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Timestamp: 2019-04-22 18:08:07+00:00

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We report time domain measurements of the group-velocity-dispersion-induced and nonlinearity-induced chirping of femtosecond pulses in subwavelength silicon-on-insulator waveguides. We observe that at a critical input power level, these two effects compensate each other leading to soliton formation. Formation of the fundamental optical soliton is observed at a peak power of a few Watts inside the waveguide. Interferometric cross-correlation traces reveal compression of the soliton pulses, while spectral measurements show pronounced dispersive (Cherenkov) waves emitted by solitons into the wavelength range of normal group velocity dispersion.
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Fig. 1 (a) Measured group index (solid squares) and 5th order polynomial fit (curve) of the SOI waveguide as a function of wavelength. (b) Group velocity dispersion (GVD), β2, as a function of wavelength. The vertical line shows the carrier wavelength of the pump pulse. The gray area shows the predicted region for Cherenkov radiation.
Fig. 2 Experimental setup. ISO: isolator; BPF: band-pass filter; Pol.: polarizer; BS: beam splitter; DUT: device under test; FM: flip mirror. Dashed lines stand for optical beams. The insert plot shows the interferometric auto-correlation trace of the input pulses.
Fig. 3 (Color online) (a) Measured interferometric cross-correlation traces with varying input power levels. The first three curves are multiplied by 3, 2.5, and 2 respectively. The symbols L, C, and T represent the leading, central, and trailing regions of the pulse. (b) FWHM of the intensity cross-correlation traces as a function of input power. The red line stands for the FWHM of the intensity auto-correlation trace of the input pulse. (c) Averaged wavelength in the leading (black squares), central (red circles), and trailing (green triangles) regions of the interferometric cross-correlation traces as a function of input power.
Fig. 4 (Color online) Measured output spectra with increasing input power (log scale). The vertical dashed line shows the zero GVD wavelength.
Fig. 5 (Color online) (a) Output spectra and (b) the corresponding cross-correlation traces for 50μW (black), 1mW (red), and 4mW (blue) of the input power, respectively.
Fig. 6 (a) Output power as a function of input power. (b) Integral of the cross-correlation traces with varying input power level. The grey area represents the error introduced by the integration process.

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