Supercontinuum generation in quadratic nonlinear waveguides without quasi-phase matching

Area of Science:

• Nonlinear Optics
• Quantum Electronics
• Materials Science

Background:

• Supercontinuum generation (SCG) efficiency relies on direct soliton excitation at the pump laser wavelength.
• Quadratic nonlinear waveguides can exhibit effective negative Kerr nonlinearity.
• Temporal solitons can be generated in the normal dispersion regime, compatible with common ultrafast laser wavelengths.

Purpose of the Study:

• To experimentally demonstrate SCG in standard lithium niobate (LN) waveguides without quasi-phase matching (QPM).
• To investigate the direct generation of negative nonlinearity solitons in the normal dispersion regime.
• To explore the potential for QPM-free designs in mid-infrared SCG.

Main Methods:

• Experimental demonstration of SCG in standard LN waveguides.
• Pumping with femtosecond pulses in the normal dispersion regime.
• Numerical simulations to support experimental observations.

Main Results:

• Achieved large bandwidths, including octave-spanning spectra, indicating the excitation of negative nonlinearity solitons.
• Confirmed soliton excitation through experimental data and numerical simulations.
• QPM-free design simplified production, extended waveguide length, and minimized spectral resonances.

Conclusions:

• QPM-free lithium niobate waveguides enable efficient SCG via negative nonlinearity solitons.
• This approach eliminates the need for waveguide dispersion engineering.
• The QPM-free design is crucial for mid-infrared SCG in nonlinear crystals where QPM is challenging.