Waveguide Measurements Research Articles

RF characterization and isolation properties of mesoporous Si by on-chip coplanar waveguide measurements

We report on the broadband electrical characterization of thick mesoporous silicon layers used as RF microplates for on-chip integration of high-Q passive devices in a CMOS-compatible process. To measure the RF losses of the microplate we have fabricated several designs of Coplanar Waveguides (CPWs), for form-factors relevant to the sizes of on-chip passive RF devices, on thick mesoporous Si layers (RF microplates) of various thicknesses, and we compared the results with those obtained from similar CPWs integrated directly on the p-type Si substrate. For maximum measurement sensitivity of the loss, the CPWs were designed to be very good transmission lines matched to 50Ω port impedances. We also characterized the grown mesoporous Si by performing electromagnetic simulations of the structure and identifying the measured and simulated S-parameters over a broadband frequency region, for the appropriate simulator input of complex permittivity. The measured results show that, for CPW features commensurate with the scale of on-chip RF passive devices, a 50-μm-thick mesoporous Si layer on the Si substrate reduces the losses to 1/6th–1/4th of the values corresponding to a p-type Si substrate, showing that mesoporous Si is an excellent material for CMOS-compatible on-chip integration of high-Q passive devices.

Performance of radar absorbing nanocomposites by waveguide measurements

Sol-gel synthesis has been investigated in order to produce stoichiometric compositions of Ba3Co2Fe24O41 (Co2Z) at lower calcination temperatures, using citric acid as quelant complex. Using this method, Co2Z ferrite could be synthesized at 950 °C, about 400 °C lower than that of conventional method. Nanocomposites (80:20% weight) of this ferrite with polychloroprene (CR) were obtained for the microwave absorption measurements by mixing, molding and curing mixtures of Ba3Co2Fe24O41 powders with polychloroprene and the additives of vulcanization. The microwave absorption measurements was carried out using the Transmission/Reflection method for the S and X-Ku bands and showed the best performance as Radar Absorber Material (RAM) in 8.0-16.0 GHz range. Thus, the material can be used by reducing the radar signature of the Brazilian Frigates' superstructures.

Metamaterial multiresonances in waveguide and metasurfaces

AbstractIn spite of the fact of its potential relevance for future advanced metamaterial design, split rings resonators high‐order resonances data are very limited in the literature. This article presents these co‐ and cross‐polarization high‐order resonances by means of numerical electromagnetic simulation and measurements in both monomode waveguides and free space propagation. A good agreement between simulation and experiments has been observed. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2825–2827, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23812

Nano Ferrites Microwave Complex Permeability and Permittivity Measurements by T/R Technique in Waveguide

There is a huge demand to accurately determine the magnetoelectrical properties of particles in the nano-sized regime due to the modern IC technology revolution and biomedical applications. In this paper, we present a microwave waveguide measurement technique for measuring complex permeability and permittivity of expensive nano-sized magnetic powder materials. We used a vector network analyzer to provide a standard TRL calibration for free space inside waveguide measurements. In order to maintain the recommended insertion phase range, a very thin prepared sample was loaded inside the calibrated waveguide. The loaded material's magnetic and dielectric effects were also considered in the cutoff wavelength calculation of the propagation constant of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> wave from the geometrical dimensions of the waveguides. These provisions make the permeability and permittivity measurements more reliable than those found by commonly used techniques. We used six different compounds of nano-sized ferrite powders (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , CuFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , CuFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Zn, F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> NiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Zn, BaFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> , and SrFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> ), in which the average diameter of nano particles is less than 40 nm, for measurement purposes. We measured the complex permeability and permittivity from 3.95 to 5.85 GHz. The results show that the dielectric permittivity of these materials is quite different from that of solid-state materials.

End-fire mode spectroscopy technique of examination of planar waveguides

A new technique of mode spectrum measurement in planar waveguides is presented. Unlike conventional m-line spectroscopy which does not provide reliable measurements of the whole mode spectra in waveguides with non-monotonic index profiles (in particular, step-index waveguides with thick cover layers or deep-buried graded-index waveguide structures) the proposed technique allows such measurements in any planar waveguides. The developed technique exploits the difference of refraction angles of different modes skew-incident to the output face of the waveguide. The viability of the technique is verified by the comparative study of mode spectra measured by the m-line spectroscopy and the proposed technique.

Dielectric and Conductor Loss Quantification for Microstrip Reflectarray: Simulations and Measurements

The conductor and dielectric loss mechanisms in microstrip reflectarray are described using simulation models and waveguide measurements. The dielectric constant and loss tangent variation with frequency is obtained for a particular substrate using existing datasheets. Variable size patch reflectarray element was studied for loss characterization. The effect of these losses is characterized and the potential cause for the loss phenomenon is provided. It is observed that the dielectric loss and copper loss occur near the patch resonance due to strong electric fields in the substrate region below the patch and the large currents on the top surface of the patch, respectively.

