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Surface plasmon polaritons (SPPs) are coherent electron-plasma oscillations at the interface of materials with opposite dielectric functions. The excitation and propagation of these polariton modes are strongly affected by material dispersion, geometric behaviour and the excitation frequency. In this paper, we studied the excitation of SPPs at metal/lithium niobate (ferroelectric) interfaces and their dispersion characteristics. The plasmonic waveguides with Ag/LiNbO.sub.3 interfaces provide the coupling of ferroelectric properties in to plasmon modes. We observed a marked propagation length, and both geometrical and material dispersion properties which ensure a sensitive plasmonic system operating at plasmon frequencies.

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Topological refractions created by valley sonic crystals (VSCs) have attracted great attentions in the communities of physics and engineering owing to the advantage of zero reflection of sound and the potential for designing advanced acoustic devices. In previous works, topological refractions of valley edge states are demonstrated to be determined by the projections of the valleys K and K7, and two types of topological refractions generally exist at opposite terminals or different frequency bands. However, the realization of tunable topological refractions at the fixed frequency band and terminal still poses great challenge. To overcome this, we report the realization of tunable topological refractions by VSCs with triple valley Hall phase transitions. By simply rotating rods, we realize 3 types of topological waveguides (T1, T2, and T3) composed of two VSCs, in which the projections of the observed valley edge states can be modulated between K and K. Additionally, based on the measured transmittance spectra, we experimentally demonstrate that these valley edge states are almost immune to backscattering against sharp bends. More importantly, we realize tunable topological refractions at the fixed frequency band and terminal, and experimentally observe the coexistence of positive and negative refractions for T1 and T3, and negative refractions for T2. The proposed tunable topological refractions have potential applications in designing multi-functional sound antennas and advanced communication devices.

The nonlocal emitter-waveguide coupling, which gives birth to the so called giant atom, represents a new paradigm in the field of quantum optics and waveguide QED. We investigate the single-photon scattering in a one-dimensional waveguide on a two-level or three-level giant atom. Thanks to the natural interference induced by the back and forth photon transmitted/reflected between the atom-waveguide coupling points, the photon transmission can be dynamically controlled by the periodic phase modulation via adjusting the size of the giant atom. For the two-level giant-atom setup, we demonstrate the energy shift which is dependent on the atomic size. For the driven three-level giant-atom setup, it is of great interest that, the Autler-Townes splitting is dramatically modulated by the giant atom, in which the width of the transmission valleys (reflection range) is tunable in terms of the atomic size. Our investigation will be beneficial to the photon or phonon control in quantum network based on mesoscopical or even macroscopical quantum nodes involving the giant atom. Keywords giant atom, single-photon scattering, quantum interference, Autler-Townes splitting

This paper presents the design of an optical transport architecture for the fronthaul segment in a 5G New Radio (NR) network based on both polarization and wavelength multiplexing using Polarization Splitters (PS) and an Arrayed Waveguide Grating (AWG), respectively. The proposed architecture is assessed by the transport of Orthogonal Frequency Division Multiplexing (OFDM) services, which allows the definition of different numerologies and service profiles; those are key aspects in the framework of 5G RN. The proposed design shows a flexible and scalable management of numerologies per polarized light component, featuring a suitable response in terms of Bit Error Rate (BER) and Error Vector Magnitude (EVM) measurements for 15 kHz, 30 kHz, and 60kHz subcarrier spacing of an OFDM based on 4QAM modulation format.

In this paper, a racetrack ring resonator design based on a subwavelength grating double slot waveguide is presented. The proposed waveguide scheme is capable of confining the transverse electric field in the slots and the gaps between the grating segments. This configuration facilitates a large light–matter interaction which elevates the sensitivity of the device approximately 2.5 times higher than the one that can be obtained via a standard slot waveguide resonator. The best sensitivity of the design is obtained at 1000 nm/RIU by utilizing a subwavelength grating double slot waveguide of period 300 nm. The numerical study is conducted via 2D and 3D finite element methods. We believe that the proposed sensor design can play an important role in the realization of highly sensitive lab-on-chip sensors.