Industry News
Types of fiber End-emitting Fiber
Fiber-optic lighting End-emitting fiber is generally a step-index multimode fiber with a large transparent core that transmits the light and thin transparent cladding that traps the light in the core in an optical process called “total internal reflection.” The core is large in comparison to the thin cladding as that makes it more efficient in coupling light from the illuminator. The cladding does not transmit light, so any light coupled into the cladding will not be transmitted by the fiber.
End-emitting fibers are generally made from plastic as it can be made in larger sizes than glass and is less expensive and easier to install. Plastic optical fiber (POF) is made in sizes from 0.1 to 20 mm in diameter. Glass fibers are generally made in much smaller sizes (hair thin, about 50-150 microns or 0.05 to 0.15 mm) and bundled together to make larger diameter cables.
The choice of core and cladding materials determines the angle of light rays accepted from sources and transmitted by the fiber (called modes), defined by a specification called numerical aperture(NA). The light will exit the fiber in a cone that shows the size of the NA with larger NA having a wider output cone of illumination. Higher NA fibers also couple light from sources more efficiently, as it will capture light at higher angles emitted by the source. Typical fibers have acceptance cones of 30-60 degrees, corresponding to NAs of 0.3-0.6. When optics are used to focus the light emitted from the fiber, the NA of the fiber must be known to choose appropriate optics.
End-emitting fibers transmit light well. Glass fibers are more efficient at transmission because glass is more transparent than plastic, but because of the inefficiencies of packing fibers into bundles, spaces between the fibers in the bundles means much of the illuminator light is not coupled into fiber cores. However, glass fibers may be more tolerant to heat generated by the illuminator, allowing greater illuminator intensity and providing more light from the end of the fiber.
