IEC 60793-1-44-2011 pdf free download – Optical fibres – Part 1-44: Measurement methods and test procedures – Cut-off wavelength.
4overview of methods
All of the methods shall use the transmitted-power technique，which measures the variationwith wavelength of the transmitted power of a fibre under test compared to a referencetransmitted-power wavelength scan.The reference scan normalizes wavelength-dependentfluctuations in the measurement equipment so that the attenuation of the LP.1mode in thespecimen can be properly characterized and the cut-off 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 A1 multimode fibre.
This procedure can determine the cut-off wavelength of a fibre specimen in either a cabled oruncabled condition.Each method has its own default configurations; the detail specificationwill give any different configuration required.
The fibre cut-off wavelength,()， measured under the standard length and bend conditionsdescribed in this standard,will generally exhibit a value larger than – c. For normal installedcable spans，it is common for the measured ?。value to exceed the system transmissionwavelength. Thus cable cut-off wavelength is the more useful description of systemperformance and capability.
For short cables，e.g. a pigtail with a length shorter (and possibly a bending radius larger)than described in this method,the cable may introduce modal noise near the cut-offwavelength when lossy splices are present (>0,5 dB).
5 Mapping functions
A mapping function is a formula by which the measured results of one type of cut-oftwavelength are used to predict the results that one would obtain from another type.
An empirical mapping function is specific to a particular fibre type and design.Generatemapping functions by doing an experiment in which samples of fibre are chosen to representthe spectrum of cut-off wavelength values for the fibre type,then measure the values usingthe two methods to be mapped.Linear regression of the respective values will often produce a satisfactory mapping function. When establishing criteria for fibre selection, residual errorsin the regression shall be taken into account.
The customer and the supplier shall agree to the confidence level of each mapping functionestablished.
6 Reference test method
Method A of cable cut-off wavelength，using uncabled fibre，is the reference test method(RTM), which shall be the one used to settle disputes.
The apparatus for each method is described in Clause 7.
7Apparatus
7.1 Light source
Provide a filtered white light source，with line width not greater than 10 nm, stable in positionand intensity.The light source should be capable of operating over the wavelength range1 000 nm to 1 600 nm for most category B fibres.An operating range of 800 nm to 1 700 nmmay be necessary for some B4 fibres,B5 fibres or some category C fibres.
7.2Modulation
Modulate the light source to prevent ambient light affecting the results,and to aid signalrecovery.A mechanical chopper with a reference output is a suitable arrangement.
7.3Launch optics
Provide launch optics，such as a lens system or a multimode fibre, to overfill the test fibreover the full range of measurement wavelengths. This launch is relatively insensitive to theinput end face position of the single-mode fibre, and is sufficient to excite the fundamentaland any higher-order modes in the specimen. If using a butt splice, provide means of avoidinginterference effects.
When using a multimode fibre,overfilling the reference fibre can produce an undesired rippleeffect in the power-transmission spectrum.Restrict the launch sufficiently to eliminate theripple effect.One example of restricted launch is in method A, attenuation by cut-back ofIEC 60793-1-40. Another example of restricted launch is a mandrel-wrap mode filter withsufficient (approximately 4 dB) insertion loss.
7.4support and positioning apparatus
Provide a means to stably support the input and output ends of the specimen for the durationof the test;vacuum chucks，magnetic chucks,or connectors may be used for this purpose.support the fibre ends such that they can be repeatedly positioned in the launch anddetection optics. When measuring c。 in method B, provide a means to suitably support thecable ends.
7.5Cladding mode stripper
Provide a means to remove cladding-mode power from the specimen. Under somecircumstances，the fibre coating will perform this function;otherwise，provide methods ordevices that extract cladding-mode power at the input and output ends of the specimen.IEC 60793-1-44 pdf download.