Sensornet ORYX DTS, Руководство пользователя

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Oryx DTS User Manual v4 Page 47
Figure 28 - Principle of DTS operation
Optical Fibre Construction
An optical fibre consists of a cylindrically symmetric strand of glass composed of a
central core which is surrounded by an outer cladding (this is known as bare fibre).
The core & cladding guide light travelling down the fibre. The Oryx DTS system is
optimised to use a 50/125 optical fibre which has a core diameter of 50 microns and
a cladding diameter of 125 microns. The bare fibre is surrounded by the primary
coating. The primary coating allows the optical fibre to be physically handled while
preventing mechanical damage to the central core and cladding. The primary
coating is commonly made from acrylate and has a diameter of 250 microns.
The 50/125 optical fibre used with Oryx DTS system is categorised as Graded
Index Multimode Fibre. The term ‘graded index’ is used to explain the glass core
which is constructed to have a parabolic refractive index gradient which increases
smoothly from a uniform value in the cladding to a maximum value at the centre of
the core. See Figure 29.
The term ‘multimode’ is used to explain the fact that the optical fibre can guide
multiple modes of light along the optical fibre core. This type of fibre gives better
signal levels for DTS systems compared to a “Singlemode” optical fibre which is
commonly used in telecommunications.