Engineering Nonlinear and Quantum Photonics in Two-Dimensional Materials

Abstract

Two-dimensional (2D) nonlinear quantum materials, especially transition metal dichalcogenides (TMDs), are highly promising for next-generation devices due to their strong light-matter interaction. A key challenge is the interface between materials and electrodes, where high contact resistivity (RC) hinders device performance. This work introduces a novel method for direct RC measurement in monolayer TMD-metal junctions using photoluminescence (PL) microscopy, a simple approach that overcomes the limitations of traditional electrical methods. Building on this, the thesis tackles the challenge of phase mismatch in nonlinear optics. It presents a quasi-phase-matching (QPM) technique using van der Waals (vdW) stacking of 3R MoS2 layers with specific twist angles, which periodically reverses the nonlinear dipole to significantly enhance second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC). To further amplify efficiency, the research explores resonant field enhancement using metasurfaces supporting quasi-bound states in the continuum (qBIC). This approach, leveraging the high refractive index and nonlinearity of 3R MoS2, led to a remarkable 2000-fold enhancement in SHG intensity, achieved by aligning the metasurface design with the material's lattice and resonances. Culminating this work, the principles of enhanced local fields were applied to the generation of quantum light. The thesis demonstrates enhanced SPDC from a vdW metasurface, producing a high-quality quantum light source. Ultimately, this thesis provides a comprehensive framework, from fundamental material characterization to advanced device engineering, paving the way for the next generation of on-chip quantum light sources and optical technologies. The methodologies and devices presented here establish 2D vdW materials as a powerful platform for the future of integrated photonics.