Femtosecond Laser Writing of Optical-Lattice-Like Cladding Structures for Three-Dimensional Waveguide Beam Splitters in LiNbO 3 Crystal

The waveguide beam splitters 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) $1 \times 3$ beam splitting 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.