Developing high-brightness, low-noise supercontinuum (SC) sources is critical for a variety of ultrafast photonics applications. A key challenge in achieving low-noise operation is the suppression of incoherent nonlinear effects and the associated noise amplification. All-normal dispersion (ANDi) SC sources exhibit considerably reduced noise levels compared to conventional soliton-based methods, but their previous lowest-noise demonstrations were limited by amplified spontaneous emission from amplified femtosecond pump laser systems, which seeds incoherent nonlinearities and degrades SC quality. Consequently, the ultimate low-noise limits of coherent SC generation have not been demonstrated by experimental results. Here, we report ultra-low noise, shot-noise-limited SC generation by directly driving the SC process with the un-amplified output of a high-power dual-comb Yb:CALGO oscillator centered at 1053 nm. The resulting SC combs each have a spectrum spanning 820–1280 nm (−20 dB), 1.6 W average power, 1.03 GHz repetition rate, and a comb-line power of ≈10 μW. We conduct detailed noise studies of the SC by analyzing various ≈15-nm-wide spectral bands. All bands reach a shot-noise-limited relative intensity noise below −160 dBc/Hz at 100-kHz to few-MHz noise frequencies. Furthermore, the central spectral bands exhibit an unprecedented noise suppression of the pump laser’s technical noise above ≈2 kHz by >20 dB, which agrees with our semiclassical simulations. Finally, we simultaneously couple both combs into a single ANDi fiber to generate a dual-comb SC with highly symmetric spectra and correlated noise properties between the combs. Coherently averaged linear optical sampling measurements on the dual-comb SC exhibit a high signal-to-noise ratio, showcasing its potential for real-time spectroscopic measurements.

Experimental observations show that broadening frequency-combs in all-normal dispersion fibers can reduce noise by up to 20 dB. Our new numerical model propagates pulse trains generated from real noise measurements and replicates this accurately.

Dual-comb supercontinuum (SC) sources are promising for metrology and spectroscopy applications as their broad bandwidth supports the detection of multiple spectral features simultaneously. However, the limited sensitivity inherent to their high relative intensity noise (RIN) and low power per comb line so far hindered their huge potential in those fields. In this work, we overcome both of these issues with the first shot-noise limited dual-comb SC with gigahertz pulse repetition rate and >1 W output power. It is based on a high-power single-cavity dual-comb Yb:CALGO oscillator centered at 1053 nm, combined with a single polarization-maintaining all-normal-dispersion (ANDi) fiber for spectral broadening. The resulting SC spans 820 nm-1280 nm and has a gigahertz pulse repetition rate enabling high power per comb line and sufficient resolution in the optical domain for most spectroscopy applications. The SC exhibits a shot-noise limited spectrally-resolved RIN power spectral density for all spectral bands, including the spectral wings of the SC and record-low integrated RIN down to 2.7 × 10⁵ for the spectral band at 1100 nm ± 8 nm for the integration range [1 kHz, 10 MHz]. This exceptional performance originates from the pump laser's low noise properties and its high output power which is sufficient to drive the SC process directly without amplification, in combination with the unprecedented noise-suppression in the ANDi fiber reaching up to >20 dB around the oscillator wavelength. To better understand the observed noise-suppression mechanisms, we perform a numerical simulation of the RIN which is in excellent agreement with our measurements. We further analyze a dual-comb interferometry measurement with this source at a repetition rate difference of ~3.95 kHz, which supports the resolution of the entire SC spectrum in parallel without spectral aliasing. The dual-comb spectroscopy figure of merit (FOM) is >1.1 × 10⁷ Hz½ for all spectral bands, making it suitable for high-sensitivity applications. Our measurements further show that recording the entire SC spectrum at once with around 30 parallel detectors would yield an exceptionally high FOM of around 5 × 10⁸ Hz½.

The recent development of fiber supercontinuum (SC) sources with ultra-low noise levels has been instrumental in advancing the state-of-the-art in a wide range of research topics. However, simultaneously satisfying the application demands of maximizing spectral bandwidth and minimizing noise is a major challenge that so far has been addressed with compromise, found by fine-tuning the characteristics of a single nonlinear fiber transforming the injected laser pulses into a broadband SC. In this work, we investigate a hybrid approach that splits the nonlinear dynamics into two discrete fibers optimized for nonlinear temporal compression and spectral broadening, respectively. This introduces new design degrees of freedom, making it possible to select the best fiber for each stage of the SC generation process. With experiments and simulations we study the benefits of this hybrid approach for three common and commercially available highly nonlinear fiber (HNLF) designs, focusing on flatness, bandwidth and relative intensity noise of the generated SC. In our results, hybrid all-normal dispersion (ANDi) HNLF stand out as they combine the broad spectral bandwidths associated with soliton dynamics with extremely low noise and smooth spectra known from normal dispersion nonlinearities. Hybrid ANDi HNLF are a simple and low-cost route for implementing ultra-low noise SC sources and scaling their repetition rate for various applications such as biophotonic imaging, coherent optical communications, or ultrafast photonics.

