  Reliable and secure communication is an important aspect of modern fiber
optic communication. In this work we consider a multi-mode fiber (MMF) channel
wiretapped by an eavesdropper. We assume the transmitter knows the legitimate
channel, but statistical knowledge of the eavesdropper's channel only. We
propose a transmission scheme with artificial noise (AN) for such a channel. In
particular, we formulate the corresponding optimization problem which aims to
maximize the average secrecy rate and develop an algorithm to solve it. We
apply this algorithm to actual measured MMF channels. As real fiber
measurements show, for a 55 mode MMF we can achieve positive average secrecy
rates with the proper use of AN. Furthermore, the gain compared to standard
precoding and power allocation schemes is illustrated.
