Reference-free dual-comb spectroscopy with inbuilt coherence.

We demonstrate a simple system for dual-comb spectroscopy based on two inherently coherent optical frequency combs generated via seeded parametric downconversion. The inbuilt coherence is established by making the two combs share a common comb line. We show that the inbuilt coherence makes it possible to use a simple numerical post-processing procedure to compensate for small drifts of the dual-comb interferogram arrival time and phase. This enables long-time coherent averaging of the interferograms.

Amplifier similariton fiber laser with a hybrid-mode-locking technique.

By employing both frequency shifting and nonlinear polarization rotation mechanisms in a Yb-doped fiber laser, similariton operation regime is demonstrated. Directly generated pulses from an oscillator has a duration of 7.8 ps with 20.5 nm spectrum width and average output power of 7.4 mW with a repetition rate of 26.4 MHz. The pulses can be externally dechirped to be 140 fs. Through numerical simulations we illustrate the details of similariton pulse formation under the simultaneous action of two mode-locking techniques and advantages of hybrid mode-locking approach.

Design guidelines for ultrashort pulse generation by a Mamyshev regenerator.

We study numerically the possibility of using various gain-switched seed laser pulse parameters and fibers for a low-cost, all-fiber Mamyshev regenerator scheme. We find that for increasing pulse durations, sufficient spectral broadening will be difficult to achieve in practice and careful design of the system parameters is required for the regenerator to function. Furthermore, an optimal input peak power level can be defined for a given fiber and pulse duration that results from a balance of competing Kerr effect and stimulated Raman scattering. We also demonstrate experimental results of 3 ps pulse generation seeded by an 80 ps gain-switched diode. Our results pave the way for designing pulse-on-demand picosecond scale fiber sources for applications.

Nanocluster Aerosol Emissions of a 3D Printer.

Many studies exist that characterize the aerosol emissions from fused filament fabrication three-dimensional (3D) printers. However, nanocluster aerosol (NCA) particles, that is particles in a size range under 3 nm, are rarely studied. The purpose of this study was to characterize the NCA emissions and the contribution of NCA to the total particle number emissions from a 3D printer. We used a particle size magnifier and a scanning mobility particle sizer to measure the time evolution of particle size distribution, which was used to calculate the average NCA emission rates during a printer operation in a chamber. The NCA emission rates ranged from 1.4 × 106 to 7.3 × 109 s-1 depending on the applied combination of filament material and nozzle temperature, showing increasing emission with increasing temperature. The NCA emissions constitute from 9 to 48% of the total emissions, that is, almost half of the particle emissions may have been previously neglected. Therefore, it is essential to include the low NCA size range in, for example, future 3D-printer-testing protocols, emission measurement standards, and risk management measures.

Experimental Measurement of the Second-Order Coherence of Supercontinuum.

We measure experimentally the second-order coherence properties of supercontinuum generated in a photonic crystal fiber. Our approach is based on measuring separately the quasicoherent and quasistationary contributions to the cross-spectral density and mutual coherence functions using a combination of interferometric and nonlinear gating techniques. This allows us to introduce two-dimensional coherence spectrograms which provide a direct characterization and convenient visualization of the spectrotemporal coherence properties. The measured second-order coherence functions are in very good agreement with numerical simulations based on the generalized nonlinear Schrödinger equation. Our results pave the way towards the full experimental characterization of supercontinuum coherence properties. More generally, they provide a generic approach for the complete experimental measurement of the coherence of broadband sources.

Machine learning analysis of extreme events in optical fibre modulation instability.

A central research area in nonlinear science is the study of instabilities that drive extreme events. Unfortunately, techniques for measuring such phenomena often provide only partial characterisation. For example, real-time studies of instabilities in nonlinear optics frequently use only spectral data, limiting knowledge of associated temporal properties. Here, we show how machine learning can overcome this restriction to study time-domain properties of optical fibre modulation instability based only on spectral intensity measurements. Specifically, a supervised neural network is trained to correlate the spectral and temporal properties of modulation instability using simulations, and then applied to analyse high dynamic range experimental spectra to yield the probability distribution for the highest temporal peaks in the instability field. We also use unsupervised learning to classify noisy modulation instability spectra into subsets associated with distinct temporal dynamic structures. These results open novel perspectives in all systems exhibiting instability where direct time-domain observations are difficult.

Real-time measurements of spontaneous breathers and rogue wave events in optical fibre modulation instability.

Modulation instability is a fundamental process of nonlinear science, leading to the unstable breakup of a constant amplitude solution of a physical system. There has been particular interest in studying modulation instability in the cubic nonlinear Schrödinger equation, a generic model for a host of nonlinear systems including superfluids, fibre optics, plasmas and Bose-Einstein condensates. Modulation instability is also a significant area of study in the context of understanding the emergence of high amplitude events that satisfy rogue wave statistical criteria. Here, exploiting advances in ultrafast optical metrology, we perform real-time measurements in an optical fibre system of the unstable breakup of a continuous wave field, simultaneously characterizing emergent modulation instability breather pulses and their associated statistics. Our results allow quantitative comparison between experiment, modelling and theory, and are expected to open new perspectives on studies of instability dynamics in physics.