IEC 60793-1-44-2011 pdf download.Optical fibres – Part 1-44: Measurement methods and test procedures – Cut-off wavelength.
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60793-1-1, Optical fibres — Part 1-1: Measurement methods and test procedures — General and guidance
IEC 60793-1-40, Optical fibres — Part 1-40: Measurement methods and test procedures — Attenuation
3 Background
Theoretical cut-off wavelength is the shortest wavelength at which only the fundamental mode can propagate in a single-mode fibre, as computed from the refractive index profile of the fibre.
In optical fibres, the change from multimode to single-mode behaviour does not occur at an isolated wavelength, but rather smoothly over a range of wavelengths. For purposes of determining fibre performance in a telecommunications network, theoretical cut-oft wavelength is less useful than the lower value actually measured when the fibre is deployed.
Measured cut-off wavelength is defined as the wavelength greater than which the ratio between the total power, including launched higher-order modes, and the fundamental mode power has decreased to less than 0,1 dB. According to this definition, the second-order (LP11) mode undergoes 19,3 dB more attenuation than the fundamental (LP01) mode at the cut-off wavelength.
Because measured cut-off wavelength depends on the length and bends of the fibre, the resulting value of cut-off wavelength depends on whether the measured fibre is configured in a deployed, cabled condition, or it is short arid uncabled. Consequently, there are two overall types of cut-off wavelength:
• Cable cut-ott wavelength, measured in an uncabled fibre deployment condition (method A). or in a cabled condition (method B);
• Fibre cut-off wavelength, measured on a short length of uncabled. primary-coated fibre.
Cable cut-off wavelength is the preferred attribute to be specified and measured.
4 Overview of methods
All of the methods shall use the transmitted-power technique, which measures the variation with wavelength of the transmitted power of a fibre under test compared to a reference transmitted-power wavelength scan. The reference scan normalizes wavelength-dependent fluctuations in the measurement equipment so that the attenuation of the LP11 mode in the specimen can be properly characterized and the cut-oft wavelength precisely determined.
The reference scan uses one of the following two techniques:
• the specimen with an additional, smaller-radius fibre bend;
• a (separate) category Al multimode fibre.
This procedure can determine the cut-off wavelength of a fibre specimen in either a cabled or uncabled condition. Each method has its own default configurations; the detail specification will give any different configuration required.
The fibre cut-off wavelength, (2) measured under the standard length and bend conditions described in this standard, will generally exhibit a value larger than A. For normal installed cable spans, it is common for the measured A value to exceed the system transmission wavelength. Thus cable cut-off wavelength is the more useful description of system performance and capability.IEC 60793-1-44 pdf download.