Laser range finder with fibre=optic propagation time component - couples two glass fibres to photodiode, one being in closed ring form or bounded at both sides by reflectors

摘要

The laser distance measuring equipment (DME) operates according to the propagation time measurement principle and mainly consists of a transmitter source emitting a short duration pulse, a receiver sensing part of the radiation reflected from a target and a fibre-optics reference path. The radiation component propagated at least once over the reference path is, indirectly or directly, decoupled in advance out of the transmission cone by means of the fibre-optics reference path provided by at least two glass-fibres (5,6) functionally coupled together via an optical coupling element (7). The latter is pref. a symmetrical directional coupler, which emits light in one direction only, and couples 2% of the radiation which arrives (at c) and emerges (at b) for example. If the distance or time resolution is less than the laser pulse-length, two directional couplers are needed. ADVANTAGE - Accurate measurement of measurement pulse transit time without extra cost.