Low Loss 1 × 16/40 Flat Type Beam Splitters on Thin Film Lithium Niobate Using Photolithography Assisted Chemo-Mechanical Etching

Integrated photonic devices based on thin film lithium niobate (TFLN) have attracted great attention due to their excellent performance. In this work, a flat type TFLN 1×N beam splitter is designed by adjusting the widths of tapered waveguides between free propagation region and arrayed waveguides. Two chips with 16 and 40 output ports, respectively, are manufactured with the femtosecond laser photolithography assisted chemo-mechanical etching technology (PLACE). The excess losses are measured ≈1.43 and 1.94 dB, respectively. In theory, the flat-type beam splitter for a single-mode structure can maintain the flat intensity distribution within a 300 nm wavelength range. Experimentally, different types of output intensity distribution such as tilted or M-shaped distributions can be obtained with the multimode structure by varying the position of the lensed fiber when the input light is TM-polarized. This work explores an efficient way for the development of multichannel optical beam splitters.