Waveguide Pattern Research Articles

Teleconnection and the Antarctic response to the Indian Ocean Dipole in CMIP5 and CMIP6 models

AbstractTropical–Antarctic teleconnections are known to have large impacts on Antarctic climate variability at multiple timescales. Anomalous tropical convection triggers upper‐level quasi‐stationary Rossby waves, which propagate to high southern latitudes and impact the local environment. Here the teleconnection between the Indian Ocean Dipole (IOD) and Antarctica was examined using daily gridded reanalysis data and the linear response theory method (LRTM) during September–November of 1980–2015. The individual contribution of the IOD over the Antarctic climate is challenging to quantify, as positive IOD events often co‐occur with El Niño events. However, using the LRTM, the extratropical response due to a positive IOD was successfully extracted from the combined signal in the composite map of anomalous 250‐hPa geopotential height. Applying the method to a set of models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), significant differences were observed in the extratropical response to the IOD among the models, due to bias in the Rossby waveguide and IOD precipitation pattern. The LRTM was then applied to evaluate the extratropical response of the 850‐hPa temperature, wind anomalies, and sea‐ice concentration anomalies in observation data, as well as models that represented both the IOD precipitation and the extratropical waveguide adequately. The IOD induced cold southerly flow over the west of the Ross Sea, Weddell Sea, and Antarctic Peninsula, causing cold surface‐temperature anomalies and the increase of sea ice, and warm northerly flow over the east of the Ross Sea and Amundsen Sea, causing warm surface‐temperature anomalies and the decrease of sea ice. We recommend the LRTM as a complementary method to standard analysis of climate variability from observations and global climate models.

RF Waveguide Pattern Engineering to Mitigate Bonding Surface Nonuniformities in CMOS Compatible Fabrication Processes

Heterogeneously integrating silicon photonic devices and circuits with other optical materials (III/V semiconductors, LiNbO3, and so on) is a promising approach toward bolstering the capabilities of silicon photonics and improving the manufacturability of other photonic platforms. An approach to heterogeneous integration is to directly bond an optical material to the surface oxide of a silicon photonic circuit or device, which requires locally and globally smooth bonding surfaces to facilitate sufficient bonding quality. However, embedded silicon photonic metal structures, such as RF waveguides for high-speed photonic devices and electrical interconnects, can impact the surface topography during planarization, resulting in nonideal bonding surfaces. In this article, we discuss and demonstrate a method of patterning the ground planes of RF waveguides to achieve a more uniform distribution of embedded metal density, in turn, providing more constant planarization rates. This provides a more uniform bonding surface which is a requirement for the high-volume manufacturing of these technologies.

Achieving high aspect ratio in plasmonic lithography for practical applications with sub-20 nm half pitch

Plasmonic lithography, which exploits a bowtie nanoaperture (BNA) for the purpose of subwavelength near-field focusing, has the capability of high-resolution patterning. However, the ultra-small feature size is achieved at the price of sharply decay of the surface plasmon waves (SPWs) in the photoresist (PR) layer, which directly leads to some unfavorable patterning issues, such as non-uniformity and shallow pattern depth even over small exposure areas. In this work, a special hybrid plasmonic waveguide (HPW) patterning system, which is composed of the plasmonic BNA-PR layer-silver reflector, is designed to facilitate high spatial frequency selection and amplify the evanescent field in the PR layer. Theoretical calculations indicate that the antisymmetric coupled SPWs and plasmonic waveguide modes excited by the HPW structure can remove the exponential decay and ensure uniform exposure over the entire depth of the PR layer. Importantly, the hyperbolic decaying characteristic of the SPWs in the PR layer plays a noticeable role in the improvement of achievable resolution, depth-of-field, and line array pattern profile. It is worth to note that the uniform periodic patterns in sub-20 nm feature can be achieved with high aspect ratio. Additionally, further numerical simulation results are presented to demonstrate the achievement of spatial frequency selection of high-k mode in HPW structure by controlling the PR thickness and gap size. Our findings may provide a new perspective on the manufacture of surface nanostructures and broaden the potential promising applications of plasmonic lithography in nanoscale patterning.

Laser-Induced Erasable and Re-Writable Waveguides within Silver Phosphate Glasses.

