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A compact microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures based on substrate integrated plasmonic waveguide (SIPW) and spoof surface plasmon polariton (SSPP) is proposed and investigated. The dispersion and transmission characteristics of the proposed unit-cell structures of SSPP and SIPW were analyzed numerically, respectively. Numerical results indicate that the high and low cut-off frequencies of the bandpass filter can be independently adjusted by changing geometric parameters of unit-cell structures of SSPP and SIPW, respectively. The proposed microwave bandpass filter has a smaller electrical size because of its better electromagnetic (EM) field constraints than the traditional SIW ones with combed groove lines SSPPs. To verify the design method and concept, a microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures has been designed, fabricated, and measured. The results demonstrate that the proposed passband is in the range of 7.3–10.1 GHz, the return loss is higher than 10 dB and the insertion loss is less than 2 dB. The microwave bandpass filter is very compact in size, only about 0.99 λ 0  × 0.35 λ 0 , where λ 0 is the wavelength at the center frequency.

Due to its amazing ability to manipulate light at the nanoscale, plasmonics has become one of the most interesting topics in the field of light–matter interaction. As a promising application of plasmonics, surface-enhanced Raman scattering (SERS) has been widely used in scientific investigations and material analysis. The large enhanced Raman signals are mainly caused by the extremely enhanced electromagnetic field that results from localized surface plasmon polaritons. Recently, a novel SERS technology called remote SERS has been reported, combining both localized surface plasmon polaritons and propagating surface plasmon polaritons (PSPPs, or called plasmonic waveguide), which may be found in prominent applications in special circumstances compared to traditional local SERS. In this article, we review the mechanism of remote SERS and its development since it was first reported in 2009. Various remote metal systems based on plasmonic waveguides, such as nanoparticle–nanowire systems, single nanowire systems, crossed nanowire systems and nanowire dimer systems, are introduced, and recent novel applications, such as sensors, plasmon-driven surface-catalyzed reactions and Raman optical activity, are also presented. Furthermore, studies of remote SERS in dielectric and organic systems based on dielectric waveguides remind us that this useful technology has additional, tremendous application prospects that have not been realized in metal systems. Plasmonics: remote surface-enhanced Raman scattering The use of plasmonic waveguides to remotely excite targets for surface-enhanced Raman scattering (SERS) offers numerous advantages over conventional direct illumination methods. The remote excitation approach — whereby energy is conveyed to a nanoscale target by propagating surface plasmon polaritons — avoids background noise due to stray illumination, isolates heat to a subwavelength area at the target, and limits the potential for sample damage. Yingzhou Huang and Mengtao Sun from Chongqing University and the Chinese Academy of Sciences' Institute of Physics in Beijing, with colleagues from around the world, have reviewed the plasmonic waveguide structures that make remote SERS possible. Plasmonic waveguides are typically realized using single-crystalline metal nanowires in various configurations, but semiconductor and organic waveguides also show significant potential for use in remote SERS.

Graphene-based photodetectors, taking advantage of the high carrier mobility and broadband absorption in graphene, have recently seen rapid development. However, their performance with respect to responsivity and bandwidth is still limited by the weak light-graphene interaction and large resistance-capacitance product. Here, we demonstrate a waveguide-coupled integrated graphene plasmonic photodetector on a silicon-on-insulator platform. Benefiting from plasmon-enhanced graphene-light interaction and subwavelength confinement of the optical energy, a small-footprint graphene-plasmonic photodetector is achieved working at the telecommunication window, with a large a bandwidth beyond 110 GHz and a high intrinsic responsivity of 360 mA/W. Attributed to the unique electronic band structure of graphene and its ultra-broadband absorption, operational wavelength range extending beyond mid-infrared, and possibly further, can be anticipated. Our results show that the combination of graphene with plasmonic devices has great potential to realize ultra-compact, high-speed optoelectronic devices for graphene-based optical interconnects.

This article addresses the past, present, and future status of hybrid plasmonic waveguides (HPWs). It presents a comprehensive review of HPW -based photonic integrated circuits (PICs), covering both passive and active devices, as well as potential application of on-chip HPWbased devices. HPW -based integrated circuits (HPWICs) are compatible with complementary metal oxide semiconductor technology, and their matched refractive indices enables the adaptation of existing fabrication processes for silicon-on-insulator designs. HPWs combine plasmonic and photonic waveguide components to provide strong confinement with longer propagation length L, of HP modes with nominal losses. These HPWs are able to make a trade-off between low loss and longer Lp, which is not possible with independent plasmonic and photonic waveguide components owing to their inability to simultaneously achieve low propagation loss with rapid and effective all-optical functionality. With HPWs, it is possible to overcome challenges such as high Ohmic losses and enhance the functional performance of PICs through the use of multiple discrete components. HPWs have been employed not only to guide transverse magnetic modes but also for optical beam manipulation, wireless optical communication, filtering, computation, sensing of bending, optical signal emission, and splitting. They also have the potential to play a pivotal role in optical communication systems for quantum computing and within data centers. At present, HPW -based PICs are poised to transform wireless chip-to-chip communication, a number of areas of biomedical science, machine learning, and artificial intelligence, as well as enabling the creation of densely integrated circuits and highly compact photonic devices.

This paper proposed a plasmonic resonator system, consisting of a metal-insulator-metal structure and two stubs, and a Fano resonance arose in its transmittance, which resulted from the coupling between the two stubs. On the basis of the proposed structure, a circle and a ring cavity are separately added above the stubs to create different coupled plasmonic structures, providing triple and quadruple Fano resonances, respectively. Additionally, by adjusting the geometric parameters of the system, multiple Fano Resonances obtained can be tuned. The proposed structure can be served as a high efficient refractive index sensor, yielding a sensitivity of 2000 nm/RIU and figure of merit (FOM) of 4.05 × 10 4 and performing better than most of the similar structures. It is believed that the proposed structure may support substantial applications for on-chip sensors, slow light and nonlinear devices in highly integrated photonic circuits.

