Excitation of pure quartic platicon in optical microresonators

We analytically derive the formulas of the threshold pump intensity and the range of possible detuning for the initiation of the pure quartic platicon (PQP) in the presence of multiphoton absorption, free-carrier absorption, and free-carrier dispersion. Theoretical investigations demonstrate a feasible approach for the excitation of PQP in the normal quartic dispersion regime via the free-carrier effects in platforms such as silicon, germanium, and their derivates. Due to the time-variant nonlinear loss related to free-carrier absorption or additional nonlinear detuning induced by free-carrier plasma dispersion, PQP can be generated through turn-key or laser frequency scanning schemes in both the three- and four-photon absorption regimes. Parameter spaces associated with varying detuning and free-carrier lifetime for the different dark, oscillating, and bright PQP states are revealed in the turn-key generation case. Such solitonic pulses are more energetic than conventional quadratic solitons with the same pulse width, especially for shorter pulse operations. In the spectral domain, PQP microcombs in the mid-infrared are desired for spectroscopy. These findings will facilitate the generation and manipulation of PQP and present promising potential for Kerr microcomb related applications.