Abstract: In this brief, a dual-mode dual-band filter based on half-mode substrate integrated waveguide (HMSIW) is presented. The proposed filter has the capability to tune the two pass-bands independently. The proposed filter consists of two HMSIW resonators coupled through a pair of ${E}$ -shaped coupling slots. Two resonating modes ( TE 101 and TE 102) are excited in each resonator. A varactor diode is used in the proposed filter for tuning purpose. The varactor diode is placed in the structure in such a way that both bands can be tuned independently. The lower passband can be tuned from 3.26 to 3.47 GHz with insertion loss of 0.2–2.9 dB. The higher passband can be tuned from 5.47 to 6.13 GHz with low insertion loss of 0.1–2.1 dB. The presented results show the flexibility of the filter to achieve desired responses and its suitability for integration with any tunable planar structure. A good agreement between the simulated and measured results is observed.

Abstract: Here, we demonstrate a microwave (MW) cavity interference enhancement method to image nano-defects on the surface of metal waveguide. The MW cavity interference system mainly consisted of a MW coaxial resonant cavity with a nano-probe. The MW signals have been evenly divided into two channels. One was the reference signal inputted into the MW waveguide and coupled into the MW cavity via the probe. Also, the coupling strength depends on the distance between the probe and the MW waveguide. Another one was directly inputted the MW cavity to interfere with the reference signal, and was enhanced in the cavity. Then, the surface topography of the metal waveguide was mapped by calculating the enhanced signals. In our experiment, a weak signal of ∼1 pW coupled from the waveguide can be detected by a MW cavity with the quality factor of ∼209. As a proof of application, the topography of nano-defects on the surface of metal waveguide in an MW chip has been mapped with a resolution of ∼15 nm. We have proved that this is a high-resolution, easy-to-manufacture, low-cost, and real-time online monitoring approach for online assessment and screening chips. This potentially has broad applications in the fields of chip manufacturing, chip inspection, nano-structure detection, and so on.

Abstract: We demonstrate a new highly tunable technique for generating meter-scale low density plasma waveguides. Such guides can enable laser-driven electron acceleration to tens of GeV in a single stage. Plasma waveguides are imprinted in hydrogen gas by optical field ionization induced by two time-separated Bessel beam pulses: The first pulse, a J_{0} beam, generates the core of the waveguide, while the delayed second pulse, here a J_{8} or J_{16} beam, generates the waveguide cladding, enabling wide control of the guide's density, depth, and mode confinement. We demonstrate guiding of intense laser pulses over hundreds of Rayleigh lengths with on-axis plasma densities as low as N_{e0}∼5×10^{16} cm^{-3}.

Abstract: An optical phased array (OPA) in silicon nitride (SiN) is conspicuously highlighted as a vital alternative to its counterpart in silicon. However, a limited number of studies have been conducted on this array in terms of wavelength-tuned beam steering. A SiN OPA has been proposed and implemented with a grating antenna that incorporated an array of shallow-etched waveguides, rendering wavelength-tuned beam steering along the longitudinal direction. To accomplish a superior directionality on a wavelength-tuned beam steering, the spectral beam emission characteristics of the antenna have been explored from the viewpoint of a planar structure that entails a buried oxide (BOX), a SiN waveguide core, and an upper cladding. Two OPA devices having substantially different thicknesses of the resonant cavities, established by combining the BOX and SiN core, were considered theoretically and experimentally to scrutinize the spectral emission characteristics of the antenna on beam steering. Both of the fabricated OPA devices steered light by an angle of 7.4° along the longitudinal direction for a wavelength ranging from 1530 to 1630 nm, while they maintained a divergence angle of 0.2°×0.6° in the longitudinal and lateral directions. Meanwhile, the OPA fabricated on a substantially thick BOX layer featured a limited steering performance to attain a stabilized response over a broad spectral region. We examined the influence of the cavity thickness on the spectral response of the antenna in terms of optical thickness. Based on the two antenna characteristics, it was confirmed that the grating antenna emitted the beam with a higher efficiency when the optical thickness of the cavity corresponded to odd integer multiples of the quarter wavelength. This work is a considerable strategy for designing a stabilized SiN OPA over a desired spectral region.

