Transmission Characteristic Of Fiber Bundle
Fiber bundles need to carry light only a few meters, so they do not have as low attenuation as communication fibers. Typical attenuation of bundled fiber is around 1 dB/m, thousands of times higher than that of communication fibers at 1550 nm.
Likewise, operating wavelengths differ. Visible light is needed for imaging and illumination, and even for other applications the short distances make it unnecessary to operate at wavelengths where fibers are most transparent.
Glass fiber bundles
Glass fiber bundles are typically usable at wavelengths of 400 to 2200 nm, and special types made from glass with good ultraviolet transmission are usable at somewhat shorter wavelengths.
Plastic fibers bundles
Plastic fibers are usable at visible wavelengths, 400 to 700 nm. Some special-purpose bundles are made of other materials, but they are not widely use.
Numerical Apertures of Fiber Bundles
Bundled fibers generally have higher numerical apertures than communication fibers, because light-collection efficiency is critical and pulse dispersion is irrelevant. The relatively large difference between core and cladding index gives bundled fibers typical NAs of 0.35 to 1.0. The same holds true for large-core single fibers used in illumination; larger NAs are better because they boost light collection efficiency.
*Bundled fibers are step-index multimode types with large NA.
*Typical attenuation of bundled fiber is around 1 dB/m.