Femtosecond direct laser writing is a well-established and robust technique for the fabrication of photonic structures. Herein, we report on the fabrication of buried waveguides in AgPO3 silver metaphosphate glasses, as well as, on the erase and re-writing of those structures, by means of a single femtosecond laser source. Based on the fabrication procedure, the developed waveguides can be erased and readily re-inscribed upon further femtosecond irradiation under controlled conditions. Namely, for the initial waveguide writing the employed laser irradiation power was 2 J/cm2 with a scanning speed of 5 mm/s and a repetition rate of 200 kHz. Upon enhancing the power to 16 J/cm2 while keeping constant the scanning speed and reducing the repetition rate to 25 kHz, the so formed patterns were readily erased. Then, upon using a laser power of 2 J/cm2 with a scanning speed of 1 mm/s and a repetition rate of 200 kHz the waveguide patterns were re-written inside the glass. Scanning electron microscopy (SEM) images at the cross-section of the processed glasses, combined with spatial Raman analysis revealed that the developed write/erase/re-write cycle, does not cause any structural modification to the phosphate network, rendering the fabrication process feasible for reversible optoelectronic applications. Namely, it is proposed that this non-ablative phenomenon lies on the local relaxation of the glass network caused by the heat deposited upon pulsed laser irradiation. The resulted waveguide patterns Our findings pave the way towards new photonic applications involving infinite cycles of write/erase/re-write processes without the need of intermediate steps of typical thermal annealing treatments.

Formation of waveguides in crystalline organic N-benzyl-2-methyl-4-nitroaniline thin films using femtosecond laser ablation process

This paper reports the feasibility of femtosecond laser etching of microstructures directly onto crystalline N-benzyl-2-methyl-4-nitroaniline (BNA) films grown on glass to realize single crystal BNA waveguides. The threshold fluence has been estimated and fluence range of 318.5–1274 mJ/cm2 at 800 nm is used for ablation. Holes with diameter ranging from 13 to 26 μm and waveguide patterns with width of 100 μm are demonstrated. Grooves with laser transit gap <20 μm is used to form smaller waveguides. Input faces of the waveguides have been simultaneously irradiated with red laser of 630 nm. The optical image of transmission confirms the wave-guiding. This study shows the feasibility of laser-etching waveguides on crystalline BNA films.

Fabrication of Si photonic waveguides by electron beam lithography using improved proximity effect correction

In this work, electron beam lithography proximity effect correction (PEC) was experimentally studied for patterning of Si photonic waveguides with a relatively thick resist mask. Beam’s energy density distribution (EDD) was experimentally extracted by the line exposure method; however, exposure lines in this work were developed after cleavage with a high-contrast process to reduce developer-related effects. The measured line spread function was fitted to a 4-Gaussian function to model mid-range energy densities accurately. The extracted EDD showed less proximity effects compared to conventional Monte-Carlo simulation performed by a commercial software. PEC processes with both techniques were experimentally compared for a Si photonic waveguide pattern with different side-cladding trench widths. Microscopic images confirmed that the presented calibration method could achieve better development conditions near the required clearance dosage. Single-mode propagation loss for a 500 × 220 nm Si wire waveguide was reduced from 3.2 to 2.4 dB cm−1 using the presented process.

Pseudospectral frequency‐domain analysis of rectangular waveguides filled by dielectrics whose permittivity varies continuously along the broad dimension

AbstractThe calculation of dispersion diagrams and field patterns of metallic rectangular waveguides filled with an inhomogeneous dielectric whose permittivity varies continuously along the broad size of the guide is considered. In general, this problem has no exact solution, thus numerical techniques should be used. In this article, the pseudospectral frequency‐domain (PSFD) method is proposed to address the problem. Starting from the Helmholtz equation, a matrix eigenvalue problem is obtained by applying the collocation technique with Chebyshev polynomials as basis functions. The results obtained are compared with those calculated by the conventional finite‐difference frequency‐domain method showing that the PSFD technique provides an excellent accuracy.

Simulations of the rectangular wave-guide pattern in the complex Maxwell vorticity equations by lattice Boltzmann method

In this paper, a lattice Boltzmann model for solving three-dimensional complex Maxwell vorticity equations is presented. Different from the classic lattice Boltzmann models, this lattice Boltzmann model is based on uniformly distributed lattice points in a three-dimensional spatiotemporal space, and we have also given the stability conditions of this complex model and the expression of the equilibrium distribution function. Numerical results reproduce the phenomena of the rectangular wave-guide pattern in complex Maxwell equations, and these numerical results do accord with classical ones.

