Waveguide Insertion Research Articles

Subwavelength dielectric waveguide for efficient travelling-wave magnetic resonance imaging

Magnetic resonance imaging (MRI) has diverse applications in physics, biology, and medicine. Uniform excitation of nuclei spins through circular-polarized transverse magnetic component of electromagnetic field is vital for obtaining unbiased tissue contrasts. However, achieving this in the electrically large human body poses a significant challenge, especially at ultra-high fields (UHF) with increased working frequencies (≥297 MHz). Canonical volume resonators struggle to meet this challenge, while radiative excitation methods like travelling-wave (TW) show promise but often suffer from inadequate excitation efficiency. Here, we introduce a new technique using a subwavelength dielectric waveguide insert that enhances both efficiency and homogeneity at 7 T. Through TE11-to-TM11 mode conversion, power focusing, wave impedance matching, and phase velocity matching, we achieved a 114% improvement in TW efficiency and mitigated the center-brightening effect. This fundamental advancement in TW MRI through effective wave manipulation could promote the electromagnetic design of UHF MRI systems.

Fiber-connectorized ultrafast-laser-inscribed K-band integrated optics beam combiner for the CHARA telescope array.

A fiber-connectorized K-band integrated-optics two-telescope beam combiner was developed for long-baseline interferometry at the CHARA telescope array utilizing the ultrafast laser inscription (ULI) technique. Single-mode waveguide insertion losses were measured to be ∼1.1d B over the 2-2.3µm window. The development of asymmetric directional couplers enabled the construction of a beam combiner that includes a 50:50 coupler for interferometric combination and two ∼75:25 couplers for photometric calibration. The visibility of the bare beam combiner was measured at 87% and then at 82% after fiber-connectorization by optimizing the input polarization. These results indicate that ULI technique can fabricate efficient fiber-connectorized K-band beam combiners for astronomical purposes.

Broadband Rectangular Waveguide TE10–TE20 Mode Converter With In-Line Ports and Compact Structure

This letter presents a compact and broadband TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10}$</tex-math> </inline-formula> –TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{20}$</tex-math> </inline-formula> mode converter for millimeter-wave and terahertz applications. The input rectangular waveguide (RWG) and output over-mode waveguide (OMWG) are in-line and orthogonal in arrangement. In this converter, the waveguide mode is converted in the short height-reduced and width-widened gradient waveguides. A simple cuboid matching structure is employed to improve bandwidth and conversion efficiency, and a bed of nails is applied to the waveguide profile to suppress electromagnetic (EM) leakage and facilitate assembly at high frequencies. For further verification, a pair of WR-4.3 band prototypes were fabricated and measured. In the range of 170–252 GHz (38.9%-bandwidth), the measured insertion loss of the back-to-back converters is found to be around 0.86 dB with the worst return loss of 14 dB except for a slight deterioration at 172 GHz. Deducting the waveguide insertion loss, the conversion efficiency is higher than 98%.

Micromachined Silicon-Core Substrate-Integrated Waveguides at 220–330 GHz

In this article, we present a new technology platform for creating compact and loss-efficient wafer-scale integrated micromachined substrate-integrated waveguides with silicon-core (Si-SIWs) for the 230-330-GHz frequency range. The silicon dielectric core enables highly integrated sub-millimeter-wave systems, since it allows for downscaling the waveguide's cross section by a factor of 11.6, and the volume of components by a factor of 39.3, as compared to an air-filled waveguide. Moreover, geometrical control during fabrication of this type of waveguides is significantly better as compared to micromachined hollow waveguides. The measured waveguide's insertion loss (IL) is 0.43 dB/mm at 330 GHz (0.14 dB/λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , normalized to the guided wavelength). A low-loss ultrawideband coplanar-waveguide (CPW) transition is implemented to enable direct measurements of devices and circuits in this waveguide platform, and this is also the very first CPW-to-SIW transition in this frequency range. The measured IL of the transition is better than 0.5 dB (average 0.43 dB above 250 GHz), which is lower than for previously reported CPW-to-SIW transitions even at 3 times lower frequencies; the return loss is better than 14 dB for 75% of the band. As devices examples implemented in this platform, a filter and H-plane waveguide bends are shown. The waveguides and the devices are manufactured by deep-silicon etching using a cost-efficient two-mask micromachining process.

Controlled flow of nonlinear surface plasmon polaritons

The control of flow of surface plasmon polaritons (SPPs) propagating at the single interface of metal and dielectric media and also in plasmonic waveguides is considered. The SPP energy flux is sufficient for appearance of the nonlinear polarization of the media. SPP flow propagates along the interface as a quasiharmonic wave in the linear regime at weak intensity and as a cnoidal wave in the form of a pulse train or solitons in the nonlinear regime at strong intensity of the flow. The forms and periods of these waves are determined by the power of external source and the boundary conditions of the SPP flow excitation. The propagation of SPP flow in plasmonic waveguides depends on the phase shift under the effect of external electric field in the waveguide insert. Thereby, the energy flux of SPPs in the plasmonic waveguide can be controlled by the power of source and the external electric field also.

