Waveguide Height Research Articles

Application of statistical method to investigate the effects of design parameters on the performance of microring resonator channel dropping filter

ABSTRACTMicroring resonator (MRR)‐based channel dropping filters have been extensively explored because of the high quality factor, compact size, and easy integration of fabrication. In order to design an excellent MRR wavelength filter, optimization of the design parameters are essential. In this paper, the design trade‐off of MRR‐based channel dropping filter was statistically studied by employing the Taguchi method. Four control factors considered were width of rings and channels, radii of the microring, upper rib waveguide height, and gap size. The analysis of variance was adopted to analyze significant trends that occurred on the free spectral range (FSR) and insertion loss (IL) performance under different sets of control factor combinations. The best parametric combination of control factors was identified in order to achieve a balance performance between large FSR and low IL using Finite‐Difference Time Domain (FDTD) simulation by RSoft Inc. After optimization, the value of FSR and IL obtained was 17 nm and 0.245 dB, respectively. Confirmation tests were carried out to verify the optimized parametric combinations and a new parametric combination considering both outputs were 16 nm and 0.215 dB. The optimal combinations were 6 µm ring radius with the separation gap of 50 nm and 350 nm × 350 nm rib waveguide cross section. Copyright © 2013 John Wiley & Sons, Ltd.

Slow-Light-Enhanced Nonlinear Characteristics in Slot Waveguides Composed of Photonic Crystal Nanobeam Cavities

We investigate slow-light-enhanced nonlinear characteristics in slot waveguides composed of photonic crystal (PC) nanobeam cavities. To evaluate the effective nonlinear coefficient, numerical simulations are performed by using 3-D vector finite-element method for periodic waveguide analysis. Results show that the maximum nonlinear coefficient of 11 600 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is obtained by optimizing waveguide width and height. This high optical nonlinearity is realized owing to strong light confinement at slotted geometry and small group velocity in PC nanobeam cavities. Also, we show that there exists tradeoff between the effective nonlinear coefficient and the bandwidth in the case of changing one-period length of the proposed structure.

TE/TM-Pass Polarizer Based on Lithium Niobate on Insulator Ridge Waveguide

We propose a TE/TM-pass polarizer based on a shallow X-cut lithium niobate-on-insulator (LNOI) ridge waveguide. In shallow X-cut LNOI ridge waveguides, the leaky mode is interchanged between TE and TM polarization waves depending on the ridge waveguide height. The phenomenon does not occur in silicon-on-insulator ridge waveguides. We use this special loss mechanism for TE/TM-pass polarizers. We evaluate structural and wavelength dependencies of polarizers by a vectorial finite-element method. The extinction ratios of 108 dB/mm and 27 dB/mm are obtained for TE-pass and TM-pass polarizers.

ELECTROMAGNETIC WAVES RADIATION INTO THE SPACE OVER A SPHERE BY A SLOT IN THE END-WALL OF A SEMI-INFINITE RECTANGULAR WAVEGUIDE

The problem of electromagnetic waves radiation into a space outside a perfectly conducting sphere through a narrow slot, cut in an end-wall of a semi-inflnite rectangular waveguide, excited by a fundamental wave of H10 type is solved using a rigorous self-consistent formulation. The starting point for the analysis is the one-dimensional integral equation for the equivalent magnetic current in the slot, obtained by using the efiective thickness of the slot. The asymptotic solution of the equation was found by the generalized method of induced magnetomotive forces (MMF). The physical adequacy of the constructed mathematical model to the real physical process is conflrmed by experimental data. In∞uence of the sphere radius upon energy characteristics of the slot radiator was investigated numerically. It was shown that at any frequency of waveguide single-mode range, the radiation coe-cient of a spherical antenna can be made close to one by choosing the slot length, the sphere radius and the waveguide height. Conditions for correct application of inflnite screen approximation for spherical scatterers with su-ciently large radii are formulated.