Thin-films microstructuration through photolithography

In recent years, micro and nanotechnology have undergone a rapid development due to their applications in different scientific areas such as metaphotonics, an emerging branch of optics that studies the interaction of light with micro and nanostructured metamaterials. Our particular interest is the development of integrated metaphotonic devices for lab-on-a-chip biosensing applications. A widely used technique for the manufacture of integrated optical devices is photolithography, which is based on the processing of UV-light-sensitive photoresists to create masks for the deposition of thin films and generate the desired devices. In this contribution, we present an experimental methodology for the patterning of plasmonic waveguides using a photolithography system for printing SU-8 photoresist masks on glass substrates. We show the necessary parameters to optimize the photoresist printing (beam waist, focal distance and fluence) under normal conditions and the characterization of the samples through atomic force microscopy. Due to the aspect ratio between the width of the waveguides and thickness of the photoresist, the obtained results approach us to the development of multilayered systems for new integrated metaphotonic devices.

Experimental Study on Flat-Glass Heating and Edge-Sealing Using Multiple Microwave Sources

There has been a recent surge of interest in vacuum insulating glass (VIG) due to its excellent thermal insulation performance. Vacuum glazing is necessary for high-performance sealing solders and various applications in sealing technology. This paper describes experimental studies into heating and edge-sealing of flat glass using microwaves. Electric–thermal coupled analysis using ANSYS was employed and heating and edge-sealing experiments were conducted on flat glass. In order to ensure a uniform electric field distribution in the microwave chamber, the electric field and temperature distributions were analyzed according to waveguide patterns. In addition, the electric field and temperature distribution were analyzed with the inclusion of carbon susceptor plates. Based on the electric simulation results by waveguide pattern, a microwave heating chamber was fabricated, and a basic experiment was conducted on both heating and edge-sealing of the glass. The cross-section of the sealed glass confirmed that it was sealed without cracks or breakage.

Deep Etched Gallium Nitride Waveguide for Raman Spectroscopic Applications

Gallium nitride (GaN) materials with a high chemical stability and biocompatibility are well suited for bio-sensing applications and evanescent wave spectroscopy. However, GaN poses challenges for processing, especially for deep etching using conventional etching techniques. Here, we present a dry-etching technique using tetraethyl orthosilicate (TEOS) oxide as an etching barrier. We demonstrate that a sharp, vertically-etched waveguide pattern can be obtained with low surface roughness. The fabricated GaN waveguide structure is further characterized using field-emission scanning electron microscopy, Raman spectroscopy, and a stylus profilometer.

On comparison of the temperature sensitivity of SU-8-based triple-arm MZI against straight rib optical waveguides patterned on silicon wafer

This study is performed to investigate the temperature sensitivity of SU-8-based triple-arm Mach–Zehnder interferometer (MZI) and straight waveguide. The proposed SU-8 2000-based rib waveguides are fabricated on a silicon wafer with 1.5-μm SiO2 thermal oxide layer. SU-8 layer of desired thickness is spin-coated onto the silicon wafer followed by patterning of the SU-8 waveguides. Temperature sensitivity of both waveguides is evaluated using the same heating source and under the same environmental conditions. Measurement results show that complex triple-arm MZI having different arm lengths offers a less linear sensitivity compared to the simple straight waveguide.

Surface plasmon propagation enhancement via bowtie antenna incorporation in Au-mica block waveguides.

The optimum geometry for waveguide propagation was determined by comparing bowtie and semicircle antenna cuts to a standard plain waveguide with a 635nm laser. The results of both experimental data and COMSOL simulations proved that the bowtie antenna increased waveguide output in comparison to the plain waveguide with the semicircle pattern showing no enhancement. It was also determined that the propagation was highest when the polarization direction of the laser was perpendicular to the direction of the waveguide for all patterns, while polarization along the propagation direction led to little or no output in all antenna and plain waveguide cases. The waveguide output of the bowtie antenna and plain structures was then measured using a tunable laser for wavelengths from 570nm to 958nm under both parallel and perpendicular polarization conditions. The results indicated that the bowtie antenna performed better over the entire range with an average increase factor of 2.12±0.40 over the plain waveguide pattern when perpendicularly polarized to the waveguide direction, and 1.10±0.48 when parallel. The measured values indicate that the structure could have applications in broadband devices.

