Manipulating light at nanoscale: Non-reciprocal, dynamic and active plasmonic effects

The study of nanophotonics promises many important applications, including, for example, telecommunication, medical imaging, and even solar energy conversion. All these applications benefit from fundamental understanding of how to control the flow of light, particularly in the nano-scale. This thesis explores the opportunities of advanced light manipulation by using the effects of non-reciprocal optics, dynamic structures, and surface plasmons.;In the second part, dynamic photonic structures are exploited for applications in integrated optics. A dynamic structure is a photonic structure with time-dependent refractive-index modulation. Such modulation provides additional degrees of freedom for light control. We show that dynamic modulation can be used to create on-chip isolators and resonators. Achieving on-chip optical signal isolation has been a fundamental difficulty in integrated photonics. The need to overcome this difficulty, moreover, is becoming increasingly urgent, especially with the emergence of silicon nano-photonics, which promises to create on-chip optical systems at an unprecedented scale of integration. Until now, there have been no techniques that provide complete on-chip signal isolation using materials or processes that are fundamentally compatible with silicon CMOS processing. Based on the effects of photonic transitions, we show in Chapter 3 and 4 that a linear, broad-band, and non-reciprocal isolation can be accomplished by spatial-temporal refractive index modulations. We further show in Chapter 5 that using photonic transitions, a high-Q integrated cavity can be created dynamically, with both quality factor and resonant frequency independently tunable.;In the last part of the thesis, we propose to exploit the unique properties of surface plasmons to enhance the signal-to-noise ratio of mid-infrared photodetectors. The proposed photodetector consists of a slit in a metallic slab filled with absorptive semiconductor material. Light absorption in the slit is enhanced due to Fabry-Perot resonances. Further absorption enhancement is achieved by surrounding the slit with a series of periodic grooves that enable the excitation of surface plasmons that carry electromagnetic energy towards the slit. Using surface plasmonic waveguides, we also show in Chapter 7 that the incorporation of gain media in only a selected device area can annul the effect of material loss, and enhance the performance of loss-limited plasmonic devices. In addition, we demonstrate that optical gain provides a mechanism for on/off switching in metal-dielectric-metal plasmonic waveguides.;We first study using non-reciprocal photonic structures to achieve unconventional one-way optical waves. One-way optical effects are of both practical and fundamental interest. Practically, they provide mechanisms to construct and miniaturize non-reciprocal components, which are crucial in optical communication systems. For this purpose, it is of interest to create large contrast between two counter-propagating waves. In chapter 1 and 2, we propose schemes to achieve one-way total internal reflection and one-way waveguides. The consequences of one-way waveguides are also discussed.