Engineering of the interband second order optical nonlinearity using asymmetric coupled quantum wells

Developing a semiconductor platform with strong second-order optical nonlinearity can enable better integration with semiconductor photonics and improved performance compared to traditional nonlinear optical materials (i.e. LiNbO₃). In a coupled quantum well structure, the quantum well thicknesses, tunneling barrier thickness, material compositions, and other parameters can be designed to tune the second-order susceptibility, χ⁽²⁾. Utilizing interband transitions allows access to energy level transitions across the bandgap, thus enabling strong, tunable χ⁽²⁾ in the near-IR. Schrodinger-Poisson methods and density functional theory were used to calculate the second-harmonic generation χ⁽²⁾ for GaAs/AlGaAs coupled quantum well structures. By using rigorous wavefunction calculation methods and considering all possible transitions contributing to second-harmonic generation, multiple methods to enhance and tailor χ⁽²⁾ have been determined. Using coupled asymmetric GaAs/AlGaAs quantum wells and varying the quantum well thicknesses, the 50 meV off-resonant wavelength for χ⁽²⁾ can be tuned across the optical communications wavelengths between 1.5 m and 1.7 m. This work lays the foundation for designing III-V superlattices and digital alloys with enhanced second-order optical nonlinearities that can be tailored for the wavelength requirements of particular applications