Femtosecond-laser-written three-dimensional waveguide beam splitters in MgO-doped stoichiometric LiTaO₃ crystal

We report on the design and fabrication of three-dimensional (3D) waveguide beam splitters in MgO-doped stoichiometric lithium tantalate (MgSLT) crystals, using femtosecond laser direct writing. A family of compact photonic-lattice-like cladding waveguides are implemented for 3D beam transformation: by introducing axial defect-tracks at certain positions, 1 × 2, 1 × 3, and 1 × 4 beam splitters have been successfully fabricated, enabling nearly equalized splitting ratios. The micro-modification of laser irradiation has been investigated through confocal micro-Raman (μ-Raman) spatial mapping experiments. The bulk crystalline properties are well-preserved in the guiding cores. This work provides an effective method for fabricating highly compact 3D devices enabling light guiding and beam steering via femtosecond laser irradiation.