Composition of a beam splitter

Beam splitters are composed of optical substrates such as glass or plastic, adhesives or coatings, and sometimes birefringent or metallic layers depending on their type and function.

Cube Beam Splitters

Cube beam splitters are typically made from two right-angle glass prisms that are glued together at their base using adhesives such as polyester, epoxy, or urethane-based resins. Historically, natural adhesives like Canada balsam were used. The adhesive layer is carefully controlled in thickness to achieve a desired reflection/transmission ratio through frustrated total internal reflection for a specific wavelength of light . One prism's hypotenuse surface may be coated with a reflective or partially reflective layer to enhance splitting performance.

Plate Beam Splitters

Plate beam splitters consist of a thin, flat glass plate with a partially reflective coating on the first surface. The second surface often has an anti-reflection coating to minimize unwanted reflections. These are commonly designed for a 45° angle of incidence and can be made from standard optical glass or other transparent substrates . The coatings can be dielectric or metallic, depending on whether the splitter is intended to be polarizing or non-polarizing.

Polarizing Beam Splitters

Polarizing beam splitters are made from birefringent materials such as calcite or specialized thin-film polarizers. They exploit polarization-dependent reflection and transmission to separate light into orthogonal polarization states. These are used in applications requiring precise polarization control, such as laser systems, interferometry, and microscopy .

Dichroic Beam Splitters

Dichroic beam splitters use optical coatings that selectively reflect or transmit light based on wavelength. They are often implemented in prism assemblies or thin-film coatings and are widely used in fluorescence imaging, color cameras, and multi-CCD systems . The coatings are typically dielectric multilayers designed for high spectral selectivity.

Metallic-Coated Beam Splitters

Some beam splitters use a half-silvered mirror design, where a thin layer of metallic coating, often aluminium, is deposited on a glass or plastic substrate using physical vapor deposition. These splitters are partially reflective and partially transmissive, suitable for broadband applications .

Fiber Optic Beam Splitters

In fiber optic networks, beam splitters can be made by fusing two single-mode optical fibers at a point, allowing light to be shared between fibers through evanescent wave coupling. This design is common in passive optical networks (PONs) . In summary, the composition of a beam splitter depends on its type and application, ranging from glass prisms with adhesives, coated plates, birefringent crystals, metallic coatings, to fiber-based fused structures, each tailored to control light splitting, polarization, and wavelength characteristics.