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Research group | Fiber Optics

Manufacturing of a multimode pump combiner. Photo: Laser Zentrum Hannover e.V.

For the development of stable and alignment-free fiber-based high power laser systems the availability of corresponding passive fiber components is essential. In particular, these include high efficiency pump combiners for Ytterbium-based la- sers emitting in the spectral region around 1 μm. For the realisation of such components different approaches have been designed and implemented. First, pump combiners based on double-clad fibers (pump core 250 μm) and up to four pump fibers were assembled. The coupling efficiency was in excess of 90 percent. Currently, investigations concerning the realisation of novel photonic crystal fiber (PCF) based combiners are being performed.

For this purpose double clad PCFs are also used. All studies have been supported by substantial numerical simulations. In addition, small-bandwidth fiber-based wavelength division multiplexers (WDM), which are necessary for the realisation of all-fiber ultrafast laser systems, have been developed. All of these components have been successfully implemented in the corresponding 1 μm fiber lasers. At the same time, thulium-based ultrafast fiber lasers emitting in the 2 μm wavelength range have been designed and investigated. These systems have a high potential, e.g. for the realisation of frequency combs in the long-wavelength range.