Abstract

Multimode (MM) or singlemode (SM) fibers for short haul have been discussed for decades.^1–3 Cables with both fiber types have been installed, with the possibility to start using multimode and then upgrade to singlemode fiber when needed. In this paper we propose, for the first time to our knowledge, a combined multimode and single-mode fiber (MM-SM-fiber) for telecommunication and FTTH applications (Swedish patent application filed 2001-07-12, No. 0102509-7). We have superposed a singlemode core concentrically on a multimode core index profile, obtaining a fiber with the advantages of both fibers. When the fiber is connected to multimode fibers at both ends, it works as a multimode fiber. When it is connected to singlemode fibers at both ends, this fiber has the same high bandwidth as a standard singlemode fiber. Upgrading or downgrading is very simple and cheap, as the only things to be changed are the connecting fibers. Furthermore, this fiber can be used for duplex communication, e.g., the SM-core downstream and the MM-core upstream.

© 2002 Optical Society of America