Fiber tapping

Also the USS Jimmy Carter, a nuclear submarine, was modified to allow tapping undersea communication cables.

A small number[quantify] of alarm systems manufacturers provide a simple way to monitor the optical fiber for physical intrusion.

In the alarmed cable scenario, the sensing mechanism uses optical interferometry in which modally dispersive coherent light traveling through the multi-mode fiber mixes at the fiber's terminus, resulting in a characteristic pattern of light and dark splotches called a speckle pattern.

A fiber-optic sensor works by measuring the time dependence of this speckle pattern and applying digital signal processing to the fast Fourier transform (FFT) of the temporal data.

PDS provides guidance for the protection of SIPRNet wire line and optical fiber to transmit unencrypted classified information.