RF characteristics of flexible circuits patterned with hybrid Ag paste

Printed electronics based on nanomaterials has been a potential alternative to conventional electronic technology and is favorable for flexible polymer substrates. However, a printed circuit has insufficient electrical performance and mechanical reliability under flexible stress. We designed hybrid Ag pastes containing Ag nanoparticles (NPs, 30–50 nm) and Ag flake (F, 2.5–3.5 μm in diameter) particles to overcome the obstacles of printed electronics. Six types of Ag paste (Ag NPs-x wt% F paste, x = 0, 10, 25, 50, 75, and 100) were screen-printed onto a polyimide substrate and sintered at 200 °C for fabricating a flexible circuit. We simulated a coplanar waveguide pattern before measuring the S-parameter using high frequency structural simulation. To investigate the radio frequency characteristics of various Ag circuits under sliding stress, a network analyzer and Cascade’s probe system in the frequency range from 1 to 10 GHz were employed before and after 100,000 sliding cycles. Hybrid Ag circuits showed stable electrical conductance and signal transmission, while pure Ag particle circuits showed a definite drop of electrical conductance (over 30% increase of electrical resistance) under cyclic sliding stress. The microstructural crack behavior demonstrated that the Ag F content within the Ag hybrid circuits effectively suppressed crack propagation, leading to improved flexibility of the sintered Ag circuit.

Fabrication of large all-PDMS micropatterned waveguides for lab on chip integration using a rapid prototyping technique

A simple method for manufacturing centimeter-long all-PDMS embedded and rib microwaveguides is presented. It allows for the fabrication of centimeter-long micromolds by direct laser ablation of a desired waveguide pattern inside an acrylic sheet to create a pattern which is then transferred to a poly-dimethylsiloxane (PDMS) layer using soft-lithography. A refractive index difference between the core and cladding of 1.3x10−3 was achieved by controlling the PDMS curing and linear attenuation of 1.27 dB/cm for embedded and 2.36 dB/cm for a rib waveguide, similar to other techniques. Finally, a beamsplitter was fabricated to demonstrate that our low-cost process is suitable to integrate waveguide devices on lab on chip platforms.

All-polymeric planar waveguide devices based on a gas-assisted thermal imprinting technique

In order to improve accuracy of replication and to simplify the fabrication process for imprinted all-polymeric planar optical waveguides and devices, the three-stage thermal imprinting technique with gas pressure load were developed to optimize the cross-sectional profile morphologies of polymer trenches directly fabricated on polymethylmethacrylate (PMMA) sheets. As a result, our investigation found that the choice of the imprinting pressure was directly dependent on the imprinting temperature. The shortest imprinting temperature holding time was correlated with combination of them. The conformal polymer waveguide patterns were obtained under uniform and low gas pressure. As a verification for a simple and efficient gas-assisted thermal imprinting technique, the 8 × 8 μm2 solid PMMA based all-polymeric single-mode planar waveguides and planar lightwave circuit devices including a 1 × 2 splitter and a 1 × 4 splitter were fabricated and characterized at the wavelength of 1550 nm. The propagation loss coefficient of these all-polymeric planar waveguides was measured to be 1.63 ± 0.02 dB/cm.

Non-annular, hemispheric signature of the winter North Atlantic Oscillation

Sensitivity experiments with an atmospheric general circulation model (AGCM) without a proper stratosphere are performed to locally force a North Atlantic oscillation (NAO)-like response in order to analyse the tropospheric dynamics involved in its hemispheric extent. Results show that the circulation anomalies are not confined to the North Atlantic basin not even within the first 10 days of integration, where the atmospheric response propagates downstream into the westerly jets. At this linear stage, transient-eddy activity dominates the emerging, regional NAO-like pattern while zonal-eddy coupling may add on top of the wave energy propagation. Later at the quasi-equilibrium nonlinear stage, the atmospheric response emphasizes a wavenumber-5 structure embedded in the westerly jets, associated with transient-eddy feedback upon the Atlantic and Pacific storm-tracks. This AGCM waveguided structure rightly projects on the observational NAO-related circumglobal pattern, providing evidence of its non-annular character in the troposphere. These findings support the view on the importance of the circumglobal waveguide pattern on the development of NAO-related anomalies at hemispheric level. It could help to settle a consensus view of the Arctic Oscillation, which has been elusive so far.

