Beamsplittere

Beamsplittere are optical devices designed to divide an incoming beam of light into two or more separate beams. They are used in a wide range of experiments and technologies, including interferometry, imaging, and quantum optics, where splitting or routing light is required.

Common implementations include plate beamsplitters and cube beamsplitters. A plate beamsplitter consists of a glass plate coated with a thin partially reflective layer that splits the light at the coated surface. A cube beamsplitter is formed by two right-angle prisms cemented together with a partial reflector on the diagonal surface, producing transmitted and reflected outputs with a fixed orientation. Variants include polarizing beamsplitters, which separate light by polarization, and non-polarizing beamsplitters, which aim for a similar splitting ratio over a range of polarizations. Dichroic (wavelength-selective) beamsplitters separate light by wavelength.

Key properties of beamsplitters include the splitting ratio (such as 50/50), wavelength dependence, polarization sensitivity, and the phase relationship between the output beams. Reflected light often undergoes a phase shift relative to transmitted light, and the exact behavior depends on the coatings and geometry. Real-world performance is affected by losses, back-reflections, coating quality, damage thresholds, and alignment.

Applications span many areas: interferometers (Michelson, Mach–Zehnder), optical coherence tomography, quantum optics experiments (e.g., beam splitting for detectors and interference), laser power monitoring, and fiber-optic or integrated photonics systems.