What is the difference between single-mode and multi-mode fiber?

The difference lies in the physical construction and how light propagates through the fiber.

Multi-Mode Fiber (MMF)

• Larger core diameter (50μm or 62.5μm)
• Light travels in multiple paths (modes)
• Modal dispersion limits distance and speed
• Uses cheaper LED or VCSEL light sources
• Common wavelength: 850nm, 1300nm
• Typical distances: 100m-2km
• Color code: orange (OM1/OM2), aqua (OM3/OM4), lime green (OM5)

Single-Mode Fiber (SMF)

• Small core diameter (8-10μm)
• Light travels in single path
• No modal dispersion — long distances possible
• Requires laser sources (more expensive)
• Common wavelengths: 1310nm, 1550nm
• Distances: 10km to 100+ km
• Color code: yellow

OM Classes (Multi-Mode)

OS Classes (Single-Mode)

• OS1: Indoor/tight buffered, up to 1310/1550nm
• OS2: Outdoor/loose tube, low water peak

When to Use Which

• MMF (OM3/OM4): Data center within building, short campus links
• SMF (OS2): Long distances, WAN, service provider, future-proofing

Cost Consideration

Fiber itself: SMF slightly cheaper. Modules: MMF cheaper for short runs, SMF cheaper for very long runs (no need for 10km+ MMF).