The low-noise and phase-coherent nonlinear transformation of a narrowband laser into a broadband supercontinuum (SC) in an optical fiber forms the basis of extremely precise applications ranging from optical frequency comb technology to ultrafast photonics and biomedical imaging. A major challenge of this process is the avoidance of incoherent nonlinear effects that amplify random quantum noise, requiring careful birefringence and dispersion engineering of the fiber. However, fundamental trade-offs exist between working in normal or anomalous dispersion regimes. Here, we combine the benefits of nonlinear dynamics in both regimes by cascading soliton compression and optical wave breaking in a hybrid fiber, formed by joining two widely available, commercial, polarization-maintaining step-index fibers exhibiting anomalous and all-normal dispersion, respectively. We experimentally demonstrate that this hybrid approach results in an ultra-low-noise fiber SC source covering the 930–2130 nm range with phase coherence near unity, spectrally resolved relative intensity noise (RIN) as low as 0.05%, and averaging 0.1% over a bandwidth of 750 nm, approaching the theoretical limits close to the pump laser noise. This corresponds to a doubling of the generated spectral bandwidth and a decrease of RIN by up to 1 order of magnitude compared to direct pumping of the individual fibers, where modulational polarization instabilities play a limiting role. Owing to its simplicity and its scalability to high repetition rates, our hybrid scheme is readily applicable to various laser platforms and could enhance the performance of applications such as hyperspectral nonlinear microscopy, coherent optical communications, and photonic signal processing.

By cascading soliton compression in an anomalous dispersion fiber and optical wave-breaking in a normal dispersion fiber, we demonstrate a coherent ultra-low noise fiber SC source covering the 930 - 2130 nm range.

Supercontinuum (SC) sources based on nonlinear spectral broadening of ultrashort pulses in specialty optical fibers have become an indispensable tool in a diverse range of application fields such as biomedical imaging, precision spectroscopy, and ultrafast photonics. After the initial race to maximize their spectral bandwidth and coverage, the noise properties of SC sources have recently shifted into focus. The large pulse-to-pulse fluctuations and correspondingly large relative intensity noise (RIN) present in commercial SC sources strongly limit the sensitivity, precision or resolution of many applications [1] . Recent work suggests that the dispersion engineering of the nonlinear fiber plays an important role for the resulting SC noise properties, as all-normal dispersion (ANDi) fibers suppress the noise-amplifying nonlinear processes that typically dominate the spectral broadening in their anomalously pumped counterparts [2] , [3] .

A new generation of ultrafast and low-noise supercontinuum (SC) sources is currently emerging, driven by the constantly increasing demands of spectroscopy, advanced microscopy, and ultrafast photonics applications for highly stable broadband coherent light sources. In this Perspective, we review recent progress enabled by advances in nonlinear optical fiber design, detail our view on the largely untapped potential for noise control in nonlinear fiber optics, and present the noise fingerprinting technique for measuring and visualizing the noise of SC sources with unprecedented detail. In our outlook, we highlight how these SC sources push the boundaries for many spectroscopy and imaging modalities and focus on their role in the development of ultrafast fiber lasers and frequency combs with ultra-low amplitude and phase noise operating in the 2 mu m spectral region and beyond in the mid-IR.

Specialty optical fiber designs are presented that minimize quantum, technical, and polarization noise amplification during supercontinuum generation. Applications in ultrafast photonics are discussed.

Highly coherent and low noise supercontinuum (SC) sources based on nonlinear spectral broadening of femtosecond pulses in all-normal dispersion (ANDi) fibers are attractive for many applications in ultrafast photonics, such as nonlinear bio-photonic imaging, ultrafast spectroscopy, coherent X-ray generation, and lownoise ultrafast fiber laser development, amongst others [1].The noise properties of the SC source are of particular importance as fluctuations translate to intensity noise, pulse duration noise, or timing jitter, affecting sensitivity, resolution, or synchronisation of ultrafast experiments.While ANDi SC exhibit superior noise properties compared to their conventional counterparts pumped in the anomalous dispersion regime, recent theoretical studies suggest that polarization modulation instability (PMI) can severely degrade their stability [2].Here we present, for the first time, detailed experimental polarization-dependent relative intensity noise (RIN) measurements of ANDi SC sources based on both polarization-maintaining (PM) and non-PM fibers, and compare them to a conventional SC source (Fig. 1).All fibers were pumped with an ultrafast Er:fiber laser (80 fs, 40 MHz, 0.05% RIN), generating SC with comparable spectral bandwidths in the range 1.2 -2.2 µm.A rotating half-wave plate in front of the fiber and a synchronized analyzer at the fiber exit controlled the plane of pump pulse and detection polarization with respect the fiber's principal axes.Integrated RIN values from 0-18 MHz were measured using a photodiode and electronic spectrum analyzer with an angular resolution of approximately 0.2°.

We simulate nonlinear compression experiments using all-normal dispersion fibers to assess the impact of quantum shot noise and technical noise on ultrafast experiments. Technical noise shows little to no impact with realistic pump pulse parameters.

Highly coherent and low-noise supercontinuum (SC) sources based on nonlinear spectral broadening of femtosecond pulses in all-normal dispersion (ANDi) fibers are attractive for many applications in ultrafast photonics. By simulating a real nonlinear pulse compression experiment, we numerically investigate the impact of shot noise and technical pump laser fluctuations on the quality and stability of single-cycle pulse generation and other multi-shot experiments based on the manipulation of the SC spectral phase. We find that for pump pulse durations of less than 600 fs, input relative intensity noise < 1 %, and correctly chosen fiber lengths, the initial fluctuations of the pump laser are at most amplified by a factor of three. We also show that the usual strong correlation between SC coherence and quality of the compressed pulses collapses in the presence of technical noise, and that in this situation the coherence is not a useful figure of merit to quantify pulse quality, noise amplification, or decoherence due to incoherent nonlinear dynamics. Our results highlight the very limited impact of technical pump laser noise on ANDi SC generation and are of practical relevance for many ultrafast photonics applications that require high-quality, low-noise SC sources.