LennonNZ:Its these. You need a Pair... (Send/Receive on Different Frequencies)
https://www.aliexpress.com/i/32908828315.html
Simplex Media Convertor. (Use a single SC<->SC terminated Single Mode Fibre )
Jeeze, I was hoping it was a bit less crappy than that, the consideration I provided for getting the fibre was more than those things cost :-).