  The optical fiber network has become a worldwide infrastructure. In addition
to the basic functions in telecommunication, its sensing ability has attracted
more and more attention. In this paper, we discuss the risk of household fiber
being used for eavesdropping and demonstrate its performance in the lab. Using
a 3-meter tail fiber in front of the household optical modem, voices of normal
human speech can be eavesdropped by a laser interferometer and recovered 1.1 km
away. The detection distance limit and system noise are analyzed
quantitatively. We also give some practical ways to prevent eavesdropping
through household fiber.
