Modbus RTU/Modbus TCP. Terminal server?

I have ~20 devices with fiber optic interfaces and modbus rtu protocol. I need to connect them to PLC with modbus TCP protocol.
Maybe anyone had similar project and can suggest other solution than installing separate converter for every device.

I was looking for serial to ip server with several serial interfaces, but with no luck yet.

the way to go would be to use rs485 and bring them back to one serial server, like a lantronix or digi. as far as connecting them to the plc, that will depend on the plc and if it supports modbus tcp.

more info you give better answer you get.

1. I have Modbus RTU devices with fiber optic interface.
2. I have PLC with ethernet port and modbus TCP protocol.
3. The task is to establish communication between plc(modbus TCP) and modbus rtu devices.

Hope this makes more sense.