Nonlinear Optics Using Resonant Metamaterials

Nonlinear optics is the study of the interaction between matter and intense laser light, which can result in frequency conversion and modulation of the interacting laser light. Consequently, nonlinear optical processes have enabled numerous technologies, such as frequency-tunable and pulsed laser sources. However, efficient nonlinear optical components are bulky and limited in functionality, making them unsuitable for modern photonic devices with microscopic dimensions. Recent advances in nanoscale fabrication have opened up avenues for replacing bulky nonlinear crystals with much smaller components. One example of these is metamaterials.

Metamaterials are artificial structures consisting of nanoscale building blocks, such as metal nanoparticles in plasmonic metamaterials. Through careful design of the individual building blocks, metamaterials can exhibit properties not often found in natural materials. These properties enable novel methods to boost and control optical responses of metamaterials. In particular, nonlinear responses of such structures have been heavily investigated due to their potential for flat nonlinear photonic components.

In this Thesis, novel plasmonic metamaterials for nonlinear optics were designed. The aim was to bring conventional enhancement methods of nonlinear processes, i.e., phase matching and multiply-resonant field-enhancement, to sub-wavelength metamaterials. Furthermore, the capabilities of nonlinear materials were broadened by proposing methods for tunable and broadband frequency conversion processes that are extremely difficult to realize with traditional materials. The presented findings pave the way towards tunable and multi-functional nonlinear components for a large variety of flat photonic devices.