Abstract: Experimental details are discussed and millimeter wave measurements presented of a W-band gyrotron traveling-wave tube (gyro-TWT) that uses a helically corrugated interaction waveguide operating at the second electron cyclotron harmonic. A method for increasing the gain by using an interaction circuit with two sections separated by a long sub-cutoff drift section has been experimentally verified. A 10-mW driving source was sufficient to enable an amplified signal output power of 3 kWs. The continuous-wave (CW) operation with a single-stage depressed collector and deposited beam power of about 20 kW is believed to be the first demonstration of its kind for a W-band gyro-TWT.

Abstract: Mid-infrared (mid-IR) absorption spectroscopy based on integrated photonic circuits has shown great promise in trace-gas sensing applications in which the mid-IR radiation directly interacts with the targeted analyte. In this paper, considering monolithic integrated circuits with quantum cascade lasers (QCLs) and quantum cascade detectors (QCDs), the InGaAs-InP platform is chosen to fabricate passive waveguide gas sensing devices. Fully suspended InGaAs waveguide devices with holey photonic crystal waveguides (HPCWs) and subwavelength grating cladding waveguides (SWWs) are designed and fabricated for mid-infrared sensing at λ = 6.15 μm in the low-index contrast InGaAs-InP platform. We experimentally detect 5 ppm ammonia with a 1 mm long suspended HPCW and separately with a 3 mm long suspended SWW, with propagation losses of 39.1 and 4.1 dB/cm, respectively. Furthermore, based on the Beer-Lambert infrared absorption law and the experimental results of discrete components, we estimated the minimum detectable gas concentration of 84 ppb from a QCL/QCD integrated SWW sensor. To the best of our knowledge, this is the first demonstration of suspended InGaAs membrane waveguides in the InGaAs-InP platform at such a long wavelength with gas sensing results. Also, this result emphasizes the advantage of SWWs to reduce the total transmission loss and the size of the fully integrated device's footprint by virtue of its low propagation loss and TM mode compatibility in comparison to HPCWs. This study enables the possibility of monolithic integration of quantum cascade devices with TM polarized characteristics and passive waveguide sensing devices for on-chip mid-IR absorption spectroscopy.

Abstract: A single-layer substrate-integrated waveguide (SIW) filtering power divider (FPD) with fully differential operation at 28 and 39 GHz is proposed in this letter. This FPD consists of three SIW cavities where the differential and common modes of each cavity were properly designed to form three-pole dual passbands, facilitate deployment of isolation resistors, and introduce transmission zeros while attaining high in-band common-mode rejection. To improve the output return loss and isolation in dual bands, a novel and simple approach to find the proper location of isolation resistors is presented. At operating frequencies, the measured differential-mode input or output return loss, minimum insertion loss, isolation, and common-mode suppression are >14.1 dB, 14.9 dB, and >30.3 dB, respectively. The amplitude and phase imbalances between outputs are < 0.48 dB and <4.2°, respectively.

Abstract: In the past few decades, silicon photonics has witnessed a ramp-up of investment in both research and industry. As a basic building block, silicon waveguide crossing is inevitable for dense silicon photonic integrated circuits and efficient crossing designs will greatly improve the performance of photonic devices with multiple crossings. In this paper, we focus on the state-of-the-art and perspectives on silicon waveguide crossings. It reviews several classical structures in silicon waveguide crossing design, such as shaped taper, multimode interference, subwavelength grating, holey subwavelength grating and vertical directional coupler by forward or inverse design method. In addition, we introduce some emerging research directions in crossing design including polarization-division-multiplexing and mode-division-multiplexing technologies.

