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The technique of attenuation measurement using an optical time domain reflectometer (OTDR) was introduced in 1976. Over the years the features, size, and performances of OTDRs have steadily improved. Today the OTDR is a well-established, mature, and ubiquitous test set. The success of the OTDR is due to its unique ability to characterize key parameters of an optical- fiber link, such as the fiber attenuation coefficient, fiber length, and splice loss and location. These measurements can be made having access to one end of the fiber only. Despite a widespread reliance upon OTDR measurements, instrument performance, specification, and calibration remain unstandardized. Standardized OTDR calibration procedures are still missing even for most fundamental parameters. This lack of standardization confuses the OTDR users community when selecting an OTDR, interpreting measurement results, and comparing measurements made with different OTDRs. In 1988 the International Electrotechnical Commission (IEC) Technical Committee 86 (TC 86) Working group 4 (WG 4): Metrology, began work on OTDR calibration techniques concerning attenuation and distance measurements. As one of the basic laboratories of the Bureau National de Metrologie (BNM) the Laboratoire Central des Industries Electriques (LCIE) is designated to work in the field of fiber optics. As a national representative it develops and/or sets new methods for standardization in collaboration with national and international partners. This paper presents the techniques related to research leading to a French proposal for IEC/TC 86/WG 4 OTDR calibration. The methods worked out by the French group are passive techniques. Their aim is to permit OTDR calibration in order to reduce resulting effects of uncertainties arising from fiber characteristics. Two complementary methods are presented: (1) A coupler method proposed by the Centre National d'Etudes des Telecommunications (CNET). (2) A cavity method proposed by the Centre d'Etudes et de Recherches de Toulouse (CERT).
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