Channel waveguide fabrication in KY(WO4)2 combining liquid-phase-epitaxy and beam-multiplexed femtosecond laser writing

Abstract In the present work we propose a 2D-channel waveguide fabrication process based on the microstructuration of the cladding of a planar waveguide by femtosecond laser writing. The core of the waveguide is formed by a layer of KY 1− x − y Gd x Lu y (WO 4 ) 2 epitaxially grown over a KY(WO 4 ) 2 substrate by means of Liquid Phase Epitaxy (LPE). A cladding of KY(WO 4 ) 2 is then grown by LPE over the core waveguide. To obtain lateral light confinement, the cladding is then micromachined using a multiplexed femtosecond laser writing beam, forming a ridge structure. Channel waveguides fabricated following this approach have been characterized in terms of their mode sizes and propagation losses at 0.98 μm and 1.64 μm, which are close to the wavelengths of interest in lasers/amplifiers based on the Er 3+ /Yb 3+ system. Experimental data are compared with simulation analysis based on the Effective Index Method and the Beam Propagation Method, showing a good accordance between experimental and numerical results.