Single mode fiber has a small core (8–10 µm) and yellow jacket, while multimode fiber has a larger core (50–62.5 µm) and typically orange or aqua jacket.

Core Differences

• Single Mode Fiber (SMF): Features a narrow core of about 8–10 micrometers, allowing only one light path to propagate. This minimizes signal loss and supports long-distance transmission, often exceeding 100 km with proper equipment. It typically uses laser light sources and is labeled as OS1 or OS2 .
• Multimode Fiber (MMF): Has a larger core of 50 or 62.5 micrometers, supporting multiple light paths simultaneously. This makes it suitable for shorter distances, usually under 500 meters, and uses LED or laser light sources. Common labels include OM1 through OM5 .

Visual Identification

• Jacket Color: Single mode cables are usually yellow, while multimode cables are orange (OM1/OM2), aqua (OM3/OM4), or lime green (OM5) .
• Labeling: Check the printed markings on the cable. For example, “OS2 9/125” indicates single mode, and “OM3 50/125” indicates multimode .

Performance and Application

• Distance: Single mode supports kilometers to hundreds of kilometers, while multimode is limited to hundreds of meters .
• Bandwidth: Single mode offers higher bandwidth due to minimal modal dispersion, whereas multimode has lower bandwidth because multiple light modes can spread out and interfere .
• Cost and Handling: Single mode fibers are more expensive and require precise handling due to the small core, while multimode fibers are easier to terminate and more cost-effective for short-range applications .

Tools for Verification

• Microscope Inspection: Viewing the fiber end under a microscope can reveal the core size.
• Optical Power Meter or OTDR: Can test signal propagation and confirm fiber type based on attenuation and distance performance. By combining visual cues, labeling, and technical testing, you can reliably distinguish single mode from multimode fiber for network installation or maintenance purposes .