Waveguide properties recovered from shallow diffractions in common offset GPR

[1] Near-surface heterogeneities produce diffractions in common offset ground-penetrating radar (GPR) data from the Gnangara Groundwater Mound, north of Perth, Western Australia. These diffracted wavefields can be enhanced and show a dispersion pattern if they propagate along a waveguide caused by a low velocity surface layer, such as moist sand on top of dry sand. Until now, GPR waveguide dispersion has been analyzed and inverted using common midpoint data. Using numerical modeling, we demonstrate that the same dispersion information can also be recovered from a diffracted electromagnetic wavefield recorded with common offset geometry. Frequency-slowness analysis of shallow diffractions in common offset GPR field data reveals high resolution dispersion curves. Inverting picked dispersion maxima to modeled curves (i.e., modal wave propagation in waveguide layer) allows estimation of waveguide height and velocities of waveguide and the underlying material. Data analysis in the frequency-wavenumber domain provides an alternative technique for extracting dispersion curves. Preliminary results validate this approach, which could be favorable in large-scale applications due to minimal processing requirement and inherent yet adjustable spatial averaging. The differences between waveguide parameters recovered from two surveys appear to be consistent with seasonal changes in moisture content and lateral changes due to variations in depositional environment. Our approach presents a new method to quantify the shallow dielectric permittivity structure of the subsurface from common offset gathers—the most commonly acquired type of GPR data. Potential applications of this method include estimation of shallow moisture distribution, early target identification for unexploded ordnance (UXO) detection, concrete slab characterization, pedological investigations, or planetary exploration.

Benzocyclobutene (BCB 4022-35) Single Mode Rib Waveguides

Design, fabrication and characterization of a photodefinable benzocyclobutene (BCB 4022-35 is a product of DowTM) single mode rib optical waveguide is presented in this work. At first, the refractive index of polymer film is measured by the method of prism coupling. We design the single mode rib waveguide based on the geometrical adjustment of rib width, total waveguide height using conventional R-soft BPM and effective index methods. Based on the design results, BCB waveguides were fabricated by using photolithographic process with wet etching, which is quite complicated and time consuming. In this work, the insertion and propagation losses of waveguide are measured by using the conventional cut back method. The insertion losses of waveguide are 3.95 dB and 4.08 dB for TE and TM modes respectively. The propagation losses of waveguide are 1.09dB/cm and 1.20dB/cm for TE and TM modes respectively. 

Investigation of a type of Mach–Zehnder modulator based on optical bias

A type of Mach–Zehnder modulator based on optical bias method which use organic polymer DR1/PMMA as the ridge waveguide material is designed. Variations of the relations between effective indexes and the structure parameters include the width, height and thickness of ridge waveguide and the upper and lower cladding thicknesses are analyzed by the effective index method (EIM). A single microstrip electrode and the ridge waveguide have been used in this modulator to achieve velocity-match between light wave and microwave. The optical field and power are simulated by BPM using the above optimized parameters of the structure. The initial phase difference between the two arms achieves 89.8° and the extinction ratio achieves 27dB in this organic polymer Mach–Zehnder modulator.

Study of an Electro-Optic Polymer Modulator

In order to characterize electro-optic polymer modulators, a full-vectorial finite-difference mode solver has been developed to solve Maxwell's equation for an optical waveguide, and a finite-element method has been employed to analyze a microwave electrode. A systematic and detailed discussion has been presented to describe and design a modulator about performance parameters: <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{\pi}L,\Delta fL, N_{m}, \alpha_{c}$</tex></formula> , and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$z_{c}$</tex></formula> with all the necessary design parameters: optical waveguide (width and height), electrode (width and height), and thickness of cladding layer. We can see that most of the results are interesting, even very different from general opinions, for example, one can observe that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{\pi}L$</tex></formula> is not always reduced with an increased width of optical waveguide. These will be helpful for an optimized design of a modulator.

