Beam splitter divides a beam of light into two or more separate beams. It's commonly used in various optical systems, such as microscopes, interferometers, and imaging devices. Beam splitters can be made from different materials and are often coated with thin layers of metal or dielectric materials to achieve the desired splitting effect. Two popular forms of beam splitter are cube and plate. A cube beam splitter consists of two right-angle prisms cemented together at their hypotenuses. The cemented surface is coated to reflect a portion of the light while allowing the rest to pass through. Plate beam splitters are flat glass plates with a partially reflective coating on one side. They are simpler and cheaper than cube beam splitters but can introduce ghosting due to reflections from the second surface.
Beam splitting ratio is an important parameter for beam splitters, which refers to the proportion of light that a beam splitter reflects and transmits. It's typically expressed as a percentage or a ratio, such as 50:50, 70:30, etc. The figure below presents a beam splitter which reflects 30% of the light and transmits 70%. This type is used when there's a need for uneven distribution of light, such as in certain imaging or illumination systems.
A major influencing factor of the beam splitting ratio is coating, since such ratio is primarily determined by the coating applied to the beam splitter. The material and thickness of the coating control how much light is reflected and transmitted. As shown in the figure above, the coating is usually at the entry surface of the plate shape beam splitter.
In Zemax OpticStudio, a plate form beam splitter is usually modeled with a “Rectangular Volume” in Non-sequential mode.
Propagation of both paths can be added with customized numbers in two configurations, i.e., a material for transmission and a mirror. Operator of NGLS, which presents the material type for non-sequential objects in the NSC Editor, is used to classify the two configurations.
The transmission ratios of both paths can be identified using coating with customized transmittance. Here we define the ratio of reflection path as 0.5%. The COATING.DAT should be added an item COAT I.005 as below:
Then the I.005 option can be added from property list
The transmittance of the beam splitter is defined as 99.5%, as below:
From Merit Function Editor, two configurations can be conveniently traced simultaneously and conveniently. Configuration 1 represents transmission path, the irradiance is 0.868 W, out of predefined 1 W. Configuration 2 represents transmission path, the irradiance is 4.161E-3 W, out of predefined 1 W also. The ratio of irradiance at both paths is divided by DIVI to a result of 208.7.
The incoherence irradiance at both detectors defined at transmission path and reflection path are presented below. The detector viewer offers a direct sense of visualization at both paths.
In summary, beam splitter with customized splitting ratio can be identified with coating setting in Zemax, and merit function can trace the irradiance of output irradiance of both paths.