Evanescent Waveguide Research Articles

Designing and studying waveguide filters of terahertz and subterahertz frequency ranges

A unit for filtering terahertz and subterahertz electromagnetic radiation, based on using selective frequency properties of an evanescent waveguide and quasi-optical (optic-waveguide) methods for matching to the environment, are presented. The design of the filtering unit, radiated in a frequency band of 100 GHz to several terahertz, and the measurement results of the amplitude-frequency characteristics of test filters in a range of 100–700 GHz, are given. The principle of the filter construction and design allows one to obtain a sharp and predicted transmission cutoff with an insignificant attenuation in the passband and a significant suppression of low-frequency radiation in the stop region. The experimentally measured attenuation is at a level of 6–12 dB in the filter transmission band and at a level of 30–60 dB out of the transmission band; in this case, the obtained result is determined by noises of the test setup. It is shown that the theoretical attenuation value beyond the passband may reach more than 60 dB, when the frequency is only 10% smaller than the critical one. The designed filter can be used for determining and studying spectra in the subterahertz and terahertz bands, especially in the cases, which call for a sharp spectral cutoff and exclusions of long-wave radiation components.

Fabrication and optical measurements of a TiO2-ALD evanescent waveguide sensor

In the present work, we report the design, fabrication and characterisation of an evanescent waveguide sensor. TiO2 deposited by Atomic Layer Deposition (ALD) on silicon wafer is used as waveguide material. In order to enhance the surface interaction between sensor and target, we have fabricated the waveguide as a freestanding structure. The sensitivity of the sensor is evaluated by evaporation of several concentrations of ethanol and isopropyl alcohol diluted in water and found to be 0.85 and 1.34dB/% (v/v), respectively. The sensor is meant to evaluate a patient condition after colon-surgery by sensing the presence of Escherichia coli in drain fluid. We carried out the deposition of a self-assembled monolayer on the waveguide as first layer of surface functionalisation using antibody to make the sensor the selective to E. coli. Preliminary optical investigations are presented.

A substrate integrated folded waveguide (SIFW) H-plane band-pass filter with double H-plane septa based on LTCC

In this paper, a novel substrate integrated folded waveguide (SIFW) H-plane band-pass filter based on low-temperature co-fired ceramic technology (LTCC) is proposed which employs double H-plane septa of a short-ended evanescent waveguide as an impedance inverter. The filter has advantages of convenient integration, compact, low cost, mass-producibility, and ease of fabrication, and it also has frequency responses similar to those of traditional E-plane double-iris waveguide band-pass filters. To validate the new proposed topology, a three-pole narrowband band-pass filter is designed and fabricated using half-wavelength resonators. A comparison between measured results and simulated results shows good agreement.

Electropolymerized bioresistant coatings of OEGylated dendron carbazoles: Design parameters and protein resistance SPR studies

The electrografting of oligoethylene glycol or (OEG)ylated carbazole linear dendrons and their protein adsorption resistance properties have been investigated by surface plasmon resonance (SPR) spectroscopy. A series of the carbazole dendron generations, G 0, G 1, G 2 were synthesized and electrodeposited by cyclic voltammetry (CV) on Au-glass substrate which also served as a surface for evanescent waveguide excitation in SPR. In addition, the films were characterized by in-situ electrochemical SPR (EC-SPR), static water contact angle, and X-ray photoelectron spectroscopy (XPS) measurements. It was observed that electropolymerized films prepared from the higher generation linear-dendron G 2, is most effective in preventing non-specific protein adsorption as observed by SPR kinetic measurements using fibrinogen as model protein. Film thickness also played a critical role in protein adsorption resistance - electrodeposition approaching monolayer thickness gave the highest protein resistance. In addition, the films were evaluated for non-specific protein binding against the smaller proteins, lysozyme and bovine serum albumin (BSA). The study provides insight to manipulating the architecture and composition of protein resistant materials deposited on metals and semi-conducting substrates and their possible use in biomedical applications.

On-chip collection of particles and cells by AC electroosmotic pumping and dielectrophoresis using asymmetric microelectrodes.

