Analysis of the effects of mode coupling on the bandwidth characteristics of step-index plastic optical fiber

The mode coupling of SI-POF is analyzed by observing the far-field radiation patterns. The results show that no obvious mode coupling occurs at a transmission distance of 5 m. While a transmission distance of 10–30 m occurs, strong mode coupling and the equilibrium mode distribution is established after 30 m. In order to clarify the mode-coupling effect on the bandwidth of step-index plastic optical fiber (SI-POF), the bandwidths of SI-POF samples were measured under different launch conditions and compared with theoretical values that neglect mode coupling. It is found that although mode coupling contributes to enhancing the bandwidth of the fiber as it averages out the total propagation delays, the energy transfer between the neighboring modes will excite high-order modes during the propagation, which functions to increase the effective numerical aperture (NA) of the incident light and will decrease the bandwidth of the fiber. The net effect of mode coupling on the bandwidths of SI-POFs at different launch conditions indicates the competition between the two effects. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 432–435, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21372