The sine of the half-angle of the acceptance cone, set by the index difference between core and cladding. Typical values are about 0.14 for singlemode, 0.20 for 50 µm multimode and 0.275 for 62.5 µm multimode. Higher NA makes it easier to couple light from a large source but supports more modes, and mismatched NA between two fibers adds connection loss in one direction.
Spec sheet lists NA 0.200 plus or minus 0.015 for the OM4, same as the patch cords, so no surprises on the jumpers.
Also heard as
- NA
Related terms
Core
The central glass region of an optical fiber where the light actually travels.
Cladding
The layer of slightly lower-index glass around the core that keeps light trapped inside it.
Multimode fiber
Fiber with a 50 or 62.5 µm core that carries many light paths at once, used for short links inside buildings and data centers.
Mandrel wrap
Multimode test jumper wound around a smooth rod to strip out high-order modes and stabilize loss readings.