Abstract: The spoof surface plasmon polariton (SPP) waveguide, which could support well-confined surface waves along an ultrathin corrugated metallic strip, is one of the most advantageous candidates in integrated circuits due to the remarkable properties of low crosstalk, low loss, and packaging minimization. Many devices based on the spoof SPP waveguide have emerged, but it is still a challenge to manipulate the SPP waves freely in real-time. Here, we propose a programmable multifunctional spoof SPP device by loading varactor diodes between adjacent metallic teeth of SPP waveguides. By programming the bias voltages of the varactor diodes dynamically, the coupling waves propagating on two SPP waveguides can be freely controlled. Simulations and experiments demonstrate that the programmable SPP device can realize high-efficiency SPP through transmission, unequal coupling, 3 dB direction coupling, and crossover transmission with better isolation effect. Different functions and operational frequency ranges can be reconfigured in real-time. The proposed method lays the groundwork for applications in large-scale microwave integrated circuits and digital communication systems.

Abstract: Ultra-wideband spoof surface plasmon polaritons (SSPPs) based on compact balanced coplanar stripline (CPS) waveguides are proposed. Compared with the conventional CPS-based terahertz (THz) SSPP unit cell, the proposed one has achieved a size reduction of 55.2% under the condition of the same asymptotic frequency. The propagation and attenuation characteristics of the proposed SSPP waveguide can be easily manipulated by adjusting the geometry dimensions of the SSPP unit cell. It indicates that the cut-off frequency of the SSPP waveguide has its tunable flexibility thereby facilitating the filter design. To further validate the proposed idea, a similar topology in microwave regime is designed and measured, where the microwave feeding can be easily realized by embedding a balun structure from unbalanced microstrip line to balanced CPS. The measurement of the microwave filter prototype illustrates ultra-wideband bandpass filtering characteristics with return losses of over 10 dB and average insertion losses of 3.2 dB in the passband of 1.9-14 GHz. The presented work may have significant potentials to develop the miniaturization of various planar plasmonic devices and integrated circuits in microwave and THz regimes.

Abstract: Scalable and low cost fabrication of light weight flexible electromagnetic (EM) wave absorbers is highly desirable for the rapid development of wearable electronic devices. A simple method has been developed involving incorporation of rationally designed FeNi3/Mo2C into cellulose fibers in the formation of thin and flexible absorbing papers with tunable electromagnetic parameters. High-performance absorption has been achieved with the minimum reflection loss (RL) reaching −51.50 dB at 13.7 GHz and an effective absorption bandwidth of 5.1 GHz with a thickness of 2.0 mm due to the synergic effects of dielectric and magnetic loss. For emerging flexible absorbers, accurate electromagnetic measurements by using a conventional coaxial method are challenging without the addition of wax or paraffin as the solidification agent. A stacking and compressing method has been developed to prepare standard-sized core samples for coaxial measurements for which the validity has been confirmed by comparison with the waveguide and arch methods. Consequently, not only a new type of effective EM absorber has been developed and verified by all the available measurement methods, but this simple and scalable method applied to fabricate flexible electronic devices is also extendable for applications in sensing, catalysis and energy storage.

Abstract: This review provides an overview of the technological advancements and miniaturization trends in Substrate Integrated Waveguide (SIW) filters. SIW is an emerging planar waveguide structure for the transmission of electromagnetic (EM) waves. SIW structure consists of two parallel copper plates which are connected by a series of vias or continuous perfect electric conductor (PEC) channels. SIW is a suitable choice for designing and developing the microwave and millimetre-wave (mm-Wave) radio frequency (RF) components: because it has compact dimensions, low insertion loss, high-quality factor (QF), and can easily integrate with planar RF components. SIW technology enjoys the advantages of the classical bulky waveguides in a planar structure; thus is a promising choice for microwave and mm-Wave RF components.

Abstract: Low propagation loss in high confinement waveguides is critical for chip-based nonlinear photonics applications. Sophisticated fabrication processes which yield sub-nm roughness are generally needed to reduce scattering points at the waveguide interfaces in order to achieve ultralow propagation loss. Here, we show ultralow propagation loss by shaping the mode using a highly multimode structure to reduce its overlap with the waveguide interfaces, thus relaxing the fabrication processing requirements. Microresonators with intrinsic quality factors (Q) of 31.8 $\pm$ 4.4 million are experimentally demonstrated. Although the microresonators support 10 transverse modes only the fundamental mode is excited and no higher order modes are observed when using nonlinear adiabatic bends. A record-low threshold pump power of 73 $\mu$W for parametric oscillation is measured and a broadband, almost octave spanning single-soliton frequency comb without any signatures of higher order modes in the spectrum spanning from 1097 nm to 2040 nm (126 THz) is generated in the multimode microresonator. This work provides a design method that could be applied to different material platforms to achieve and use ultrahigh-Q multimode microresonators.

