Single-mode fiber optic cable typically has only one core for transmitting light. Among their many features, the number of fiber cores directly affects data capacity and network performance. This article. The secret lies in fiber optic technology, and understanding the basics—1-core, 2-core, Single Mode (SM), and Multi-mode (MM)—is key to mastering this field. Generally, single-core cables are the least expensive to manufacture as well. The core is where the light signals travel through, while the cladding helps to keep the. For example, if you have three optical fiber access switches, you need to have three cores.