The X14 is a one to four fiber-optic fan-out type device. It receives a single optical level and repeats that signal to 4 separate outputs with minimal latency added. The X14 is intended to help system designers spread out a single trigger or synchronization signal to multiple destinations.
For unidirectional TTL to fiber applications that can drive 30mA the TF-1 may be a simpler choice.
If your application requires bidirectional conversion see the X22 device.