Engineering lattice matching, doping level, and optical properties of KY(WO₄)₂:Gd, Lu, Yb layers for a cladding-side-pumped channel waveguide laser

Aravazhi, S., Geskus, D., Van Dalfsen, K., Vázquez-Córdova, S.A., Grivas, C., Griebner, U., García-Blanco, S.M. and Pollnau, M. (2013) Engineering lattice matching, doping level, and optical properties of KY(WO₄)₂:Gd, Lu, Yb layers for a cladding-side-pumped channel waveguide laser. Applied Physics B: Lasers and Optics, 111 (3), 433-446. (doi:10.1007/s00340-013-5353-1).

Abstract

Single-crystalline KY_1-x-y-z Gd_xLu_yYb_z(WO₄)₂ layers are grown onto undoped KY(WO₄)₂ substrates by liquid-phase epitaxy. The purpose of co-doping the KY(WO₄)₂ layer with suitable fractions of Gd³⁺ and Lu³⁺ is to achieve lattice-matched layers that allow us to engineer a high refractive-index contrast between waveguiding layer and substrate for obtaining tight optical mode confinement and simultaneously accommodate a large range of Yb³⁺ doping concentrations by replacing Lu³⁺ ions of similar ionic radius for a variety of optical amplifier or laser applications. Crack-free layers, up to a maximum lattice mismatch of ~0.08 %, are grown with systematic variations of Y³⁺, Gd³⁺, Lu³⁺, and Yb³⁺ concentrations, their refractive indices are measured at several wavelengths, and Sellmeier dispersion curves are derived. The influence of co-doping on the spectroscopy of Yb³⁺ is investigated. As evidenced by the experimental results, the lattice constants, refractive indices, and transition cross-sections of Yb³⁺ in these co-doped layers can be approximated with good accuracy by weighted averages of data from the pure compounds. The obtained information is exploited to fabricate a twofold refractive-index-engineered sample consisting of a highly Yb³⁺-doped tapered channel waveguide embedded in a passive planar waveguide, and a cladding-side-pumped channel waveguide laser is demonstrated.

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