The recent development of microfluidic "lab on a chip" devices requiring sample sizes <100 μL has given rise to the need to concentrate dilute samples and trap analytes, especially for surface-based detection techniques. We demonstrate a particle collection device capable of concentrating micron-sized particles in a predetermined area by combining AC electroosmosis (ACEO) and dielectrophoresis (DEP). The planar asymmetric electrode pattern uses ACEO pumping to induce equal, quadrilateral flow directed towards a stagnant region in the center of the device. A number of system parameters affecting particle collection efficiency were investigated including electrode and gap width, chamber height, applied potential and frequency, and number of repeating electrode pairs and electrode geometry. The robustness of the on-chip collection design was evaluated against varying electrolyte concentrations, particle types, and particle sizes. These devices are amenable to integration with a variety of detection techniques such as optical evanescent waveguide sensing.

Goos–Hänchen shift as a probe in evanescent slab waveguide sensors

The present paper deals with three-layer planar waveguide optical sensor. Different from the conventional slab waveguide sensors in which the effective refractive index of the propagating mode is taken to be the probe for detection changes in the analyte refractive index, we adopt Goos–Hänchen (GH) shift as the sensing probe for the proposed sensor. We show that the GH shift is strongly dependent on the refractive index of the cladding, thus it is a good candidate for detection changes in the analyte refractive index. We present and study the sensitivity of the GH shift at the cladding–film and substrate–film interfaces. It is found that GH shift has a high sensitivity and can be used for versatile optical slab waveguide sensors.

Evanescent waveguide-based polarisation-agile antenna elements

Polarisation-agile, evanescent waveguide-based antenna elements are proposed, which allow below waveguide cutoff operation from 1.07 to 1.49 GHz or below and above waveguide cutoff operation from 1.54 to 1.89 GHz for return loss &lt;−10 dB. Here square evanescent waveguide with 1.7 GHz cutoff is shunt loaded, respectively, with orthogonal pairs of coaxially excited cylindrical metal posts or flat metal strips positioned across the aperture of the waveguide. It is shown that linear or circular polarisation may be achieved depending on the excitations supplied to the input ports of the antenna.

Optimization-Oriented Design of RF/Microwave Circuits Using Inverse-Linear-Input Neuro-Fuzzy-Output Space Mapping With Two Different Dimensionality Simulators

In this paper, an efficient optimization technique aligning three-dimensional (3-D) electromagnetic simulator responses with two-dimensional (2-D) electromagnetic simulator responses around space mapped solution, for the electromagnetic design of radiofrequency and microwave 3-D circuits is presented. The interface between 2-D and 3-D electromagnetic simulators is obtained from an inverse linear input space-mapping approach and an output modeling process based on a fuzzy logic technique. It is shown that the technique provides a highly accurate estimation of the 3-D design parameter space of the 3-D radiofrequency and microwave circuits to be designed, for initially fixed design specifications. Designs of first-order, second-order and sixth-order C-band 3-D evanescent rectangular waveguide bandpass filters with dielectric posts show the performance of our approach.

Detection of colored nanomaterials using evanescent field-based waveguide sensors

We have developed an optical system designed for detecting colored nanomaterials in aqueous solutions, using the concept of evanescent-field-coupled waveguide-mode sensors. In this study, we found that the waveguide modes induced in the sensor are intrinsically sensitive to a change in optical absorption, or a 'change in color'. The system detects less than one gold nanoparticle (diameter: 20 nm) adsorbed per square micrometer. It is also demonstrated that significant signal enhancement due to adsorption of molecules is achieved using a dye. The developed sensor rarely suffers from a drawback of impurity adsorption. The system is expected to be applied as an effective sensing tool for metal colloids, nanoparticles, and colored biomolecules in solution.

Monolithic optical gates based on integration of evanescently-coupled uni-traveling-carrier photodiodes and electroabsorption modulators

We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photodiodes (EC-UTC-PDs) and intra-step quantum well electroabsorption modulators (IQW-EAMs) on n-InP substrates. These devices exhibit simultaneously 2.1 GHz and −6.2 dB RF-gain at 21 GHz with a 450 Ω thin-film resistor and a bypass capacitor integrated on a chip.

