a. Illustration of the soliton crystal state used in this paper. We infer from the generated spectrum that the state was a single temporal defect crystal across the ring. The state had a characteristic ‘scalloped’ micro-comb spectrum, corresponding to the single temporal defect crystal state. b Photograph of the fibre-optic packaged micro-ring resonator chip used for soliton crystal generation. The full chip is 5 mm × 9 mm, of which we use devices and access waveguides on ~ ¼ of the area. The AUD $2 coin (20.5 mm diameter) shown for scale is similar in size to a USD nickel or a 10 Euro cent coin. Inset is a microscope image of the ring resonator element, with a scale bar. Visible distortions are due to an overlayer of glue from the fibre array. c Experimental setup. A CW laser, amplified to 1.8 W, pumped a 48.9 GHz FSR micro-ring resonator, producing a micro-comb from a soliton crystal oscillation state. The comb was flattened and optically demultiplexed to allow for modulation, and the resulting data optically multiplexed before the subsequent transmission through fibres with EDFA amplification. At the receiver, each channel was optically demultiplexed before reception. ECL edge-coupled laser, WSS wavelength-selective switch, Rx receiver.