Beam splitter and preparation method thereof

The invention relates to a beam splitter which comprises a first double-polished flat sheet and a second double-polished flat sheet which are overlapped and bonded, and the bonding surface of the first double-polished flat sheet, which is used for being bonded with the second double-polished flat sheet, is plated with a light splitting film. The exposed surface of the first double-polished flat sheet is plated with a visible light antireflection film, the exposed surface of the second double-polished flat sheet is plated with a visible light and infrared light dual-band antireflection film, and the light splitting film comprises a first ZnS layer, an Ag layer and a second ZnS layer which are sequentially arranged from the position close to the surface of the first double-polished flat sheet to the position away from the surface of the first double-polished flat sheet. The beam splitter has visible and infrared double-wide-spectrum characteristics, T is larger than 90%@400-700 nm, and R is larger than 90@at 8-