Beamsplitting

Beam splitting is the process of dividing an incident optical beam into two or more beams by a beam splitter. A common beam splitter is designed to transmit part of the light and reflect part, with a specified splitting ratio (for example, 50:50). The device is passive and often wavelength-specific, meaning its performance depends on the light’s wavelength and the geometry of the interface.

Common types include plate beam splitters, which use coatings on a single substrate, and cube beam splitters, which join two right-angle prisms at an optical interface to form a compact, sealed unit. Polarizing beam splitters separate light by polarization, typically transmitting one polarization while reflecting the orthogonal one. Non-polarizing beam splitters aim to minimize polarization dependence. Tunable beam splitters use interferometric arrangements, such as Mach-Zehnder configurations or directional couplers, to adjust the splitting ratio.

Principles: A beam splitter works by partial reflection and transmission at an interface, with coatings engineered to achieve a desired ratio over a target wavelength range. In coherent systems, the reflected and transmitted fields can interfere, affecting the resulting phase and amplitude. Polarization, wavelength, and angle of incidence influence performance, as do losses and coating quality.

Applications: Interferometers such as Michelson and Mach-Zehnder rely on beam splitters to split and recombine light for precise measurements. In communications and photonics, they route signals within networks and on integrated chips. In quantum optics, beam splitters are fundamental components for experiments that demonstrate interference and enable certain quantum information protocols.

Considerations: Practical performance is limited by losses, polarization sensitivity, wavelength dependence, and alignment tolerances. In fiber optics, beam splitters are implemented as fiber couplers or directional couplers; in integrated photonics, they appear as multimode interference devices or directional couplers.