Search Results (889)

This paper presents a systematic numerical investigation of a hybrid plasmonic–photonic Panda-ring antenna with an embedded gold grating, designed to enable efficient dual-mode radiation for optical and terahertz communication systems. The proposed structure integrates high-Q whispering-gallery mode (WGM) confinement in a multi-ring dielectric resonator with plasmonic out-coupling at the metal–dielectric interface, allowing controlled conversion of resonantly stored photonic energy into free-space radiation. The electromagnetic behavior is analyzed through a hierarchical structural evolution, progressing from a linear silicon waveguide to single-ring, add–drop, and Panda-ring resonator configurations. Gold is modeled using a dispersive Drude formulation with complex permittivity to accurately capture frequency-dependent plasmonic response at 1.55 µm. Power redistribution within the resonator system is described using coupled-mode theory, with coupling and loss parameters evaluated consistently from full-wave numerical simulations. Full-wave simulations using OptiFDTD and CST Studio Suite demonstrate that purely photonic resonators exhibit strong WGM confinement but negligible radiation, while plasmonic gratings alone suffer from low efficiency due to the absence of coherent photonic excitation. In contrast, the proposed hybrid Panda-ring antenna achieves stable and directive far-field radiation under WGM excitation, with a realized gain of approximately 8.05 dBi at 193.5 THz. The performance enhancement originates from synergistic hybrid SPP–WGM coupling, establishing a WGM-driven radiation mechanism suitable for Li-Fi and terahertz wireless applications. Full article

The rapidly increasing demand for compact, high-performance beam-steering solutions in LiDAR systems has driven substantial advances in vertical-cavity surface-emitting laser (VCSEL) technologies. In this paper, we present a high-power, ultra-low-divergence VCSEL-based beam scanner array that integrates multi-wavelength seed lasers with extended-length optical amplifiers, thereby simultaneously achieving wide-angle beam steering, near-diffraction-limited beam quality, and watt-class output power. The proposed architecture exploits slow-light modes supported by laterally extended VCSEL waveguides incorporating precisely engineered surface gratings. This design enables fully electronic beam steering over an angular range exceeding 30°, with an angular resolution surpassing 1600 resolvable points. Systematic characterization of seed lasers with distinct grating periods confirms robust single-mode operation and yields a cumulative wavelength tuning range exceeding 22 nm. When integrated with optical amplifiers up to 6 mm in length, the system achieves a record-low beam divergence of 0.018°, approaching the theoretical diffraction limit. Under continuous-wave operation and without active thermal management, the device delivers output powers exceeding 1.6 W. By overcoming the long-standing trade-offs among steering range, beam quality, and output power, this work establishes a transformative paradigm for compact VCSEL-based beam-steering systems and represents a significant step toward next-generation solid-state LiDAR technologies. Full article

This work presents a millimeter-wave half-mode substrate integrated waveguide filter with high selectivity, using through glass via technology. Compared to a traditional printed circuit board, the benefits of high precision and integration afforded by the glass-based process enable the substrate-integrated waveguide to be employed at a higher operating frequency. A novel negative coupling structure is proposed for achieving a quasi-elliptic function response, and its coupling mechanism is investigated to explore the properties of the finite transmission zeros. The proposed coupling slots allow for flexible adjustment of the coupling between the half-mode substrate integrated waveguide cavities from positive to negative by modulating the corresponding geometrical parameters. As a prototype, a glass-based fourth-order bandpass filter is synthesized, simulated, fabricated and measured. Subsequently, good matching is captured, confirming the validity of the topology. The proposed glass-based negative coupling structure is promising for realizing substrate integrated waveguide filters with a quasi-elliptic function response, especially operating at millimeter-wave band. Full article

