Fiber optic cable moisture monitoring system

Abstract

The invention provides a monitor for monitoring the condition of fibre optic communication cables. The system employs one or more of the optical fibres of a cable to monitor the cable structure for damage or kinks. By using two separate laser sources and simultaneously monitoring the optical losses at two distinct and separate wavelengths, the loss signature of the monitored fibre is determined, analyzed and related to the mechanical condition of the cable structure. To monitor splice points for moisture, a special optical splice sensor unit detects any penetration of water into the splice and transmits a coded alarm signal over the monitored fibre to the optical receiver. Every splice location is assigned a unique sensor code. The optical splice sensor is driven by moisture detection cell, which forms a single cell water activated battery. Water entering the monitored splice closure wets the tape, which activates the cell. The cell generates sufficient voltage and current to power timing, code generation and modulator circuits in the sensor unit for an extended period of time. The activated circuit drives a modulator which modulates the light travelling down the fibre. The modulated light is monitored at the equipment office and the address of the alarming sensor decoded.