Waveguide Dimensions Research Articles

On-Chip Electro-Optic Modulator With Loss Compensation Based on Polymeric Active-Integrated Waveguides

In this paper, an on-chip electro-optic (EO) modulator with loss compensation based on polymeric active-integrated waveguides was demonstrated. An erbium-doped waveguide amplifier was investigated and integrated with the EO modulator to compensate for signal loss. Polymeric active-integrated waveguides were based on the Mach-Zehnder interferometer structure, which consists of an amplified waveguide formed by two symmetric Y-junction branches and an EO waveguide formed by two decoupled waveguide arms. The dimensions of the polymeric active-integrated waveguides and the modulator were carefully designed and simulated. Moreover, a six-level spectroscopic model pumped at 980 nm was presented. The rate equations and propagation equations were solved, and the gain characteristics were simulated. The internal gain of 4.65 dB was achieved when the signal power was 0.1 mW at 1550 nm, the pump power was 100 mW at 980 nm, the Er 3+ concentration was $9.3\times 10^{25}/\text{m}^{3}$ , and the Yb 3+ concentration was $8.6\times 10^{26}/\text{m}^{3}$ in one Y-junction branch with a length of 1.5 cm. With the integrated waveguide amplifier, the loss of the EO modulator can be compensated at 9.3 dB in the two symmetric Y-junction branches. The light output intensity was also statistically presented. The proposed device with active-integrated waveguides could be used in polymer-based photonics integrated circuits.

A Four-Corner-Fed Slotted Waveguide Sparse Array for Near-Field Focusing

This article presents a double-layer four-corner-fed slotted waveguide sparse array antenna designed for the near-field-focused applications in the X-band. Generally, it is challenging to realize the ideal phase distribution of the near-field focused array antenna, especially for the near-field focusing array antenna with a focal distance less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\lambda $ </tex-math></inline-formula> . We propose a four-corner-feed structure associated with appropriate waveguide dimensions to realize approximately ideal phase distribution for a focus at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\lambda $ </tex-math></inline-formula> . The sparse array based on the particle swarm optimization is adopted to suppress the sidelobes and the grating lobes on the focal plane caused by the residual phase errors. A test antenna is designed at the center frequency of 10 GHz, and is fabricated by Direct Metal Laser Sintering technique for demonstration. It is verified by the experiment that we achieve satisfying near-field focusing effects, especially in terms of the focal spot size and sidelobe levels on the focal plane 45 mm away from the antenna aperture.

ВПЛИВ КОНСТРУКТИВНИХ РІШЕНЬ КОМПОНУВАННЯ ТА ПОХИБОК ВИГОТОВЛЕННЯ ЕЛЕМЕНТІВ ШИРОКОСМУГОВОЇ РУПОРНОЇ АНТЕНИ НА ЇЇ ТЕХНІЧНІ ХАРАКТЕРИСТИКИ

The results of the research of the main releases of arrangement of horn antenna with two ridges, which differ in the ways of fixing the elements: bolt connection (rivets) and soldering (welding), are presented in the article. The influence of inaccuracies in the manufacture of particular antenna elements (errors in the geometric dimensions of the waveguide and the horn aperture, errors in the location of the feed pin, differences in the relative permittivity of the insulating material from the calculated one and others) and their interconnections (the width of the slots between the horn aperture plates, the distance between the ridges at the feeding point) on the main antenna characteristics (voltage standing-wave ratio, gain, radiation pattern). The researches were carried out using software environments for computer-aided designing, modeling and optimizing three-dimensional electromagnetic systems ANTENNA MAGUS and CST STUDIO SUITE. It has been found that with the same accuracy of manufacturing the constituent elements of a wideband horn antenna, the considered releases of arrangement provide similar technical characteristics. The research of manufacturing errors of the antenna elements and their interconnections showed that the longitudinal waveguide dimensions, the distance between the ridges at the point of excitation, the location and diameter of the feed pin, and also the dielectric characteristics of the insulating material have the greatest influence on the characteristics of the antenna. It has been established that a change in particular antenna sizes by 10% can lead to a significant deterioration in its matching. The system of tolerances for the sizes and connections of antenna elements, the adherence of which will ensure the conformity of the characteristics of the manufactured example to those obtained in the process of modeling and optimization using specialized software, is justified.

