What is a Beam Splitter?
A beam splitter is an optical component that splits an incoming light beam into two parts: one part is transmitted through the beam splitter, and the other part is reflected. This split is achieved by placing the beam splitter at an angle to the incoming light, effectively redirecting the reflected beam.
Beam Splitting with Coherent and Incoherent Light
Beam splitters can process both coherent light (such as lasers) and incoherent light (such as normal ambient light). They can also work in both directions, allowing two beams from different directions to be combined into a single output.
Key Points for Selecting a Beam Splitter
Beam splitters are important optical devices that can separate light into transmitted and reflected components, and they play a vital role in everything from scientific research to consumer electronics. Their function is differentiated by whether or not they use coherent light, and they can also split light based on intensity, wavelength, or polarization. Therefore, when choosing a beam splitter, we must consider the requirements of reflection transmittance, wavelength range, and polarization. Manufacturers such as Mok Optics offer a variety of standard and custom beam splitters to meet specific needs.
Beamsplitting methods
By intensity:
This is accomplished by applying a thin dielectric or metallic coating to a transparent material (usually glass).
The thickness of the coating determines the R/T ratio, which varies depending on the application needs (common ratios include 50:50, 30:70, or 40:60).
By wavelength:
Using dichroic mirrors, light is reflected or transmitted depending on wavelength.
Hot mirrors divert infrared (IR) light away from the sensor, while cold mirrors reflect visible light.
By polarization:
Unpolarized light is separated into two different polarizations: S polarization (reflected) and P polarization (transmitted).
Non-polarizing beam splitters maintain the original polarization of the incident light.
Considerations for selecting a beam splitter
Functionality and form factor: Different beam splitters have various functions and come in many forms.
R/T ratio: Choose the appropriate reflection-transmission ratio for your specific application.
Wavelength range: Select a beam splitter that operates in the wavelength range relevant to your application.
Polarization requirements: Determine if you need polarization preserving or splitting.
Beamsplitter Form Factors
Plate beamsplitter:
Flat optical mirror with coating on the front side.
Usually mounted at 45° to the incident beam.
Limitations: May cause slight shift of transmitted light and produce faint “ghost” reflections.
Cube beamsplitter:
Made up of two right angle prisms with hypotenuse surfaces bonded together.
Reflects a portion of incident light at 90° while transmitting the rest.
Advantages: No shift of transmitted light, requires perpendicular incident light.
Polarizing beamsplitter:
Usually made with dielectric thin film coatings, usually bonded cubes.
Recommended for applications with wider bandwidths.
Nonpolarizing beamsplitter:
Achieved with a combination of dielectric thin film and metal coatings.
Great for single band applications, but may lose some energy due to metal absorption.
Dichroic mirror:
Usually made as a plate; wider transition bands but less steep when made in a cube format.
Other types:
Transmission grating and dot configurations similar to plate beamsplitters.
Applications of Beam Splitters
Interferometry: Used to measure distances via interference patterns, such as in Michelson interferometers.
Fluorescence Spectroscopy: Dichroic beam splitters filter by wavelength, directing only the emitted fluorescence to the detector.
Camera-Based Imaging Systems: Plate-type beam splitters are often used for coaxial illumination.
Thermal Radiation Protection: Cold mirrors protect sensors from harmful thermal radiation.
Illumination Systems: Dichroic filters reduce red light content to enhance blue illumination.
Choosing the Right Beam Splitter
Application: Determine if your goal is to split or combine beams or filter light by wavelength.
Light Source: Consider the light source type; for high-power lasers, plate beam splitters are often preferred due to lower heat generation.
Packaging: Consider any space constraints; cube beam splitters may be better suited for compact applications.
Mok Optics offers a range of beam splitters, including plate, dichroic (hot and cold mirrors), and transmission grating types. We also design custom beam splitters for specific needs to meet specific application requirements. Please contact us to discuss your specific requirements.