So, to cut right to the chase, you can generally tell if fiber is multimode or singlemode by examining the cable's jacket color, looking for printed markings on the jacket, checking the connector type, and if all else fails, by measuring the core diameter or using an optical. So, to cut right to the chase, you can generally tell if fiber is multimode or singlemode by examining the cable's jacket color, looking for printed markings on the jacket, checking the connector type, and if all else fails, by measuring the core diameter or using an optical. Choosing the right type of fiber optic cable is essential for reliable and cost-effective network performance. The two main types — Single Mode (SM) and Multimode (MM) — differ in construction, performance, and application. Fiber optic cables transmit data as pulses of light through. But not all fiber cables are created equal: multimode (MM) and single mode (SM) fibers are the two primary types, each engineered for specific use cases, from short-range data center connections to transcontinental telecom backbones. This guide breaks down their technical differences, performance. The nagging question pops into your head: How to tell if fiber is multimode or singlemode? It's a common predicament, one I've personally wrestled with more times than I care to admit.