Remote Terminal Unit Dual Ring Fiber Optic Network over Modbus TCP/IP

I suppose the short answer is maybe...

You have not given details of the remote unit working platform - let us assume it's serial data at 9600 baud.
You have not given details of the SCADA network. let us assume it's TCP/IP on fibre.

So you need a serial to fibre converter which can handle TCP/IP.
I not sure there would be a converter with dual fibre connection; in addition, would the fibre network existing protocols be able to handle mixed protocols operating simultaneously, mindful something has to be in place on the network to send Modbus commands for the remote unit to receive.

Sorry the above gives more questions than answers - but you are looking at two extremes of comms. on the physical layer. An alternative would be to connect the remote device to a PLC - from there I would expect you to be able to convey data to almost anywhere.
Please see above image, showing the detailed connections.
The dual fiber optic cables will be connected to fiber optic patch panels, and then patch cords will be connect the Patch Panels to two separate industrial ethernet managed switches.
The main question here is if the RTU have dual ethernet interface (dual RJ45 ports), will these dual ethernet interfaces be able to work as redundant ? as in each one connect to an ethernet switch which is connected to the ring FO network, thus creating a dual ring FO network (The SCADA network protocol specified is Modbus TCP/IP)
This is a design drawing, currently there is no selection done since it will be done by the contractor during construction.
The ones i checked that i have more than one RJ45 ports are from schneider electric ScadaPack 574