Quantum-well metasurface for free-space-accessible enhanced nonlinear polarization

Key Points:

• Researchers have developed a co-designed GaAs/AlGaAs multi-quantum-well (MQW) heterostructure combined with a dielectric metasurface that achieves giant, free-space-accessible effective second-order nonlinear susceptibilities for near-infrared-to-visible light conversion, reaching approximately 14 nm V⁻¹—over 270 times larger than that of LiNbO₃.
• The MQW heterostructure exploits engineered interband transitions between coupled quantum wells with different widths to create strong electron displacement and spatial asymmetry, significantly enhancing second-order nonlinear effects near the HH2-to-CB2 transition energy.
• The dielectric metasurface excites a guided-mode resonance (GMR) that converts incident polarization and enhances local electric fields, enabling efficient second-harmonic generation at near-normal incidence, overcoming limitations of conventional excitation schemes requiring out-of-plane field components.
• Experimental measurements confirm a fourfold increase in intrinsic MQW nonlinear susceptibility compared to bulk GaAs and demonstrate a 57-fold enhancement of the critical field product in the heterostructure when coupled with the metasurface, validating the design's effectiveness.
• The approach allows spectral tuning of the nonlinear response through MQW design and metasurface optimization, offering a pathway for miniaturized, efficient nonlinear photonic devices without complex phase-matching or long propagation distances.