"Exploring Dynamic Photonics with Transparent Conducting Oxides" 

Jae Ik Choi, MSE PhD Candidate 

Advisor: Professor Alexandra Boltasseva

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ABSTRACT

The exploration of dynamic photonics is critical for advancing next-generation technologies, particularly by developing materials and structures that exhibit strong nonlinearities and ultrafast dynamics. Transparent conducting oxides (TCOs) have emerged as a promising class of materials in this domain, due to their epsilon near zero (ENZ) properties, unprecedented nonlinearities, and sub-picosecond recovery times. This review discusses the intrinsic and extrinsic nonlinearities of TCOs, focusing on their dynamic modulation of intensity-dependent refractive index (IDRI). The intrinsic nonlinearities of TCOs in the ENZ region are primarily governed by real electronic transitions involving higher-order nonlinear susceptibilities such as \(\chi^{(3)}\), \(\chi^{(5)}\) and \(\chi^{(7)}\). Extrinsic enhancements boost the nonlinearities through enhanced light-matter interactions facilitated by electric field enhancements and slow light effects in the ENZ region, which can be further amplified using optical cavities like Tamm plasmon polaritons (TPP). Deep learning-based inverse design methods allow the TPP structures optimization of layer thickness and carrier concentration, enabling perfect confinement of light in deeply sub-wavelength TCO films and enhanced dynamic responses. The overall nonlinear response can be effectively modeled through hot electron dynamics, employing the two-temperature model (TTM) capturing the electron temperature changes within plasmonic cavities. This review highlights how TCOs can be an excellent candidate for next-generation dynamic photonic applications, that open the fascinating regime of controlling light not only in space but also in time.