Compact 1 x 3 waveguide beam splitters with variable splitting ratios in LiNbO3 crystal fabricated by femtosecond laser direct writing

In this Letter, waveguide beam splitters (1 x 3) with type I modifications are fabricated in a LiNbO3 crystal by femtosecond laser direct writing. The influence of the relative positions of three sub-waveguides on power splitting ratios are investigated in detail and the corresponding output intensities as functions of the relative positions in the numerical simulation are plotted, which are in good accordance with the experimental results. In addition, the waveguide beam splitter with a 1:1:1 splitting ratio is fabricated by changing the relative widths of the three branch-waveguides. Guiding performances at 532 nm are measured and analyzed by a typical end-face coupling system. The simulation and experimental results demonstrate that the beam splitting ratio of the waveguide splitter can be precisely regulated by the positions and widths of the sub-waveguides.