We demonstrate the supercontinuum (SC) generation in a suspended-core As₂S₃ chalcogenide microstructured optical fiber (MOF). The variation of SC is investigated by changing the fiber length, pump peak power and pump wavelength. In the case of long fibers (20 and 40 cm), the SC ranges are discontinuous and stop at the wavelengths shorter than 3500 nm, due to the absorption of fiber. In the case of short fibers (1.3 and 2.4 cm), the SC ranges are continuous and can extend to the wavelengths longer than 4 μm. The SC broadening is observed when the pump peak power increases from 0.24 to 1.32 kW at 2500 nm. The SC range increases with the pump wavelength changing from 2200 to 2600 nm, corresponding to the dispersion of As₂S₃ MOF from the normal to anomalous region. The SC generation is simulated by the generalized nonlinear Schrödinger equation. The simulation includes the SC difference between 1.3 and 2.4 cm long fiber by 2500 nm pumping, the variation of SC with pump peak power in 2.4 cm long fiber, and the variation of SC with pump wavelength in 1.3 cm long fiber. The simulation agrees well with the experiment.

Bulk transition metal dichalcogenides (TMDs) have found widespread applications on nanophotonics, condensed matter physics, and quantum optics, due to their high refractive index and stable excitonic response at room temperature. In this paper, based on the finite-element method simulations, we demonstrate that the high refractive index enables the fabrication of bulk $\mathrm{W}{\mathrm{S}}_2$ into high-quality-factor metasurfaces that support chiral quasibound states in the continuum (Q-BICs). Interestingly, the Q-BIC resonance can in turn hybridize with excitons in the $\mathrm{W}{\mathrm{S}}_2$ metasurface itself. The self-hybridized exciton-polaritons, induced by the strong coupling between a Q-BIC and excitons, exhibit a typical anticrossing behavior with the Rabi splitting up to 136.5 meV. Such remarkable anticrossing behavior is also well elucidated by the coupled oscillator model. Intriguingly, we numerically verify that the self-hybridized exciton-polaritons are photonic spin-controlled, attributed to the chiral Q-BIC with the circular dichroism approaching 0.91. Therefore, we can control the exciton-photon interaction by simply changing the helicity of incident light. We believe that the outstanding self-hybridized exciton-polaritons in a $\mathrm{W}{\mathrm{S}}_2$ metasurface itself, without external microcavities, could pave the way for large-scale, low-cost integrated polaritonic devices at room temperature. Additionally, the chiral Q-BIC will enrich the toolbox for engineering exciton-photon interactions in bulk TMDs and other semiconductors. The photonic spin-controlled self-hybridized exciton-polaritons would find utility in ultrafast all-optical switches, modulators, chiral light-emitting devices, and valleytronic devices.

High flatness, wide bandwidth, and high-coherence properties of supercontinuum (SC) generation in fibers are crucial in many applications. It is challenging to achieve SC spectra in a combination of the properties, since special dispersion profiles are required, especially when pump pulses with duration over 100 fs are employed. We propose an all-solid microstructured fiber composed only of hexagonal glass elements. The optimized fiber possesses an ultraflat all-normal dispersion profile, covering a wide wavelength interval of approximately 1.55 μm. An SC spectrum spanning from approximately 1030 to 2030 nm (corresponding to nearly one octave) with flatness $<3\mathrm{dB}$ is numerically generated in the fiber with 200 fs pump pulses at 1.55 μm. The results indicate that the broadband ultraflat SC sources can be all-fiber and miniaturized due to commercially achievable 200-fs fiber lasers. Moreover, the SC pulses feature high coherence and a single pulse in the time domain, which can be compressed to 13.9-fs pulses with high quality even for simple linear chirp compensation. The Fourier-limited pulse duration of the spectrum is 3.19 fs, corresponding to only 0.62 optical cycles.

Soliton self-frequency shift (SSFS) and third-harmonic generation (THG) are observed in a four-hole As2S5 chalcogenide microstructured optical fiber (MOF). The As2S5 MOF is tapered to offer an ideal environment for SSFS. After tapering, the zero-dispersion wavelength (ZDW) shifts from 2.02 to 1.61 μm, and the rate of SSFS can be enhanced by increasing the energy density of the pulse. By varying the average input power from 220 to 340 mW, SSFS of a soliton central wavelength from 2.206 to 2.600 μm in the mid-infrared is observed in the tapered segment, and THG at 632 nm is observed in the untapered segment.

High-refractive-index nanostructures offer versatile opportunities for nonlinear optical effects, due to their ability to strongly confine field into a subwavelength scale. Herein, we propose a rhomboidal amorphous silicon metasurface to realize high-efficiency dual-band third-harmonic generation (THG), based on the supported dual quasi-bound states in the continuum (Q-BICs). Owing to the very large field confinement inside the metasurface empowered by Q-BICs, the THG efficiency up to 3.74 × 10−3 with the peak pump intensity of 30 MW/cm2 is observed. Meanwhile, thanks to the very high quality factor of Q-BICs, the ultra-narrow nonlinear process with the full width at half maximum less than 1 nm is also witnessed, suggesting the good monochromaticity. Interestingly, the dual-band THG is verified to be polarization-dependent and polarization-insensitive, respectively. The finite element method simulations exhibit that the polarization-dependent THG is attributed to the Q-BIC driven by the electric quadrupole characterized by a pair of anti-parallel electric dipoles along the x axis, which are only excited by the x-linearly polarized light. On the contrary, the polarization-insensitive THG is enabled by another Q-BIC governed by the magnetic dipole resonance with circular electric field vectors, which can be excited by any linearly polarized light. The polarization-controlled and polarization-independent dual-band THG enabled by the physics of Q-BICs would open possibilities for designing switchable nonlinear light sources. The proposed dual Q-BICs scheme undoubtedly can serve as a universal recipe for other nonlinear effects, including sum-frequency generation, difference-frequency generation, and high-order harmonics.