Diffractive Beam Splitters

By  //  August 2, 2023

The purpose of diffractive beam splitters is to split a single input beam to generate multiple output beams from the source beam. Even though the output beams possess different propagation angles, all other characteristics of the new beams remain the same as the input beam.

A diffractive beam splitter is a special type of diffractive optical element (DOE), a family of optical elements that can be used to manipulate laser beams using the wave nature of light.  This article aims to discuss the design and applications of diffractive beam splitters.

The Design of Diffractive Beam Splitters

During the design of diffractive beam splitters, one needs to determine the number of output beams and their desired arrangement in the subsequent array. The dots or the array of output beams can be arranged in a circular shape, in a hexagonal shape, or in a uniform rectangular grid, or any other desired arrangement. Furthermore, the dots need not always be uniform. Instead, there can be pseudo-randomly arranged dots or missing dots in the target pattern as needed. Once the desired output is determined, the discretized phase structure of the DOE is determined using an optimization algorithm for the design of diffractive beam splitters.

The setup where a diffractive beam splitter is used typically involves an inbound parallel monochromatic beam, such as the beam from a laser, that travels through the diffractive beam splitter and is focused by a lens. The array of split beams will be created in angular space and converted into an array of spots with fixed separations. As the separation, efficiency, and all other beam splitter specs are strongly affected by the wavelength of the input beam, diffractive beam splitters are typically used with laser beams, as these are monochromatic. There are other types of beam splitters. However, the major difference between diffractive beam splitters and other types of beam splitters is that diffractive beam splitters help to generate multiple output beams in any arrangement of geometrical shape, while other splitters only split to two beams at 90 deg angle to each other.

The Applications of Diffractive Beam Splitters:

There are numerous applications of diffractive beam splitters. One of the major applications of diffractive beam splitters is found in aesthetic laser treatments or skin resurfacing in the medical field. This process involves the expansion of a laser beam into a spot array through a 2D diffractive beam splitter. They are also useful in monitoring high-power lasers. Laser dicing and laser perforation are some other notable areas where you can find the use of diffractive beam splitters. A diffractive beam splitter is useful for the creation of a couple of additional beams known as beam samplers as well as helping in enabling parallel processing and enhancing a system’s throughput.

In object depth calculation, diffractive beam splitters have significant applications. This process involves an array of beams that structurally sample an object along with an irregular topography. This process is found effective in 3D apparatus vision. LIDAR systems for vehicles is a recent notable application of a diffractive beam splitter and this application is quite similar to the application of object depth calculation. One can design a diffractive beam splitter in this application in a way that it provides a structured light illumination pattern in order to retrieve information regarding distance.

Interestingly, if the diffractive beam splitter is used here to transform a laser beam into multiple beams, we will be able to get more information by sampling a larger volume of space.