Propagation characteristics of polychromatic light through polymer optical fibers

Low efficiency and poor color characteristics of fiber optic lighting systems have limited their use to niche applications. Most manufacturers in this industry are working to expand the use of fiber optic lighting systems. To make these systems attractive for general lighting applications, system performance needs to be improved. Poor system efficiency has been mainly attributed to coupling loss at the lamp to fiber interface. Therefore, manufacturers have been working on development of new reflectors to improve system performance. Presently, most commercial illuminators have large numerical aperture (NA=0.5 or greater) reflectors to couple light into the fiber. An experimental study was conducted to investigate the effect of light-coupling geometry, spectral content of the input beam at various angles, and geometry of the large-core plastic (LCP) optical fiber on system performance. The results of this study indicate that system performance can be improved by coupling light into the fibers at low angles. Therefore, developing fiber optic illuminators with low NA reflectors (unlike the current high NA reflectors) and a light source spectrally tuned to compensate for the color shift caused by the optical fibers could significantly enhance fiber optic lighting system performance and make them attractive for a wider range of lighting applications. The destructive nature of this testing method did not allow many different types of fibers to be characterized. The specific fiber properties determined here are for illustrative purposes only and will not apply to other types of plastic optical fibers. However, the overall trend for the results will be the same. In other words, coupling light at high NAs will increase light loss and color shift for all fibers, but their magnitudes will not be the same for all plastic optical fibers.