This theoretical study presents a hybrid quantum system that combines the geometry of a T-shaped plasmonic waveguide with an embedded common cavity and applies quantum feedback control to enhance and preserve quantum discord between two quantum dots (QDs). Building upon previous work on entanglement generation in T-shaped waveguides and feedback-enhanced discord in V-shaped waveguides, we demonstrate that the T-shape geometry with its specific boundary conditions, coupled with active feedback, offers superior control over quantum correlations. The system consists of two QDs placed at strategic positions within the waveguide: one at the node and the other at the end of the finite arm, both embedded in a common cavity. We derive the system’s dynamics using a real-space Hamiltonian approach and solve the time-independent Schrödinger equation to obtain scattering amplitudes. Quantum discord is then calculated for the two-QD subsystem. Our results show that by applying symmetric quantum feedback based on Wiseman-Milburn formalism, we can significantly enhance the steady-state quantum discord, achieving values up to for Werner states under optimal parameter conditions. We identify three distinct decay regimes for discord and demonstrate that parameters such as the phase accumulation ( , where is the plasmon wavevector) along the finite arm, providing cavity-QD couplings ( , ), detunings ( , ), and dipole-dipole interaction strength ( f ) provide multiple control knobs for tuning quantum correlations. This work provides a comprehensive framework for designing actively controlled nanophotonic quantum devices that leverage both plasmonic field enhancement and quantum feedback for robust quantum information processing at room temperature.

This study describes the underpinning theories and principles in the field of surface plasmon polariton generation and waveguide construction, as well as many design structures based on these waveguides that generate diverse optical resonances and their use for sensing refractive index and temperature variation. Firstly, the investigation of the topologies of plasmonics refractive index sensors based on Bragg grating structures and resonators (cavity and ring) that are coupled to the main bus waveguide is done. Secondly, these architectures’ theories and analytical frameworks are summarized. Following that, contemporary sensor development trends based on metal–insulator–metal–resonators (ring or cavity) architecture have been discussed. They have also been compared in terms of performance measures like sensitivity and figure of merit. The results of the comparison demonstrated that sensitivity can be greatly improved, but the figure of merit and quality factor still need to be improved in plasmonic-based sensors. Finally, some recent instances of hybrid plasmonic waveguides connected to a ring resonator have been manifested, which significantly improve the figure of merit and quality factor as compared to plasmonic waveguide–based sensors. Moreover, such structures are easily fabricated due to their CMOS compatibility.

This paper presents an all-optical 4 × 2 encoder based on graphene-plasmonic waveguides for operation in the wavelength range of 8–12 μm. The basic plasmonic waveguide consists of a silicon (Si) strip and a graphene sheet supported by two dielectric ridges. Surface plasmon polaritons (SPPs) are stimulated in the spatial gap between the graphene sheet and the Si strip. The effect of geometric parameters and chemical potential of the graphene sheet changes on the suggested waveguide’s waveguiding behavior is meticulously investigated using the three-dimensional finite-difference time-domain (3D-FDTD) method. The encoder comprises a straight waveguide to detect the state of the In 0 input and two Y-combiners with outputs Out 0 and Out 1 to detect the state of the In 1 , In 2 , and In 3 inputs. The encoder exhibits a minimum extinction ratio ( ER min ) of 19 dB at a wavelength of 10 μm. In addition, the cross-talk ( CT ) and insertion loss ( IL ) values are −21.3 and −1.31 dB, respectively. The encoder offers an ultra-compact structure with a total footprint of 4.25 μm 2 . Due to its exceptional waveguiding features, low CT and IL values, and high ER min , the proposed encoder holds promise for various communication and signal processing applications.

The development of low-cost sensing devices with high compactness, flexibility, and robustness is of significance for practical applications of optical gas sensing. In this work, we propose a waveguide-based resonant gas sensor operating in the terahertz frequency band. It features micro-encapsulated two-wire plasmonic waveguides and a phase-shifted waveguide Bragg grating (WBG). The modular semi-sealed structure ensures the controllable and efficient interaction between terahertz radiation and gaseous analytes of small quantities. WBG built by superimposing periodical features on one wire shows high reflection and a low transmission coefficient within the grating stopband. Phase-shifted grating is developed by inserting a Fabry–Perot cavity in the form of a straight waveguide section inside the uniform gratings. Its spectral response is optimized for sensing by tailoring the cavity length and the number of grating periods. Gas sensor operating around 140 GHz, featuring a sensitivity of 144 GHz/RIU to the variation in the gas refractive index, with resolution of 7 × 10−5 RIU, is developed. In proof-of-concept experiments, gas sensing was demonstrated by monitoring the real-time spectral response of the phase-shifted grating to glycerol vapor flowing through its sealed cavity. We believe that the phase-shifted grating-based terahertz resonant gas sensor can open new opportunities in the monitoring of gaseous analytes.

Nowadays, mental–insulator–metal (MIM) waveguides are widely used in the design of optical plasmonic waveguides due to their superior ability to confine surface plasmons up to sub wavelength scale. This research proposes the design of series and parallel circuits using cascaded plasmonic Mach–Zehnder interferometers (PMZIs). Each PMZI employs a nonlinear arm to switch light across the output port via the insertion of the nonlinear Kerr material poly(2-methoxy-5-(28-ethylhexyloxy)-PPV). The proposed design is having footprint of 104 µm × 11 µm. The finite-difference time-domain method is used to study, design, and analysis all optical series and parallel circuit proposals.