Highly-Efficient, Ultra-Compact and Polarization-Insensitive Electro-Absorption Modulator Driven by Hybrid Silicon-Indium Tin Oxide-Based MOS Capacitors

Polarization-insensitive modulation plays a key role to be compatible with the current fiber communication systems and the further high-capacity multiplexing transmissions on-chip. Here, we propose a highly-efficient, ultra-compact and polarization-insensitive electro-absorption modulator (EAM), which is driven by the hybrid silicon-indium tin oxide (ITO) based metal-oxide-semiconductor (MOS) capacitors. The hybrid silicon-ITO waveguide is formed by embedding an ITO layer in the silicon waveguide center and depositing a second ITO layer on the waveguide surface, thus the light-matter interaction can be strongly enhanced inside the silicon waveguide based on the epsilon-near-zero (ENZ) effect of ITO rather than the commonly employed outside cladding region. By choosing the optimum ENZ condition of ITO layers at the designated wavelength and optimizing the waveguide dimensions, polarization-insensitive modulation is realized with a high modulation efficiency (ME) of ~3.18 dB/ $\mu \text{m}$ (ME discrepancy $\mu \text{m}$ ) for both polarizations, which is superior to the previous reports. Benefiting from this excellent modal modulation feature, we further design a polarization-insensitive EAM in a length of only $8~\mu \text{m}$ . The modulation depth and insertion loss are higher than 25 dB and lower than 0.24 dB at $1.55~\mu \text{m}$ for both polarizations, respectively. Moreover, the corresponding wavelength bandwidth and electric properties are also analyzed including fabrication procedures. The proposed EAM is expected to be applied in the polarization multiplexing transmissions on-chip.

Large on-chip Brillouin net amplification in silicon-based nano-photonics

Recent developments in on-chip forward Brillouin scattering open up potential applications such as RF photonic signal processing, on-chip Brillouin amplification, and on-chip Brillouin lasers. The stimulated Brillouin scattering gain coefficients become significant with a small optical mode area, and the Brillouin net amplification has been believed to be strong with a small mode area, too. However, here, we present a theoretical study of higher net amplification with a large optical mode area than that with a small mode area and explain this counter-intuitive phenomenon by examining the contribution of various optical forces to Brillouin gain coefficients for various optical waveguide dimensions. The simulation results show that a waveguide with large optical waveguide dimensions can yield significant net amplification by high Brillouin gain coefficients and low optical losses at high pump power even if the Brillouin gain coefficients are lower than that with a small waveguide dimension. Therefore, it is necessary to optimize the optical waveguide dimensions to achieve maximum net amplification for the development of Brillouin lasers and amplifiers in silicon-based nanophotonics.

Glide-Symmetric Holey Leaky-Wave Antenna With Low Dispersion for 60 GHz Point-to-Point Communications

In this article, two novel efficient leaky-wave antennas (LWAs) with stable radiation patterns operating in the 60 GHz band are proposed. The LWAs are implemented in groove-gap waveguide (GGW) technology. To mitigate the beam squint due to the dispersive nature of LWAs, complementary-dispersive prisms are coupled to the LWA radiation aperture. The antennas are implemented in fully metallic purely holey periodic structures, resulting in a more cost-effective and robust manufacturing process compared to previously reported pin-based structures. Two prisms are proposed, one with mirror symmetry and one with glide symmetry. When the prism possesses a glide symmetry, much fewer holes are required while maintaining a similar performance, which even further decreases the fabrication costs. The complex propagation constant is optimized for low sidelobe levels (SLLs) with tailored hole diameters and waveguide dimensions, thus for the first time demonstrating the capability of using glide-symmetric holes to control the leakage rate. Two prototypes with mirror- and glide-symmetric prisms are theoretically synthesized and validated by the simulated and experimental results. A frequency bandwidth of 11% is achieved for both prototypes with the beam squint within ±0.9° (mirror) and ±1.7° (glide), SLLs below -15 dB (mirror) and -13 dB (glide), total efficiency almost 90%, and realized gain of 17 ± 0.5 dB at a fixed observing angle. The developed antennas are intended for mm-wave point-to-point communications.