This paper presents a nanoscale sensor based on a metal–insulator–metal (MIM) waveguide coupled with a composite resonant cavity, where the ring resonator is embedded with triangular, semicircular, and rectangular structural elements. The transmission characteristics and sensing performance of the structure were systematically analyzed using the finite element method. The results indicate that the interference between the continuous mode in the waveguide and the discrete mode in the resonant cavity generates a distinct asymmetric Fano resonance. The optimized sensor achieves a sensitivity of 2960 nm/RIU and a figure of merit (FOM) of 59.79. Experimental verification confirms that the structure exhibits high responsiveness in temperature sensing, providing an effective solution for integrated photonic devices. Full article

Tweeks are ELF/VLF radio signals originating from lightning discharges that exhibit dispersion due to their propagation in the Earth-ionosphere waveguide. Examples of the waveforms of tweeks and their dynamic frequency-time spectra are presented and interpreted. Tweeks observed in the daytime and night-time are compared and contrasted. Tweeks observed during a solar eclipse are also discussed, as are those due to volcanic lightning and those claimed to be recorded some hours or days before a strong earthquake. The variations of tweek occurrence with season and geomagnetic activity, and with variations of solar radiation over the 11-year solar cycle, are reviewed. Wherever possible, geophysical interpretations are discussed. Theoretical models of tweek waveforms and spectra are considered; they vary according to the lightning current model used, the distance from the source (≥1 Mm), the vertical profile of ionospheric D-region ionisation and the specific mode theory used. The simplest interpretation shows that the first-order tweek cut- off frequency ~1.8 kHz is explained as reflection by the ionosphere at a height of ~83 km where the electron density is ~27 × 10⁶ m⁻³. More complex interpretations are also reviewed and compared with electron density observations made by rockets and with profiles given by lower ionospheric models such as the International Reference Ionosphere or the Faraday International Reference Ionosphere. Full article

This study presents the subdomain method with local coordinates and the mode-matching method to compute the dispersion relations of sectoral corrugated waveguides. Fields are expanded in local Fourier–Bessel series, and boundary conditions are enforced by mode-matching, which produces a block-circulant system matrix. The method reduces computational cost while preserving accuracy, as verified by numerical results. Full article

The sustained interest in efficient, low-cost, and straightforward-to-manufacture lasers has prompted intense research into organic semiconductor laser emitter materials in recent decades. The main focus of this research is determining the optical gains and losses of amplified spontaneous emission (ASE) in order to describe materials by their amplification signature. A method that has been used for decades as the standard technique for determining gain characteristics is the variable-stripe-length (VSL) method. The success of the VSL method has led to the development of further measurement techniques. These techniques provide a detailed insight into the nature of optical amplification. One such method is the scattered emission profile (SEP) method. In this study, we present an extension of the SEP method, the Diffracted Emission Profile (DEP) method. The DEP method is based on the detection of ASE by partial decoupling of waveguide modes diffracted by a one-dimensional grating integrated into a planar waveguide. Diffraction causes a proportion of the intensity to exit the waveguide, transferring the growth and decay process of the waveguide mode to the transverse mode profile of the diffracted mode. In the present article, an approach to determine the amplification signature of an organic copolymer is presented, utilizing partial decoupled radiation. Full article

In this paper, a flower-shaped spoof surface plasmon polaritons (SSPPs) unit with strong slow-wave effect is proposed to construct bandpass filters (BPFs). Benefiting from extended current path induced by addition of rotated stubs around rectangular unit, the proposed SSPPs unit exhibits reduced asymptotic frequency. Following this, a single-band filter boasting multiple transmission zeros (TZs) in its upper stopband is developed by embedding the unit into half-mode substrate integrated waveguide (HMSIW). To improve suppression of the lower stopband, a pair of open circuited stubs are loaded to produce TZs and enhance its frequency selectivity. Consequently, the single-band BPF realizes an impressive roll-off rate of 0.116 dB/MHz. Subsequently, geometric dimensions of the open-circuited stubs are modified to dispose the TZs into passband and acquire dual-band operation. In addition, defected ground structures (DGSs) are loaded to broaden the bandwidth of notch between two passbands. Finally, a dual-band filter with a wide suppression band of 0.50 GHz is developed. With roll-off rates of 0.096 and 0.119 dB/MHz, the filter demonstrates good selectivity as well. Full article

