How can you tell if a fiber is single mode or multimode?

To determine whether a fiber optic cable is single-mode or multimode, you can perform a visual inspection or check the cable markings. Here are a few methods to identify the type of fiber:

1.Visual Inspection: Single-mode and multimode fibers have visual differences that can help you identify them:
Single-Mode Fiber: Single-mode fiber typically has a smaller core size (around 9 microns) compared to multimode fiber. When observing the fiber end-face, the core of a single-mode fiber appears as a small, pinpoint-sized dot surrounded by a larger cladding area.
Multimode Fiber: Multimode fiber usually has a larger core size (typically 50 or 62.5 microns). When examining the fiber end-face, the core of a multimode fiber appears as a larger, more prominent area compared to the cladding.
Visual inspection can provide a rough indication, but it may not be definitive, especially when dealing with smaller core sizes or specialty fibers. It is recommended to use additional methods for accurate identification.

2.Cable Markings: Fiber optic cables often have markings printed on their jackets or connectors that indicate the fiber type. Look for labels or printing that may include terms such as "SMF" (Single-Mode Fiber) or "MMF" (Multimode Fiber). These markings can provide a reliable indication of the fiber type.

3.Documentation and Specifications: If available, consult the cable documentation, datasheets, or specifications provided by the manufacturer or supplier. These documents typically specify whether the cable is single-mode or multimode.

If visual inspection and cable markings don't provide clear identification, you'll need to use specialized equipment, such as a microscope or optical time-domain reflectometer (OTDR), to more accurately analyze the fiber.