Ultra-low power all-optical wavelength conversion of high-speed data signals in high-confinement AlGaAs-on-insulator microresonators

Wavelength conversion technology is imperative for the future high-speed all-optical network. Nonlinear four-wave mixing (FWM) has been used to demonstrate such functionality in various integrated platforms because of their potential for the realization of a chip-scale, fully integrated wavelength converter. Until now, waveguide-based wavelength conversion on a chip requires a pump power beyond the reach of available on-chip lasers. Although high-quality factor (Q) microresonators can be utilized to enhance the FWM efficiency, their narrow resonance linewidths severely limit the maximal data rate in wavelength conversion. In this work, combining the ultrahigh effective nonlinearity from a high-confinement aluminum gallium arsenide waveguide and field enhancement from a microring resonator with a broad resonance linewidth, we realize all-optical wavelength conversion of a 10-Gbaud data signal by using a pump power, for the first time, at a submilliwatt level. With such a low operation power requirement, a fully integrated high-speed wavelength converter is envisioned for the future all-optical network. The waveguide cross-sectional dimension is engineered in a submicron scale to enhance the light confinement, which pushes the device effective nonlinearity to 720 W−1 m−1 while maintaining a broad operation bandwidth covering the telecom S-, C-, and L-bands. Moreover, we demonstrate that a single microring resonator is capable of handling a high-speed data signal at a baud rate up to 40 Gbit/s. All the wavelength conversion experiments are validated with bit-error rate measurements.

Improving the performance of nanostructure multifunctional graphene plasmonic logic gates utilizing coupled-mode theory

Nanostructure ring resonators are suitable devices for photonic integrated circuits. A nano-scale multifunctional logic device based on plasmon-induced transparency (PIT) is presented here. This device consists of a pair of hexagonal ring resonators coupled with two parallel metal–insulator–metal (MIM) waveguides. According to the coupled-mode theory, the appropriate detuning between the resonances wavelengths of two resonators acts as the key factor to achieve the PIT phenomenon. For this purpose, the PIT phenomenon for several metals utilized in MIM waveguides is studied. Also, graphene has been employed as the replacement for the metal under the hexagonal ring resonator and its parallel waveguides. However, the interaction of light with graphene as a 2D material is weak, by varying the dimensions of waveguides, rings, and their distances, and also, incident light wavelength and graphene chemical potential, we have achieved the desired couplings in the structure. Finite-difference-time-domain (FDTD) simulations confirm that “1” and “0” logic states which represent the high and low levels of the optical power can be achieved at the through and drop ports by changing the refractive index. It has been demonstrated that the proposed structure implements the function of logical operations including XOR and XNOR, simultaneously.

Spoof surface plasmonic waveguide and its band-rejection filter based on H-shaped slot units

To reduce the transverse width of the SSPP (spoof surface plasmon polaritons) waveguide, the complementary structure of the SSPP waveguide based on the H-shaped conductor periodic unit is used. In this structure, periodic H-shaped slots are cut in the conductor film on the substrate interface. Fed by the coplanar waveguide with flared ground planes, this SSPP waveguide with a small width can achieve broadband transmission characteristics below 10 GHz. Inserting small H-shaped conductor units inside the slot can form the complementary split ring resonators, and the band-stop filter is realized without increasing the lateral dimension of the original SSPP waveguide. The experimental results show that the notch frequency of the proposed filter can be effectively regulated by the height of embedded H-shaped conductor units.

Optimized waveguide coupling of an integrated III-V nanowire laser on silicon

The recent integration of III-V semiconductor nanowire (NW) lasers on silicon waveguides marked a key step toward their usage as coherent light sources for future silicon photonics applications. However, the low index contrast between III-V semiconductors and silicon results in a weak modal reflectivity, calling for improved design structures that enable both low-threshold lasing and good in-coupling efficiency into waveguides. Here, we perform numerical simulations to explore how the alternating refractive index of a silicon waveguide with a thin SiO2 interlayer can be used to significantly improve the reflectivity at the III-V–silicon interface to values of up to 83%. We further investigate the frequency dependencies of the end-facet reflectivity and in-coupling efficiency as a function of the nanowire and waveguide dimensions. Our results are kept general by the normalization to the nanowire radius R and show for a waveguide width of 2.75⋅R a maximum coupling efficiency of 50%. Variations in waveguide height or SiO2 interlayer thickness by ±0.1⋅R increase the coupling efficiency by a factor of 2, with little effect on the end-facet reflectivity. Ultimately, a prototypical NW-laser structure consisting of a 1.3-μm emitting InGaAs MQW active region in a core-multishell structure was simulated, showing an optimized low-threshold gain of &amp;lt;500 cm−1 for a TE01 mode with a coupling efficiency of ∼13%. By simplified approximations, we illustrate that these analyses can be adapted to a variety of material systems and serve as guidelines in the construction of optimized nanowire lasers on silicon-on-insulator waveguides for future on-chip optical interconnects.

