A novel surface plasmon waveguide structure is proposed for highly integrated planar lightwave circuits. By etching a small trench through a metallic thin film on a silica substrate, a guided mode with highly confined light fields is realized. The mode properties of the proposed structure are studied. The necessity of using a polymer upper-cladding is discussed. The coupling between two closely positioned waveguides and a 90° bending are also studied numerically. Sharp bending and high integration can be realized with the present surface plasmon waveguide. The proposed structure is easy to fabricate as compared with some other types of surface plasmon waveguides for high integration.

We propose and numerically analyze surface plasmon Bragg gratings formed by a periodic variation of the width of the insulator in a metal-insulator-metal waveguide. The results indicate that very good filtering characteristics can be achieved in these plasmonic Bragg gratings. To suppress the sidelobes in the transmission spectrum, we further propose S-shaped Bragg cells and find better performance. By introducing a defect into the grating, a defect state with high Q-value is introduced into the bandgap and a Fabry-Peacuterot-like structure is formed

Toroidal dipole (TD) with weak coupling to the electromagnetic fields offers tremendous potential for advanced design of photonic devices. However, the excitation of high quality ( Q ) factor TD resonances in these devices is challenging. Here, we investigate ultrahigh‐ Q factor TD resonances at terahertz frequencies arising from a distortion of symmetry‐protected bound states in the continuum (BIC) in all‐dielectric metasurface consisting of an array of high‐index tetramer clusters. By elaborately arranging the cylinders forming an asymmetric cluster, two distinct TD resonances governed by BIC are excited and identified. One is distinguished as intracluster TD mode that occurs in the interior of tetramer cluster, and the other one is intercluster TD mode that arises from the two neighboring clusters. Such TD resonances can be turned into ultrahigh‐ Q leaky resonances by controlling the asymmetry of cluster. The low‐loss TD resonances with extremely narrow linewidth are very sensitive to the change in the refractive index of the surrounding media, achieving ultrahigh sensitivity level of 489 GHz/RIU. These findings will open up an avenue to develop ultrasensitive photonic sensor in the terahertz regime.

Surface plasmon polaritons (SPPs) are electromagnetic (EM) modes propagating along metal-dielectric interfaces, in which surface collective excitations of free electrons in the metal are coupled to evanescent EM fields in the dielectric. Various SPP modes can be supported by flat and curved, single and multiple surfaces, exhibiting remarkable properties, including the possibility of concentrating EM fields beyond the diffraction limit, i.e. on the nanoscale, while enhancing local field strengths by several orders of magnitude. This unique feature of SPP modes, along with the ever-increasing demands for miniaturization of photonic components and circuits, generates an exponentially growing interest in SPP-mediated radiation guiding and SPP-based waveguide components. Here we review the current status of this rapidly developing field, starting with a brief presentation of the main planar SPP modes along with the techniques employed for their excitation and manipulation by sets of nanoparticles. We then describe in detail various SPP-based waveguide configurations that ensure two-dimensional mode confinement in the plane perpendicular to the propagation direction and compare their characteristics. Excitation of SPP waveguide modes and recent progress in the development of SPP-based waveguide components are also discussed, concluding with our outlook on challenges and possible future developments in this field.

Excitation of localized and delocalized surface plasmon resonances can be used for turning excellent reflectors of visible light, such as gold and silver, into efficient absorbers, whose wavelength, polarization or angular bandwidths are however necessarily limited owing to the resonant nature of surface plasmon excitations involved. Nonresonant absorption has so far been achieved by using combined nano- and micro-structural surface modifications and with composite materials involving metal nanoparticles embedded in dielectric layers. Here we realize nonresonant light absorption in a well-defined geometry by using ultra-sharp convex metal grooves via adiabatic nanofocusing of gap surface plasmon modes excited by scattering off subwavelength-sized wedges. We demonstrate experimentally that two-dimensional arrays of sharp convex grooves in gold ensure efficient (>87%) broadband (450–850 nm) absorption of unpolarized light, reaching an average level of 96%. Efficient absorption of visible light by nanostructured metal surfaces open new exciting perspectives within plasmonics, especially for thermophotovoltaics.

We demonstrate the realization of on-chip plasmonic analogue of electromagnetically induced transparency (EIT) in integrated plasmonic devices using detuned Fabry-Perot resonators aperture-side-coupled to a metal-insulator-metal (MIM) waveguide, with the transmission peak occurring at the intermediate wavelength. Strong MIM mode confinement along with localized side-coupling allows one to realize subwavelength photonic components with EIT-like transmission. Numerical results show that MIM components exhibiting pronounced EIT-like spectra in near infrared with the footprint of < 0.15 μm² and group index of ~26 can be designed.