can move tens of terabits per second overseas. Speeds improved rapidly in the previous few years, with 40 Gbit/s having been offered on that route only three years earlier in August 2009. 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. While in theory, a great circle route (GCP) between London and New York City is only , this requires several land masses (Ireland, Newfoundland, Prince Edward Island and the isthmus connecting New Brunswick to Nova Scotia) to be traversed, as well as the extremely tidal Bay of Fundy and a land route along Massachusetts' north shore from Gloucester to Boston and through fairly built up areas to Manhattan itself. In theory, using this partial land route could result in round trip times below 40 ms (which is the speed of light minimum time), and not counting switching. Along routes with less land in the way, round trip times can approach speed of light minimums in the long term. 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. WDM is limited by the optical bandwidth of the amplifiers used to transmit data through the cable and by the spacing between the frequencies of the optical carriers; however this minimum spacing is also limited, with the minimum spacing often being 50 GHz (0.4 nm). The use of WDM can reduce the maximum length of the cable although this can be overcome by designing equipment with this in mind. 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. The diode is often a high power 980 or 1480 nm laser diode. This setup allows