Frequency comb generation in a pulse-pumped normal dispersion Kerr mini-resonator

Abstract

Kerr microresonators driven in the normal dispersion regime typically require the presence of localized dispersion perturbations, such as those induced by avoided mode crossings, to initiate the formation of optical frequency combs. In this work, we experimentally demonstrate that this requirement can be lifted by driving the resonator with a pulsed pump source. We also show that controlling the desynchronization between the pump repetition rate and the cavity free-spectral range (FSR) provides a simple mechanism to tune the center frequency of the output comb. Using a fiber miniresonator with a radius of only 6 cm we experimentally present spectrally flat combs with a bandwidth of 3 THz whose center frequency can be tuned by more than 2 THz. By driving the cavity at harmonics of its 0.54 GHz FSR, we are able to generate combs with line spacings selectable between 0.54 and 10.8 GHz. The ability to tune both the center frequency and frequency spacing of the output comb highlights the flexibility of this platform. Additionally, we demonstrate that under conditions of large pump-cavity desynchronization, the same cavity also supports a new form of Raman-assisted anomalous dispersion cavity soliton.

Dissipative solitons and switching waves in dispersion folded Kerr cavities

“…5(c). In order to reach the required driving powers for the regime where the Floquet dynamics due to the presence of dispersion bands can be accessed and to ensure the generation of a single dissipative structure, pulse-driving using an electro-optic comb is employed (EO-comb) [48] as it has been done previously for experiments in resonators with a similar GHz-domain FSR [15,23,49]. It yields a pulse train of pulses approximately 1.4 ps in duration with an RF controllable repetition rate f eo set near 15 GHz (see appendix for further).…”

“…Such a crossing implies the phase-matching between the states and leads to enhanced power at the crossing modes. This creates the flattened spectral profile of the SW [6,49].…”

“…The left inset in this figure shows the detected power trace from the output of the cavity while the laser centerfrequency is scanned across the cavity resonance from blue-detuned to red-detuned, showing different stages in the way the trace dips in power. The first dip and plateau corresponds to the initial build-up of power in the resonator, and the subsequent formation of the switching wave comb by wave-breaking [6,49]. The second dip, past halfway, marks the sudden growth of satellite combs.…”

Synchronization of nonsolitonic Kerr combs

“…The pair of switching waves locks to one another and leads to a phase-locked, low-noise comb state, exhibiting intricate temporal and spectral features with high conversion efficiencies and slow spectral power falloffs in the region of interest ( 19 , 20 ). Normal GVD combs can be generated through pump modulation at the microresonator free spectral range (FSR) ( 33 , 34 ) or through local perturbations in the dispersion to enable modulation instability, a source of switching wave excitation ( 35 , 36 ). A common method to create these perturbations is through the coupling between different mode families of a microresonator ( 19 , 20 , 23 , 31 , 36 , 37 ).…”

Synchronization of non-solitonic Kerr combs

“…The pair of switching waves lock to one another and lead to a phase-locked, low-noise comb state exhibiting intricate temporal and spectral features with high conversion efficiencies and slow spectral power falloffs in the region of interest [19,20]. Normal-GVD combs can be generated through pump modulation at the microresonator free spectral range (FSR) [33,34] or through local perturbations in the dispersion to enable modulation instability, a source of switching-wave excitation [35,36]. A common method to create these perturbations is through the coupling between different mode families of a microresonator [19,20,23,31,36,37].…”