23-08-2012, 04:11 PM
TEST AND MEASUREMENT
1TEST AND MEASUREMENT.ppt (Size: 2.54 MB / Downloads: 51)
Scattering
Scattering, Primarily Rayleigh scattering, also contributes to attenuation. Scattering causes the light energy to be dispersed in all directions, with some of the light escaping the fiber core. A small portion of this light energy is returned down the core and is termed “backscattering”.
Absorption
Absorption may be defined as the conversion of light energy to heat, and is related to the resonance in the fiber material. There are intrinsic absorption (due to fiber material and molecular resonance) and extrinsic absorption (due to impurities such as OH- ions at around 1240 nm and 1390 nm).
Bending Loss
Bending losses which are caused by light escaping the core due to imperfections at the core/clad boundary (microbending), or the angle of incidence of the light energy at the core/cladding boundary exceeding the Numerical Aperture (internal angle of acceptance) of the fiber due to bending of the fiber (macrobending).
Single mode fibers (for example) may be bent to a radius of 10 cm with no significant losses, however after the minimum bend radius is exceeded, losses increase exponentially with increasing radius. Minimum bend radius is dependent on fiber design and light wavelength.
Principles Of OTDR
An OTDR is a fiber optic tester characterizing fibers and optical Networks
The aim of this instrument is to detect,locate and measure events at any location in the fiber optic link
An OTDR can test a fiber from only one end,that is it operates as a one dimensional Radar System
The OTDR technique produces geographic information with regard to localized loss and reflective events providing a pictorial and permanent record which may be used as a permanent baseline