Selecting the Right Beamsplitter

Hi, I’m Katie, one of the Opto-Mechanical engineers here at Edmund Optics. Today I’m going to talk about the different types of beamsplitters we offer and provide you with information that will help you choose what beamsplitter would work best for your application. Beamsplitters are optical components that split light in two directions. For example, they are typically used in interferometers in order for a single beam to interfere with itself. In this setup, you can see laser light passing through a cube beam splitter. Some of the light continues in the direction of the laser, and some of the light is reflected at 90 degrees. We offer several different types of beamsplitters: plate, cube, pellicle and polka dot beamsplitters. A plate beamsplitter is a common type of beamsplitter that is composed of a thin glass substrate with an optical coating optimized for a 45-degree angle of incidence. Advantages of a plate beamsplitter include less chromatic aberration, less absorption due to less glass, and smaller and lighter design compared to a cube beamsplitter. Disadvantages of the plate beamsplitter are the ghost images produced by having light reflect off both surfaces of the glass, lateral displacement of the beam due to thickness of the glass, difficulty to mount without deformation, and their sensitivity to polarized light, which I will discuss later. Cube beamsplitters are essentially composed of two right angle prisms cemented together at the hypotenuse with a partially reflective coating in between. Advantages of the cube include easy mounting, durability of the optical coating since it is between the surfaces, and no ghost images, since reflections propagate back in the direction of the source. Disadvantages of the cube are that it is bulkier and heavier than other types of beamsplitters and doesn’t cover as wide a wavelength range as pellicle or polka dot beamsplitters, though we do offer many different coating options. Also, cube beamsplitters should only be used with collimated beams, since converging and diverging beams contribute to considerable image quality degradation. Pellicle beamsplitters are very thin optical grade film stretched over an aluminum ring and bound in place. They are useful because they have a broad wavelength range of operation, and therefore no chromatic aberration. They have no ghost image, because the front and back surfaces have negligible thickness. They are very lightweight and take up little space in optical systems. The disadvantages of a pellicle beamsplitter are that they are very delicate and easily punctured. Touching the surface will likely ruin the beamsplitter, and great care must be taken when mounting a pellicle to reduce stress and vibration, as these can adversely affect performance. Pellicles are most useful for interferometric applications but can prove to be too costly and delicate for common applications. Polka dot beamsplitters do not split light as typical beamsplitters. Rather, they have a polka dot surface, in which the ‘dots’ are reflective material that cover half the surface, with the other half being transparent. This splits the light much like a conventional beamsplitter does, but has a completely reflective patterned coating, rather than a partially reflective continuous coating as seen in conventional beamsplitters. Advantages of polka dot beamsplitters are that they have a broad wavelength range and their performance is not angle dependent. A disadvantage of polka dot beamsplitters is their lower efficiency, usually around 85%, meaning that about 15% of the light is lost through the system. You may notice that some of our beamsplitters are labeled as ‘polarizing’ or ‘non-polarizing’. Polarizing beamsplitters will reflect S-polarized light and transmit P-polarized light. With non-polarizing beamsplitters, given randomly polarized input light, there will still be some polarization effects, but they depend on the specific type of beamsplitter. For the Edmund Optics TechSpec non-polarizing cube beamsplitters, for example, the difference in reflection and transmission for S and P-pol is less than 6%. If polarization states are not critical for your application, we recommend using non-polarizing beamsplitters I hope this answers your questions about different types of beamsplitters we offer, and which suit your needs. You can browse more of our technical application notes and videos to learn more key concepts and find answers to common questions on our website.