Beam Splitters: Characteristics and Applications

Beam splitters are one type of diffractive optical element that can split a laser beam into multiple output beams. Even though a beam splitter generates multiple output beams from a single beam, the characteristics of these beams do not change—only the angle of propagation and power change in the output beams.

Beam splitters can be of different types; each beam splitter type has unique characteristics and creates a unique output. Here, we will discuss three common types of beam splitters and their characteristics.

Beam Splitters and Their Characteristics

• One of the most important beam splitters is the plate beam splitter. This beam splitter generates two different output beams from a single input beam, called the reflected beam and the transmitted beam. The direction and angle of propagation of the output beams depend on the input beam’s angle of incidence. Usually, the two output beams propagate perpendicularly to each other. In this beam-splitting, the divergence and beam size remain the same as those of the input beam.
• Microlens array is another beam splitter with a long list of industrial and medical applications. This beam splitter involves a setup of a series of small lenses or lenslets. Each lens of the lenslets array has an identical radius of curvature and size. Microlens array generates multiple output beams from a single input beam. After emerging from the lenses, the output beams converge at the focal plane.  However, the bam do not have the same characteristics as the input beam , due to the clipping by the lenslet apertures.
• The most useful and versatile beam splitters are diffractive beam splitters. While plate beam splitters and microlens arrays work based on the principle of refraction, diffractive beam splitters use the diffractive principle to exploit the input beam’s wave nature. Diffractive beam splitters can generate an geometrical patterns of split beams, all with equal separations. Therefore, depending on the application area, these beam splitters can be customized for a specific beam pattern that best suits the application. By customizing the diffractive beam splitters, we can also achieve the desired spatial separation and angular orientation for the output beams.

Applications

As diffractive beam splitters are one of the most versatile types of beam splitters, they have numerous applications in the industrial, medical, and academic fields. In aesthetic skin treatments, multi-spot diffractive beam splitters have useful applications. The multi-spot diffractive beam splitters generate an array of output beams from a single input beam and when the output beams converge at the focal plane, they create an irradiance pattern covering a larger skin area than possible with a single spot. We can also find applications of diffractive beam splitters in laser dicing, laser scribing, 3D sensors, and fibre optics. Some notable applications of microlens arrays are laser microscopy, imaging, and 3D sensing, whereas plate beam splitters are useful for fibre optics.