Fiber optic light guides are bundles of optical fibers used for the controlled deliver of light. They tend to be more rigid, and transmit well in both the visible and near-infrared (near-IR) regions of the electromagnetic spectrum. Fiber optic light guides are sometimes called fiber optic light pipes (fiber optic lightpipes).
Fiber optic light guides use three basic types of fiber bundles: spot-to-spot, spot-to-line, and fused-end. Spot-to-spot fiber bundles have diameter measurements that are designated as A, B, C, D, and E. Spot-to-line fiber bundles carry diameter measurements that correspond to the letters A through K. For both types of fiber optic light guides, length is an additional consideration. Normally, round ferrules made of stainless steel are used. If a rectangular connector is required, then aluminum is the material of choice.
Fused-end fiber bundles are used in fiber optic light guides for high-power and high-temperature applications. Some products are used in UV curing, spectroscopy, and pyrometry. Others are used with analytical instruments, semiconductors, or sensors. An alternative to liquid light guides, fused-end fiber bundles are not immune to the interstitial voids that are often found in multiple-fiber bundles. By filling these gaps with an epoxy, however, increased bundle transmission can be achieved. Product specifications for fused-end fiber optic light guides include operating wavelength, a measurement which is expressed in nanometers (nm); the active bundle diameter at the common (input) end; and the fiber distribution from the common end to the legs.
Like other fiber optic assemblies, fiber optic light guides are made with different types of optical fibers. Common choices include silica, fluoride, chalcogenide, erbium-doped, and polarization maintaining (PM). Silica fibers are clad with plastic or coated with polymer. They differ in terms of acceptance angle and temperature range. Fluoride fibers are made with fluoride-based glass and are designed to operate in the mid-infrared (mid-IR) range. Chalcogenide fibers are flexible, but do not have the tensile strength of silica fibers. They have both a chalcogenide core and chalcogenide cladding. Erbium-doped fibers provide a large gain and large output power. Fiber optic light guides with polarization maintaining fibers (PMF) are also available. These fiber bundles are used with integrated optics, gyros, sensors, and pigtails because there is little or no cross-coupling of optical power between the polarization modes.