Determining the deformation and resulting coupling efficiency degradation of ultrastable fiber-coupled optical benches under load

Abstract

Fiber-coupled optical benches are an integral part of many laser systems. The base of such an optical bench is usually a slab of solid material, onto which optical components are fixed. In many environments, the ability to retain high fiber coupling efficiency under mechanical loads is essential. In this article, we study the fiber-to-fiber coupling efficiency under the application of static mechanical loads experimentally and theoretically: We constructed a simple three-point bending setup to interferometrically measure the deformation of an optical bench under load. Using the same setup, we further recorded the resulting coupling efficiency variations. The examined optical benches are based on Zerodur optical benches used in sounding rockets and International Space Station missions. We also developed an analytical model that incorporates an Euler-Bernoulli beam deformation model and a simple model for calculating the coupling efficiency, to which the experimentally obtained data are compared. Furthermore, we use a finite element method simulation to compare to the recorded deformation data. Recorded data, the analytical model, and simulations show good agreement. We also show how the presented analytical model can easily be expanded to contain more complex beam paths and, thus, be used to estimate coupling losses for experimentally relevant optical benches under load.