Capacity In September 2012, NTT Japan demonstrated a single fiber cable that was able to transfer 1
petabit per second () over a distance of 50 kilometers. Although larger cables are available, the highest strand-count single-mode fiber cable commonly manufactured is the 864-count, consisting of 36 ribbons each containing 24 strands of fiber. These high fiber count cables are used in
data centers, In some cases, only a small fraction of the fibers in a cable may actually be in use. Companies can lease or sell the unused fiber to other providers who are looking for service in or through an area. Depending on specific local regulations, companies may overbuild their networks for the specific purpose of having a large network of
dark fiber for sale, reducing the overall need for trenching and municipal permitting. Alternatively, they may deliberately under-invest to prevent their rivals from profiting from their investment.
Reliability and quality Optical fibers are very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions. There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigue, and zero-stress aging. Telcordia GR-20,
Generic Requirements for Optical Fiber and Optical Fiber Cable, contains reliability and quality criteria to protect optical fiber in all operating conditions. The criteria concentrate on conditions in an outside plant (OSP) environment. For the indoor plant, similar criteria are in Telcordia GR-409,
Generic Requirements for Indoor Fiber Optic Cable.
Propagation speed and delay Optical cables transfer data at the
speed of light in glass. This is the speed of light in vacuum divided by the
refractive index of the glass used, typically around 180,000 to , resulting in 5.0 to 5.5 microseconds of latency per km. Thus, the round-trip delay time for 1000 km is around 11 milliseconds.
Losses Signal loss in optical fiber is measured in
decibels (dB). A loss of 3 dB across a link means the light at the far end is only half the intensity of the light that was sent into the fiber. A 6 dB loss means only one quarter of the light made it through the fiber. Once too much light has been lost, the signal is too weak to recover and the link becomes unreliable and eventually ceases to function entirely. The exact point at which this happens depends on the transmitter power and the sensitivity of the receiver. Typical modern multimode graded-index fibers have 3 dB per
kilometre of attenuation (signal loss) at a wavelength of
850 nm, and at 1300 nm. Single-mode loses at 1310 nm and at 1550 nm. Very high quality single-mode fiber intended for long-distance applications is specified at a loss of at 1550 nm.
Plastic optical fiber (POF) loses much more: 1 dB/m at 650 nm. POF is large core (about 1 mm) fiber suitable only for short, low-speed networks such as
TOSLINK optical audio or for use within cars. Each connection between cables adds about 0.6 dB of average loss, and each joint (splice) adds about 0.1 dB. Many fiber optic cable connections have a
loss budget, which is the maximum amount of loss that is allowed. Invisible infrared light (750 nm and larger) is used in commercial glass fiber communications because it has lower attenuation in such materials than visible light. However, the glass fibers will transmit visible light somewhat, which is convenient for simple testing of the fibers without requiring expensive equipment. Splices can be inspected visually and adjusted for minimal light leakage at the joint, which maximizes light transmission between the ends of the fibers being joined. The charts
Understanding wavelengths in fiber optics and
Optical power loss (attenuation) in fiber illustrate the relationship of visible light to the infrared frequencies used, and show the absorption water bands between 850, 1300 and 1550 nm.
Environmental considerations Fiber-optic cabling is significantly more efficient than copper which means that less energy is consumed compared to traditional copper cable infrastructures. This contributes to greater environmental sustainability both for the transmission itself and also by reducing cooling demands in data centers and network hubs.
Safety The infrared light used in telecommunications cannot be seen, so there is a potential
laser safety hazard to technicians. The eye's natural defense against sudden exposure to bright light is the
blink reflex, which is not triggered by infrared sources. In some cases the power levels are high enough to damage eyes, particularly when lenses or microscopes are used to inspect fibers that are emitting invisible infrared light. Inspection microscopes with optical safety filters are available to guard against this. More recently, indirect viewing aids are used, which can comprise a camera mounted within a handheld device, which has an opening for the connectorized fiber and a USB output for connection to a display device such as a laptop. This makes the activity of looking for damage or dirt on the connector face much safer. Small glass fragments can also be a problem if they get under someone's skin, so care is needed to ensure that fragments produced when
cleaving fiber are properly collected and disposed of appropriately. ==Cable types==