Length dependence of the effective cutoff wavelength in single-mode fibers

The effective cutoff wavelength of a depressed cladding single-mode fiber in either a cabled or a loose state depends upon the length of the fiber. This dependence can be accurately represented by a linear function of the logarithm of the fiber length for lengths between 1 m and 1 km. Cutoff will shift 55-66 nm per decade length for slightly and moderately depressed cladding designs, respectively. Neglecting all sources of differential mode attenuation except leaky-mode loss, the computed behavior of cutoff as a function of fiber length agrees reasonably well with the observed behavior for a moderately depressed cladding design. On the other hand, agreement is poor for a slightly depressed cladding design. A knowledge of the length dependence of cutoff is essential for establishing a production requirement for cutoff based upon the needs of the system.