Today I saw a cool device in a data centers that needs no electricity

I saw a cool device today. One of my customers manages data centers and they have a new data center and need to connect it to their old ones, so they've bought/rented some "dark fiber" between their data centers and have fiber multiplexers at each end so that lots of fiber-optical devices at each end can all talk to one another over this single dark fiber. (Or something like that – I don't know too much about networking equipment!)

So basically this multiplexer looks like any other switch thing, a long horizontal device with a bunch of identical ports on the back, each with a number etc, and one "master" port which connects to the dark fiber. (only the optical sockets look slightly different from e.g. RJ45 sockets..)

But then i noticed, this device only had the identical data ports/master port on the back. I couldn't find a power socket, I looked at all of its sides, and was confused for a while. Until i worked out the reason why I couldn't see the power socket – the device was purely optical and didn't need power!

Imagine that, data center, a bunch of hard-core networking and computing equipment, the last thing one expects is devices that don't need power!