FIBER OPTIC GLOSSARY
Physical Characteristics
BDF: Minimum point of entry where fiber (from Telco) is delivered to a building/facility.
Bend Radius: 2 guidelines offered:
During installation: loaded, since the cable is experiencing tensile load; typical measure 20 x O.D.
Long term: no load, typical measure 10x O.D.
NOTE: If you bend the cable too much attenuation occurs.
Buffer: is applied directly over core and cladding for strength. Most fibers are buffered to 250 microns before going to cabling.
Central Member: an anti-bucking element in the cable for mechanical stability; can be steel, fiberglass or glass reinforced plastic
Cladding: applied directly over the core to maintain the integrity of the core. Cladding is of a different index of refraction than the core. The cladding for single-mode 8 micron, multi-mode 50micron and multi-mode 62.5 micron is generally 125 micron. The cladding for multi-mode 100-micron is 140 micron. The numbers are represented like this:50/125, 62.5/125, 100/140.
Core: the transmission medium where the light travels.
Typical sizes are:
8 micron--single mode
50 micron--multi-mode
62.5 micron--multi-mode
100 micron--multi mode
Dielectric: non-metallic, therefore non-conductive
IDF: Junction point along Fiber backbone within a building/campus where 'local' networks can attach to LAN/WAN.
Loose tube cable: fibers are "buffered up" to 250microns only, then are fitted into an oversize tube with gel compound for both moisture and mechanical protection. Most, but not all, outdoor fiber optic cable is Loose Tube.
Micron (µ): 1 millionth of a meter, the basic measure of the fiber's physical size
Tight buffer cable: fibers are "buffered up" to 900microns, then cabled with the addition of Kevlar(r) strength members. Light weight, easy to handle and terminate.
Transmission Characteristics
Attenuation: loss of signal strength experienced at specific wavelength., measured in dB (decibels) per Kilometer at a specified wavelength(nm). Lower is better. Attenuation at a splice is ideally targeted to be a small fraction of a dB.
Broadband: transmission facilities capable of handling a wide range of frequencies simultaneously, permitting multiple channels. Fiber is inherently broadband.
Decibel (dB): a measure of the strength of the light signal , used to indicate relative performance of different glass sizes and types over standard Kilometer distance. 3.0 dB/Km @ 850 nm represents the ratio of light input to light output through a multi-mode fiber. In single-mode fibers, the input to output ratio would be typically less than 1dB/Km at 1300 nm and 1550 nm.
Loss Budget: the tolerable difference between the light impulse where it originates and the light impulse where it arrives at the receiving end. If too much light power has been lost along the way through deficiencies in the cable or connectors, the signal cannot be read and interpreted. Both cable and connector suppliers are accountable for identifying maximum loss.
Megahertz (MHz): bandwidth, frequency. In multi-mode fiber (not a feature of single-mode fiber), typical operating bandwidths are:
50 micron fiber--200-600 MHz
62.5 micron fiber--100-600 MHz
100 micron fiber--100-500 MHz
Multi-mode: used where broad-band information carrying capacity is required, typically data systems (i.e. Networks/LANS).
NOTE(s): Max Transmission distance 1.2 miles (up to 2 km)
Used to connect between internal points on the network (IDF).
Multi-mode fiber usually has an orange jacket.
Nanometer (nm): a billionth of a meter, used to measure wavelength. Typical operating wavelengths for multi-mode fiber are 850-1300nm; for single-mode fiber 1300-1550 nm.
Single-mode: used where clear transmission over long distances is the critical requirement; typically telephone long distances or local exchange areas such as outdoor, inter-exchange, and switch to switch (i.e. TELCOS).
NOTE(s): Max Transmission distance 18.6 miles (up to 30 km)
Used to bring the circuit into the customer site (BDF).
Single-mode fiber usually has a yellow jacket.
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