Fiber optic test equipment - evaluation of OTDR dead zones and ORLM return loss

This paper discusses methods to evaluate optical time domain reflectormeter (OTDR) and optical return loss meter (ORLM) for field applications. Variable reflectance references for multimode and single mode fibers were built to evaluate the attenuation dead zones of OTDRs. Evaluation of the OTDR attenuation dead zone against a reflectance event of -40 dB with recovery to within 0.5 dB of backscatter reflection is discussed. Methods of measurement related to the IEC 61746 standard are discussed. Optical return loss is another important parameter to determine the quality of a single mode fiber network. A variable reflection standard was built to evaluate ORLM models from three different manufacturers in the range of [10 dB to 45 dB] of return loss with an accuracy of +/-0.5 dB. The standard was verified down to -45 dB return loss within +/-0.5 dB. Testing showed that equipment adapter and fiber connector geometries, fiber contact cleanliness, and skill are also critical to the evaluation. Schematics depict setups are presented. Data collection, data analysis, skills, and difficulties in evaluation process are discussed.