Practical upper limits to cutoff wavelength for single mode fibers based on a modal noise approach

A relationship is established between the attenuation of the LP ₁₁ cutoff mode and the length dependence of cutoff wavelength. On the basis of this relationship, a formula is developed to predict the upper limit of cutoff wavelength for four fiber designs commonly seen in commercially available fiber. It is found that, depending on the fiber design, the upper limit of the factory-measured cutoff wavelength is anywhere from 20 nm to 60 nm above the system operating wavelength, even for a worst-case straight fiber layout. Under actual field layout conditions, where bends of approximately 7.5 cm diameter are induced to the fiber at the splice enclosures, these limits converge to 65 nm above the system operating wavelength for all four fiber designs. The practical upper limit predicted here is confirmed through an experimental evaluation of modal noise affects in a 1.2 Gb/s single-mode-fiber system