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 LiNbO3, GaSe and CdSiP2 provide phase-stable infrared ultra-short pulses with simultaneous brightness exceeding a synchrotron(10), while cascaded nonlinearities in LiNbO3 yield four octaves simultaneously (0.350-5.6 mu m). We anticipate that these advances will be enabling for basic and applied spectroscopy, microscopy and phase-sensitive nonlinear optics.