A six-octave optical frequency comb from a scalable few-cycle erbium fibre laser

A coherent, compact and robust light source with coverage from the ultraviolet to the infrared is desirable for heterodyne super-resolution imaging 1 , broadband infrared microscopy 2 , protein structure determination 3 and standoff trace-gas detection 4 . To address these demanding problems, frequency combs 5 combine absolute frequency accuracy with sub-femtosecond timing and waveform control to enable high-resolution, high-speed and broadband spectroscopy 6 – 9 . Here we demonstrate a scalable source of near-single-cycle pulses from robust and low-noise erbium fibre (Er:fibre) technology. With a peak power of 0.56 MW we generate a comb spanning six octaves, from the ultraviolet (350 nm) to the mid-infrared (22,500 nm), achieving a resolving power of 10 10 across 0.86 PHz of bandwidth. Second-order nonlinearities in LiNbO 3 , GaSe and CdSiP 2 provide phase-stable infrared ultrashort pulses with simultaneous brightness exceeding a synchrotron 10 , while cascaded nonlinearities in LiNbO 3 yield four octaves simultaneously (0.350–5.6 μm). We anticipate that these advances will be enabling for basic and applied spectroscopy, microscopy and phase-sensitive nonlinear optics.