Unusual Nonlinear Optical Absorption Dispersion in a:SiN_x Aperiodic Photonic Structures

Area of Science:

• Nonlinear optics
• Materials science
• Photonics

Background:

• Photonic crystals confine light, influencing light-matter interactions for optical device applications.
• Nonstoichiometric amorphous silicon nitride (a:SiNₓ) layers with contrasting properties enable the creation of aperiodic microcavities.

Purpose of the Study:

• To investigate the nonlinear optical responses of a spatially inhomogeneous quasi-periodic a:SiNₓ microcavity under intense femtosecond laser propagation.
• To understand the switching mechanism between different nonlinear absorption regimes.

Main Methods:

• Fabrication of aperiodic microcavities using Si-rich and N-rich a:SiNₓ layers.
• Probing the photonic miniband region with high-intensity femtosecond laser (740-900 nm).
• Wavelength-dependent and angle-resolved studies at the miniband edge (~750 nm).
• Optical field simulations and comparative studies with periodic microcavities.

Main Results:

• Observed anomalous switching from one-photon-induced saturable absorption (SA) to two-photon-induced reverse saturable absorption (RSA) near the photonic miniband edge.
• Demonstrated that fractal defect energies in N-rich a:SiNₓ layers coupled with photonic confinement expedite this nonlinear optical switching.
• Optical simulations confirmed the unusual nonlinearities and supported the role of fractal effects.

Conclusions:

• Fractal effect-induced resonant photonic modes in aperiodic microcavities lead to unpredictable nonlinear optical responses.
• This study establishes a novel route for photon manipulation and control, modulating photonic device capabilities.
• Provides insights into geometrical influences on photonic modes and nonlinear optical responses.