Nonlinear optical oscillation in on-chip erbium-doped lithium niobate microring resonators

Erbium-doped lithium niobate(LN) on insulator active devices, such as lasers and amplifiers, have received increasing attention. The nonlinear optical oscillation in them at high power destabilizes the output of signals and cannot be ignored. In this study, we reported the experimental observation and theoretical analysis of the nonlinear optical oscillation in erbiumdoped lithium niobate-on-insulator(LNOI) microring resonators while scanning the pump wavelength. Under the same pump power, the number of oscillation cycles decreases when the wavelength scanning rate increases from 10.6 to 33.9 nm/μs. A theoretical model based on the competition between the thermo-optic nonlinearity and the photorefractive effect was introduced to interpret the oscillation in transmission. A series of parameters were obtained from the comparison between the theoretical and experimental results; some of them, the relaxation rates of the thermal and the electric field, are significantly different from those of undoped LNOI microcavities. This work provides a valuable reference for future applications of active LNOI devices.