A few corrections
>>"One of the best ways to cut down networks’ power consumption is to get rid of the power-hungry electronics that does most of the heavy lifting."
It's not quite as simple as that. Service speeds tend to be a lot lower than backbone data rates (especially as DWDM moves towards coherent super-channels). So you *can* build all-optical networks, and they may appear to have a lower CapEx and power consumption, but they will be inefficiently filled unless you can do electronic grooming of services in the core network. There are several mathematical studies of this if anyone's interested.
>>"Optical communications is based on the 1530 nm wavelength band – the entire ITU frequency grid for DWDM systems (G.694.1) fits between 1530 nm and 1625 nm – a tiny amount of the near infrared (the vertical red line on the graph above)."
No. Let me see if I can rewrite this to keep it both accurate and concise.
Optical communications is based on a range of near infrared wavebands, including the C-Band (1530-1565nm), and the L-Band (1565-1625nm) - both of which are used for DWDM long haul optical transmission. Other wavebands (O, E, S Bands) are used, along with the C and L bands, in Coarse WDM transmission.
>>We don’t use visible wavelengths, because the ubiquitous Erbium-doped optical amplifier, cheap and everywhere, works at the 1530 nm band.
We don't use visible light because the attenuation of silica-based fibers at those wavelengths is way too high - whether you have workable amplifiers or not. Multimode, lower data rate LAN systems make use of red LEDs, but only for very short reach applications.
You are correct that EDFAs work best in the C-Band - in fact they "define" the C-Band. EDFAs can also be made to operate in the L-Band (but they are different EDFAs). Because of the energy levels in the Erbium atom, EDFAs do not work in the O, E and S Bands.
Semiconductor Optical Amplifiers (SOAs) work in all of these bands, but there is a long-held perception that SOAs are not suitable for WDM operation. EDFAs are defintely better - but the fact is that optical attenuation outside of the C and L Bands are generally too high for high data rate, long haul transmission.