Artificially engineered structures, namely metamaterials and their two-dimensional (2D) counterpart –metasurfaces, have been proven as promising platforms to realize unusual light-matter interactions. Such structures have enabled the efficient manipulation of electromagnetic waves in unprecedented ways that cannot be obtained using conventional materials and thus have triggered exciting applications such as hyperlensing, canalization of light, negative refraction, hyperbolic dispersion, cloaking, or the enhancement of the spontaneous emission rate of dipole emitters, amongst many others. Moreover, the discovery of graphene and other 2D materials, and their electrical tunability, have enabled the use of surface plasmon polaritons at terahertz and infrared frequencies in numerous nanophotonic applications.

In this thesis, I propose novel nano-optical plasmonic tweezers based on hyperbolic and nonreciprocalmetasurfaces to efficiently trap and manipulate nanoparticles in the near field with superior performance compared to the state of the art. To this purpose, I develop a rigorous theoretical framework able to compute optical forces on dipolar Rayleigh nanoparticles located near the metasurfaces. The theoretical model is based on Lorentz force within the dipole approximation combined with the scattered dyadic Green’s function of the system. Analytical expressions show that the force strength is directly proportional to the fourth power of wavenumber of the supported surface plasmons. This tells that the strength can be dramatically enhanced by the proper choice of metasurfaces that support ultra-confined surface plasmons with larger wavenumber. One potential candidate to achieve such response is the use of hyperbolic metasurface that supports surface plasmons with wavenumbers up to ~200 times larger than the ones supported in free space. My theoretical and numerical results using full wave simulations show that the use of hyperbolic metasurfaces enables unusual enhancement of the force strength (up to 3 orders of magnitude) in comparison to the one obtained above conventional isotropic media. Importantly, such response enables stable lateral trapping and efficient manipulation of nanoparticles using low-power laser beam thus reducing the photodamage threat. However, these general optical tweezers are static in the sense that their response cannot be dynamically controlled.

In this context, drift-biased nonreciprocal graphene has emerged as a promising platform to electrically tuneand manipulate the dispersion characteristic of the supported modes. I propose the use of this platform as a planar plasmonic hyperlens that provides ultra-subwavelength imaging with remarkable resolution over a broadband frequency range that cannot be obtained by other artificially engineered structure. In addition, drift-biased graphene can also readily be applied in the context of optical tweezers to provide novel responses: (i) particles can be manipulated unidirectionally independent to the direction of the incoming light, overcoming beam alignment challenges occurring in conventional optical tweezers; and (ii) the location of optical traps can efficiently be manipulated over a few microns range thanks to the electrically tunable response. In summary, I envisage that the proposed nano-optical hyperbolic and nonreciprocal plasmonic tweezers may open unprecedented venues for routing, trapping, and assembling nanoparticles and can effectively address some of the shortcomings of current techniques.

Manipulation of terahertz (THz) waves provides an avenue for exploration and technological advancement because of their capability to interface with biological systems, imaging, security, space exploration, and sensing, as well as enabling ultra-fast communications (1000x current speeds). Unfortunately, this part of the electromagnetic spectrum is susceptible to substantial loss through the atmosphere, sizable enough to make it unusable over long distances in communication. However, over short distances (such as within the human body or on a chip) or in atmosphere-free conditions (such as space), THz can be capable of delivering unprecedented responses. The last decade has seen a surge in THz research for these applications due to advances in sources, detectors, and nanofabrication. Miniaturizing such systems is of importance because of their capability to be introduced into bioelectronic and microelectronic systems. Graphene has been a material of interest since its experimental discovery in 2004 [1] because of its exceptional electronic, mechanical, and electromagnetic properties [2]. In addition, its compatibility with current CMOS (complementary metal oxide semiconductor) processes make it interesting to study using current semiconductor analysis techniques. Graphene’s strong interaction with infrared and THz radiation make it a great candidate material for systems that exploit these regions of the electromagnetic spectrum. Its atomic thickness makes it appealing for the next generation of small scale electronics and its biocompatibility opens new doors for researchers in various fields of bioengineering to utilize this 2D material in their systems. This thesis proposes and develops graphene-based devices that demonstrate state-of- the-art quality. These devices are then characterized electrically, optically, and at THz frequencies. Methodology to further test these devices is proposed and future capabilities as well as potential application are described. This thesis starts by introducing the state of the art of THz

and graphene technologies in Chapter 1. Chapter 2 introduces graphene’s interesting electronic properties. Chapter 3 reports the fabrication of graphene-based devices, and Chapter 4 evaluates the quality of such devices. Chapter 5 subsequently reports the device's response to infrared (IR) light, and explores the influence of light polarization & intensity coupled with electronic stimulation. Chapter 6 reports the THz response and a methodology for determining the Faraday rotation in the THz spectrum. Chapter 7 finalizes the thesis and proposes how all of these fields of study can be combined to develop and implement novel graphene based devices that interact with the electromagnetic spectrum in innovative ways that would enable future research and exciting applications.

