Interlaboratory measurement comparisons, or round robins, are a useful diagnostic tool during the standards development process. A round robin can test the robustness of a given test procedure or the equivalence of multiple procedures, as well as determine the need for, or effectiveness of, calibration standards. The National Institute of Standards and Technology (NIST) often acts in the role of unbiased arbiter and is trusted to maintain the confidentiality and anonymity of data in such comparisons. Since the early 1980s, NIST’s Optoelectronics Division has provided coordination and/or data refereeing for more than 20 round robins for the fiber industry, usually on behalf of the Telecommunications Industry Association’s Fiber Optics Committee (TIA FO-4), though occasionally for other organizations (IEEE, IEC, ITU, etc.).
A TIA round robin completed in 2005 compared measurements of Raman gain efficiency (RGE) from four laboratories using a recently published TIA informative test memorandum (TIA ITM-22; equivalent to IEC TR-62324). Round-robin results gave a snapshot of the state of the industry in making RGE measurements for a variety of fiber types. Interestingly, this round robin showed that an approximate equation given in these nonnormative test procedures could be misapplied and lead to large measurement errors. TIA and IEC have updated both publications as a result of this finding.
Currently, a round robin for measurements of optical return loss (ORL) is being coordinated by TIA FO-4, with NIST performing data analysis. More than 25 participants, including TIA FO-4 and IEC TC86 members, are anticipated. Singlemode and multimode specimens, comprising a wide range of nominal ORL values, are being measured using several different methods (CW ORL meters and OTDRs, as well as optical frequency-domain and low-coherence reflectometers). Interlaboratory agreement observed in this comparison will help determine the potential need for ORL calibration-standards development.
TimDrapela oversees calibration-support and other industry-relation issues for the Optical Fiber and Components Group in NIST’s Optoelectronics Division and is chair of TIA FO-4.5.1, Round Robin Testing and Measurement Verification. He can be reached at email@example.com.