This section introduces aspects that may help facilitate a better understanding of the disclosed invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Today's fiber-optic optical transmission systems are either based on single-polarization or polarization-division multiplexed single-transverse-mode transmission, or on multi-mode transmission where all modes essentially carry the same data. Both such systems are vulnerable to tapping, which is done by bending the transmission fiber such that a small amount of light is coupled out at a local bend. The tapped light is then detected by a sensitive receiver at the location of the fiber bend, giving an eavesdropper access to the full wavelength-division multiplexed (WDM) spectrum transmitted over the fiber. The small amount of extra loss is not easily detectable at the rightful receiver located at the end of the transmission fiber, which permits the eavesdropper to go unnoticed.
A method of detecting the presence of an eavesdropper in a single-mode fiber system is furnished in U.S. Patent Application Publication No. 2008/001888, by D. Butler et al, published Jan. 24, 2008, and entitled “Intrusion Detection in Optical Fiber Networks,” which application is incorporated herein by reference in its entirety, and wherein transmission is done at several optical wavelengths, and a change in the differential loss between these wavelength is used as an indicator for the presence of an eavesdropper.