A Mode-Filtering Scheme for Improvement of the Bandwidth-Distance Product in Multimode Fiber Systems

In this paper, we investigate a scheme in which the bandwidth-distance product of a multimode fiber is extended, so that it can nearly support the transmission rate of singlemode systems. Some pioneering work suggest that limited mode launch may improve the system performance by reducing the modal dispersion and increasing the system bandwidth. The scheme investigated in this paper is based on selective launching of lower order modes into the fiber at the transmitting end and on filtering out at the receiver the fraction of the energy that was coupled into the higher order modes throughout the propagation in the multimode fiber. We investigate here the power penalty and the dispersion performance of the scheme. In particular, we show that the scheme carries about 6.5-dB penalty and we demonstrate doubling of the bandwidth x distance value. Moreover, the effect of splices on the scheme performance is also presented. We envision that the scheme may be used for upgrading the existing multimode systems without the need to rewire these installations. For example, the scheme can be used to replace the FDDI installations with future high-speed networks, when transmission rates increase from megabits per second to gigabits per second.