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We present theoretical and experimental evidence of high-gain far-detuned nonlinear frequency conversion, extending towards both the visible and the mid-infrared, in a few-mode graded-index silica fiber pumped at 1.064 $\mu$m, and more specifically achieving gains of hundreds of dB per meter below 0.65 $\mu$m and beyond 3.5 $\mu$m. Our findings highlight the potential of graded-index fibers in terms of strong modal confinement over an ultrabroad spectral range for enabling high-gain wavelength conversion. Such advancements require an accurate interpretation of intramodal and intermodal four-wave mixing processes., Comment: 8 pages, 4 figures

Chiral coupling, which allows directional interactions between quantum dots (QDs) and photonic crystal waveguide modes, holds promise for enhancing the functionality of quantum photonic integrated circuits. Elliptical polarizations of QD transitions offer a considerable enhancement in directionality. However, in epitaxial QD fabrication, the lack of precise control over lateral QD positions still poses a challenge in achieving efficient chiral interfaces. Here, we present a theoretical analysis in which we propose to optimize the polarization of a QD emitter against the spatially averaged directionality and demonstrate that the resulting emitter offers a considerable technological advantage in terms of the size and location of high-directionality areas of the waveguide as well as their overlap with the regions of large Purcell enhancement, thereby improving the scalability of the device. Moreover, using $\mathbf{\mathit{k}}\cdot\mathbf{\mathit{p}}$ modeling, we demonstrate that the optimal elliptical polarization can be achieved for neutral exciton transitions in a realistic QD structure. Our results present a viable path for efficient chiral coupling in QD-based photonic integrated circuits, to a large extent overcoming the challenges and limitations of the present manufacturing technology., Comment: Some text modifications in the Introduction, references added, typos corrected, Fig. 7 updated, and the title changed

We provide a complete analysis, from theory to experiment, of the spontaneous emergence of a discretized conical wave of X-type (i.e., a localized 2D+1 space-time wavepacket) when an intense ultrashort pulse nonlinearly propagates in a multimode fiber. In particular, we reveal that this spatiotemporal phenomenon corresponds to broadband intermodal dispersive wave emission from an unsteady localized wave structure formed during nonlinear propagation. Theoretical phase-matching predictions are experimentally and numerically confirmed in a commercially-available step-index multimode fiber. Our results provide a general understanding of phase-matched radiations emitted by nonlinear waves in multidimensional dispersive optical system., Comment: 6 pages, 4 figures

We report on trapped pulse generation in birefringent microstructured optical fiber. Linearly polarized fs pulses are injected into the microstructured fiber in anomalous dispersion regime. We observed experimentally that soliton pulse polarized along the fast fiber axis partially transfers its energy to the orthogonal polarization. The generated pulse is amplified through the orthogonal Raman gain. The two polarization components are located at group-velocity matched wavelengths. The experimental works are supported with numerical simulations. The obtained results are important for the light sources using self-frequency shifted solitons in applications demanding high polarization purity., Comment: 8 pages, 5 figures

This study investigated the nonlinear frequency conversions between the six polarization modes of a two-mode birefringent fiber. The aim was to demonstrate that the selective excitation of different combinations of linearly polarized spatial modes at the pump wavelength initiates distinct intermodal vector four-wave mixing processes. In particular, this study shows that exciting two orthogonally polarized LP01 and LP11 modes can result in simultaneous generation of up to three pairs of different spatial modes of orthogonal polarizations at different wavelengths. The role of the phase birefringence of the spatial modes in the phase-matching of such a four-wave mixing process was explained. Moreover, the theoretical predictions were verified through numerical simulations based on coupled nonlinear Schrodinger equations and also confirmed experimentally in a commercially available birefringent fiber., Comment: 11 pages, 2 figures

The propagation of pulses in optical fibers is described by the generalized nonlinear Schrodinger equation (GNLSE), which takes into account the fiber losses, nonlinear effects, and higher-order chromatic dispersion. The GNLSE is a partial differential equation, whose order depends on the accounted nonlinear and dispersion effects. We present gnlse-python, a nonlinear optics modeling toolbox that contains a rich set of components and modules to solve the GNLSE using the split-step Fourier transform method (SSFM). The numerical solver is freely available, implemented in Python language, and includes a number of optical fiber analysis tools. Code and data are available at https://github.com/WUST-FOG/gnlse-python., Comment: 10 pages, 7 figures

We report the design of a microstructured silica-based fiber for widely tunable soliton self-frequency shift, suitable for pumping with two most common fiber laser wavelengths: 1.04 {\mu}m and 1.55 {\mu}m. Depending on the pump source, the output spectrum can be continuously tuned up to 1.67 {\mu}m (pump at 1.04 {\mu}m) or 1.95 {\mu}m (pump at 1.55 {\mu}m) in the same 1.5 m-long fiber sample, with pump-to-soliton conversion efficiency higher than 20%. The fiber is highly birefringent, which results in an excellent polarization extinction ratio of the soliton, reaching 26 dB. The shifted solitons have a high degree of coherence confirmed by pulse-to-pulse interference measurement. The available soliton tuning range covers the wavelengths inaccessible for fiber lasers, e.g., 1.3 {\mu}m and 1.7 {\mu}m, highly important for multi-photon microscopy and imaging. Our work shows that it is possible to design and fabricate one universal optical fiber that supports soliton shift when pumped at two different wavelengths separated by over 500 nm.