The beamsplitter cubes are constructed by cemented two matched right angle prisms.  The hypotenuse are coated with partial dielectric coating.

Beamsplitter Cubes have several advantages over  beamsplitters plates,  beamsplitters cubes are easy to mount, and ideal for beam superposition, also have less deformation 

The beamsplitter cubes are recommended for use with collimated or nearly collimated beam. Convergent or divergent beam will contribute spherical aberration.

The absorption loss of partial dielectric coating is negligible.

Reflectance: (Rs+Rp)/2 average

Transmittance: (Ts+Tp)/2 average

Typically R/T: 50/50% tolerance: ±5% @45°