Abstract: We demonstrate ultrabroadband supercontinuum generation from ultraviolet to mid-infrared wavelengths in single-crystalline aluminum nitride waveguides. Tunable dispersive waves are observed at the mid-infrared regime by precisely controlling the waveguide widths. In addition, ultraviolet light is generated through cascaded second-harmonic generation in the modal phase-matched waveguides. Numerical simulation indicates a high degree of coherence of the generated spectrum at around the telecom pump and two dispersive waves. Our results establish a reliable path for multiple octave supercontinuum comb generation in single-crystalline aluminum nitride to enable applications including precision frequency metrology and spectroscopy.

Abstract: In this paper, a two-dimensional structure based on photonic crystal for adding three input bits is proposed. The dielectric rods used in this work are made of chalcogenide with a dielectric constant of 9.61. The lattice constant of the structure is 510 nm and the radius of the fundamental rods is 0.206 times the lattice constant. Three waveguides transmit the optical wave from input ports to the main waveguide. Based on the optical intensity in the main waveguide, two nonlinear cavities drop the waves toward the SUM and CARRY output ports. For using the optical Kerr effect, a rod made of the doped glass with a nonlinear coefficient of 10–14 m2/W is placed in each cavity. The radii of these rods are 1.12 and 1.06 times the radius of the fundamental rods. To calculate the band diagram and optical wave propagation throughout the proposed structure, the plane wave expansion and the finite difference time domain methods have been used. The maximum rise time of this structure is 400 fs that is less than one for the previous works. Furthermore, the area of the structure is around 115 µm2 which is proper to the optical circuits. Also, the obtained difference between margins of logic 0 and 1 is equal to 82%. According to the obtained results, one can be optimistic about the designed structure to be considered in optical processing applications.

Abstract: Polarization selective devices, such as polarizers and polarization selective resonant cavities (e.g., gratings and ring resonators), are core components for polarization control in optical systems and find wide applications in polarizationdivision- multiplexing, coherent optical detection, photography, liquid crystal display, and optical sensing. In this paper, we demonstrate integrated waveguide polarizers and polarization-selective micro-ring resonators (MRRs) incorporated with graphene oxide (GO). We achieve highly precise control of the placement, thickness, and length of the GO films coated on integrated photonic devices by using a solution-based, transfer-free, and layer-by-layer GO coating method followed by photolithography and lift-off processes. The latter overcomes the layer transfer fabrication limitations of 2D materials and represent a significant advance towards manufacturing integrated photonic devices incorporated with 2D materials. We measure the performance of the waveguide polarizer for different GO film thicknesses and lengths versus polarization, wavelength, and power, achieving a very high polarization dependent loss (PDL) of ~ 53.8 dB. For GOcoated integrated MRRs, we achieve an 8.3-dB polarization extinction ratio between the TE and TM resonances, with the extracted propagation loss showing good agreement with the waveguide results. Furthermore, we present layer-by-layer characterization of the linear optical properties of 2D layered GO films, including detailed measurements that conclusively determine the material loss anisotropy of the GO films as well as the relative contribution of film loss anisotropy versus polarization-dependent mode overlap, to the device performance. These results offer interesting physical insights and trends of the layered GO films from monolayer to quasi bulk like behavior and confirm the high-performance of integrated polarization selective devices incorporated with GO films.

Abstract: A tunable metamaterial (MM)-based silicon (Si) waveguide is presented that is composed of an MM nanodisk array on a Si-on insulator substrate. A significant modulation efficiency of transmission intensity could be realized by elevating individually or simultaneously the column number of MM nanodisks. For a convenient description, an MM-based Si waveguide with one, two, three, four, and five columns of MM nanodisks are denoted as MM-1, MM-2, MM-3, MM-4, and MM-5, respectively. Transmission intensity of MM-based Si waveguides could be switched between on and off states by driving different columns of MM nanodisks on the Si waveguide surface. Transmission intensities could be attenuated from 100% to 56%, 24%, 6%, 1%, and 0% for MM-1, MM-2, MM-3, MM-4, and MM-5, respectively, at the wavelength of 1.525 µm. Furthermore, the MM-5 device is exposed to an ambient environment with different refraction indices. It exhibits a linear relationship of resonance dips and refraction indexes. The proposed design of the MM-based Si waveguide provides potential possibilities in an optical switch, variable optical attenuator, and sensor applications.

