The cladding diameter in single-mode fiber is ______ microns.

The cladding diameter in single-mode fiber is ______ microns.

• A. 90
• B. 125
• C. 150
• D. 200

Answer: (B)

In single-mode optical fiber, the cladding diameter is standardized at 125 micrometers. This fixed size defines the boundary that guides light by total internal reflection and ensures compatibility across connectors, splices, and other fiber components. The core is much smaller—about 8 to 10 micrometers—so the cladding provides the surrounding material that keeps the light confined to a single mode. The 125 µm figure is the established cladding size used in most telecom fibers, while the other numbers correspond to core size or nonstandard cladding values.

In single-mode optical fiber, the cladding diameter is standardized at 125 micrometers. This fixed size defines the boundary that guides light by total internal reflection and ensures compatibility across connectors, splices, and other fiber components. The core is much smaller—about 8 to 10 micrometers—so the cladding provides the surrounding material that keeps the light confined to a single mode. The 125 µm figure is the established cladding size used in most telecom fibers, while the other numbers correspond to core size or nonstandard cladding values.