Mode-dependent spectral narrowing of polarized soliton in asymmetric C-rich SiC channel waveguide

Owing to the anomalous group-velocity dispersion (GVD) and polarization mode dispersion (PMD) that occur in the C-rich SiCx channel waveguide with an asymmetric core aspect, the unique spectral linewidth narrowing phenomenon of a negatively chirped femtosecond soliton pulse induced by the interaction between anomalous GVD and nonlinear self-phase modulation (SPM) effects is demonstrated. Under the variation of TE/TM orthogonal polarization incidences, the optical pulse suffers from different levels of spectral linewidth suppression with the changed TE/TM polarization ratio, as it simultaneously experiences the interplay among negative chirp, normal PMD, anomalous GVD, and strong SPM mechanisms in the polarization-selective waveguide when detuning the polarization ratio of the incident soliton. The spectral linewidth can be suppressed from 6.6 to 5.05 nm, associated with a maximal shrinkage of up to 25% when increasing the average power of the soliton pulse from 10 to 45 mW. Numerical fitting with the nonlinear Schrödinger equation determines the anomalous GVD of −2.4 × 103 ps2/m and −6×102 ps2/km for the 9-mm-length C-rich SiCx under TM-mode and TE-mode incidences, respectively. Conversely, the input pulse gradually evolves into a perfect soliton with a broadened spectrum when detuning the anomalous GVD from negative to positive values. Such a birefringent C-rich SiCx waveguide can serve as a tunable pulse shaper and a chirp adjuster by interplaying the mode-dependent GVD/PMD/SPM to induce spectral and temporal reshaping of a chirped soliton for future group-IV integrated photonic system-on-chips.