S/PDIF data can be transmitted over fibre-optic cable using TOSLINK or ST-type optical transmitters and receivers. Optical interfaces have the advantage that they do not require any electrical connection, so they are useful for connecting to electrically noisy devices.
A common problem is that optical receivers often use an automatic gain control amplifier (AGC), because the intensity of light reaching the receiver varies with the cable length, cable loss and other factors. AGC amplifiers are inherently jittery, so better performance is usually available from an electrical S/PDIF interface.