Fig. 1: Operation principle of the tunable multi-band Raman laser.
Suppression of the competing nonlinear FWM in thin-film lithium niobate (TFLN) microring resonators for Raman lasing. a A schematic example of the multi-band Raman lasing where the multiple Raman-active phonon branches of lithium niobate (LN) lead to multi-wavelength Raman lasing while the generated Stokes lines can also act as new pumps to induce cascaded Raman lasing, further extending the Raman lasing range. The gradient lobes represent the Raman gain envelope with the Raman frequency shifts ΩRi (i = 1, 2, 3…). b The integrated dispersion profile in three different dispersion regions. The competing nonlinear FWM process may lead to Kerr comb generation in a TFLN microring resonator (inset) for both anomalous dispersion (green) and normal dispersion with avoided-mode crossing (AMX) (blue). In contrast, the device with normal dispersion without AMX (red) can suppress the nonlinear FWM and thus favor its counterpart process: Raman lasing. c Schematic resonances of the fundamental mode of a multi-mode microresonator (corresponding to the blue dispersion in b) influenced by the AMX. The inter-mode coupling would induce resonance shift and cause a periodic dispersion deviation around AMX points, where the group index of the coupled modes determines the AMX period.
