Jauregui, CesarCesarJaureguiLimpert, JensJensLimpert2025-12-192025-12-1920209781785617515https://publica.fraunhofer.de/handle/publica/50242710.1049/pbcs054e_ch72-s2.0-85114571117Optical fibers have demonstrated, against all early predictions, that their geometry is extremely well-suited for handling high optical powers. However, over the years, many refinements have been done to the basic structure of these waveguides to allow guiding and generating high-powers. As a result of this development the fibers employed in high-power laser systems differ significantly from those typically used in other fields such as telecommunications and/or sensors. Therefore, this chapter is devoted to describing and explaining the main intricacies of those optical fiber designs presently used for high-power operation. In this context, the main goal of this chapter is that the reader gets an overview of the different fiber designs and building blocks of high-power optical fibers. The chapter is divided into three main parts: a brief historical overview of the evolution of this technology, a description of the main constituents of fibers for high-power operation (including the core, the pump cladding and materials), and, finally, an outlook in which novel trends in the design of these waveguides are briefly described.enfalseFibre lasersHigh optical powersHigh-power laser systemsHigh-power operationHigh-power optical fibersLaser beamsOptical design techniquesOptical fiber designsOptical fibre claddingOptical pumpingOverviewPump claddingReviewsWaveguidesbook article