Externally Pumped Photonic Chip-Based Ultrafast Raman Soliton Source

The advantages of low cost, compact size, and reduced power consumption makes a photonic chip-based ultrafast laser source an appealing technology for diverse applications such as all-optical signal processing, frequency metrology, spectroscopy, and sensing. To date, on-chip ultrafast sources are typically generated by microresonator-based Kerr-comb solitons, which require precise phase tuning and frequency agile lasers to access the soliton state. Here, this work reports the first experimental demonstration of an externally pumped on-chip ultrafast soliton laser source based on Raman soliton self-frequency shift. By capitalizing on strong optical nonlinearity and versatile dispersion control in Ge28Sb12Se60 chalcogenide glass waveguides, 185 fs duration Raman soliton generation has been demonstrated, possessing continuous wavelength tunability from 1589 to 1807 nm with signal-to-noise ratios consistently exceeding 65 dB. The source operates with pump pulse energies as low as 1.08 pJ, representing over three orders of magnitude improvement compared to fiber-based Raman soliton sources. In addition, the generated solitons exhibit excellent spectral purity and stability free from parasitic sidebands. These experimental results are further validated by theoretical analysis, revealing insights into the soliton dynamics and critical device design guidelines. This work therefore enables a new class of broadly tunable, energy-efficient, compact, and potentially cost-effective on-chip ultrafast laser sources.