Spin-controlled Nonlinear Harmonic Generations from Polaritonic Metasurface

Department of Electrical EngineeringMetasurfaces develop various applications, such as nonlinear holography, nonlinear wave mixing, and novel nonlinear light sources. In nonlinear optics, nonlinear harmonic generation from nonlinear metasurface provide a new degree-of-freedom. Nonlinear metasurfaces have various interesting properties, such as the relaxed phase matching constraints, efficient frequency mixing, and nonlinear local phase control. There have been studied, but the development of a single nonlinear metasurface platform is still needed to develop practical applications. In this thesis, I experimentally demonstrate a novel class of a nonlinear polaritonic metasurface platform using nanoantenna structures with three- or four-fold rotational symmetry. Using the metasurface, spin-controlled giant 2nd and 3rd order nonlinear responses can be generated simultaneously or selectively on the same chip. Furthermore, under a circular polarized beam condition, nonlinear local phases can be simply tuned continuously by changing the rotation angle of the meta-atom based on the Pancharatnam-Berry phase. -Based on continuous local nonlinear phase control, nonlinear beam-steering that maintain spin-controlled giant nonlinear response for the second- and third-harmonic generations, was experimentally demonstrated via gradient nonlinear polaritonic metasurfaces. The nonlinear metasurface platform that proposed in this study can be used to develop future practical applications such as nonlinear holography, nonlinear communication and so on.clos

Low-threshold optically pumped lasing in highly strained Ge nanowires

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavorable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be any successful demonstration of lasing from this seemingly promising material system. Here, we demonstrate a low-threshold, compact group IV laser that employs germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently surmount optical losses at 83 K, thus allowing the first observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm^-^2. Our demonstration opens up a new horizon of group IV lasers for photonic-integrated circuits.Comment: 31 pages, 9 figure

E-band metasurface based Orbital Angular Momentum Multiplexing and Demultiplexing

Orbital angular momentum (OAM) has received considerable attention regarding high-capacity communication owing to its spatial orthogonality. However, it is still challenging to build a compact communication system that can generate multiple coaxial OAM beams and receive information from each. In this work, OAM multiplexing and demultiplexing at the E-band frequency using a single metasurface structure is proposed and experimentally demonstrated. For OAM multiplexing, the metasurface used as a transceiver generates two orthogonal coaxial OAM beams for Gaussian incident beams with different incidence angles. For OAM demultiplexing, the same metasurface flipped 180?? as a receiver forms a Gaussian beam in different off-axis directions depending on the topological charge of the coaxially incident OAM beam. The Gaussian beam measured at the receiver end exhibits a high signal-to-noise ratio of more than 33 dB compared with the background OAM beam. OAM multiplexing and demultiplexing based on a single metasurface may provide a route for high-capacity and compact free-space communication systems

A Comprehensive Study on EMI Shielding Performance of Carbon Nanomaterials-Embedded CFRP or GFRP Composites

The rapid advancement of electrical and telecommunication facilities has resulted in increasing requirements for the development of electromagnetic interference (EMI) shielding composites. Accordingly, an experimental study was conducted to evaluate the EMI shielding performance of carbon nanomaterial (CNM)-embedded carbon-fiber-reinforced polymer (CFRP) or glass-fiber-reinforced polymer (GFRP) composites. Nine combinations of CNMs and carbon or glass fibers were used to fabricate the composites. The synergistic effects of CNMs on the EMI shielding performance were systematically investigated. The results indicated that plate-type CNMs (i.e., graphene and graphite nanoplatelets) have more prominent effects than fiber-type CNMs (carbon nanofibers). The composites fabricated with CFRP afforded higher EMI shielding than the GFRP-based composites. Among the eighteen samples, 3% CNT-GNP in CFRP composites, which included plate-typed CNM, exhibited the best EMI shielding performances, showing 38.6 dB at 0.7 GHz. This study helps understand the shielding performance of CNM-embedded CFRP and GFRP composites in electrical and telecommunication facilities