Testing the next generation of novel infrared sensorsin a research setting can be a time-consuming and expensive procedure. To address this challenge, an automated solution for characterizing miniaturized optical sensing devices is presented. The system enables rapid, automated characterization of thou- sands of miniaturized devices. The advantages of this system include its low cost, high flexibility, and speed. It enables fast and unique statistical analysis to determine performance and optimal design parameters by individually testing thousands of devices. The proposed system uses a single microprobe to individually test and characterize thousands of devices using optical and RF interrogation techniques, individually spending 20 seconds on each sequential device. Without any need for human input the system allows for the collection of massive amounts of data. Furthermore, the system can easily adapt to different device types, chip layouts and light sources. It uses a precision 2D stage retrofitted with open-source electro-mechanical hardware and software to allow accessibility to any chip. This versatile system can be employed to characterize a wide variety of different devices. Experimentally, the system successfully characterized thousands of meta-surface enhanced aluminum nitride contour mode MEMS resonators. The figures of merit evaluated in the experiments include quality factor, fluctuation-induced noise, re- sponsivity, and noise equivalent power. The best device observed was a detector with a noise equivalent power of 85.6 pW/√Hz; for this device, the quality factor, responsivity, and fluctuation noise spectral density was found to be 2531, 4.32 Hz/nW, and 0.37 Hz/√Hz . Overall, this automated system offers an efficient and cost-effective solution for characterizing the next generation of miniaturized optical sensing devices. It provides researchers with a powerful tool for data collection and analysis, enabling quick advancements in the development of IR sensors.

Breaking reciprocity lies in the heart of modern electromagnetic devices such as circulators, isolators, filters, and antennas. Generally, breaking reciprocity can be realized by biasing the device with a physical quantity that is odd symmetric under time-reversal. Conventionally, such response has been achieved by magnetically biasing ferromagnetic compounds and garnets. In the past decade, magnetless approaches based on nonlinear responses, spatiotemporal modulation, drifting electrons, and opto-mechanical effects have been explored across the electromagnetic spectrum. Recently, circular dichroism has been demonstrated to be an efficient tool to break reciprocity in 2D materials due to the optically-driven non-degenerate valleys.In this thesis, I propose a novel method to break reciprocity in 2D materials based on the use of circularly polarized light and strain engineering. To this purpose, I review and calculate the optical conductivity of graphene under uniform strain and discussed the impact of non-uniform strain on graphene. The results show a close resemblance between pseudomagnetic field and the effect of non-uniform strain. The utilization of non-uniform strain gives rise to energy level quantization in graphene and thus provides easily addressable optical transition between discrete energy levels using optical pump. I review the formalism and algorithm of a rigorous theoretical framework able to deal with Bloch equations regarding the population of different energy levels. The incorporation of some scattering mechanisms also closely reproduces what happens to the carrier population in picosecond time scale after the presence of an optical pump. The results show the population imbalance in the two non-degenerate valleys in graphene which indicates the broken reciprocity. This approach of breaking reciprocity unleashes large non-reciprocal response in graphene using magnetless implementations. In a related context, the field of plasmonics has opened new possibilities to control and manipulate light beyond the diffraction limit and has enabled countless applications in areas such as sensing, spectroscopy, and healthcare. The emerge of ultrathin metasurfaces and 2D materials have provided new knobs to excite, process, and route SPPs, while also enabling unexpected possibilities to manipulate and enhance nonreciprocal responses. Unfortunately, the design of quasi-optimal nonreciprocal metasurfaces is usually quite challenging and require significant computational resources. This thesis unveils the fundamental limits of linear and nonreciprocal plasmonic metasurfaces in terms of isolation and loss. The proposed bounds are related to surface waves and only depend on the nonreciprocal material employed within the metasurface, thus being independent of geometrical considerations and the presence of other materials. We apply these fundamental limits to explore two different platforms, namely drift-biased and magnetically-biased graphene metasurfaces. For each platform, we first analytically derive the upper bounds in terms of graphene conductivity. Then, we explore devices proposed in the literature and benchmark their response against their upper bounds. Results highlight that drift-biased hyperbolic metasurfaces exhibit outstanding performance in the mid-infrared region, whereas magnetically-biased devices are better suited for the low terahertz band. More broadly, our bounds allow to quickly assess the performance of nonreciprocal plasmonic metasurfaces with respect to their fundamental limit, thus streamlining the device design process and preventing that significant efforts are dedicated to marginal performance improvements. The proposed bounds pave the way toward the development of quasi-optimal nonreciprocal metasurfaces, with important applications in sensing, imaging, communications, and nonlinear optics, among many others.