Frequency tunable electromagnetic metamaterial using ferroelectric loaded split rings

Measurements of a frequency tunable magnetic metamaterial using metallic split rings loaded with barium strontium titanate thin film capacitors are presented. The resonant frequency of this medium is voltage tunable across a 140MHz band centered at 1.75GHz. S-parameter measurements in a microstrip waveguide reveal that the effective relative permeability of the slab has a roughly Lorentzian shape that reaches minimum values between −2 and −3 for biases from 0to5V. The permeability of the slab can tune between positive and negative values, making it useful in applications requiring a state switchable magnetic permeability.

Design, Fabrication, and Measurement of Two-Dimensional Photonic Crystal Slab Waveguides

Two-dimensional photonic crystal slab waveguides on SOI wafer are designed and fabricated. Photonic band gap, band gap guided mode, and index guided mode are observed by measuring the transmission spectra. The experimental results are in good agreement with the theoretical ones.

Microwave (8–50 GHz) Characterization of Multiwalled Carbon Nanotube Papers Using Rectangular Waveguides

Multiwalled carbon nanotubes (MWNTs) are characterized at X-, Ku-, Ka-, and Q-bands by rectangular waveguide measurements. The scattering parameters (S-parameters) of thin MWNT papers containing a large ensemble of randomly oriented nanotubes are measured by a vector network analyzer from 8 to 50 GHz. A rigorous extraction algorithm has been developed to compute the effective complex permittivity ( epsiv = epsiv'- jepsiv") and permeability ( mu = mu' - jmu") of the nanotube papers from the measured -parameters. The extracted effective medium parameters are verified by finite-element simulations using Ansoft's High Frequency Structure Simulator (HFSS). The uncertainties for this characterization method are analyzed. The systematic uncertainties are found larger at lower frequencies than at higher frequencies. The extracted conductivity of the nanotube papers is in the range of 810-1500 S/m and the dielectric constant is from 250 to 700. The extracted complex permittivity can be fitted with the Drude-Lorentz model for the 8-50-GHz frequency range. The effective medium theory is then applied to remove the impact of air in the nanotube paper.

Light-intensity measurements in optical waveguides using prism couplers

In view of its central role in many optical waveguide applications, the absolute measurement of the actual light intensity propagating within a planar waveguide has been critically revised. Using prism couplers and proton exchanged LiNbO3 waveguides, several approaches have been experimentally checked and compared. A method is proposed and demonstrated, which combines the measurements of the light power out coupled from the waveguide edge and from the output prism. Reliable power measurements are obtained within a 5% error. A simplified version consists in a previous calibration of the setup in order to measure only the power coming from output coupler. Although inaccuracy rises up to ∼15%, it can be useful in many practical applications because of its simplicity. To assess and compare both methods, they have been applied to the measurement of light-intensity dependences of photovoltaic currents and optical damage thresholds in proton exchanged LiNbO3 guides.

Optical gain measurements in porous silicon planar waveguides codoped by erbium and ytterbium ions at 1.53μm

The on-off optical gain measurements as a function of the pump power were performed on porous silicon planar waveguides codoped by erbium and ytterbium ions. These measurements were obtained for different ratios of Yb concentration to Er concentration. The highest value of the gain was reached when the Yb concentration is three times higher than that of Er at a moderate 980nm pump power value equal to 70mW. Optical losses measurements have been performed on these waveguides and were equal to 2.1dB∕cm and an internal gain of about 6.4dB∕cm was obtained.

Fabrication of nanoporous silicon nitride and silicon oxide films of controlled size andporosity for combined electrochemical and waveguide measurements

We demonstrate a method for controlled etching of vertical nano-sized pores overmacroscopic areas. The method employs particle lithography to define a pattern,for which the density can be varied in a wide range and the size of the porescan be varied independently. The particle pattern is transferred into a chromemask on the substrate. We show how a thin nano-patterned mask is sufficientto etch sub-100 nm pores in dielectric materials at an aspect ratio of 20:1. Thiscreates possibilities to reach optimal design parameters for porous waveguides forincreased sensitivity and simultaneous electrochemical measurements. The feasibilityof these applications is also demonstrated by applying the process to makingfunctional plasmon-coupled waveguides with buried electrochemical electrodes.

High Precision Radar Distance Measurements in Overmoded Circular Waveguides

Distance measurements in overmoded waveguides are an important application for industrial radar systems. The accuracy of the measurements is deteriorated by the appearance of higher order modes in the metal tube, although the frequency-modulated continuous-wave method is used with a large bandwidth. This paper describes the problems caused by dispersion and multimode propagation and presents a solution in the form of mode-matched antennas for feeding the overmoded waveguide. It is shown that different modes, e.g., the H11 and H01 modes, are equally well suited for precision distance measurements, as is demonstrated both by simulations and measurements.

