Soliton based χ⁽²⁾ combs in high-Q optical microresonators.

Area of Science:

• Nonlinear optics and photonics
• Microresonator-based frequency combs
• Second-order nonlinear (χ(2)) phenomena

Background:

• Frequency combs in third-order nonlinear (χ(3)) microresonators are well-established, utilizing soliton-based regimes.
• Comb-soliton studies in second-order nonlinear (χ(2)) microresonators, involving coupled first harmonic (FH) and second harmonic (SH) envelopes, are emerging.
• χ(2) microresonators offer unique mechanisms for frequency comb generation through second harmonic generation and optical parametric oscillation.

Purpose of the Study:

• To explore and report on a novel family of dual frequency combs in χ(2) microresonators.
• To investigate the conditions and parameters favorable for generating spectrally broad dual first harmonic (FH) and second harmonic (SH) combs.
• To provide theoretical predictions for the realization of these combs in lithium niobate microresonators.

Main Methods:

• Theoretical investigation of dual soliton-comb formation in high-Q microresonators.
• Analysis of the influence of parameters such as pump power, group velocity matching, and resonator properties.
• Modeling of comb and dissipative soliton parameters, including dependence on pump power, wavelength deviation from phase matching, modal quality factors, and frequency detunings.

Main Results:

• Demonstration of a vast accessible dual χ(2) soliton-comb family in high-Q microresonators.
• Identification of the vicinity of equal first harmonic (FH) and second harmonic (SH) group velocities as optimal for generating spectrally broad dual combs.
• Prediction of specific parameters for radial poling in lithium niobate resonators required for comb generation.

Conclusions:

• The study establishes a solid theoretical foundation for the realization of dual χ(2) frequency combs.
• The findings highlight the potential of χ(2) microresonators for generating novel and spectrally broad optical frequency combs.
• This work opens new avenues for research and applications in nonlinear optics and frequency metrology.