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Unrepeated cables are cheaper than repeated cables and their maximum transmission distance is limited, although this has increased over the years; in 2014 unrepeated cables of up to 380 kilometres (240 mi) in length were in service; however these require unpowered repeaters to be positioned every 100 km. The first long distance AC line was 34 kilometres (21 miles) long, built for the 1884 International Exhibition of Electricity in Turin, Italy. The C Line opened as the Green Line in 1995. It operated mostly in the median of Interstate 105 between Redondo Beach, the LAX area and Norwalk. While power loss can also be reduced by increasing the wire's conductance (by increasing its cross-sectional area), larger conductors are heavier and more expensive. Switching and all-by-sea routing commonly increases the distance and thus the round trip latency by more than 50%. For example, the round trip delay (RTD) or latency of the fastest transatlantic connections is under 60 ms, close to the theoretical optimum for an all-sea route. The US military, for example, uses the submarine cable network for data transfer from conflict zones to command staff in the United States.

A light cable or unprotected core must therefore be regarded at best as an experiment, with the chances against the successful laying, and still more against its existing as a permanent property. Multiple sources and loads can be connected to the transmission system and they must be controlled to provide orderly transfer of power. This capability is important because fiber-optic cable must be laid straight from the stern, which was another factor that copper-cable-laying ships did not have to contend with. This type of cable is basically used for the telephone cables and the resistance can be measured by the number of wires used. C-OTDR (Coherent Optical Time Domain Reflectometry) is used in submarine cables to detect the location of cable faults. 129, 132, 151 C. C. A. 205, L. R. A. 1917C, 907. At the new trial the plaintiff again got a verdict and judgment, but the Circuit Court of Appeals set them aside, this time simply reversing the judgment without ordering a new trial.

DWDM or dense wavelength division mulltiplexing around 2007. Each fiber can carry 30 wavelengths at a time. The type of optical fiber used in unrepeated and very long cables is often PCSF (pure silica core) due to its low loss of 0.172 dB per kilometer when carrying a 1550 nm wavelength laser light. The large chromatic dispersion of PCSF means that its use requires transmission and receiving equipment designed with this in mind; this property can also be used to reduce interference when transmitting multiple channels through a single fiber using wavelength division multiplexing (WDM), which allows for multiple optical carrier channels to be transmitted through a single fiber, each carrying its own information. One reason for this development was that the capacity of cable systems had become so large that it was not possible to completely back up a cable system with satellite capacity, so it became necessary to provide sufficient terrestrial backup capability. Both Nikola Tesla and Hidetsugu Yagi attempted to devise systems for large scale wireless power transmission in the late 1800s and early 1900s, without commercial success.

Launching a pump frequency (pump laser light) at a power of just one watt leads to an increase in reach of 45 km or a 6-fold increase in capacity. Pumping the pre-amplifier with a 980 nm laser leads to a noise of at most 3.5 dB, with a noise of 5 dB usually obtained with a 1480 nm laser. The ROPA contains a doped fiber that uses the pump light (often a 1480 nm laser light) to amplify the data signals carried on the rest of the fibers. The diode is often a high power 980 or 1480 nm laser diode. Another way to increase the reach of a cable is by using unpowered repeaters called remote optical pre-amplifiers (ROPAs); these still make a cable count as unrepeatered since the repeaters do not require electrical power but they do require a pump laser light to be transmitted alongside the data carried by the cable; the pump light and the data are often transmitted in physically separate fibers. Optical post amplifiers, used to increase the strength of the signal generated by the optical transmitter often use a diode-pumped erbium-doped fiber laser.

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