Not good at all.You are looking at getting a normal phone line and transporting it via fiber.
The device used on the router side will need to be a FXO device and the one used on the remote side needs to be a FXS device.
If you have many lines like that nad expenses are not a trouble, the best bet will be two channel banks and a fiber to t1 converter.
The cahnnel banks do the conversion from phone line to T1 or E1 format and the T1 or E! to fiber converter will do the second conversion to be able to send over fiber.
Not easy, lot of settings and a cost on the thousand of dollars.
If you are on the US ,you could give the guys on “back Box corporation” a call.
They may have some kind of converter to extend a single phone line over fiber, but I have not seen one.
Specify to them that you will be coming out of a PBX like device (the router, and ending on a single line phone).
That will be the FXO and FXS ends.
And if you get something like that, do not connect them reverse.
Another option will be getting the cheapest gateways that you could get, one FXO and the other FXS and using those ethernet to fiber converter point them one to each other.
Build a data pipe, with two I.P. addresses, one for each gateway .
Plug the gateways on the ethernet converters and the phone line side of the gateways on the router and phone.
You still looking at few hundr3ed dollars minimun.
Lets say that no less than $600 to $800 dollars on gateways alone.
Anyone knows of a good point to point FXO to FXS solution????????