect is supported by a larger refractive index change due to stronger stress at the inner part of the outer curve and results in the shift and deformation. The multimode behavior of the S-curved waveguides can be explained by the mode mismatch between the straight and curved part of these devices [26].…”

Laser oscillation in Yb:YAG waveguide beam-splitters with variable splitting ratio

“…Furthermore, by employing a section within the beam-splitting structure allowing for multi-mode interference (MMI), we could realize a variable splitting ratio of the two arms. In addition, some improvements of straight waveguide lasers are presented.The waveguide fabrication scheme, including the writing parameters, is the same as in [16]. There s-curved waveguide lasers were fabricated in Yb(7%):YAG with a combination of scheme B and C as defined in this reference.…”