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Uncertainty of OTDR Loss Scale Calibration using a Fiber Standard

The calibration of the power scale of an OTDR instrument is presented where the accurately measured loss of a fiber standard is used as a defined test unit to check the linearity of the power scale. The deviation of the displayed power scale from the true power scale is determined in dependence on the optical power at the input end or the fiber standard. The achievable uncertainty of this deviation is derived from the uncertainties of the different parameters involved in the calibration process. The single uncertainties are fixed or estimated and the total uncertainty is calculated. The capability of the calibration is checked in a test measurement. It is shown that the loss values of an unknown fiber measured with the help of the cut-back method and with the help of a calibrated OTDR instrument are within the combined uncertainty of both measurements