Design of an Electro-Absorption Modulator Based on Graphene-on-Silicon Slot Waveguide

Compact high-performance electro-optic (EO) modulators are key elements for optical communications. An electro-absorption modulator is theoretically designed. Due to the introduction of graphene film over the silicon slot waveguide, the modulation efficiency is strongly improved. The effect of waveguide dimensions, dielectric insulator thickness, and carrier mobility on performances of the proposed EO modulator have been comprehensively investigated. For the 120- μ m-long graphene-on-silicon waveguide modulator, the extinction ratio 28 dB and insertion loss 1.28 dB can be obtained at 1550 nm when drive voltage is 1.91 and 0.59 V, respectively. The 3 dB bandwidth of 117 GHz can be obtained at a small power consumption of 212 fJ/bit. The proposed modulator possesses a high figure-of-merit of 20.5. Its benefits of small size, power saving, and process compatible promises possible applications in on-chip signal processing.

Investigation of Hybrid Silicon-Nitride/Polymer Waveguides for Second-Harmonic Generation

We propose a hybrid silicon-nitride (Si3N4 or SiN for short)/nonlinear polymer waveguide to achieve second-harmonic generation of an input 1550 nm signal by modal phase-matching between zero-order spatial mode at 1550 nm and second-order mode at 775 nm. We explore and optimize two cases, single channel waveguide and slot waveguide, by varying the waveguide dimensions. For TE polarized light, the optimum slot waveguide exhibits an effective interaction area A eff of about 16 μ m2, which is an order-of-magnitude improvement over the single channel waveguide and can translate to a high value of effective nonlinearity. We also show that the optimum slot waveguide geometry is robust with respect to fabrication uncertainties and bending effects.

HWCVD a-Si:H interlayer slope waveguide coupler for multilayer silicon photonics platform.

We present interlayer slope waveguides, designed to guide light from one level to another in a multi-layer silicon photonics platform. The waveguide is fabricated from hydrogenated amorphous silicon (a-Si:H) film, deposited using hot-wire chemical vapor deposition (HWCVD) at a temperature of 230°C. The interlayer slope waveguide is comprises of a lower level input waveguide and an upper level output waveguide, connected by a waveguide on a slope, with vertical separation to isolate other crossing waveguides. Measured loss of 0.17 dB/slope was obtained for waveguide dimensions of 600 nm waveguide width (w) and 400 nm core thickness (h) at a wavelength of 1550 nm and for transverse electric (TE) mode polarization.

Synthesis and Characterization of Fe-Based Nanocomposites

This study reports on the elaboration and characterization of bulk nanocomposites samples obtained by dispersion of metallic powders at the nanoscale as reinforcements in a polymer matrix. Elemental Fe powders were successfully nanostructured via high-energy ball milling. Structural characterization of the produced powders was conducted using X-Ray Diffraction (XRD) analysis and Scanning Electron Microscopy (SEM). The Halder-Wagner approach was adopted to determine the powder’s average grain size, internal strain, lattice parameters and the mixing factors. Structural parameters evolution and morphological changes according to milling progression are discussed. Bulk nanocomposites samples were shaped in a home moulder by dispersion of coarse Fe and nanostructured Fe powders in a continuous matrix of commercial epoxy resin. The obtained bulk samples match the metallic X-band wave-guide WR-90 dimensions used for electromagnetic characterization. The two-port Sij scattering parameters were measured via an Agilent 8791 ES network analyzer. The measured scattering parameters served to calculate the loss factor of samples and to extract the dielectric permittivity via the Nicholson-Ross-Weir conversion. Spectra evolution of the scattering parameters, the loss factor and the dielectric constant for epoxy resin with coarse Fe and nanostructured Fe reinforcements are commented.

High-quality factor, high-confinement microring resonators in 4H-silicon carbide-on-insulator.

Silicon carbide (SiC) exhibits promising material properties for nonlinear integrated optics. We report on a SiC-on-insulator platform based on crystalline 4H-SiC and demonstrate high-confinement SiC microring resonators with sub-micron waveguide cross-sectional dimensions. The Q factor of SiC microring resonators in such a sub-micron waveguide dimension is improved by a factor of six after surface roughness reduction by applying a wet oxidation process. We achieve a high Q factor (73,000) for such devices and show engineerable dispersion from normal to anomalous dispersion by controlling the waveguide cross-sectional dimension, which paves the way toward nonlinear applications in SiC microring resonators.