Theoretical proposal for a biosensing approach based on a linear array of immobilized gold nanoparticles

We propose a sensing mechanism for detection of analytes that can specifically recognized. The sensor is based on closely-spaced chains of functionalized gold nanoparticles (NPs) immobilized on a waveguide surface, with the signal detected by evanescent waveguide absorption spectroscopy. The localized surface plasmon spectrum of a linear array of closely-spaced, hemispherical gold NPs is calculated using the discrete dipole approximation. The plasmon band is found to broaden to a nanowirelike spectrum when a dielectric coating is put on the particles, and the light polarization is along the NP chain. The origin of this broadening is shown to be the polarization-dependent overlap of the evanescent fields of adjacent NPs upon application of the dielectric coating. These features suggests a mechanism for biosensing with an improved sensitivity compared with traditional NP biosensor methods.

HALF MODE SUBSTRATE INTEGRATED FOLDED WAVEGUIDE (HMSIFW) AND PARTIAL H-PLANE BANDPASS FILTER

In this paper, a half mode substrate integrated with folded waveguide (HMSIFW) and a HMSIFW partial H-plane bandpass fllter are proposed. The proposed fllter employs H-plane slot of open-ended evanescent waveguide and H-plane septa of short-ended evanescent waveguide as admittance inverter and impedance inverter, respectively. The fllter has advantages of convenient integration, compact size, low cost, mass-producibility and ease in fabrication. In order to validate the new proposed topology, a four-pole ultra-narrowband bandpass fllter, with quarter wavelength resonators, is designed and fabricated using standard printed circuit board process. The tapered line is used as transition between HMSIFW and microstrip-line for easy integration and measurement. The measured results are in good agreement with simulated ones, and good selectivity is achieved.

Substrate Integrated Folded Waveguide (SIFW) Partial H-Plane Filter with Quarter Wavelength Resonators

In this paper, the design and experiment of a novel substrate integrated folded waveguide (SIFW) partial H-plane bandpass filter, consisting of quarter wavelength resonators, is presented. In the proposed filter, two adjacent quarter wavelength resonators are coupled by connecting an admittance inverter and an impedance inverter alternately. Here, the admittance inverter and impedance inverter are realized by H-plane slot of open-ended evanescent waveguide and H-plane septa of short-ended evanescent waveguide, respectively. In order to validate the new proposed topology, a four-pole narrowband bandpass filter is designed and fabricated using standard printed circuit board process. The tapered line is used as transition between SIFW and microstrip-line for easy integration and measurement. The measured results are in good agreement with simulated results.

TiO2 ALD nanolayer as evanescent waveguide for biomedical sensor applications

In this paper, a low surface roughness and highly homogenous TiO2 layer was deposited by Atomic Layer Deposition (ALD) and used as an evanescent waveguide for biomedical sensing applications. Anastomosis is an operation to continue an organ like colon, bowel, pancreas etc. If there is leakage in during an anastomosis surgery (often indicated by a high bacteria concentration), it probably will cause some problems to the patients. The diagnostic of the leakage must be done soon to avoid multi complications and mortality. The research aims at developing optical sensor to detect the leakage by bacteria concentration detection in the drain fluid. In this present paper, we will report preliminary results of our research such as the simulation, fabrication and optical measurement of TiO2 optical waveguide. Freestanding structure is introduced to enhance sensitivity of such a sensor. Low stress SiN is deposited using LPCVD as interlayer material and etching stop-layer in between the Si substrate and the TiO2 waveguide. To estimate the optimum SiN thickness especially in the freestanding region, simulation was done by effective index method (EIM). Propagation and coupling losses measurement were conducted using the cut-back technique.

A Partial H-plane Substrate Integrated Folded Waveguide (SIFW) Bandpass Filter Based on H-plane Slot

This paper presents a novel partial H-plane bandpass filter based on substrate integrated folded waveguide (SIFW), which employs H-plane slot of open-ended evanescent waveguide as admittance inverter. In order to validate the new proposed topology, a three-pole narrowband bandpass filter is designed and fabricated using standard printed circuit board process. The tapered line is used as transition between SIFW and microstrip for easy integration and measurement. The filter is considerably smaller than its metallic waveguide counterpart. The measured results are in good agreement with simulated results.

