Generation of platicons and frequency combs in optical microresonators with normal GVD by modulated pump

Abstract

We demonstrate that flat-topped dissipative solitonic pulses, "platicons", and corresponding frequency combs can be excited in optical microresonators with normal group velocity dispersion using either amplitude modulation of the pump or bichromatic pump. Soft excitation may occur in particular frequency range if modulation depth is large enough and modulation frequency is close to the free spectral range of the microresonator.Optical frequency combs generated in mode-locked lasers have revolutionized optical measurements. Last years optical microresonators have been attracting growing attention as a promising platform for microresonator-based Kerr frequency-combs [1][2][3]. It was demonstrated both theoretically and experimentally that frequency comb consisting of equidistant optical lines in spectral domain may appear in a nonlinear microresonator pumped by a c.w. laser due to the cascaded four-wave mixing processes. The frequency spacing between comb lines corresponds to the free spectral range (FSR, typically tens of GHz up to THz) of the microresonator which is the inverted round-trip time of light in the cavity. Microresonator-based combs were shown to perform at the level required for optical-frequency metrology applications [5] and for optical communications [6]. However, such systems often suffer from significant frequency and amplitude noise [7,8] due to the formation of sub-combs [9]. In contrast to conventional mode-locked laserbased frequency combs microresonator combs do not correspond, generally, to stable ultrashort pulses in the time domain because of arbitrary phase relations between the comb lines obtained in the process of formation. Kerr solitons solve this problem with a c.w. laser beam converted into a train of pulses, corresponding to a low-noise frequency comb having smooth spectral envelope in the spectral domain. This regime was demonstrated experimentally in optical crystalline and integrated ring microresonators with anomalous group velocity dispersion (GVD) [10,11]. The limitation of this approach is the difficulty to obtain anomalous GVD in broad band for arbitrary centered wavelength in microresonators since material GVD in the visible and near IR is mostly

Nonlinear and Quantum Optics with Whispering Gallery Resonators

“…The stability range of the mode-locked combs in normal GVD resonators is rather narrow [403,409]. A different type of stable pulses can exist in this case, enabled by irregularities of the WGM spectrum due to the modes anti-crossing [410].…”

“…These include flat-topped dissipative solitonic pulse generation [410] and parametric seeding for stabilization of a conventional Kerr frequency comb [411,412]. The parametric seeding can be used to improve the combs stability and achieve low frequency and phase noise.…”

On Frequency Combs in Monolithic Resonators

“…Both narrow (hyperparametric oscillation like) [207,208] and broad Kerr frequency combs were demonstrated under conditions of normal GVD [92,205] and no visible interaction of the resonator spectrum due to mode crossings. The existence domain of the stable normal GVD mode locked combs is rather narrow [121,209] and a different type of stable pulses can exist in this case provided a possibility of small interruption of the mode spectrum due to the resonator mode families anti-crossing [152,153]. It was noticed recently, that the dark pulses are related to so-called switching waves [210][211][212].…”

“…The impact of pump modulation on comb formation was studied in several other works [88,101,[151][152][153][154]. These include flat-topped dissipative solitonic pulse generation [152] and parametric seedling for stabilization of a conventional Kerr frequency comb [88,101].…”

“…These include flat-topped dissipative solitonic pulse generation [152] and parametric seedling for stabilization of a conventional Kerr frequency comb [88,101]. The parametric seedling or injection locking of the frequency combs can be used for improvement of their stability as well as for achieving low frequency phase noise.…”