Titolo della tesi: Design and Optimization of Advanced Nanophotonic Devices based on Plasmonic and Optical soliton technology
This doctoral thesis presents a comprehensive investigation into the design, optimization, and synergistic integration of novel nanophotonic devices, aimed at overcoming fundamental, long-standing limitations in plasmonics and nonlinear optics. The research confronts three critical challenges that obstruct the development of chip-scale integrated plasmonic devices: inefficient light coupling, debilitating propagation loss of Surface Plasmon Polaritons (SPPs), and the inherent instability of reconfigurable waveguides. By combining the subwavelength confinement of plasmonics with the ultra-low-loss photorefractive soliton interconnections, this work provides a complete technological "blueprint" for a new class of hybrid, adaptive nanophotonic systems.
The principal contributions of this research are fourfold. First, a new class of "Bilayered Conventional and Buried Grating" (BCBG) couplers for SPPs is proposed and numerically optimized. These structures are shown to solve the critical input problem by achieving a high coupling efficiency of approximately 30.3% while simultaneously suppressing parasitic light transmission to an unprecedented low of 0.3%, thereby eliminating a key source of noise and crosstalk in dense circuits.
Second, a novel "nonlinearly-assisted propagation" paradigm is introduced to circumvent the high ohmic losses of short-wavelength SPPs. We demonstrate that by generating a 532 nm SPP via second-harmonic generation from a low-loss, long-propagating 1064 nm fundamental SPP, the effective propagation distance of the visible-light SPP can be extended by a factor of approximately 30 by CW and 120 by medium short pulse, opening the door to practical visible-light plasmonics and sensing.
The design of the core hybrid architecture: an ultra-broadband "SPP-to-soliton-to-SPP" interconnect. This system is designed to solve the long-distance routing problem by converting a nanoscale SPP into an ultra-low-loss solitonic waveguide (0.04-0.07 dB/cm) that bridges centimeterscale distances. A key innovation is the use of a multilayer ITO structure to control SPP diffraction via Fabry-Perot resonance, ensuring an efficient launch of the soliton.
The critical barrier of instability in reconfigurable waveguides is solved. We discover and analyze a novel "charge anchoring" mechanism, which, by using a new propagation geometry with a cathode at the output, leverages electrostatic boundary conditions to completely suppress the detrimental self-bending of photorefractive solitons. This breakthrough transforms the soliton from an unstable phenomenon into a perfectly stable, immobilized, and spatially addressable waveguide.
Finally, this thesis demonstrates the power of this stable solitonic platform for advanced nonlinear applications. We show, through experiment and simulation, that the self-formed solitonic waveguide enables highly efficient Parametric Down-Conversion, even far from traditional phasematching conditions. This is achieved through a phase-locking mechanism that ensures perfect mode-overlap and interaction.
Collectively, these contributions establish a viable pathway for the first reconfigurable, low-loss, solitonic-plasmonic interconnects capable of routing signals over centimeter-scale distances between nanoscale components. This work lays the essential groundwork for future advancements in on-chip optical networks, neuromorphic computing, and reconfigurable quantum light sources.