This approach became essential for constructing negative index media, which laid a strong foundation for the burgeoning field of metamaterial photonics. Split-ring resonators as the basic building blocks of metamaterials were first proposed to be made up of metallic inclusions at the microwave frequencies. [9] However, beyond the microwave frequencies, metals show considerable Ohmic loss, which created the need for all-dielectric resonator platform with the promise to offer low-loss meta-optics and photonics. The last few years have witnessed an unprecedented use of dielectrics in optical metamaterials based on high-index dielectric materials that have strongly emerged as an alternative approach to disrupt the lossy metalbased subwavelength photonics. [10][11][12][13][14][15][16][17][18] Several interesting phenomena of metamaterials are driven by strong resonances, and their quality (Q) factors become an extremely important parameter that determines the strength of light-matter interaction. The structures with high Q factors offer a new route for strong localization of electromagnetic energy in near fields that allow ultrasensitive sensors and other optical devices. [19][20][21][22][23] Recent trends in this field are based on so-called bound statesThe authors declare no conflict of interest. Keywordsall-dielectric metasurface, bound states in the continuum, optically active metadevices, terahertz, ultrafast switching

Incorporating semiconductors as active media into metamaterials offers opportunities for a wide range of dynamically switchable/tunable, technologically relevant optical functionalities enabled by strong, resonant light-matter interactions within the semiconductor. Here, a germanium-thin-film-based flexible metaphotonic device for ultrafast optical switching of terahertz radiation is experimentally demonstrated. A resonant transmission modulation depth of 90% is achieved, with an ultrafast full recovery time of 17 ps. An observed sub-picosecond decay constant of 670 fs is attributed to the presence of trap-assisted recombination sites in the thermally evaporated germanium film.

Advances in plasmonic metamaterials have been rapidly evolving with innovations aimed at developing metadevices for real-world applications. In reality, energy losses in plasmonic systems are prevalent and it is of paramount importance to come up with solutions that could overcome the limitations that impede further advancements toward the miniaturization of optoelectronic metadevices. High-Q Fano resonance as a scattering phenomenon can be easily triggered by introducing asymmetry into plasmonic systems, and thus it offers a simple approach for reducing radiative losses through lineshape engineering. High-Q Fano resonance possesses narrow linewidth and intensely confined electromagnetic fields, which makes it viable for widespread applications. The purpose of this review is to consolidate the current advances and contributions that high-Q Fano resonance has made in the metamaterial community. Two general modes of energy loss including radiative and nonradiative losses are introduced and possible ways to overcome these challenges are examined. Furthermore, applications based on high-Q Fano resonance including sensors, lasing spasers, and optical switches are discussed, embracing the future of Fano resonance based high performance photonic technologies.

The observation of Fano resonance phenomena is universal across several branches of physics. Photonics is one of the most important areas of physics that mainly deals with the control of light propagation and localization through its interaction with natural and artificially engineered media. In an era of miniaturization, manipulation of light at micro-nanoscales has assumed unprecedented significance due to its potential to satisfy the mankind with disruptive future technologies. In this work, we present our study on the universality of high quality factor Fano resonances in planar metamaterials across terahertz and infrared parts of the electromagnetic spectrum. The narrow linewidth asymmetric Fano resonant metamaterials have tremendous potential to find applications in micro-nanoscale flat lasers, sensors, and ultra-resolution spectrometers.

We report on an experimental and computational (multipole decomposition) study of Fano resonance modes in complementary near-IR plasmonic metamaterials. Resonance wavelengths and linewidths can be controlled by changing the symmetry of the unit cell so as to manipulate the balance among multipole contributions. In the present case, geometrically inverting one half of a four-slot (paired asymmetric double bar) unit cell design changes the relative magnitude of magnetic quadrupole and toroidal dipole contributions leading to enhanced quality factor, figure of merit and spectral tuning of the plasmonic Fano resonance. *Email: ranjans@ntu.edu.sg 2 Metamaterials have been a subject of intense interest due to their ability to exhibit optical properties not commonly found in natural materials. By suitably engineering the size and geometry of metamaterials at the sub-wavelength scale, researchers have been able to exploit and manipulate electromagnetic waves to achieve various phenomena such as invisibility cloaking, 1-4 super lenses, 5-8 electromagnetically-induced transparency [9][10][11] , and high quality- Here, we introduce a comparison between complementary nanostructures of paired ADBs in so-called "Fano" and "iFano" configurations (iFano denoting a 180˚ inversion of one ADB relative to the Fano geometry -as shown in Fig. 1), and report that in the iFano configuration, a larger figure of merit and quality factor can be achieved in the infrared regime as compared to the Fano configuration. Numerical simulations attribute the origin of a broad dipolar resonance to the electric dipole, and the asymmetric Fano lineshape is a consequence of the electric dipole interacting with the magnetic quadrupole and the toroidal dipole. Via a decomposition of the multipoles, we find that the magnetic quadrupole competes on the same scale as the toroidal dipole to narrow down the linewidth of the resonance. In addition, the iFano configuration offers large spectral tunability without the need to alter the periodicity or dimensions of the unit cell. The reflectance spectra of fabricated nanostructures were measured using a microspectrophotometer (Jasco MSV-5200) with y-polarized incident light. Numerical simulations were carried out using commercial finite-difference time-domain Maxwell solver software (Lumerical FDTD) assuming plane wave illumination polarized in the y-direction.Periodic boundary conditions were imposed in the x-and y-directions; perfectly matched layers were set in the z-direction so that any incident waves do not reflect at the boundaries but are strongly absorbed. The optical constants of gold were taken from Johnson and Christy 44 and the refractive index of the quartz substrate was set to 1.5.Figs. 2(a, b) show the reflectance spectra measured for y-polarized incident light propagating normal to the plane of the nanostructures. They clearly illustrate that in both configurations, the Fano resonance red-shifts with decreasing asymmetry accompanied by linewidth narrowing.For a pair of symmetric double ...

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This dissertation is the result of my own work and includes nothing, which is the outcome of work done in collaboration except where specifically indicated in the text. It has not been previously submitted, in part or whole, to any university of institution for any degree, diploma, or other qualification.

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