Efficient terahertz-wave generation via four-wave mixing in silicon membrane waveguides

Terahertz (THz) wave generation via four-wave mixing (FWM) in silicon membrane waveguides is theoretically investigated with mid-infrared laser pulses. Compared with the conventional parametric amplification or wavelength conversion based on FWM in silicon waveguides, which needs a pump wavelength located in the anomalous group-velocity dispersion (GVD) regime to realize broad phase matching, the pump wavelength located in the normal GVD regime is required to realize collinear phase matching for the THz-wave generation via FWM. The pump wavelength and rib height of the silicon membrane waveguide can be tuned to obtain a broadband phase matching. Moreover, the conversion efficiency of the THz-wave generation is studied with different pump wavelengths and rib heights of the silicon membrane waveguides, and broadband THz-wave can be obtained with high efficiency exceeding 1%.

Numerical model of the polymer electro-optic waveguide

A numerical design model is presented for the polymer waveguide in an electro-optic modulator. The effective index method is used to analyze the height of the core waveguide and rib waveguide, an improved Marcatili method is presented to design the rib waveguide width in order to keep the strong single mode operation and have a good match with the standard fiber. Also, the thickness of the upper cladding layer is discussed through calculating the effective index of the multilayer planar waveguide structure has been obtained by setting the optical loss due to the metallic absorption to an acceptable value (<0.1dB/cm). As a consequence, we take the EO polymer waveguide structure of UV15:CLD/APC:UFC170 as an example, an optimized design is reported.

Propagation of guided waves through weak penetrable scatterers

The scattering of a scalar wave propagating in a waveguide containing weak penetrable scatterers is inspected in the Born approximation. The scatterers are of arbitrary shape and present a contrast both in density and in wavespeed (or bulk modulus), a situation that can be translated in the context of SH waves, water waves, or transverse electric/transverse magnetic polarized electromagnetic waves. For small size inclusions compared to the waveguide height, analytical expressions of the transmission and reflection coefficients are derived, and compared to results of direct numerical simulations. The cases of periodically and randomly distributed inclusions are considered in more detail, and compared with unbounded propagation through inclusions. Comparisons with previous results valid in the low frequency regime are proposed.

Athermal waveguides for optical communication wavelengths

We report on the design, fabrication, and characterization of temperature insensitive strip silicon-on-insulator racetrack resonators. The influence of various parameters, such as waveguide width, waveguide height, ring radius, coupling length, ring gap, and operating wavelength, on temperature-dependent wavelength shift is examined. A resonant wavelength shift of 0.2 pm/K at a 1550 nm wavelength is measured for 335 nm × 220 nm waveguides. A significant reduction of waveguide propagation losses, improved ring Q value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding.

Enhancement of nonreciprocal phase shift by magneto-optical slot waveguide with a compensation wall

We demonstrated that the nonreciprocal phase shift (NPS) can be efficiently enhanced by introducing a low-index magneto-optical (MO) slot with a compensation wall (CW) in a high-index non-MO waveguide. The proposed structure has been examined by a perturbation theory and it is found that by adjusting the slot width and waveguide height, more than 20 times enhancement of NPS comparing with the rib waveguide with a CW can be realized.

Plasma-filled rippled wall rectangular backward wave oscillator driven by sheet electron beam

Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the dispersion relation and the growth rate have been derived and analysed numerically for plasma-filled rippled wall rectangular waveguide driven by sheet electron beam. To see the effect of plasma on the TM01 cold wave structure mode and on the generated frequency, the parameters used are: relativistic factor γ = 1.5 (i.e. v/c = 0.741), average waveguide height y0 = 1.445 cm, axial corrugation period z0 = 1.67 cm, and corrugation amplitude e = 0.225 cm. The plasma density is varied from zero to 2 ×1012 cm − 3. The presence of plasma tends to raise the TM01 mode cut-off frequency (14 GHz at 2 ×1012 cm − 3 plasma density) relative to the vacuum cut-off frequency (5 GHz) which also causes a decrease in the group velocity everywhere, resulting in a flattening of the dispersion relation. With the introduction of plasma, an enhancement in absolute instability was observed.

