Investigation of Optical Return Loss (Back-Reflection) in Optical Fiber Transmission Links

Abstract

Optical Return Loss (ORL) is the total amount of light returned from an optical fiber relative to the injected light. ORL can adversely affect fiber optics systems which indirectly affects the quality of the fiber network. One of the effects of this loss (multiple reflections) contributes greatly to the noise levels at the optical detector. Optical Return Loss could be caused by intrinsic material scattering (Rayleigh scattering) and Fresnel reflection. This paper however, focuses on the investigation of ORL using an Optical Time Domain Reflectometer (OTDR) amongst Optical Continuous Wave Reflectometer (OCWR), Optical Low Coherence Reflectometer (OLCR), and Optical Frequency Domain Reflectometer (OFDR). The OTDR was able to establish the ORL in every portion of the fiber under test. An ORL average level of 72.54 dB was obtained over span length of 2.86709 – 2.868.11 km. This is beyond the acceptable tolerance level (32 dB) of both the transmission and receiving equipment suggesting serious problem with the links. By implication, ORL can be used to determine the overall efficiency or performance of a fiber plant.