Surface plasmon resonance (SPR) sensors based on photonic crystal fibers (PCFs) hold significant promise for high-precision detection in biochemical and chemical sensing. However, achieving high sensitivity in low-refractive-index (RI) aqueous environments remains a formidable challenge due to weak light-matter interactions. To address this limitation, this paper designs and proposes a novel dual-channel D-shaped PCF-SPR sensor tailored for the refractive index range of 1.34–1.40. The sensor incorporates a dual-layer gold/titanium dioxide film, with gold nanoparticles deposited on the surface to synergistically enhance both propagating and localized surface plasmon resonance effects. Furthermore, a D-shaped polished structure integrated with double-sided microfluidic channels is employed to significantly strengthen the interaction between the guided-mode electric field and the analyte. Finite element method simulations demonstrate that the proposed sensor achieves an average wavelength sensitivity of 5733 nm/RIU and a peak sensitivity of 15,500 nm/RIU at a refractive index of 1.40. Notably, the introduction of gold nanoparticles contributes to an approximately 1.47-fold sensitivity enhancement over conventional structures. This work validates the efficacy of hybrid plasmonic nanostructures and optimized waveguide design in advancing RI sensing performance. Full article

To address the critical demand for high-gain, low-sidelobe, and high-efficiency antennas in W-band arrays, this work presents a low-sidelobe all-metal array antenna based on ridge gap waveguide technology. The design employs a three-layer contactless metal structure, integrating a stepped-ridge feeding network with Taylor amplitude distribution and a higher-order mode resonant cavity. This integration enables efficient power distribution and low-loss transmission while eliminating the need for conventional welding or bonding processes. Measurement results indicate that the antenna exhibits a reflection coefficient below −10 dB across the 92.5–103.5 GHz. The in-band gain exceeds 25.8 dBi with less than 1 dB fluctuation, and the radiation efficiency surpasses 78%. Specifically, the sidelobe levels in both E- and H-planes remain below −17.5 dB, reaching under −19.5 dB at 94 GHz, while cross-polarization is better than −30 dB. The proposed antenna demonstrates high gain, low sidelobe, and high efficiency, showing promising potential for applications in millimeter-wave radar, imaging, and 6G communication systems. Full article

Reconfigurable mode switches can provide more flexible and advanced data exchange functions for complex on-chip optical networks. A reconfigurable mode-selective optical switch based on adiabatic progressive three-waveguide coupling (TWC) is proposed. As a proof of concept, the switching of E₀₀ (E₂₀)/E₁₀ (E₃₀) dual-mode channels was successfully implemented and demonstrated. At 1550 nm, the insertion losses for E₀₀/E₁₀ and E₂₀/E₃₀ mode switches were lower than 7.86 and 10.76 dB, respectively. These values include the loss of the mode demultiplexer. The crosstalk was lower than −22.84 (−18.28) dB at 1550 nm. The switching rise time (10–90%) and fall time (10–90%) were 0.86 ms and 0.64 ms, respectively. On the silica platform, the scalability of the structural scheme was also verified, and the arbitrary selection and switching of the E₀₀, E₁₀, E₂₀, and E₃₀ modes were achieved via the cascading of TWCs. The device can be used as an important component for the future large-scale integration and flexible switching of on-chip optical networks. Full article

