The Guide to Beam Splitters for Optical Applications

Beam splitters are the unsung heroes of the optics world. These optical components divide incident light into two distinct beams: one reflected and one transmitted. This precise ability to direct light paths makes beam splitters essential in various applications, including imaging systems, laser systems, and telecommunications. Choosing the right beam splitter is crucial, as each type offers unique properties and capabilities.

Types of Beam Splitters

Plate Beam Splitters

Sturdy and reliable, plate beam splitters are a popular choice for small labs or lower-budget projects. Plate beam splitters are flat optical components that reflect and transmit incident light, with a 45-degree angle of incidence. These plates are typically made of high-quality glass coated with a thin, anti-reflective film. The coating helps to minimize issues with annoying back reflections, such as ghosting, which can degrade the quality of the image or signal being transmitted.

Cube Beam Splitters

If plate beam splitters are the dependable workhorses, cube beam splitters are the versatile, cutting-edge innovators, offering greater flexibility and precision for advanced applications. Like other beam splitters, cube beam splitters also segment light into two distinct beams. Much like the name suggests, these components are shaped like a cube, often with a clear, prismatic coloring. The cube is formed by assembling two, right-angle prisms together. One of the prisms has a specific coating applied to its hypotenuse, where the prisms meet. This allows the incident light to converge, with portions of light reflecting from the cube.

Key Properties Affecting Light Reflection and Transmission

Polarizing vs Non-Polarizing

When incoming, unpolarized light reaches the beam splitter, it splits into two divergent paths. Some of the light reflects off the surface, while the rest passes through. This division of light is called the reflection-to-transmission (R/T) ratio.

Think of polarizing beam splitters as traffic guards– as cars approach the guard, they will be directed in one of two directions, with small sedans directed straight and bulky trucks and SUVs directed to turn. In this scenario, the cars are equivalent to incident light, and the size of the car equals the light’s polarization. When the light reaches the polarizing beam splitter, it’s segmented into divergent polarizations, reflecting S-polarized beams and transmitting P-polarized beams. Polarized beam splitters typically use a 50:50 R/T ratio; However, their most important quality is the ability to segment each linear polarization in two different directions. This is especially useful for optical isolation or in polarization-sensitive applications.

In contrast, non-polarizing beam splitters separate light based on a predetermined R/T ratio, regardless of the incident light’s polarization. To refer back to the traffic guard scenario, imagine non-polarizing beam splitters as guards who direct cars based solely on maintaining a balanced flow, disregarding the size of the vehicles. This means that the S-polarized and P-polarized beams are reflected and transmitted, together, at a specific ratio. Applications that require maintained polarization or an even distribution of light can benefit from non-polarized beam splitters.

Dichroic Beam Splitters

If polarization is similar to directing traffic, dichroic beam splitters are like sorting laundry, with lights and darks going in separate baskets. In this analogy, the clothing’s color is equivalent to the light’s wavelength. A similar concept to polarization, dichroic beam splitters divide incoming light based on wavelength. Long-pass dichroic beam splitters are designed to transmit longer wavelengths of light and reflect shorter wavelengths, while short-pass dichroic beam splitters do the opposite. While this type of beam splitter is less common, it can be useful for fluorescent applications, such as microscopy.

Choosing the Right Beam Splitter for Precise Applications

Factors to Consider

At Blue Ridge Optics, we know that choosing the right beam splitter can make or break your project. Many companies require specific components tailored to their precise needs, making it difficult to find the right solution. Here are some key factors to consider when choosing a beam splitter for your project.

Angle of Incidence

The point where incoming light first encounters a beam splitter is called the point of incidence. Drawing a line at this point, perpendicular to the incident line, and measuring the distance between the two lines allows you to determine the angle of incidence (AOI). The AOI impacts the amount of light being reflected and transmitted. For example, most plate beam splitters have an AOI of 45 degrees, which may limit those who need more flexibility. Cube beam splitters are more versatile, often with 0-degree AOI.

Light Source

Not all beam splitters are capable of handling the full range of light wavelengths. For example, a beam splitter designed for visible light may not perform well with infrared or ultraviolet light. The coherence, polarization, and stability of the light source can also affect how the light interacts with the beam splitter. Matching the beam splitter’s specifications to the characteristics of the light source ensures optimal performance. This minimizes light losses and aberrations while maintaining the integrity of the split beams for precise applications.

Polarization

Plate and cube beam splitters can be polarized or non-polarized. If a beam splitter is polarization-sensitive, it will split light into S-polarized and P-polarized beams. This feature can be useful for optical isolation but may not be suitable for projects that require an even distribution of light. Neglecting polarization effects can lead to unwanted losses, reduced accuracy, and inconsistent results. Therefore, understanding and accounting for the polarization of your light source is crucial for meeting the specific requirements of your application.

Side-by-Side Comparison of Cube and Plate Beam Splitters

For more precise applications, Blue Ridge Optics designs custom components to meet the necessary specifications for your project.

Have questions? Contact us! Our team is available right now to chat throught through your next project and find the right solution to meet your needs.