Up to the late 90's @ a regen shelter you needed to WDMdemux-Regen-OPAmp-WDMmux. Late 90's Nortel came out with MOR (Multiple Wavelength Optical Repeater) cards. Which replaced the WDMs and wavelength specific transmit regen cards but still used OPAmps. The OPAmps of the day had a theoretical range of 90 miles (at least Pirelli and Siemens did). Depending on the condition and quality of the OSP fiber you also need DSMs (Dispersion Compensation Modules). Latter Siemens and Ciena systems today do Regen and Amplify all in one. You must regen. Just amplifying degrades the signal too much. You are also referring to subsea cable. Which is a totally different doped glass compared to the stuff used on land.