Design of planar waveguide based on patterning substrate and oriented polymer film

Semiconducting conjugated polymersused for light emitting devices (LEDs), lasers and amplifiers have received considerable attention due to their low cost and easy fabrication through spin-coating and photochemical processing. A promising material for LED and laser applications is poly(9, 9-dioctylfluorene-co-benzothiadiazole) (F8BT). F8BT has a low stimulated emission threshold and exhibits a large net optical gain at 570 nm. It also shows liquid crystallinity and can be readily aligned into a monodomain by using an alignment layer, polyimide (PI). Oriented film of F8BT exhibits that its charge carrier mobility is increased by more than one order of magnitude compared with isotropic film. The refractive index of the material is also greatly affected by the orientation of the polymer chain. Furthermore, it has been reported that low threshold laser can be achieved by blending P3 HT or red-F solution into F8BT via energy transfer.Here we report a planar waveguide structure obtained via patterning chain oriented area on F8BT: red-F (9 : 1) blend polymer film. The blend solution is obtained by mixing the F8BT solution with red-F solution (with the same concentration, 20 mg/ml in toluene) with a ratio of 9 : 1. The designed waveguide patterns are obtained by inkjet-printing the PI solution onto the pre-cleaned quartz substrates. Thin films (150-200~nm thick) of F8BT: Red F are deposited onto PI by spin coating (2000 rpm). The chain alignment treatment is performed by the following procedure: the films are kept in N2 at 265 ℃ for 2 min, then they are cooled down to 235 ℃ at a rate of 1 ℃/min, finally they are cooled down to room temperature sharply. The PI contacted area on the film becomes anisotropic, while the area without PI keeps isotropic. The refractive index parallel (perpendicular) to the chain direction is significantly increased (reduced) in the PI contacted area compared with outside the PI area. Therefore, the waveguide confinement could be achieved without changing the thickness of the film. Experimental investigations, including AFM images, polarized microscopy images, polarized absorption, and PL spectra of the patterned samples, clearly show the difference between the aligned area and isotropic area.The large percentage of overlap between the emission spectrum of F8BT and the absorption spectrum of red-F solution leads to an efficient energy transfer from F8BT (host) to red-F solution (guest), resulting in a red emission at a wavelength between 600-670 nm from the blend. The polarized absorption and PL spectra of the aligned F8BT: red-F film demonstrate that the absorption intensity of the polarized light parallel to the aligned chain is 5.9 times that perpendicular to the aligned chain at a wavelength of 477 nm, and their ratio is 5.5 at a wavelength of 631 nm.Our demonstration suggests that patterning chain oriented area can be a promising approach to achieving planar waveguide devices by utilizing the refraction index contrast within and beyond the chain oriented region, and the substrate of polyimide (PI) could be patterned with various widths and shapes by the use of inkjet printing technology.

Silicon nanoridge array waveguides for nonlinear and sensing applications.

We fabricate and characterize waveguides composed of closely spaced and longitudinally oriented silicon ridges etched into silicon-on-insulator wafers. Through both guided mode and bulk measurements, we demonstrate that the patterning of silicon waveguides on such a deeply subwavelength scale is desirable for nonlinear and sensing applications alike. The proposed waveguide geometry simultaneously exhibits comparable propagation losses to similar schemes proposed in literature, an enhanced effective third-order nonlinear susceptibility, and high sensitivity to perturbations in its environment.

Design, fabrication, and optical characteristics of freestanding GaN waveguides on silicon substrate

Freestanding GaN waveguides were fabricated on a silicon substrate by a combination of Cl2 plasma reactive ion etching and XeF2 gas selective etching. The freestanding GaN waveguides ranged from 0.23 to 8 μm in width and were supported in air by bridge structures. The bridge structures were designed via rigorous electromagnetic simulations using the finite-difference time-domain method. The GaN layer was grown epitaxially on a silicon (111) substrate using a buffer layer to compensate for the crystal lattice constant mismatch. Using two types of masks, the GaN layer was etched using a Cl2 inductively coupled plasma. The 625-nm-thick GaN layer was etched by the Cl2 plasma at a substrate temperature of −17 °C to form the GaN waveguide patterns, at the expense of a 92-nm-thick HfO2 mask layer. The etching rate of the GaN layer was 170 nm/min and the etching ratio between the GaN and HfO2 layers was 6.8:1. The silicon substrate was then isotropically etched using XeF2 gas to generate air gaps underneath the GaN waveguides. The transmittance of the fabricated freestanding GaN waveguides was measured using a visible (406 nm) laser and an infrared (1550 nm) laser. The waveguide losses for a 730-nm-wide and 625-nm-thick waveguide were 2.6 dB/mm at 406 nm and 2.2 dB/mm at 1550 nm. These results indicate that the structures are likely to be useful for several visible waveguide devices combined with blue GaN light emitting diodes and for optical telecommunication waveguide devices using the wide transmission window of the GaN crystal.