Mid-infrared frequency comb generation via cascaded quadratic nonlinearities in quasi-phase-matched waveguides

Abstract

We experimentally demonstrate a simple configuration for mid-infrared (MIR) frequency comb generation in quasi-phase-matched lithium niobate waveguides using the cascaded-${\chi }^{(2)}$ nonlinearity. With nanojoule-scale pulses from an Er:fiber laser, we observe octave-spanning supercontinuum in the near-infrared with dispersive-wave generation in the 2.5--3 $\text{μ}$m region and intra-pulse difference-frequency generation in the 4--5 $\text{μ}$m region. By engineering the quasi-phase-matched grating profiles, tunable, narrow-band MIR and broadband MIR spectra are both observed in this geometry. Finally, we perform numerical modeling using a nonlinear envelope equation, which shows good quantitative agreement with the experiment---and can be used to inform waveguide designs to tailor the MIR frequency combs. Our results identify a path to a simple single-branch approach to mid-infrared frequency comb generation in a compact platform using commercial Er:fiber technology.

References in corpus (2)

• Ultrabroadband supercontinuum generation and frequency-comb stabilization using on-chip waveguides with both cubic and quadratic nonlinearities
• Review of measurements of Kerr nonlinearities in lithium niobate: the role of the delayed Raman response

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• Towards optical frequency comb generation in continuous-wave pumped titanium indiffused lithium niobate waveguide resonators
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