Cut-off wavelength is a critical parameter for single-mode fibers. The primary purpose of specifying this quantity is to ensure that the cut-off wavelength of single-mode fiber systems is lower than the operating wavelength

thereby eliminating the possibility of modal noise problems. The cable cut-off wavelength is more relevant to the user because it represents a functional value of cut-off wavelength which can be used in system design. Cabling the fiber tends to shift the cut-off value to shorter wavelengths

therefore a conservative estimate of cable cut-off can be made by measuring un-cabled fiber in the cable cut-off configuration

as recommended by CCITT. 650

[1]

.Fifty SIECOR single^mode fiber samples were measured for the cable cut-off wavelength and the fiber cut-off wavelength according to the above mentioned CCITT recommendation. In the cable cutoff measurements

the 20 m length of uncabled fiber to be deployed in an essentially straight condition was loosely wound on a standard measurement drum of 175 mm radius. The coiling of the fiber length in loops of relatively large radius simulates the cabling effect. To simulate the effects of a splice organizer

one loop of 40 mm radius within 1 m of each end was applied to each fiber end.The measurement results show a mean downward shift in the cut-off wavelength of about 110 nm. A mapping function was developed between the cable cut-off wavelength and the fiber cut-off wavelength. This mapping function can be used to confidently predict the cable cut-off wavelength from the measured fiber cut-off wavelength.As a worst case estimation

the SIECOR fibers will meet a maximum cable cut-off wavelength of 1260 nm

which is recommended by CCITT Recommendation G. 652

[1]

when the fiber cut-off wavelength is not greater than 1330 nm.