No, data diodes are a different (but related) concept. An airgap implies no information transfer, either in or out. Use an airgap when information leakage must be stopped (as well as remote attacks), use a data diode when information can be released but you need to stop remote attacks.

Fiber optic connections aren't required, anything with separate transmit and receive lines can be turned into a data diode (as long as the protocols used permit it). RS232 null modem cables with the RX lines disconnected are a classic.