Crossover from self-defocusing to discrete trapping in nonlinear waveguide arrays

Area of Science:

• Nonlinear optics
• Photonics
• Condensed matter physics

Background:

• Periodic photonic lattices guide light waves.
• Nonlinear optical effects alter light propagation based on intensity.
• Self-focusing and self-defocusing describe beam profile changes.

Purpose of the Study:

• To predict and demonstrate the transition from nonlinear self-defocusing to discrete self-trapping.
• To investigate the role of refractive index contrast in this transition.
• To experimentally validate theoretical predictions in a practical system.

Main Methods:

• Theoretical prediction using beam propagation models.
• Experimental demonstration in periodically poled lithium niobate (LiNbO3) waveguide arrays.
• Single-site excitation of a narrow Gaussian beam.

Main Results:

• A sharp crossover from nonlinear self-defocusing to discrete self-trapping was predicted with increasing refractive index contrast.
• Nonlinear discrete localization of light was experimentally confirmed.
• Defocusing nonlinearity was observed in the LiNbO3 waveguide arrays.

Conclusions:

• Refractive index contrast is a critical parameter controlling light localization in photonic lattices.
• Discrete self-trapping can be achieved in defocusing nonlinear media.
• The findings have implications for optical switching and light manipulation in integrated photonic devices.