Fig. 1. (a) Schematic description of the beam splitter. The output powers of (b) the left waveguide, (c) the middle waveguide, and (d) the right waveguide as functions of W₁ and W₂ of the splitters, and the incident power is normalized. The triangle, the circle, and the diamond marks in each image correspond to splitters BS₁, BS₂, and BS₃ respectively.

Fig. 2. Schematic description of the beam splitter in the LiNbO₃ crystal. W₁ and W₂ are the distances between the left waveguide and the middle waveguide and between the right waveguide and the middle waveguide, respectively. The inset is the transmission microscopic image of the beam splitter BS₁.

Fig. 3. Raman spectra collected from the non-processed bulk area (black solid line) and the waveguide area (red solid line) excited by a 785 nm laser. Corresponding molecular phonon modes are marked out on every peaks.

Fig. 4. Near-field mode intensity distribution results at 532 nm are exhibited as 2D (bottom) and 3D (top) images. (a), (b), (c), and (d) correspond to splitters BS₁, BS₂, BS₃, and BS₄, respectively. The x-axis is located at the height of the centers of the three sub-waveguides at the output end.

Fig. 5. Normalized power ratios obtained from the coupling results. (a), (b), (c), and (d) correspond to splitters BS₁, BS₂, BS₃, and BS₄, respectively.