Ka‐band compact and high‐performance bandpass filter based on multilayer air‐filled SIW

A substantial reduction of Substrate Integrated Waveguide (SIW) insertion loss can be achieved through the use of air as dielectric instead of usual dielectric material. However, Air-Filled SIW (AFSIW) circuits exhibit larger footprint compared to their dielectric-filled counterparts. In this letter, a compact multilayer AFSIW bandpass filter is proposed to realize both high performance and small footprint. For demonstration purpose, a Ka-band multilayer 4th order AFSIW bandpass filter has been designed and fabricated. Measured and simulated results are in good agreement. Retro-simulations, taking into account fabrication tolerances, are also presented. Finally, a performance comparison with other multilayer technologies is presented.

Experimental demonstration of a two-mode (de)multiplexer based on a taper-etched directional coupler.

We experimentally demonstrate a compact, low-cross talk and fabrication-tolerant two-mode (de)multiplexer on the silicon-on-insulator platform. The device consists of a silicon wire waveguide coupled to a taper-etched waveguide. The partially etched taper structure is used to relax fabrication tolerance and thus to ensure high mode-conversion efficiency. The device is 68 μm in length, with a TE0-to-TE1 mode conversion loss of better than -0.8 dB demonstrated over the C-band wavelengths. In addition, the device demonstrates a low TE0-to-TE0 through waveguide insertion loss of better than -1.3 dB with modal cross talk lower than -26 dB, over a 65 nm wavelength range. Finally, we have experimentally demonstrated that the device is tolerant of fabrication errors of up to 20 nm. Better than -6 dB TE0-TE1 conversion loss with a cross talk lower than -23 dB over a 55 nm bandwidth has been obtained with a fabrication tolerance as large as 40 nm.

Silicon-on-Glass Dielectric Waveguide—Part II: For THz Applications

A low-loss sub-millimeter-wave/THz integrated dielectric waveguide is presented. The proposed waveguide consists of a highly resistive Silicon (Si) guiding channel bonded to a glass substrate. To reduce the waveguide insertion loss due to the glass substrate, part of the substrate below the Si guiding channel is etched. A periodic configuration of supporting beams is used to hold the Si guiding channel over the glass substrate. A low-cost and high-precision fabrication process, which is fully compatible with current Si-based fabrication technologies, is developed for the proposed waveguide. Numerical simulations and experiments are conducted to investigate the performance of the proposed waveguide. Measured attenuation constant of the proposed waveguide is 0.0346 dB/ $\lambda_{0}$ (average value) over the 440–500 GHz band.

Thermal Stability of Optical Coupling Solutions in Silicone-Based Optical Interconnects

The thermal stability of different coupling solutions (butt coupling and mirror coupling) in polymer optical interconnects has been investigated by means of the finite volume method based software, FLOTHERM. According to this approach, thermal simulations are performed to study and compare the thermal behavior of vertical-cavity surface-emitting diodes (VCSELs), photo diodes (PDs), and polymer waveguide layers within polymer optical interconnects with different coupling solutions. In the case of butt coupling, the maximum temperatures on the VCSEL and PD chips, as well as the influence caused by changes of the optical interconnect length, are discussed. In the case of mirror coupling, temperature distributions and gradients in the key waveguide layer are analyzed and also compared with optical interconnects using butt coupling. With this simulated temperature distribution and the experimentally evaluated refractive indices and thermooptic coefficients of core and cladding silicones, the influence on the maximum data transmission capability in silicone-based waveguides is discussed, as well as the impact on waveguide insertion loss figures at 850 nm.

Single Stage Ultrafast Laser Inscription of a Side-Polished Fiber-Like Waveguide Sensor

Ultrafast laser inscription (ULI) has been used to fabricate an 18 mm long sub-surface optical waveguide in fused silica. The waveguide started and terminated 75 below the substrate surface, approaching it to a minimum depth of for the central section. The device was fabricated in a single step, exhibiting a fiber-to-fiber insertion loss of 2.6 dB. When a high refractive index oil was placed on the substrate surface, the polarization-averaged waveguide insertion loss increased by 3.7 dB. This work demonstrates that a single ULI stage can be used to fabricate optical waveguides sufficiently close to a substrate surface for evanescent field sensing applications.

Ti-free optical waveguiding regions produced by LiNbO_3 etching during the indiffusion of Ti

We report the observation, first to our knowledge, of optical waveguiding found beneath trenches etched in congruent lithium niobate using the recently reported etching during the indiffusion of Ti process. Observations of multi-mode and single-mode guiding at visible wavelengths and preliminary measurements of waveguide insertion losses are presented.

