Two-color platicons in quadratically nonlinear optical microresonators

Abstract

During the last decade generation of frequency combs and different types of dissipative solitons was demonstrated and well-studied in high-Q optical microresonators with Kerr nonlinearity. However, recently, it was shown that it is also possible in microresonators with quadratic nonlinearity. In our work, we studied numerically the generation of coherent frequency combs in quadratically nonlinear microresonators via conventional frequency scan method for both second harmonic generation and downconversion processes. We revealed that under particular conditions it is possible to generate two-color flat-top solitonic pulses, platicons, using pump amplitude modulation or controllable mode interaction approach, if the signs of the group velocity dispersion (GVD) coefficients at interacting harmonics are opposite. For SHG process at each combination of GVD coefficients platicon generation was observed at both positive and negative pump frequency detunings from the linear microresonator resonance. Platicon generation was also demonstrated for the downconversion process. Platicon excitation was observed at positive detunings for the normal GVD at pump frequency and at negative detunings in the opposite case. For both SHG and downconversion processes, for the efficient platicon excitation one needs simultaneous accurate matching of the free spectral ranges at interacting harmonics and resonant eigenfrequencies. Excitation conditions and platicon generation domains were revealed for different generation methods, and properties of generated platicons were studied for various combinations of medium parameters.