Measuring Insertion Loss and Return Loss using the LWA or OBR

Insertion loss (IL) and return loss (RL) are two of the most fundamental parameters measured in optical system characterization. IL describes how much optical power is transmitted through a device and sets the optical power budget, while RL describes how much power is reflected back toward the source and governs source stability and interference susceptibility.

The attached application note explains what each parameter represents physically, how Luna's sign conventions work, and how the Lightwave Analyzer (LWA) derives IL from Rayleigh backscatter rather than an end-to-end power reference. It then covers the two settings that most affect accuracy, laser tuning range and integration width, along with polarization and calibration effects, common-mode versus residual error sources, and the test conditions under which the IL accuracy specification applies.

This note focuses on the Lightwave Analyzer, but the principles and theories hold true for the Optical Backscatter Reflectometer (OBR) as well.