A supercontinuum optical pulse source provides a combined supercontinuum. The supercontinuum optical pulse source comprises one or more seed pulse sources, and first and second optical amplifiers arranged along first and second respective optical paths. The first and second optical amplifiers are configured to amplify one or more optical signals generated by said one or more seed pulse sources. The supercontinuum optical pulse source further comprises a first microstructured light-guiding member arranged along the first optical path and configured to generate supercontinuum light responsive to an optical signal propagating along said first optical path, and a second microstructured light-guiding member arranged along the second optical path and configured to generate supercontinuum light responsive to an optical signal propagating along said second optical path. The supercontinuum optical pulse source further comprises a supercontinuum-combining member to combine supercontinuum generated in at least the first and second microstructured light-guiding members to form a combined supercontinuum. The supercontinuum-combining member comprises an output fiber, wherein the output fiber comprises a silica-based multimode optical fiber supporting a plurality of spatial modes at one or more wavelengths of the combined supercontinuum.