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 imaging1, broadband infrared microscopy2, protein structure determination3 and standoff trace-gas detection4. To address these demanding problems, frequency combs5 combine absolute frequency accuracy with sub-femtosecond timing and waveform control to enable high-resolution, high-speed and broadband spectroscopy6–9. 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 1010 across 0.86 PHz of bandwidth. Second-order nonlinearities in LiNbO3, GaSe and CdSiP2 provide phase-stable infrared ultrashort pulses with simultaneous brightness exceeding a synchrotron10, while cascaded nonlinearities in LiNbO3 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. Ultralow-noise erbium:fibre comb technology allows the generation of a comb spanning six octaves, from the ultraviolet (350 nm) to the mid-infrared (22,500 nm), with a resolving power of 1010 across 0.86 PHz of bandwidth.