Energy tunneling through narrow waveguide channel and design of small antennas

In this paper we investigate the conditions for energy tunneling through narrow channel obtained by reducing the height of rectangular waveguide. Tunneling of the energy occurs at the frequency for which the effective dielectric permittivity of the channel becomes equal to zero, so it can be treated as an ENZ (epsilon-near-zero) metamaterial. We investigated how geometry of the channel and dielectric permittivity affect the transmission coefficient and field density in the channel. Adding slots in the channel, which are placed orthogonally to the wave propagation, we designed a small antenna with directivity of 5.44 dBi at the frequency of 3 GHz.

Dispersion parameters and nonlinear optical properties of silicon nitride rib waveguides

Silicon nitride rib waveguides are numerically studied by use of a full-vectorial mode solver program based on finite difference method. Dispersion parameters, up to the third-order, are computed for waveguides of heights 0.8μm, 0.9μm, and 1μm. Like silicon-on-insulator waveguides, silicon nitride rib waveguides allow us to tailor dispersion parameters at telecom wavelengths. Deeply-etched silicon nitride rib waveguides of height up to 1.5μm are investigated for correct geometries to achieve polarization independence. The computations lead to a minimum etch depth which can be written as linear function of the waveguide height. Etch-depth and waveguide height dependencies of the nonlinear refractive index coefficient of the silicon nitride are studied. It is shown that third-order optical nonlinearities in silicon nitride rib waveguides can be enhanced by suitable choices of waveguide parameters.

Propagation models in the ocean acoustic field with hard soil.

This paper addresses the human interest for lossless data transmission by water sound waves, knowing that electromagnetic waves dramatically attenuate in sea water. A normal mode method is employed in order to determine varying frequency propagating modes and waveguide height to observe individual mode contribution. It considers a shallow water waveguide between the hard soil (sand) and the sea surface. Transmitter and receiver will be several kilometers away from each other, and the future intended applications include object detection and submarine communication.

Synthesis of Slot Arrays on Integrated Waveguides

An improved synthesis procedure is presented in this letter for the design of waveguide slot arrays directly integrated on the substrate of the exciting microstrip line. To take into account the smallness of the waveguide height, the standard shunt-admittance model usually adopted for the single radiating slot is properly modified into an improved T-network model. Accordingly to this choice, a two-step synthesis procedure is developed to accurately determine the radiating slots' parameters. Experimental validations are discussed for the design of an 8-GHz linear array with a -20-dB Taylor pattern.

Rib waveguides for mid-infrared silicon photonics

Design rules for both single-mode and polarization-independent strained silicon-on-insulator rib waveguides at the wavelength of 3.39 μm are presented for the first time to our knowledge. Waveguide geometries with different parameters, such as waveguide height, rib width, etch depth, top oxide cover thickness and sidewall angle, have been studied in order to investigate and define design rules that will make devices suitable for mid-IR applications. Chebyshev bivariate interpolation with a standard deviation of less than 1% has been used to represent the zero-birefringence surface. Experimental results for the upper cladding stress level have been used to determine the influence of top oxide cover thickness and different levels of upper cladding stress on waveguide characteristics. Finally, the polarization-insensitive and single-mode locus is presented for different waveguide heights.

Representation of the field of a point source in a spherical waveguide via a solution of the field problem in a plane waveguide

At present, it is almost impossible to take into account arbitrary anisotropy in the model of spherical waveguide for the problems of radio wave propagation. In this paper, we propose a method for calculation of the field in a single-mode spherical waveguide with arbitrary anisotropy, which is based on the solution of the problem of the field in a single-mode plane waveguide. This method can be applied to calculation of the electromagnetic field in the Earth-ionosphere waveguide at frequencies below 1 kHz at the distances from the source, which exceed the effective waveguide height, but do not exceed one quarter of the great circle. The method has been brought to the stage of software implementation. The plots of the field amplitude as a function of the distance to the source are presented.