A fiber-optic adapter — sometimes called a coupler or bulkhead coupler — is a passive mechanical interface that mates and aligns two terminated optical fibers (i., two fiber connectors) such that light can reliably pass from one to the other with minimal insertion loss and maximum. 📦 For purchasing, use the RP Photonics Buyer's Guide for fiber-optic adapters. What Are Fiber-optic Adapters? A. Fiber optic adapters are devices used to connect two fiber optic cables, ensuring seamless data transmission with minimal signal loss. Using the wrong type or neglecting cleaning can lead to signal loss and unstable connections. LC, MU, SMA connectors with round or square type press button.