Measurement of radiation induced attenuation in irradiated active fibers using optical frequency domain reflectometry

Abstract

Radiation induced attenuation (RIA) is a major factor affecting the performance of fiber laser systems operated in adverse environments. To investigate the output characteristics of lasers with irradiated active fibers, measurement of detailed RIA profiles is required. Here, a novel method is proposed to explore the attenuation characteristics of irradiated active fibers using optical frequency domain reflectometry (OFDR), which enables propagation loss measurement by acquiring the spatial-resolved backscattered optical signals. With this technique, the RIA data of Yb-doped fibers (YDFs) under uniform radiation is derived by linear fitting of the OFDR traces. And, conventional optical transmission (OT) method is also exploited for comparison. Analysis show that the measured results of the two approaches are consistent. Then, the capability of OFDR is further verified for non-uniform RIA profile measurement of YDFs. For a pump bleached YDF, an upward parabolic RIA profile is attained by taking derivative of the smoothed polynomial fitting of the OFDR trace. Finally, the impacts of RIA profile on the output characteristics of Yb-doped fiber lasers are examined theoretically with a multiphysics thermal model, further validating the necessity of RIA profile measurement.