Mid-infrared frequency combs and staggered spectral patterns in χ⁽²⁾ microresonators.

Area of Science:

• Integrated photonics
• Nonlinear optics
• Mid-infrared spectroscopy

Background:

• Generating mid-infrared (mid-IR) frequency combs is crucial for various spectroscopic applications.
• Existing mid-IR comb sources are scarce and often complex.
• Integrated photonic platforms offer a promising avenue for miniaturized comb generation.

Purpose of the Study:

• To demonstrate a novel method for generating mid-IR microcombs.
• To explore the potential of cascaded three-wave-mixing in microresonators for mid-IR comb generation.
• To develop a simple and integrated mid-IR frequency comb source.

Main Methods:

• Utilizing a cadmium silicon phosphide (CdSiP2) microresonator.
• Pumping the microresonator at a 1.55 µm wavelength with a low-power continuous-wave laser.
• Employing cascaded three-wave-mixing (χ(2) process) to generate comb lines.

Main Results:

• Successfully generated mid-IR frequency combs centered at 3.1 µm with a spectral span of approximately 30 nm.
• Observed both ordinary comb states and staggered patterns of spectral lines.
• Demonstrated the feasibility of generating combs via cascaded nonlinear processes in integrated devices.

Conclusions:

• The cascaded three-wave-mixing scheme provides a new route for on-chip mid-IR microcomb generation.
• The approach is compatible with standard telecom lasers, enabling simpler integration.
• This work paves the way for compact and accessible mid-IR frequency comb sources.