Silicon–nitride (SiN) waveguides have emerged as fundamental building blocks in silicon photonic integrated circuits (Si-PICs), offering advantages that compensate for the intrinsic limitations of silicon-on-insulator (SOI) and silica-on-silicon (SOS) platforms. In this work, two sizes of single-mode SiN strip waveguides are investigated: (i) 600 nm wide strip waveguide cores on a 400 nm thick Si₃N₄ film and (ii) 1.0 µm wide strip waveguide cores on a 1.0 µm thick Si₃N₄ film. First, we design two AWG architectures and develop a generalized theoretical model for one of the key specifications—polarization mode dispersion (PMD)—by considering a pair of orthogonal polarization states in these two waveguides. Then, as the two-size SiN waveguides are generally fabricated via multiple operating processes of coating, photolithography, and etching, we investigate the dependences of PMD performances on the device errors of the two AWG architectures caused by the coating/manufacturing qualities and accuracies, and the dependences of PMD performance on the refractive index errors of the waveguide core. As a consequence, the softwaretool simulations for the two AWG architectures of 40-channel 0.8 nm channelspacing show that the average PMDs of the above two waveguide sizes are <0.50 ps and <0.35 ps, respectively, and the PMD responses to the ±10% fabrication error are < ±0.20 ps and ±10% fluctuation, respectively, but the ±2.5% variations have no obvious impacts upon the PMD performance. Therefore, it turns out that the PMD performance of a smaller waveguide has a relatively strong error sensitivity to the AWG architecture, while the larger waveguide size has a relatively weak error sensitivity to the AWG architecture. Full article

In this paper, low-pass corrugated filters based on half-mode groove gap waveguide (HMGGW) technology are proposed for the first time. The design process starts from the equivalent classical low-pass implementation in corrugated rectangular waveguide. Then, the final response is achieved after a slight re-optimization of groove widths and lengths. As a proof of concept, two corrugated low-pass filters with upper cutoff frequencies at 27 and 29.5 GHz, and maximum attenuation rejection at 34.5 and 39 GHz, respectively, have been designed and manufactured. In spite of the frequency range of operation, the return losses are better than 19.5 dB for both tuning-less filter prototypes, while measured insertion losses are lower than 0.25 dB and 0.3 dB, respectively, in almost the entire passband. The very good agreement between simulations and measurements fully validates the use of this new emerging technology for the implementation of low-pass filters at high frequency bands. Full article

This work addresses the challenge of realizing broadband, low-loss fiber-to-waveguide coupling in the short-wavelength near-infrared range (700–1050 nm), where the required fine structural dimensions and taper tips approach or even exceed current fabrication limits, resulting in tight fabrication tolerances and degraded coupling efficiency. We propose a broadband trilayer adiabatic edge coupler on a thin-film lithium tantalate platform that requires only two standard lithography and etching steps. The design integrates a crossed bilayer taper and a dual-core mode converter to achieve adiabatic mode transformation from a ridge to a thin strip waveguide, ensuring excellent fabrication tolerance and process simplicity. Simulations predict a minimum coupling loss of 0.57 dB at 850 nm, which includes the transmission through the complete edge-coupler structure, along with a 0.5-dB bandwidth exceeding 140 nm. The proposed structure provides a broadband, low-loss, and fabrication-tolerant interface for short-wavelength photonic systems such as quantum photonics, biosensing, and visible-light communications. Full article

The m-lines spectroscopy is a precise, non-destructive and contactless method, and one of its main applications is the determination of the geometric-optical parameters of a thin film deposited over a substrate, namely the refractive index and the thickness of the film under analysis. The method was first described in 1969 with the seminal work of Tien, more than half a century ago, and, since then, it has been reported in the literature that at least two modal indices of the same polarization are required to unequivocally determine a given film’s refractive index and thickness. This constraint imposes a limit on the waveguide’s thickness, for it leaves out the possibility of determining the geometric-optical parameters of all films where only single-mode propagation is feasible. In this work, we propose and validate a strategy that extends the applicability of the method to single-mode operation, enlarging its operational thickness detection range. Moreover, the results obtained demonstrate that restricting the parameter extraction to fundamental modes leads to a measurable increase in precision. This improvement is attributed to the lower susceptibility to experimental uncertainties, lower sensitivity to surface roughness and nearby structures, and higher confinement that characterize fundamental modes as opposed to higher-order ones. Full article