A Comparison Between Cut-Back and Standard Reference Fiber Techniques in Calibrating the Attenuation Scale of Optical Time Domain Reflectometers

In this paper, a comparison between the calibration of the attenuation scale of an Optical Time Domain Reflectometer (OTDR) using two different techniques is discussed and implemented. The first technique is the external modulation method (EM). A setup is proposed to calibrate an OTDR over a dynamic range of around 15 dB based on the EM method. Afterwards, the OTDR is calibrated using two standard reference fibers (SRFs). Both SRFs are calibrated using cut-back technique; one of them is calibrated at our home institute (the National Institute of Standards – NIS) while the other at the National Physical Laboratory (NPL) of the United Kingdom to confirm our results. In addition, the parameters contributing to the calibration uncertainty are thoroughly investigated. The measurement results are compared to that of the NPL through a previously calibrated fiber artifact. The OTDR calibration uncertainty of the EM method is found to be around
= ± 0.1 dB/dB, while the calibration uncertainty of the SRF method is found be around
= ± 0.04 dB/dB for both 1310 nm and 1550 nm OTDR wavelengths.