Figure 2. Experimental setup.

An external cavity laser (ECL) at 1550.3 nm is phase modulated (PM) and amplified in an erbium-doped fibre amplifier (EDFA) before injection in SMF-28 single-mode fibre. The input noisy continuous wave breaks up into a random breather train which is measured using an optical spectrum analyser (OSA) and a time-lens magnifier (PicoLuz UTM-1500). The time lens uses two dispersive propagation steps (D₁ and D₂), one on each side of an element that applies a quadratic temporal phase. In our experiments, the quadratic phase was applied from four wave mixing (FWM) with a linearly chirped pump pulse co-propagating in a silicon waveguide. The chirped pump pulses of duration ∼90 ps are generated from a femtosecond pulse fibre laser at 100 MHz subsequently stretched through propagation in a fibre of dispersion D_p. Optimal fidelity in the time lens requires polarization control (PC) for the pump-signal FWM in the silicon waveguide. The wavelength-converted idler after FWM (with applied quadratic phase) is filtered before further propagation in segment D₂. The overall temporal magnification is 76.4 such that the stretched replica of the input at the output of D₂ can be resolved using a 30 GHz bandwidth detection system (photodiode and ultrafast oscilloscope). The output signal takes the form of a sequence of noisy breather peaks separated by 10 ns. Note that the figure plots results over a timespan of 50 ps, but peak detection used only a 25 ps region of the measurement window. We also show three representative signals obtained from experiment (at 17.3 km propagation) plotting both unfiltered raw data (black traces), and data after filtering (see ‘Methods' section) to remove instrumental noise (red curves).