The cable is for LF, so it doesn't matter what Zk is, that's why is not documented. For high speed communication there are other cables, ethernet, RS485, CAN, Profibus,....there you have the exact specification.
Since the manual says not to use flow control all you likely really need is to find TX, RX, and ground and connect a terminal at 38400,N,8,1 and to disable flow control in your PC terminal program.
The additional pins should not need connection at all, provided that you disable flow control such that your PC is willing to transmit with them unconnected.
There are two "standards".
A) carries pin numbering through (ribbon cable wire #2 goes to D-sub pin 2)
B) carries pin location through (ribbon cable wire #2 goes to D-sub pin 6)
B is more common (in my experience). The B wiring is what you would get if the D-sub were an insulation-...
Why can't simple optical communication systems transmit and receive light of a single wavelength in parallel?
Because it's difficult to isolate the receiver from the transmitter, and the transmitter on the near side will overwhelm the receiver, so it won't be able to see the transmitted light from the far side.
Why doesn't the same problem occur when using ...
Fiber is so cheap it's common to bury lots more than you need and just leave it for the future. Conversely receivers are not cheap, so you don't want to add unnecessary complexity if you don't have to. Since the goal is to send as many bits per second for the lowest cost, you typically just use more fiber, especially for "simple" systems.