In depends on if you are running half or full-duplex connection. Half-duplex can work with as few as 1 strand, while full-duplex requires at least 2 strands available.
Multimode
Uses a dual ring of single-mode or multimode fiber-optic.
multimode fiber network + Guide to networks pg 106-108
Multimode fiber
Singlemode fiber has a lower power loss characteristic than multimode fiber, which means light can travel longer distances through it than it can through multimode fiber. Not surprising, the optics required to drive singlemode fiber are more expensive. When to use each: Both singlemode and modern multimode fiber can handle 10G speeds. The most important thing to consider is the distance requirement. Within a data center, it's typical to use multimode which can get you 300-400 meters. If you have very long runs or are connecting over longer distance, single mode can get you 10km, 40km, 80km, and even farther - you just need to use the appropriate optic for the distance required, and again, the prices go up accordingly. Compatibility issues: They are not compatible. You cannot mix multimode and singlemode fiber between two endpoints. The optics are not compatible either.
850 and 1300nm
Multimode
850nm laser-optimized 50/125-micron multimode fiber
Multimode fiber optic cable at 850nm
Multimode fiber (MMF.
A graded index multimode fiber will transmit 800 modes, and has a varying refractive index. A step index multimode will transmit 228 modes.
Fiber optic Cable bearing many fibers independently sheathed and capable of carrying unrelated signals