Two-photon absorption-induced self-phase modulation in GaAs-AlGaAs waveguides for surface-emitted second-harmonic...

Area of Science:

• Optoelectronics
• Semiconductor Physics
• Nonlinear Optics

Background:

• Surface-emitted second-harmonic generation (SE-SHG) is crucial for frequency conversion.
• GaAs-AlGaAs multilayer waveguides are key components in SE-SHG devices.
• Pulse distortion can limit the efficiency and performance of optical devices.

Purpose of the Study:

• Investigate the cause of asymmetric spectral distortion in fundamental pulses.
• Analyze the impact of free carrier generation on waveguide performance.
• Validate simulation models for nonlinear optical effects in waveguides.

Main Methods:

• Experimental transmission of fundamental pulses through GaAs-AlGaAs multilayer waveguides.
• Spectroscopic analysis of transmitted pulses to identify spectral distortions.
• Numerical simulations incorporating two-photon absorption (TPA) and free carrier effects.
• Measurement of the TPA coefficient in GaAs layers.

Main Results:

• Observed significant asymmetric distortion in the spectra of transmitted fundamental pulses.
• Attributed distortion to refractive index changes caused by free carrier accumulation.
• Free carriers are generated via two-photon absorption in the GaAs layers.
• Numerical simulations accurately reproduced experimental spectral distortions.

Conclusions:

• Two-photon absorption in GaAs layers is the primary cause of performance-limiting spectral distortion.
• Free carrier dynamics significantly influence the nonlinear optical response of these waveguides.
• Accurate modeling of TPA and free carrier effects is essential for designing efficient SE-SHG devices.