A Millimeter-Wave E-Plane Band-pass Filter using Multilayer Low Temperature Co-Fired Ceramic (LTCC) Technology

This paper presents a substrate integrated waveguide (SIW)-based millimeter-wave E-plane band-pass filter (BPF) with multilayer Low Temperature Co-fired Ceramic (LTCC) technology. The vertical metal walls of SIW and metal fins of the evanescent waveguides are realized by closely spacing metallic via-holes. A three-order Chebyshev E-plane BPF is developed and verified by full-wave simulation. The proposed filter is fabricated using LTCC technology, and a tapered line is designed as the transition between the SIW and microstrip line. Good agreement between simulated and measured results is observed.

Performance analysis and comparison of symmetrical and asymmetrical configurations of evanescent mode ridge waveguide filters

In this paper, the trade‐offs between out‐of‐band performance, filter length, power‐handling capability, and insertion loss of both symmetrical and asymmetrical evanescent mode ridge rectangular waveguide filters are investigated. As a result, clear design methodologies for optimizing such performances are proposed. The developed methodologies are then applied to design several evanescent mode filters, and a complete performance analysis of the symmetrical and asymmetrical structures is performed. From the performance analysis results, the designer can choose the more appropriate filter topology and design strategy to satisfy the prescribed specifications.

InGaAsP/InP evanescent mode waveguide optical isolators and their application to InGaAsP/InP/Si hybrid evanescent optical isolators

We theoretically investigated InGaAsP/InP evanescent mode waveguide optical isolators and proposed their application to InGaAsP/InP/Si hybrid evanescent optical isolators. InGaAsP/InP evanescent optical isolators are composed of semiconductor optical amplifier (SOA) waveguides having InGaAsP multiple quantum well (MQW) active layer and upper InGaAsP waveguide layer with ferromagnetic layer. Optical isolation is obtained for evanescent optical mode in the InGaAsP waveguide layer. InGaAsP/InP/Si hybrid evanescent optical isolators are theoretically proposed based on the idea of InGaAsP/InP evanescent optical isolators. InGaAsP/InP/Si hybrid evanescent optical isolators are composed of ferromagnetic metal loaded silicon evanescent waveguides with wafer-bonded InGaAsP/InP optical gain material. The optical isolation and propagation loss are discussed with the structure of silicon evanescent waveguides, and optical isolation of 8.0 dB/mm was estimated. The concept of semiconductor evanescent mode optical isolators is feasible with InP based photonic integrated circuits and advanced silicon photonics.

Birefringent waveguide sensor using a polarizer rotating technique

A birefringence measurement system is introduced to get high phase resolution for detection of low contents of biochemicals. By using a fixed quarter-wave plate and a rotating polarizer, the phase difference between two orthogonal polarizations is transformed into phase delay of output sinusoidal signal. Analyzing the output phase, birefringence change could be detected with a phase noise of 0.14 degrees. As well as the birefringence measurement system, an optical evanescent waveguide sensor was developed. A rib-type silica waveguide overlaid with TiO2 film was fabricated, and a developed birefringence measurement technique was employed in evaluating a refractive index change on waveguide surface. For the fabricated waveguide with a 40-nm-thick TiO2 film, experiment results showed that the minimum detectable index change was 5.9x10(-7).

2D to 3D rectangular waveguide filter designs from linear iterated prediction space mapping optimization

AbstractIn this article, an optimization procedure is described to align electromagnetic (EM) three‐dimensional (3D) models with two‐dimensional (2D) models for the design of RF/microwave circuits. The optimization procedure is realized from a modified standard space mapping (SM) approach. The mapping function between the 2D and 3D parameter spaces is directly obtained from a linear iterated prediction method, which reduces the computational cost and also avoids inverse transformations. The linear iterated prediction 2D to 3D SM optimization of evanescent rectangular waveguide bandpass filters with inductive posts for the 2D models and non‐inductive posts for the 3D models illustrate the advantages and the challenges of this approach. The proposed method is simple to be implemented, it requires a reduced computational cost and it can be useful for CAD environment with 2D and 3D circuit structure electromagnetic (EM) analysis. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1979–1983, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24459