Quality Standardization for Polydimethysiloxane-Based Optical Interconnect Production From Optical Aspects

The influences of waveguide materials, fabrication conditions, and packaging substrates on the optical waveguide properties of electrical-optical circuit boards have been investigated by systematic variation of these conditions. Pt catalyst in polydimethysiloxane, casting mould sidewall roughness, interlay thickness, and packaging substrates show sensitive impact on optical waveguide insertion loss and in terms of defined target of optical loss, the basic quality criteria can be defined before production.

Diffraction model of a semiconductor amplifier

A three-dimensional diffraction model of a semiconductor heterostructure amplifier is developed. The model describes the field propagation and optical mode establishment taking into account the amplification kinetics within the framework of the diffusion equation for current carriers in a quantum well. The results of application of this model are presented for an amplifier with an asymmetric broad waveguide and an antiwaveguide structure in the lateral direction that does not confine the field. It is shown that the length of establishment of the fundamental mode for such a structure is comparable with the length over which a weak signal is enhanced by two orders of magnitude. The balance between the gain and loss for the steady-state mode as a function of the waveguide insert width is analysed. The effect of this width on the properties of the fundamental optical mode, including the far-field intensity distribution, is studied.

Low-Noise Semiconductor Amplifier of Middle Part of Millimeter-Wave Range

To decrease the loss of a parametric two-circuit amplifier is a main problem of paper. The use of dielectric inserts with inclined face as a circuit of non-load frequency is considered in the study. Results of electrodynamic simulation of oscillatory processes in a dielectric insert in a rectangular waveguide are represented. Experimental amplitude and noise characteristics of the breadboard model of the parametric amplifier on the basis of the considered filter are given. Within the range of 60 GHz the amplification factor no less than 12 dB over a half-power bandwidth of 1.2 GHz has been obtained with a noise temperature of 550 K.

Polysiloxane optical waveguide layer integrated in printed circuit board

A hybrid electrical-optical circuit board is demonstrated using polysiloxane as low-loss and high-temperature stable waveguide material system. After board lamination at 180°C for two hours and a subsequent annealing at 230°C for 5 minutes the waveguide insertion loss is 0.05 dB/cm at 850 nm wavelength.

FDTD-analysis of the wave diffraction from dielectric waveguide discontinuities

The problem of the guided mode reflection from the planar dielectric waveguide end is studied by the finite difference time domain method. The influence of facet deformations on the scattering characteristics is considered. The reflectivity problem for the system with the nonlinear dielectric waveguide insert is examined.

Upper and lower bounds of 180° unit element of a ridge waveguide: Calculations and measurements

AbstractThe upper and lower bounds on the actual solution of any microwave structure is of general interest. The purpose of this letter is to compare some calculations using the mode‐matching and finite‐element methods, with some measurements on a 180° ridge waveguide insert between standard WR62 rectangular waveguides. The work suggests that the MMM produces an upper bound, while the FEM places a lower bound on the measurement. © 2001 John Wiley &amp; Sons, Inc. Microwave Opt Technol Lett 31: 260–261, 2001.

Integration of a laser diode with a polymer-based waveguide for photonic integrated circuits

The fabrication and characterization of BRS lasers monolithically integrated with butt-coupled polymer-based buried strip waveguides is presented. Threshold currents of lasers with one cleaved and one etched mirror facets are 15-18 mA and waveguide output powers are in excess of 5 mW at 100 mA laser driving currents and for 600 μm long waveguides. The device exhibits a total waveguide insertion loss less than 5 dB. The integrated device is potentially suitable as a building-block for photonic integrated circuits.

A rigorous cad of millimeter wave bandpass filter with all-metal insert in waveguide

In this paper, a bandpass filter with all-metal insert, an inductive strip in the E-plane of a waveguide is analyzed by a prototype filter and the scattering matrix of the strip is calculated by electromagnetic fields theory theoretically. By means of matrix combining technique, the scattering matrix of a bandpass filter of this type is obtained. And a rigourous error function is used to optimize the CAD program by Powell's method and make the experimental results agree well with the theory design at V-band.

Microwave characterization of the contiguous domain oscillator

Summary form only given. The authors report the first observation of microwave oscillation in the contiguous domain oscillator (CDO). Computer simulations indicate that, if the channel field V/sub GG//L is in the regime of negative differential mobility for electrons in GaAs, a contiguous sequence of charge domains will form spontaneously along the entire length of the channel, continuously drifting into the drain. Experimental devices were fabricated using a standard ion-implanted MESFET process, modified to include a WSiN resistive gate. The gate resistivity is 30 k Omega /sq, channel doping is 1.2*10/sup 17/ cm/sup -3/, and channel thickness is 150 nm. Channel widths range from 200 to 400 mu m and lengths from 10 to 50 mu m. Devices were mounted in a waveguide insertion unit, and operation was characterized between 26 and 140 GHz using a Tektronix 2755P spectrum analyzer. Modulation of the oscillation frequency by the gate-to-source V/sub G1-s/ was observed, as predicted by the computer simulation. >