Ceramic fiber combiner platform for single-mode coupling of multiple high-power lasers of different wavelengths into a polarization-maintaining endlessly single-mode large-mode-area fiber

When combining different laser sources in a polarization-maintaining (PM) fiber, only certain spectral ranges can be coupled with minimal loss. In particular, coupling different laser sources in a polarization-maintaining step-index fiber in the visible and near-infrared (NIR) range results in considerable losses. Furthermore, coupling higher laser powers in highly integrated systems can lead to thermally induced misalignment of the coupling optics, as well as destruction of the fiber end face or the PM fiber used. As part of the investigation, three laser sources were coupled with low loss over a bandwidth of more than 500 nm into an endless single-mode, polarization-maintaining photonic crystal fiber. To achieve this, the fiber was equipped with special customized end caps. Coupling was performed via a highly integrated ceramic optical bench and transfer-coated micro-optics. The surfaces of the manufactured micro-optics and fiber end caps can be cost-effectively coated using the developed broadband transfer coating. The ceramic platform enables thermal conductivity to be increased by up to ten times, with similar or lower expansion coefficients than those of conventionally applied alloys (e.g. COVAR). The developed source reduces thermally induced misalignment thanks to the ceramic micromechanical coupling concept. Additionally, the stiff ceramic platform construction is largely unaffected by vibrations and mechanical deformation.