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 return loss. Fiber optic adapters are small but essential components that ensure precise alignment between connectors. Using the wrong type or neglecting cleaning can lead to signal loss and unstable connections. They are essential for maintaining network performance in data centers, telecommunications, and industrial applications. Most fiber optic connectors are composed of.