Abstract: In this research article , we present theoretical and numerical investigations concerning the effects of temperature on the transmittance properties of one dimensional annular photonic crystals. The theoretical basis of our study adopts the modified transfer matrix method applied to optical fiber waveguides. The numerical results showed many features that could be of interest. In this regard , we investigate this design to enhance the values of sensitivity based on its geometry. Our design exhibits a remarkable response to temperature changes with a sensitivity of about 0.033 nm/°C which is considered significantly high . Also, it is found that the upper edge of the photonic band gap increases considerably with temperature changes, while the lower edge is almost unchanged . The effects of the core radius and number of periods on the transmittance of our annular photonic crystals design have been also investigated. It is found that an appropriate choice for the core would give flexibility of fabrication and stability of transmission output. In addition, this study reveals that the phase shift of the reflected cylindrical waves within the core is strongly dependent on temperature. We believe our structure is potentially promising in designing and fabrication of novel high-performance temperature sensors and integrated waveguide devices such as optical switches and filters.

Abstract: As one of the most important optical filtering devices, Bragg gratings have been extensively used in various systems. A long Bragg grating is desired for many applications including frequency selection in semiconductor lasers and dispersion control for ultra-short pulses. As a prominent example, integrated spiral Bragg grating waveguides (SBGWs) have drawn much attention in the years. However, until now, the length of an integrated grating is still limited to a few milli-meters due to total waveguide loss. In this work, we propose and demonstrate a novel long chirped SBGW with waveguide loss as low as 0.05 dB/cm on a silicon nitride (Si3N4) platform. A 13.8 cm SBGW is fabricated, which is the longest on-chip waveguide grating reported so far. The SBGW’s reflection bandwidth is 9.2 nm from 1556.3 nm to 1565.5 nm, and it provides a total of 1440 ps group delay, that is, −156.5 ps/nm of dispersion. The group delay response shows great linearity and temperature stability. This integrated device holds great potential for various applications including in-line dispersion compensation, optical true delay phase array, and microwave photonics.

Abstract: This paper presents results of development and analysis of new Ku-band compact polarizers based on a square waveguide with irises. Main advantages of electromagnetic waves with circular polarizations, which are obtained in satellite antenna systems with polarizers, are listed and discussed in the article. The designs of compact waveguide polarizers with 3, 4 and 5 irises have been optimized to provide effective polarization and matching performance in the operating Ku-band 10.7-12.8 GHz. The dependences of electromagnetic characteristics of polarizers on frequency were simulated and optimized using finite integration technique. The alteration of sizes of optimal structures and improvement of their characteristics have been analyzed for the polarizers with number of irises from 3 to 5. The best performance among the considered designs is provided by the square waveguide polarizer with 5 irises. Voltage standing wave ratios of the polarizer with 5 irises for both linear polarizations are less than 1.13. The optimized differential phase shift lies within the range $90^{\circ}\pm 2.6^{\circ}$. The axial ratio of the polarizer with 5 irises is less than 0.40 dB. The XPD is higher than 32.9 dB. Therefore, developed new compact square waveguide polarizer with 5 irises provides efficient performance in the operating Ku-band 10.7-12.8 GHz and can be widely used in modern satellite television and other information systems.

