Fig. 1. (A) Experimental setup. DM, dichroic mirror; MS, Martinez stretcher; ISO, isolator; POL, polarizer; ND filter, neutral density filter; NS, nanospike; FTIR, Fourier transform IR spectrometer. (B) Measured auto-correlation trace and (C) the corresponding optical spectrum of the output pulses after the amplifier at an average power of 1.2 W. (D) Optical image of the As2S3-silica nanospike waveguide. The core diameter increases from 0 to 5.4 μm along the 250-μm-long taper transition region. (E) Simulated GVD (top), nonlinearity (bottom) and (F) propagation loss of the hybrid waveguides plotted against wavelength for different core diameters.

Fig. 2. (A) Measured SC spectra generated by the As2S3-silica waveguide with d=5.4  μm under different coupled pump pulse energies. Inset: measured near-field mode image at the output end at 480 pJ coupled pulse energy. (B) Simulated SC spectrum (black) and its coherence (red) at the output face of the waveguide under a coupled pulse energy of 480 pJ. (C) Simulated SC spectral evolution along the 11-mm-long waveguide. (D) Simulated SC coherence evolution along the waveguide. (E) Simulated SC temporal evolution along the waveguide. (F) Long-term stability test of the waveguide under lab condition. (G) Water-resistant test of the hybrid waveguide. Inset: experimental setup.

Fig. 3. (A) Measured SC spectra generated by the As2S3-silica waveguide with d=1.3  μm at different launched pump pulse energies. Inset: measured output near-field mode image at 4.5 μm wavelength and 220 pJ coupled pulse energy. (B) Simulated output SC spectrum (black) and its coherence (red) for the cleaved 2.5-mm-long waveguide. (C) Simulated SC spectral evolution along the waveguide. (D) Simulated SC coherence evolution along the waveguide. (E) Simulated SC temporal evolution along the waveguide.

Fig. 4. (A) Core diameter of the dispersion-varying As2S3-silica waveguide plotted against distance. (B) Contour plot of the waveguide GVD versus wavelength and propagation distance for the waveguide in (A). Inset: calculated phase mismatch Δβ versus wavelength for d=5.4  μm (red solid) and 3.0 μm (black solid). The dashed line marks the phase-matching condition (Δβ=0) for DW generation. (C) Contour plot of waveguide nonlinearity γ over propagation length for the waveguide in (A). (D) Simulated SC temporal evolution along the waveguide. (E) Optical image for one section of the fabricated tapered waveguide. (F) Measured SC spectra generated in the tapered waveguide shown in (A), compared with those generated in waveguides with constant core diameters. The launched pump energy was 490 pJ. (G) Simulated SC spectrum (black) and its coherence (red) for the tapered waveguide. (H) Simulated SC spectral evolution along the tapered waveguide. (I) Simulated SC coherence evolution along the tapered waveguide.