2. Fiber optic testing

2.1 Presence detector

In many measuring instruments incorporating an optical fiber, the latter is only used to carry light between the sensor and the point where the light signal is processed.

• The simplest example is the passage detector, which is nothing other than a light curtain with its optical source and photoelectric detector. The application of this detector to the safety of people working near dangerous machinery (or even to counting) seems immediate. It can be integrated into a fiber-optic alarm system: the protected fence, for example, consists of a strip of barbed wire with a longitudinal groove in the center, into which the fiber-optic sensor is inserted. Light-emitting diode transceivers are placed along the fence. Any attempt...