VAPOR-REDISSOLUTION TECHNIQUE FOR REDUCTION OF POLYMER/Si ARRAYED WAVEGUIDE GRATING LOSS

An efficient vapor-redissolution technique is used to greatly reduce sidewall scattering loss in the polymer arrayed waveguide grating (AWG) fabricated on a silicon substrate. Smoother sidewalls are achieved and verified by scanning electron microscopy. Reduction of sidewall scattering loss is further measured for the loss measurement of both straight waveguides and AWG devices. The sidewall loss in straight polymer waveguide is decreased by 2.1 dB/cm, the insertion loss of our AWG device is reduced by about 5.5 dB for the central channel and 6.7 dB for the edge channels, the crosstalk is reduced by 2.5 dB, and 3-dB bandwidth is narrowed by 0.05 nm after the vapor-redissoluton treatment.

Reduction of sidewall roughness, insertion loss and crosstalk of polymer arrayed waveguide grating using vapor-redissolution technique

An efficient vapor-redissolution technique is used to greatly reduce sidewall scattering loss in the polymer arrayed waveguide grating (AWG) fabricated on a silicon substrate. Smoother sidewalls are achieved and verified by a scanning electron microscopy. Reduction of sidewall scattering loss is further measured for the loss measurement of both straight waveguides and AWG devices. The sidewall loss in straight polymer waveguide is decreased by 2.1 dB/cm, the insertion loss of our AWG device is reduced by about 5.5 dB for the central channel and 6.7 dB for the edge channels, and the crosstalk is reduced by 2.5 dB after the vapor-redissoluton treatment.

Structure Tuning of Line-Defect Waveguides Based onSilicon-on-Insulator Photonic Crystal Slabs

We present fabrication and experimental measurement of a series ofphotonic crystal waveguides. The complete devices consist of aninjector taper down from 3 μm into a triangular-lattice air-holesingle-line-defect waveguide with lattice constant from 410 nm to 470 nmand normalized radius 0.31. We fabricate these devices on asilicon-on-insulator substrate and characterize them using a tunablelaser source over a wavelength range from 1510 nm to 1640 nm. A sharpattenuation at photonic crystal waveguide mode edge is observed formost structures. The edge of guided band is shifted about 30 nm with the10 nm increase of the lattice constant. We obtain high-efficiencylight propagation and broad flat spectrum response of the photoniccrystal waveguides.

Accurate Magnified Near-Field Measurement of Optical Waveguides Using a Calibrated CCD Camera

A fast and accurate magnified near-field (NF) measurement technique that employs a charge-coupled device (CCD) camera is described to measure the two-dimensional (2-D) intensity distributions of optical waveguides with arbitrary refractive-index profiles. Calibration of the InGaAs CCD camera used in the system is essential in terms of correction for bad pixels, linearity, and uniformity in order to obtain accurate results. The magnification factor of the system is obtained using a calibrated optical dimensional standard. The NF measurement system with the calibrated CCD camera is validated from the mode field diameter (MFD) measured for six single-mode fibers with different refractive-index profiles. The MFD results from the magnified NF technique exhibit good agreement with those obtained from the far-field scanning technique to within 2.3%. An error of about 15% in the MFD would result if corrections to the CCD camera were not applied to the raw measured data. The refractive-index profiles computed from the measured data for a single-mode fiber and a Ti:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> waveguide are also presented. The radial-index profile of the fiber exhibits good agreement with the profile measured from the refracted NF technique

Improved method for loss measurements in planar waveguides

A method employing an isosceles prism and a right-angle one is developed for loss measurement in planar waveguides. During the measuring process, the isosceles prism is fixed and the right-angle prism fixed on the waveguide slides by following the waveguide. Only by adjusting the gap thickness we can realize the loss measurement in planar waveguides. The method is demonstrated with an Ag/Na ion-exchanged waveguide fabricated on BK7 glass from AgNO 3 melt diluted with NaNO 3 (mass ratio 1:9), with the condition of 4 h and 335 ∘ C . The experimental results show that the method has the advantages on convenient operation, accurate results and no required end polishing.

Model-independent method for the determination of guiding thin-film optical parameters

A method for the determination of the optical constants of thin films based on the combination of a waveguide measurement procedure with the spectroscopic measurements made from the UV to the IR is presented. As a test material AlN thin film on sapphire substrates is investigated.

Surface plasmon optical detection of β-lactamase binding to different interfacial matrices combined with fiber optic absorbance spectroscopy for enzymatic activity assays

In this study, we describe the attachment of biotin-functionalized beta-lactamase to different types of interfacial architectures. Generic biotin-NeutrAvidin binding matrices were assembled using biotin-terminated alkanethiol and poly (L-lysine)-g-poly (ethylene glycol) polymer. Quantitative comparisons were made between different matrices and binding strategies. In addition, the feasibility of regeneration was tested. Our results show that in general all matrices were well suited for the binding of the protein, although quantitative differences were observed and will be discussed. Furthermore, the results obtained by surface plasmon resonance spectrometer and optical waveguide measurements show excellent correlation. For all five matrices investigated, real time enzymatic activity assays of beta-lactamase were performed by a detection scheme that combines an affinity and a catalytic sensor. The results show that the surface-immobilized enzymes are stable and sufficiently active for highly sensitive catalytic activity measurements. The effect of surface immobilization on the catalytic activity of the enzyme is discussed.