I need to transmit several tripping and control signals via an OPGW. The distance is only 300m, but across a river. OPGW will be installed on the HV transmission line.

Does anybody know some kind of a converter or multiplexer, which transfers electrical binary inputs over a fibre optic cable?

 

I like the Weed Instruments single-fiber contact multiplexer. I use their analog units, but the discrete units appear to work just the same. Although I use PLC's for this sort of thing most of the time, it's nice to see a product that just does what's required, and does it reliably.

http://www.weedinstrument.com/fiber/widl.html