A Compact Relativistic Magnetron With Lower Output Mode

A compact relativistic magnetron (RM) with novel axial output configuration is proposed, which extracts lower order cylindrical mode (TM01 or TE11 mode) or coaxial mode (TEM or TE11 mode) in the output region. In this output configuration (namely, multiantenna output RM), several conducting rods are connected to the anode vanes of the magnetron and arranged in the axial direction to serve as the extraction antennas. High-frequency analysis demonstrates that this output structure excites lower order cylindrical RF modes efficiently without the significant expansion of the output waveguide dimension that brings a more compact magnetic field-producing system which reduces the whole volume and weight of the tube remarkably. The maximum microwave efficiency of 47% has been obtained for an L-band RM with the multiantenna output structure in particle-in-cell simulations. Primary experiments had been carried out, which validated that RM with multiantenna output has the capacity to generate high- power microwave over 1 GW.

Optimizations of optical polymer waveguide dimensions for ammonia sensor applications

In this paper, we investigated the optimum dimension of waveguide for ammonia sensor applications. The waveguide material was poly methyl methacrylate (PMMA) on with glass substrate. The study was conducted by comparing the change in refractive index of analyte against electric field for each dimensions of waveguide. We simulated the variation of width and height by using the finite element method technique (FEM) in COMSOL Multiphysics®. The result shows the change of electric field depends on height of waveguide. The electric field change becomes the basic for sensor applications.

Wedge Surface Plasmon Polariton Waveguides Based on Wet-Bulk Micromachining

In this paper, we propose and investigate the modal characteristics of wedge surface plasmon polariton (SPP) waveguides for guiding surface plasmon waves. The wedge SPP waveguides are composed of a silver layer deposited onto the surface of a wedge-shaped silicon dielectric waveguide. The wedge-shaped silicon dielectric waveguides are explored from the anisotropic wet etching property of single crystal silicon. The wedge SPP waveguides are embedded in a dielectric medium to form the metal–dielectric interface for guiding the surface plasmon waves. The propagation characteristics of the wedge SPP waveguides at the optical telecommunication wavelength of 1.55 μm are evaluated by a numerical simulation. The influence of the physical parameters such as the dimensions of the wedge SPP waveguide and the refractive index of the dielectric medium on the propagation of the surface plasmon wave is investigated. In addition, by comparing the propagation characteristics, we derive the wedge SPP waveguide with the optimal performance.

Spatially resolved cross-sectional refractive index profile of fs laser-written waveguides using a genetic algorithm.

Laser-written waveguides in glass have many potential applications as photonic devices. However, there is little knowledge of the actual profile of the usually asymmetric refractive index (RI) change across the femtosecond (fs) laser-written waveguides. We show, here, a new nondestructive method to measure any symmetric or asymmetric two-dimensional RI profile of fs laser-written waveguides in transparent materials. The method is also suitable for the measurement of the RI profile of any other type of waveguide. A Mach-Zehnder interferometer is used to obtain the phase shift of light propagating transversely through the RI-modified region. A genetic algorithm is then used to determine the matching cross-sectional RI profile based on the known waveguide shape and dimensions. A validation of the method with the comparison to a RNF measurement of the industry-standard SMF-28 is presented, as well as a demonstration of its versatility with measurements on fs laser-written waveguides.

Analysis for system errors in measuring the sidewall angle of a silica waveguide with confocal laser scanning microscope (CLSM)

This article reports on the limitation analyses for the sidewall angle (SWA) measurements of microstructures with a confocal laser scanning microscope (CLSM). Under the resolutions of three-dimensional imaging process of CLSM and its spatial frequency spectrum distribution, the optical phase signal of an object is studied to model the signal-noise-ratio (SNR) performance of measurements and the point spread function theory is applied to discuss the limitation to the measurement accuracy of SWA. Then, the characteristics of both the relative SNR performance and the measurement accuracy are numerically simulated with these two theoretical models. As a result, two important characteristics of CLSM measurements for SWA are found as that the relative SNR is quickly decreasing with SWA; the intrinsic measurement error linearly decreases with SWA. Furthermore, for a fabricated device sample having the waveguide dimension of 6 × 10 µm2, with a scanning section of 10nm and a detector aperture of PH = 0.3 Airy Unit, a CLSM image of 300 × 300 µm2 is acquired and reconstructed, in which 10 waveguide channels is covered. For a selected channel, based on ten measurements the averaged values of the left and right SWAs are 85.68° ± 0.32° and 86.59° ± 0.24°, respectively, after being compensated with the intrinsic measurement errors. Finally, the distribution and uniformity of SWA values among the ten waveguide channels in the image are analyzed.