This instruction describes the procedure for determining the modal launch condition and category of a light source or fiber end by measuring its coupled power ratio (CPR).
This instruction is applicable for all multimode light sources with particular emphasis on LED sources.
This instruction has been written around 50 µm fiber core CPR measurement. For measuring CPR of 62.5 µm systems, substitute 62.5 µm MM patch leads and lookup table data as appropriate .
Note: Connectors on the above patch leads shall have losses <= 0.5 dB (@ 850 & 1300 nm).
Note: Connectors with PC finish are best as they inhibit Fresnel reflections.
Note: Keep the patch-lead as straight as possible (avoid bends of less than 50 mm diameter) as could affect the modal power distribution and hence the measurement accuracy).
Figure 1 – First MM measurement
Figure 2 – Final SM measurement
Measure & record the power output (L2) of the MM to SM pigtail combination.
Table 1 – 850 nm CPR Categories |
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Fibre Size | Category 1 Overfilled |
Category 2 | Category 3 | Category 4 | Category 5 Greatly under filled |
50 ?m | 20-24 | 16-19.9 | 11-15.9 | 6-10.9 | 0-5.9 |
62.5 ?m | 25-29 | 21-24.9 | 14-20.9 | 7-13.9 | 0-6.9> |
100/140 ?m | 30-34 | 26-29.9 | 18-25.9 | 10-17.9 | 0-9.9 |
Table 2 – 1300 nm CPR Categories |
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Fibre Size | Category 1 Overfilled |
Category 2 | Category 3 | Category 4 | Category 5 Greatly under filled |
50 ?m | 16-20 | 12-15.9 | 8-11.9 | 4-7.9 | 0-3.9 |
62.5 ?m | 21-25 | 17-20.9 | 12-16.9 | 7-11.9 | 0-6.9 |
100/140 ?m | 26-30 | 22-25.9 | 15-21.9 | 8-14.9 | 0-7.9 |
TIA/EIA 526-14A OFSTP-14, Optical Power Loss Measurements of Installed Multimode Fiber Cable Plant IEC 61280-4-1 Fibre-Optic Communication Subsystem Basic Test Procedures – Part 4-1: Test procedures for fibre-optic cable plant links – Multimode fibre-optic cable plant attenuation measurement.
IEC 61300-3-31 Fibre optic interconnecting devices and passive components – Basic T&M procedures – Part 3-31: Examinations and measurements – Coupled power ratio measurement for fibre optic sources.
At time of writing it is understood that the standard bodies ISO/IEC, IEC and CLC are seeking a method to create a multimode, mode conditioning patch cord which can be used to create a light source with a defined launch condition. ‘Launch’ date is scheduled for September 2004.