The original/basic Fiber Distributed Data Interface (FDDI) Physical Layer…

A network standard can define more than one physical-medium-dependent (PMD) variant. Each PMD identifies the transmission medium and compatible optical transmitter; a wide-core multimode link is commonly paired with an LED, while a narrow-core single-mode link is paired with a laser diode for longer reach.

For FDDI, ISO/IEC 9314-3 defines the original/basic multimode-fibre PMD, while ISO/IEC 9314-4 defines the single-mode-fibre PMD extension. The qualifier “original/basic PMD” is therefore essential: under that scope, the specified pairing is multimode fibre with LEDs.

• single mode fibers and LEDs: this combines the narrow core of single-mode fibre with the broader emission pattern of an LED; it is not the original/basic FDDI MMF-PMD pairing.

• multimode fibers and LEDs: this combines a wide multimode core with an LED source and is the pairing specified by the original/basic FDDI MMF-PMD.

• single mode fibers and ILDs: this is the laser-based pairing used by the standardized FDDI SMF-PMD extension, rather than by the original/basic MMF-PMD.

• multimode fibers and ILDs: this combines multimode fibre with a laser source, but it is not the source pairing named by the original/basic FDDI MMF-PMD.

Cross-check: ISO/IEC 9314-3 is the multimode-fibre PMD and ISO/IEC 9314-4 is the single-mode-fibre extension. Hence the narrowed question has one answer by value: multimode fibers and LEDs.