Abstract: We demonstrate adiabatically tapered fibers terminating in sub-micron tips that are clad with a higher-index material for coupling to an on-chip waveguide. This cladding enables coupling to a high-index waveguide without losing light to the buried oxide. A technique to clad the tip of the tapered fiber with a higher-index polymer is introduced. Conventional tapered waveguides and forked tapered waveguide structures are investigated for coupling from the clad fiber to the on-chip waveguide. We find the forked waveguide facilitates alignment and packaging, while the conventional taper leads to higher bandwidth. The insertion loss from a fiber through a forked coupler to a sub-micron silicon nitride waveguide is 1.1 dB and the 3 dB bandwidth is 90 nm. The coupling loss in the packaged device is 1.3 dB. With a fiber coupled to a conventional tapered waveguide, the loss is 1.4 dB with a 3 dB bandwidth extending beyond the range of the measurement apparatus, estimated to exceed 250 nm.

Abstract: In this article, a novel planar annular leaky-wave antenna (LWA) based on substrate integrated waveguide (SIW) for generating conical beam is proposed, which exhibits properties of beam angle designable in the elevation plane, low profile, and small size. It contains two layers, i.e., radiating layer and feeding layer. Propagation properties of wave in the radiating layer are analyzed, which provide theoretical basis for design procedure. In the feeding layer, a coupled feeding network is utilized for improving impedance bandwidth. Three types of the proposed LWA with different sizes are fabricated and measured to validate the design. The measurement results agree well with the simulation results. This kind of antenna can be a suitable candidate for mobile communication.

Abstract: Resonant dispersive wave (RDW) emission in gas-filled hollow waveguides is a powerful technique for the generation of bright few-femtosecond laser pulses from the vacuum ultraviolet to the near infrared. Here we investigate deep-ultraviolet RDW emission in a hollow capillary fibre filled with a longitudinal gas pressure gradient. We obtain broadly similar emission to the constant-pressure case by applying a surprisingly simple scaling rule for the gas pressure and study the energy-dependent dispersive-wave spectrum in detail using simulations. We further find that in addition to enabling dispersion-free delivery to experimental targets, a decreasing gradient also reduces the pulse stretching within the waveguide itself, and that transform-limited pulses with 3 fs duration can be generated by using short waveguides. Our results illuminate the fundamental dynamics underlying this frequency conversion technique and will aid in fully exploiting it for applications in ultrafast science and beyond.

Abstract: In this research we carried out mathematical modeling, development and optimization of square waveguide sections with irises and antiphase posts. The presented mathematical model applies scattering and transmission matrices of the structure elements for the calculation of general scattering matrix of the whole waveguide section. Depending on linear polarization type of the fundamental mode the irises are simulated as inductances or capacitances, which are connected in parallel into the equivalent transmission line. Two antiphase posts in a square waveguide are modeled as a parallel resonant circuit in the equivalent transmission line. Using the developed mathematical model the matching characteristics and differential phase shift of square waveguide sections with two irises and two posts were calculated theoretically. In order to check the performance of developed mathematical model the simulations of the same waveguide sections were performed using finite integration technique. Presented waveguide sections can be tuned by changing the length of their posts. Both optimized designs of square waveguide sections with two irises and two posts provide voltage standing wave ratio less than 1.4 for both polarizations. Differential phase shifts of developed polarizer sections are 30°±0.7° and 45°±1.75°. Therefore, suggested new simple mathematical technique for calculation of characteristics of the waveguide sections with irises and antiphase posts can be widely used for the development of new tunable waveguide filters, phase shifters and polarization processing devices.

Abstract: The topological interface state for an elastic wave in a one-dimensional system, as reported in the literature, mainly occurs through Bragg scattering, making it difficult to achieve subwavelength wave control and flexible tunability. Here, inspired by the band-folding mechanism, this paper confirms that an interface state can likewise be excited by local resonance. The topological phase transition is accomplished by purposely arranging the locations of local resonators. The system is composed of a uniform thin beam with periodically attached local resonators made from an electrorheological elastomer subjected to adjustable electric fields. By simply doubling the primitive unit cell, the passing bands in the dispersion relation are folded and a folding point falls below the locally resonant bandgap, which can be lifted up by simply tuning the distance between two local resonators to realize a topological phase transition. Furthermore, we demonstrate the dynamic tunability of the working frequency of the topological interface state by using an external electric field to adjust the starting frequency of the local resonance. Since the excited frequency of the interface mode is lower than the resonance frequency, this work overcomes the ineffectiveness of the Bragg topological phononic crystal at low frequencies. Moreover, the use of an electroactive resonator whose parameters are readily tuned also enables the flexible design of a frequency-variable topological system without requiring a geometrical modification of the base structure. This technique may have potential applications, such as vibration isolation or in fabricating a robust waveguide.

