Efficient supercontinuum generation in quadratic nonlinear waveguides without quasi-phase matching

TL;DR

This paper demonstrates efficient supercontinuum generation in lithium niobate waveguides without quasi-phase matching, enabling broader spectra and simpler fabrication for mid-infrared applications.

Contribution

It experimentally shows supercontinuum generation in standard LN waveguides without QPM, leveraging self-defocusing solitons at common ultrafast laser wavelengths.

Findings

Octave-spanning supercontinuum observed with femtosecond pumps in 1.25-1.5 μm range

QPM-free design simplifies fabrication and extends waveguide length

Potential for broader spectra with optimized mid-IR waveguide design

Abstract

Efficient supercontinuum generation (SCG) requires excitation of solitons at the pump laser wavelength. Quadratic nonlinear waveguides may support an effective self-defocusing nonlinearity so solitons can directly be generated at common ultrafast laser wavelengths without any waveguide dispersion engineering. We here experimentally demonstrate efficient SCG in a standard lithium niobate (LN) waveguide without using quasi-phase matching (QPM). By using femtosecond pumps with wavelengths in the $1.25-1.5 \mu\rm m$ range, where LN has normal dispersion and thus supports self-defocusing solitons, octave-spanning SCG is observed. An optimized mid-IR waveguide design is expected to support even broader spectra. The QPM-free design reduces production complexity, allows longer waveguides, limits undesired spectral resonances and effectively allows using nonlinear crystals where QPM is inefficient or impossible. This result is important for mid-IR SCG, where QPM-free self-defocusing waveguides in common mid-IR nonlinear crystals can support solitons directly at mid-IR ultrafast laser wavelengths, where these waveguides have normal dispersion.