A power meter measurement is an absolute measurement. In the case of the MultiFiber Pro, it has a power meter measurement uncertainty of ± 0.35 dB. A fiber loss measurement is a relative measurement, so the measurement uncertainty is going to be a different value. This article describes how the fiber loss measurement uncertainty is calculated.
As optical fiber networks handle more traffic and transport speeds increase, testing attenuation to loss budgets as low as 1.9dB places more demand on the accuracy of test equipment. When measurements are critical and high accuracy becomes a premium, questions around measurement uncertainty are asked. Measurement uncertainty has always been the domain of metrology experts responsible for the calibration of optical test equipment such as an optical power meter (OPM). However, in the last several years, more fiber optic Standards added uncertainty guidelines to their documents. When making attenuation measurements on a fiber optic link, one should expect a measurement uncertainty from the tester supplier. This article provides the measurement uncertainty for a multimode attenuation measurement of optical cabling using the MultiFiber Pro using the 1-cord reference method.
A fiber optic channel is an optical fiber cabling configuration that includes a longer fiber trunk and relatively short cables attaching to equipment. For testing and certifying attenuation of this network, a light source and power meter can be used. When using a light source and power meter, to measure loss, the first step is to reference the power meter to the light source as “0 dB”. After this, the light source and power meter are connected to opposite ends of the fiber cabling under test.
For both singlemode and multimode testing, the contributions to uncertainty include:
- Light source stability at 0.1 dB
- Power meter linearity at 0.1 dB
- Power meter polarization error at 0.005 dB
- Power meter resolution at 0.005 dB
- Connector insertion loss at 0.1 dB (assumes reference to a large area detector)
There is an assumption that the power meter calibration and wavelength have no effect on uncertainty because measurements are relative not absolute. Also, multimode launch conditions are not included in the calculations. That means the power meter uncertainty value of ± 0.35 dB found on the data sheet has no impact of fiber loss measurement uncertainty.
The connector insertion loss repeatability is stated at 0.1 dB. It is covered under a filed patent.
Using the following work table, the measurement uncertainty can be calculated for both singlemode and multimode. Calculations show a 5 % uncertainty which is 0.21 dB.
In summary, one should expect up to 5% or 0.21 dB uncertainty when performing fiber optic loss testing per industry standard procedures using the MultiFiber Pro. It is important to minimize additional uncertainty introduced by ill advised reference methods and dirty or non compliant test reference cords.