Abstract: This article utilizes a topology optimization approach to design planar multilayer transitions between substrate integrated waveguides (SIWs) and rectangular waveguides (RWGs). The optimization problem is formulated based on the modal field analyses and Maxwell’s equations in the time domain solved by the finite-difference time-domain (FDTD) method. We present a time-domain boundary condition based on the Klein–Gordon equation to split traveling waves at homogeneous waveguide ports. We employ the boundary condition to compute portal quantities and to devise an adjoint-field system that enabled an efficient computation of the objective function gradient. We solve design problems that include more than 105 000 design variables by using less than 400 solutions of Maxwell’s equations. Moreover, a new formulation that effectively combats the development of in-band resonances in the design is presented. The transition configuration allows the direct mount of conventional RWG sections on the circuit board and aims to cover the entire K-band. The guiding structure of the optimized transition requires blind vias, which is realized by a simple and cost-efficient technique. In addition, the transition is optimized for three different setups that can be used to provide different field polarizations. The proposed transitions show less than 1-dB insertion loss and around 15-dB return loss over the frequency interval 18–28 GHz. Several prototypes are fabricated with an excellent match between the simulation and measurement results.

Abstract: Self-imaging is an important function for signal transport, distribution, and processing in integrated optics, which is usually implemented by multimode interference or diffractive imaging process. However, these processes suffer from the resolution limit due to classical wave propagation dynamics. We propose and demonstrate subwavelength optical imaging in one-dimensional silicon waveguide arrays, which is implemented by cascading straight and curved waveguides in sequence. The coupling coefficient between the curved waveguides is tuned to be negative to reach a negative dispersion, which is an analog to a hyperbolic metamaterial with a negative refractive index. Therefore, it endows the waveguide array with a superlens function as it is connected with a traditional straight waveguide array with positive dispersion. With a judiciously engineered cascading silicon waveguide array, we successfully show the subwavelength self-imaging process of each input port of the waveguide array as the single point source. Our approach provides a strategy for dealing with optical signals at the subwavelength scale and indicates functional designs in high-density waveguide integrations.

Abstract: We propose a bent corrugated substrate integrated waveguide (BCSIW) structure that can be used to design a high gain leaky wave antenna (LWA). The design removes the need for a metallic via fabrication process needed for standard substrate integrated waveguides (SIW) and displays superior performance to previously reported structures. We use simulations to compare the performance of the proposed BCSIW LWA to equivalent standard SIW and corrugated SIW (CSIW) structures, as well as experimentally characterize a fabricated BCSIW LWA. Simulation results show that the BCSIW structure can help improve the impedance bandwidth of a slotted LWA by about 14.7% while still maintaining high gain (about 13.2-17.4 dBi) as compared to an LWA based on a CSIW structure. Measurement results indicate that the proposed BCSIW LWA has a wide impedance bandwidth (32.6%) and a high peak gain (12-16.2 dBi) throughout a large frequency range from 22 to 29.2 GHz with a large beam angle range from -69° to -10°.

Abstract: A novel slow wave structure (SWS), called double tunnel staggered grating (DTSG), which originates from the double staggered grating (DSG) and folded waveguide (FW), is proposed to develop a dual-beam traveling wave tube (TWT) with high power and electron efficiency in Terahertz (THz) band. Using two key techniques: (1) the rectangular holes are opened in the grating-ridges, and the operating mode is cut-off at holes; (2) specific grating-height, the DTSG-SWS possesses the wide operating band as DSG-SWS, high interaction impedance as the rectangular grating (RG) SWS, and good transmission characteristics as FW-SWS. In addition, it is not only suitable for the dual-beam TWT, but also is simple and easy of fabrication as DSG-SWS. The particle-in-cell simulation analysis confirms that the saturated power and electron efficiency of TWT using DTSG-SWS have been significantly improved compared with the TWT using DSG-SWS.