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The waveguide beamsplitters with diverse configurations in LiNbO 3 crystal have been produced by direct femtosecond laser writing of a family of optical-lattice-like cladding structures. By on demand design of the lattice tracks with "defect" lines, the efficient beam guiding and tailoring have been implemented in the structures. With a family of three-element integration of structures, three-dimensional (3-D) 1 × 3 beamsplitting at the telecommunication wavelength of 1550 nm was realized. Different from the Type I modification of LiNbO 3 waveguides, the guiding cores of the optical-lattice-like cladding waveguide structures we fabricated locate in regions that are surrounded by the laser-induced-tracks. This paper opens the alternative way to construct complex integrated platforms in LiNbO 3 crystal by using femtosecond laser writing.

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We report on the fabrication of the dual-line waveguides and cladding waveguide in z-cut MgO:LiNbO 3 crystal by femtosecond laser inscription. Due to the diverse modification of refractive index along TE/TM polarization induced by femtosecond laser pulses, the two geometries exhibit different guiding performances: the dual-line waveguides only support extraordinary index polarization, whilst the depressed cladding waveguide supports guidance along both extraordinary and ordinary index polarizations. The measured optical damage of these waveguides at the wavelength of 532 nm is higher than that of the previously reported ion-implanted waveguides in Zr-doped LiNbO 3 . The propagation loss of depressed cladding waveguide is measured as low as 0.94 dB/cm at 632.8 nm wavelength. It is found that the optical damage threshold (~10 5 W/cm 2 ) of the dual-line waveguide is one order of magnitude higher than that of the cladding waveguide (~10 4 W/cm 2 ).

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We fabricated a three-dimensional microstructured optical waveguide (MOW) in a single-crystal using femtosecond-laser writing and phosphoric acid etching techniques, and observed excellent midinfrared waveguiding performance with low loss of ∼0.5 dB∕cm. Tracks with a periodic arrangement were written inside the yttrium aluminum garnet (YAG) crystal via femtosecond laser inscription, and then etched by the phosphoric acid (H 3 PO 4 ) to form hollow structures. The evolution of the microstructure of tracks was investigated in detail. The function of the MOW was analyzed by different numerical methods, indicating the proposed MOW can effectively operate in quasi-single-mode pattern in the midinfrared wavelength range, which agrees well with our experiment results.

In this work, we report on the fabrication of deeply embedded optical-lattice-like structures in a Ti:Sapphire crystal by applying femtosecond laser inscription (FLI) to implement two-dimensional (2D) one-to-two and three-dimensional (3D) one-to-four beam splitting. Such a family of photonic microstructures is characterized at near-infrared both experimentally and numerically, showing excellent capability of simultaneous light confinement and beam tailoring at two orthogonal polarizations. The confocal micro-Raman image of the obtained structure reveals that the optical properties of the substrate have been well-preserved in the waveguide's active volumes. Our results pave a way to construct complex integrated waveguide splitters in Ti:Sapphire crystals by using FLI for photonic applications.