Supercontinuum (SC) generation via femtosecond pumping in all-normal dispersion (ANDi) fiber is predicted to offer completely coherent broadening mechanisms, potentially allowing for substantially reduced noise levels in comparison to those obtained when operating in the anomalous dispersion regime. However, previous studies of SC noise typically treat only the quantum noise, typically in the form of one-photon-permode noise, and do not consider other technical noise contributions, such as the stability of the pump laser, which become important when the broadening mechanism itself is coherent. In this work, we discuss the influence of amplitude and pulse length noise of the pump laser, both added separately and combined. We show that for a typical mode-locked laser, in which the peak power and pulse duration are anti-correlated, their combined impact on the SC noise is generally smaller than in isolation. This means that the supercontinuum noise is smaller than the noise of the mode-locked pump laser itself, a fact that was recently observed in experiments, but not explained. Our detailed numerical analysis shows that the coherence of ANDi SC generation is considerably reduced on the spectral edges when realistic pump laser noise levels are taken into account.

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The physics and applications of fiber-based supercontinuum (SC) sources have been a subject of intense interest over the last decade, with significant impact on both basic science and industry. New uses for SC sources are also constantly emerging due to their unique properties that combine high brightness, multi-octave frequency bandwidth, fiber delivery and single-mode output. The last few years have seen significant research efforts focused on extending the wavelength coverage of SC sources towards the 2 to 20 µm molecular fingerprint mid-infrared (MIR) region and in the ultraviolet (UV) down to 100 nm, while also improving stability, noise and coherence, output power and polarization properties. Here we review a selection of recent advances in SC generation in a range of specialty optical fibers including: fluoride, chalcogenide, telluride, and silicon-core fibers for the MIR; UV-grade silica fibers and gas-filled hollow-core fibers for the UV range; and all-normal dispersion fibers for ultra-low noise coherent SC generation.

We report an octave-spanning coherent supercontinuum (SC) fiber laser with excellent noise and polarization properties. This was achieved by pumping a highly birefringent all-normal dispersion (ANDi) photonic crystal fiber with a compact high-power ytterbium femtosecond laser at 1049 nm. This system generates an ultra-flat SC spectrum from 670 nm to 1390 nm with a power spectral density higher than 0.4 mW/nm and a polarization extinction ratio of 17 dB across the entire bandwidth. An average pulse-to-pulse relative intensity noise (RIN) down to 0.54% from 700 nm to 1100 nm has been measured and found to be in good agreement with numerical simulations. This highly-stable broadband source could find strong potential applications in biomedical imaging and spectroscopy where improved signal to noise ratio is essential.

We report on an environmentally stable, all-PM-fibre, Er-doped, mode-locked laser with a central wavelength of 1550 nm. Significantly, the laser possesses large net-normal dispersion such that its dynamics are comparable to that of an all-normal dispersion fibre laser at 1 µm with an analogous architecture. The laser is mode-locked with a nonlinear amplifying loop mirror to produce pulses that are externally compressible to 500 fs. Experimental results are in good agreement with numerical simulations.Mode-locked fibre laser systems producing ultrashort (< 500 fs) pulses have numerous applications in fields such as micro-machining, spectroscopy, and nonlinear imaging [1][2][3][4][5][6][7][8][9]. Because the performance of the endapplication is often correlated with the characteristics of the mode-locked pulses, significant research efforts have been invested to devise new and improved laser configurations.To a large extent, the overarching performance and dynamical behaviour of a mode-locked fibre laser is dictated by the dispersion landscape of the cavity. In particular, depending on the cavity dispersion profile, the laser can support one of several distinct pulse regimes, which include e.g. conventional solitons [10], dispersion-managed solitons [11], and similaritons [12].Over the last decade, lasers constructed out of allnormal dispersion (ANDi) fibres and components have attracted particular attention [13][14][15]. This is because such ANDi lasers have been shown to outperform alternative cavity designs in terms of pulse characteristics (e.g. energy, bandwidth), whilst simultaneously simplifying the overall cavity design. These lasers have been dominantly investigated in the 1 µm emission band of Ytterbium, partly because of the applications in that wavelength region, but also because all standard fibres exhibit normal dispersion at 1 µm. In many circumstances, however, the applications a laser can service depends critically on the lasers wavelength of operation [4,16,17]. In particular, for certain applications, operation at 1 µm may not be feasible or optimal, and several studies have accordingly endeavoured to translate ANDi technologies developed in the 1 µm range to other wavelengths, such as 1.55 µm (Erbium) or 2 µm (Thulium) [18][19][20][21][22].The realisation of ANDi-like lasers at the 1.55 µm emission band of Erbium (and the 2 µm of Thulium) is hindered by the fact that most conventional fibres exhibit normal dispersion only for wavelengths shorter than 1.3 µm. Nevertheless, there has been several successful demonstrations of designs that leverage dispersion management so as to achieve ANDi-like performance through a sufficiently large net-normal dispersion, both around 1.55 µm and 2 µm [12,[22][23][24][25][26][27][28]. Whilst these realisations have demonstrated impressive performance, their choice of mode-locking element (nonlinear polarisation rotation or real saturable absorbers) presents potential deficiencies in terms of environmental stability and long-term performance. In particular, nonli...