Fiber Patch Cable Length

Fiber Cable Length

Why is there a minumum cable length?

The minimum fiber patch cable length is 1 m for both single-mode and polarization-maintaining fibers. Since there can be issues with even shorter fiber cables we recommend only using fibers with that minimum length. If you need a smaller cable length please contact us and we can discuss the issue in detail.

When you couple radiation into a single-mode fiber, not all the radiation is coupled to the fiber core since the overlap between the fiber mode field and the spot focused on the fiber end-face generally is < 1. The residual radiation is reflected or is coupled to cladding modes of the fiber.

However, even these cladding modes are guided, although with high losses. In case of a very short fiber length radiation coupled to these cladding modes may reach the fiber end. This radiation then is superimposed with the radiation guided by the fiber core, causing interference effects. 

Please note: The ability of the cladding modes to guide radiation, depends on the condition of the fiber. If the fiber is bent, the cladding modes have significantly more loss than for a straight fiber. We therefore recommend to coil the excess length of the fiber cable.