How to determine if an optical cable is multimode

You can identify a multimode fiber optic cable by its jacket color, printed labeling, core size, connector type, or by using specialized testing equipment.

Visual Identification

• Jacket Color: Multimode cables are typically orange (OM1/OM2), aqua (OM3/OM4), or lime green (OM5), while singlemode cables are usually yellow .
• Printed Labels: Check the cable jacket for markings such as OM1, OM2, OM3, OM4, or OM5, which indicate multimode fiber. Singlemode cables are often labeled OS1, OS2, or SMF .
• Core Size: Multimode fibers have a larger core diameter, usually 50 µm or 62.5 µm, compared to singlemode fibers at around 9 µm .

Connector Clues

• Connector Color: While not universal, beige or black connectors are commonly used for multimode fiber, whereas blue connectors are often associated with singlemode fiber .

Testing Methods

• Visual Fault Locator (VFL): Shining a visible light through the fiber can help observe how light propagates; multimode fibers allow multiple light paths .
• Optical Time-Domain Reflectometer (OTDR): Measures fiber length, loss, and reflections, helping confirm whether the fiber is multimode or singlemode .
• Fiber Inspection Microscope: Allows direct observation of the core size to distinguish multimode from singlemode .
• Flashlight Test: For a simple check, shine an LED flashlight into one end of the fiber and observe the light at the other end; multimode fibers are easier to illuminate due to the larger core .

Practical Considerations

• Distance and Application: Multimode fiber is ideal for shorter distances, such as within buildings or data centers, typically under 500 meters, and supports multiple light modes simultaneously .
• Network Planning: Correctly identifying multimode fiber ensures compatibility with network equipment, proper installation, and optimal performance. By combining visual inspection, labeling, connector type, and testing tools, you can confidently determine if a fiber optic cable is multimode.