After a decade of existence, and driven by a remarkable expansion in research and development, plasmonics -the technology that exploit the unique optical properties of metallic nanostructures to enable routing and actively manipulating light at the nanoscale- has entered a defining period in which researchers will seek to answer a critical question: can plasmonics provide a viable technological platform which includes both passive and active nanodevices? The design of these devices is driven by a two-fold objective: 1) to manipulate electromagnetic energy at the nanoscale, including harvesting, guiding and transferring energy, with high lateral confinement down to a few tens of nanometers, and 2) to generate ultrafast (a few femtoseconds) and strong non-linear effects with low operating powers to produce basic active functions such as transistor or lasing actions. Utilizing the resonant properties -field enhancement and spectral sensitivity- of Surface Plasmons Polaritons (SPPs) is generally thought to represent a practical avenue to achieving this objective. However, our ability to control and manipulate light at this scale dynamically -i.e. to produce active functionalities- and in real-time through low-energy external control signals is a missing link in our aim to develop a fully integrated sub-wavelength optical platform. To date, active plasmonic systems, including thermo- and electro-optic media, quantum dots, and photochromic molecules, are achieving sensitive progress in switching and modulation applications. However, high switching times (>nanosecond) or the need for relatively strong control energy (~microJ/cm^2) to observe sensible signal modulation (35% to 80%), limit the practical use of such structures as signal processing or other active opto-electronic nanodevices. In this context, this research aims to assess the potential for defects to enhance the non-linear optical properties of hybrid plasmonic crystals. The objective is to integrate defects, made of plasmonic cavities, in plasmonic crystals to create a focal point for electromagnetic energy stored in surface plasmon waves at the crystal's interfaces. The role of the defect is then to transfer this energy to a neighbouring non-linear material in order to change its optical properties at the femtosecond timescale, thus creating an active functionality. This research, largely based on ultrafast time-resolved near-field optical microscopy, is also expected to enhance our understanding of ultrafast energy transfers at the nanoscale- a critical expertise in designing nanodevices.