Structured Wiring > Optical fiber
Fiber optics are strands of glass or polymeric materials, made in order to conduct the light. They are normally available in the form of cables. They are flexible, immune to electrical noise and the weather more extreme and not very sensitive to temperature changes. They have a diameter of 125 micrometers (about the size of a hair) and weigh very little: a single fiber it weighs about 60 g / km, including the sheath that covers.
Each individual Optical fiber consists of two concentric layers of extremely pure transparent material, a cylindrical central core, or core, and a coat or
cladding around it.
The core has a very small diameter of about 10 m for single mode and 50m for Multi-modal, while the cladding has a diameter of about 125 µm.
The two layers are made of materials with refractive index slightly different, the cladding should have a lower index of refraction (typically holds 1,475) than the core (that is approximately 1.5).
As an additional feature the mantle (Buffer) should have a thickness greater than the length of the wave damping evanescent, characteristic of the transmitted light so as to capture the light that is not reflected in the core.
Within a fiber optic signal can propagate in a straight line, or reflected a very high number of times. The method of rectilinear propagation is said of order zero. Single mode fibers allow the propagation of light in a way only have a core diameter of between 8 m 10 m, the multi-modal allow the propagation of more ways, and have a core diameter of 50 m or 62.5 m. The cladding typically has a diameter of 125 µm.
The multi mode fiber allows the use of more economic, but suffer the problem of inter-modal dispersion, whereby different modes propagate at slightly different speed, and this limits the maximum distance at which the signal can be received correctly.
Single mode fibers of control have a much higher price than the multi-modal, but can cover distances and reach significantly higher speed.
Multimodal fibers can be further divided in step index fibers and graded index
• In step index fiber, the index of refraction is constant throughout the section of the core and change unexpectedly when you encounter the cladding
• In graded index, fiber the index of refraction changes gradually from the core to the cladding, allowing the use of light multi chromatic.
The main benefits of fiber compared to copper cables in telecommunications are:
• low attenuation, which allows transmission over long distance without repeaters;
• large capacity to carry information;
• immunity to electromagnetic interference, including nuclear electromagnetic pulse (may be damaged by alpha and beta waves);
• High electrical resistance, and then can use fiber equipment near high-potential, or between different potential sites;
• Weight and small footprint;
• Contained in low-power signals;
• Absence of crosstalk;
• Excellent resistance to adverse weather conditions;
• Low values of BER.
A fiber optic cable, because it contains more fiber, more usually very small and light of a wire or coaxial cable with similar capacity of the channel. More easy to handle and install.
The fiber optic cable for secure communications as it is very difficult to intercept and as easy to track.
The cables are normally installed within structured cabling installations found to panels permutation. A link therefore the use of two cables in allowance
(from each device connected to the panel permutation), and then of 4 connectors.
Commercially available equipment arrives speed transmission of 40 Gbit / s. Using WDM technology can be transmitted over a single fiber pair up to some hundreds of thousands of channels in frequency, reaching a maximum capacity of the order of Tbit / s.
Electrical civil and industrial systems, burglar alarms, sat and earth TV, CAD drawings and schemes, PLC And automation programming
