Applications of Nonlinear Optics in 3D Direct Laser Writing and Integrated Nanophotonics

Abstract

This thesis presents novel applications of nonlinear optics in laser fabrication and sources of entangled photons for quantum optics. Femtosecond direct laser writing in transparent media enables mask-less fabrication of sub-micrometer scale features with flexibility in feature shape and position in the x, y, and z-directions. Different applications in optics can be enabled by working in a variety of material platforms. We explore direct laser writing of metal structures in polymer matrices for applications in diffraction optics and modification of hydrogenated amorphous silicon (a-Si:H) for integrated optical devices. These topics explore how nonlinear optical interactions are applied to alter material properties using light. Conversely, nonlinear interactions can be used for wavelength conversion. Nonlinear interactions in nanoscale waveguides can be leveraged to produce efficient sources of entangled photons for applications in quantum optics. We explore using a novel photonic platform, titanium dioxide (TiO2), to realize third-order spontaneous parametric down-conversion (TOSPDC) for direct generation of entangled photon triplets.

There is a need for new fabrication techniques that enable true 3D fabrication on the sub-micrometer scale. Diffraction optical elements have many potential applications in imaging, wavelength selection, and dispersion compensation. Multi-layer diffraction optical elements could be used to integrate imaging systems on-chip for lab-on-chip devices, such as microfluidic systems. We explore using 3D laser-written metal structures in polymer matrices for 3D gratings and diffractive elements, such as zone plates and pinholes. We demonstrate diffraction from 3D gratings and imaging using zone plates.

3D fabrication of waveguides has enabled fabrication of complex optical systems within optical fibers and bulk glasses. We explore using femtosecond laser interactions with hydrogenated amorphous silicon to introduce refractive index changes. a-Si:H could be directly integrated with CMOS devices and has the potential for much higher index contrast than bulk glasses, enabling dense, multi-layer optical devices.

Efficient sources of three or more entangled photons are necessary for advances in quantum photonics. Current techniques are highly limited because they rely on cascaded second order down-conversion processes to produce entangled photon triplets and often are based in bulk optics. We leverage the high transparency, high linear refractive index, and high chi(3) nonlinearity in TiO2 to develop integrated, on-chip nano-scale waveguide sources of entangled photon triplets via TOSPDC. We present the phase-matching and nonlinear overlap conditions necessary and explore important experimental design considerations.