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How to Achieve Optimal Collimation with Fiber Optics

Collimated light is required for many fiber optic applications. Using the proper setup, fiber optic collimating lenses or ball lenses, and some optical know-how, you can achieve optimal collimation. Join Katie Schwertz, Design Engineer, as she defines key terms and provides quick tips for collimating light from fiber optic light guides.

Hi, I am Katie, one of the Opto-Mechanical engineers here at Edmund Optics. Today, I'd like to discuss fiber optics and collimation from a fiber. In many fiber optic applications, customers need collimated light to emerge from their fiber optic cable. As we discussed in our collimation and focal length video, we know that in order to collimate light, we must place the lens at a distance equal to its focal length away from the source. In order for this to work with the fiber optic cable, Edmund Optics offers fiber optic collimator and focuser assemblies. These products attach to standard connectors on the end of our fiber optic cables and position the lens at its focal length away in order to collimate the light. They are designed for specific wavelengths since the focal length of a lens shifts slightly with wavelength. Fibers and fiber optics collimators are also specified by their numerical aperture, which defines the angle of the cone of light accepted by the optic or the fiber. In this equation, n is the index of refraction and theta is the maximum half angle of the light accepted by the component. Typically, this system is in air so n equals 1. Ideally, the numerical aperture of the collimating lens should match with the numerical aperture of the fiber or source. If the numerical aperture of the source is greater than the numerical aperture of the optic, the optic is considered overfilled and not all of the light will be collected by the optic. If the numerical aperture of the source is smaller than the numerical aperture of the optic, the optic is considered underfilled and all the light will be collected, but it will not span over the entire clear aperture of the optic. Let's look at a common setup of a fiber optic illuminator and a light guide. If I move the stage further from the light guide, you can see that the light diverges. By attaching one of our fiber light focusing lenses, the light can be collimated. A common optical component used to couple light from a laser into a fiber optic is a ball lens. Ball lenses are excellent for improving signal coupling between fibers, emitters and detectors. They can focus or collimate light depending upon the geometry of the input source. The choice of ball lens depends on the numerical aperture of the fiber and the source. And our earlier discussion on underfilling and overfilling is applicable to ball lenses as well. For more details on how to choose a proper ball lens, see our Understanding Ball Lenses application note in the technical support section of our website. This is an easy and simple way to achieve the collimated light you need for your application. I hope this video has helped you understand collimation in relation to fiber optics. 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.