DD IEC PAS 60793-1-49:2002 pdf download Optical fibres — Part 1-49: Measurement methods and test procedures — Differential mode delay
1Introduction
1.1Intent
This technical specification describes a method for characterizing the modal structure of agraded-index multimode fibre. This information is useful for assessing the bandwidthperformance of a fibre when used with laser sources.
With this method, the output from a fibre that is single-mode at the test wavelength excites themultimode fibre under test. The probe spot is scanned across the endface of the fibre undertest, and the optical pulse delay is determined at specified offset positions. The difference inoptical pulse delay time between the fastest and slowest modes of the fibre under test isdetermined. The user specifies the upper and lower limits of radial offset positions over whichthe probe fibre is scanned in order to specify desired limits of modal structure.
1.2Scope
This technical specification applies only to multimode, graded-index glass-core (category A1)fibres. The test method is commonly used in production and research facilities, but is not easilyaccomplished in the field.
Definitions1.3
The user of this standard specifies the inner (RINNER) and outer (ROuTER) limits of radial offsetpositions on the endface of the fibre under test over which the probe spot is scanned. Theestimated difference in optical pulse delay time between the fastest and slowest modes excitedfor all radial offset positions between and including RINNER and ROuTER will be called DifferentiaMode Delay(DMD).
2 Normative References
The following normative documents contain provisions, which, through reference in this textconstitute provisions of this technical specification. For dated references, subsequentamendments to, or revisions of, any of these publications do not apply. However, parties toagreements based on this technical specification are encouraged to investigate the possibility ofapplying the most recent editions of the normative documents indicated below. For undatedreferences, the latest edition of the normative document referred to applies. Members of lEC andSO maintain registers of currently valid International Standards.
EC 60825-1: Safety of laser products – Part 1: Equipment classification, requirements and
user’s quide.IEC 60825-2: Safety of laser products – Part 2: Safety of optical fibre communication systems.EC 60793-1-1: Optical fibres – Part 1: Generic specification – Section 1: GeneralEC 60793-1-22: Optical fibres – Part 1-22: Measurement methods and test procedures – Length
measurementEC 60793-1-42: Optical fibres – Part 1-42: Measurement methods and test proceduresChromatic dispersion
EC 60793-1-45: Optical fibres – Part 1-45: Measurement methods and test procedures – Modefield diameter
3Apparatus
3.1 Optical source
Use an optical source that introduces short duration, narrow spectral width pulses into the probe fiber
The temporal duration of the optical pulse shall be short enouah to measure the intended differentiadelay time. The maximum duration allowed for the optical pulse, characterized as full width at 25% ofmaximum amplitude, will depend both on the value of DMD to be determined and the sample length. Forexample, if the desired DMD limit is 0.20 ps/m over a sample of length 500 m, the DMD to be measured is100 ps, and a pulse of duration less than ~110 ps is needed. Testing to the same DMD limit in a10 000 m length of fiber requires measuring a DMD of 2000 ps, and a pulse a wide as -2200 ps may beused. Detailed limits are given in section 6.1, and may depend on the source spectral width.
Chromatic dispersion induced broadening resulting from source spectral width shall be within the limitsindicated in Annex B. The requirement on spectral width may be met either by using a spectrally narrowsource, or alternatively by the use of appropriate optical filtering at either the source or detection end.
The centre wavelength shall be within : 10 nm of the nominal specified wavelength.
A mode locked Titanium-Sapphire laser is an example of a source usable for this application.
3.2Stability
Devices shall be available to position the input and output ends of the test specimen withsufficient stability and reproducibility to meet the conditions of sections 3.3.3 to 3.3.6 andsection 3.4.1.
3.3Launch system
3.3.1The probe fibre between the light source and test sample shall propagate only a singlemode at the measurement wavelength. The mode field diameter of the probe fibre at 入shall be (8.7入 -2.39) + 0.5 um, where 入 is the measurement wavelength in micrometers,and the mode field diameter is determined using IEC 60793-1-45. This equationproduces a mode field diameter of 5 um at 850 nm and 9 um at 1310 nm, whichcorresponds to commercially available single-mode fibres.
3.3.2Ensure that the outout of the probe fibre is sinale-mode, One method to do this is to striphigher order modes by wrapping the probe fibre three turns around a 25-mm diametermandrel.
3.3.3The output spot of the probe fibre shall be scanned across the endface of the test samplewith a positional accuracy less than or equal to + 0.5 um.
DD IEC PAS 60793-1-49:2002 pdf download
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