[en] Charged lepton flavour violation is highly suppressed in the Standard Model, which results in a prediction for the branching ratio of μ"+→e"+e"+e"- below O(10"-"5"4). The Mu3e experiment will search for this rare decay with a sensitivity of 10"-"1"6. An observation would be a clear sign for new physics. A high muon stopping rate of 2.10"9 Hz is required so that sufficient statistics can be accumulated in about one year of data taking. The high event rate and the requirement of a full online track reconstruction demand a fast readout system which should provide a bandwidth above 1 Tbit/s. Reconfigurable devices, namely FPGAs, can easily parallelise the data processing, so it becomes possible to sort, merge, pack and route the data with low latency at high throughput. Optical fibres are the only option for the interconnection between different FPGA-based boards. The fibres also reduce the crosstalk and signal attenuation, especially over long distance links. As part of the readout system prototyping, firmware for synchronous merging of different data streams is being developed. In addition, the optical links have been tested and show a bit error rate below O(10"-"1"6) at 6.4 Gbit/s for a single fibre.