Waveguide Formation Research Articles

Three-dimensional numerical simulation on the directly written waveguide formation with 320nm UV laser in lithium niobate

Three-dimensional numerical simulation on the directly written waveguide formation with 320nm UV laser in lithium niobate

Interplay of Luminophores and Photoinitiators during Synthesis of Bulk and Patterned Luminescent Photopolymer Blends.

Four-dimensional printing with embedded photoluminescence is emerging as an exciting area in additive manufacturing. Slim polymer films patterned with three-dimensional lattices of multimode cylindrical waveguides (waveguide-encoded lattices, WELs) with enhanced fields of view can be fabricated by localizing light as self-trapped beams within a photopolymerizable formulation. Luminescent WELs have potential applications as solar cell coatings and smart planar optical components. However, as luminophore-photoinitiator interactions are expected to change the photopolymerization kinetics, the design of robust luminescent photopolymer sols is nontrivial. Here, we use model photopolymer systems based on methacrylate-siloxane and epoxide homopolymers and their blends to investigate the influence of the luminophore Lumogen Violet (LV) on the photolysis kinetics of the Omnirad 784 photoinitiator through UV-vis absorbance spectroscopy. Initial rate analysis with different bulk polymers reveals differences in the pseudo-first-order rate constants in the absence and presence of LV, with a notable increase (∼40%) in the photolysis rate for the 1:1 blend. Fluorescence quenching studies, coupled with density functional theory calculations, establish that these differences arise due to electron transfer from the photoexcited LV to the ground-state photoinitiator molecules. We also demonstrate an in situ UV-vis absorbance technique that enables real-time monitoring of both waveguide formation and photoinitiator consumption during the fabrication of WELs. The in situ photolysis kinetics confirm that LV-photoinitiator interactions also influence the photopolymerization process during WEL formation. Our findings show that luminophores play a noninnocent role in photopolymerization and highlight the necessity for both careful consideration of the photopolymer formulation and a real-time monitoring approach to enable the fabrication of high-quality micropatterned luminescent polymeric films.

Optical properties of the O3+-ion implanted and femtosecond-laser ablated ridge waveguide in the Er3+-doped germanate glass

Er3+-doped germanate glass is a kind of polyfunctional material for optical and photonic applications. The work reports on the preparation and properties of O3+-ion implanted and femtosecond-laser ablated Er3+-doped germanate glass optical ridge waveguide. The energy is 6.0 MeV and the fluence is 5 × 1014 ions cm−2 for the O3+-ion implantation. The pulse energy and the scanning speed of the femtosecond-laser ablation are 3 μJ and 50 μm s−1, respectively. The SRIM 2013 is used to calculate the vacancy profile induced by the implantation in the Er3+-doped germanate glass for the physical mechanisms of the waveguide formation. The optical microscopy images of the cross-section of the waveguide are captured by the Nikon microscope. The light-guiding properties of the ion-implanted and laser-ablated waveguides are studied by the end-face coupling system. The ridge waveguide has been produced by combining the FS ablation with ion implantation technologies for the first time in the Er3+-doped germanate glass. The propagation of light field indicates that it has the potential for photonics applications based on the planar and ridge Er3+-doped germanate glass waveguides.

Fast, Precise, High Contrast Laser Writing for Photonic Chips with Phase Aberrations

AbstractIntegrated photonic chips have significant potential in telecommunications, classic computing, quantum systems, and topological photonics. Direct laser writing offers unique capability for creating three‐dimensional photonic devices in an optical glass chip with quick prototyping. However, it is a challenge for existing laser writing schemes to create index‐modified structures in glass that precisely match the laser focal shape while also achieving high refractive index contrasts and high scanning speeds. Here, we introduce a refractive index modification scheme that combines the advantages of non‐thermal and thermal regime fabrication methods. We also propose a waveguide formation model that is verified through a thorough study on the effects of phase aberrations. The presented new photonic chip fabrication scheme uses a novel focal intensity distribution, where pulse energy is relocated to the bottom of a laser focus by manipulating primary and higher order spherical aberrations. The technique can produce index modifications with high scanning speed (can be 20 mm/s or higher), high index contrast (ranging from 0.009 to 0.021), and high precision to fabricate with arbitrary cross‐sections. This method has potential to expand the capabilities of photonic chips in applications that require small‐scale, high precision, or high contrast refractive index control.

Formation of optical planar waveguides on fused quartz by MeV ion implantation

AbstractThe optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 1012 to 2 × 1016 ion/cm2, according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation‐induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre‐coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high‐quality waveguides at low current density MeV ion implantation (≤80 nA/cm2) without post‐implantation annealing.

Optical properties of the proton-implanted waveguide in the Dy3+-doped Y3Al5O12 transparent ceramic

The high-quality waveguide structure in the Dy[Formula: see text]-doped Y3Al5O[Formula: see text] transparent ceramic is of significance for the application of integrated micro-light elements. However, there have been no reports on the preparation of optical waveguides by ion implantation in the Dy[Formula: see text]-doped Y3Al5O[Formula: see text] transparent ceramic. The work reports on the formation of optical planar waveguides by using the proton implantation in the Dy[Formula: see text]-doped Y3Al5O[Formula: see text] transparent ceramic. The acceleration energy and the dose of the protons are 400[Formula: see text]keV and [Formula: see text] ions/cm2, respectively. The structure of the fabricated waveguide is captured with the high-res/mag images by a metallurgical microscope. The dark-mode spectrum and the refractive index distribution are gained by the prism coupling system and the RCM software, respectively. The measurement and simulation of the near-field intensity distribution indicate the propagation of light field in the waveguide. The results are of potential to the compact devices in the photonics.

Extreme heat waves in June 2021 over Europe regulated by shrinking Eurasian snow cover in mid–high latitudes

Europe has experienced many extreme heat waves over the past few decades. In this study, the physical processes underlying these long-lasting and wide-ranging heat wave events are investigated based on a case study in Europe in June 2021. Heat waves are associated with barotropic anticyclonic anomalies accompanied by positive geopotential height anomalies locally. These anomalies persist under the conditions of increased meridional air temperature gradients of the mid–upper troposphere in the high latitudes of Eurasia and the formation of the Arctic front jet. The shrinking high-latitude snow cover in April–May favors higher surface temperatures and larger meridional temperature gradients in June in the mid–upper troposphere due to the soil moisture–evaporation–temperature positive feedback process. The summer Arctic front jet is then strengthened, and the mid-latitude westerly winds are weakened. This atmospheric circulation background favors waveguide formation and wave resonance that produces high-amplitude atmospheric waves and the stagnation of ridges in the mid-latitudes. Numerical experiments using the Community Atmosphere Model version 5 verify the proposed physical mechanisms, with the climatic responses in sensitivity experiments to anomalous snowfall rates closely resembling the observational results. Therefore, in June 2021, under the identified atmospheric circulation background and the perturbation of the upstream positive phase of the North Atlantic Oscillation, the large-scale barotropic high pressure and barotropic anticyclonic circulation in the study region tended to be stable and persistent, which is favorable for the production of long-lasting and wide-ranging heat wave events.

Optical Waveguides Fabricated via Femtosecond Direct Laser Writing: Processes, Materials, and Devices

AbstractAs the most fundamental unit of photonic integration, optical waveguides offer the possibility of developing efficient and practical photonic chips by facilitating the on‐chip integration of devices with different functions. Femtosecond direct laser writing (FsDLW), as a burgeoning 3D microfabrication technology, can realize the rapid formation of arbitrary optical waveguides without any mask inside versatile materials, such as crystalline dielectric crystals, glasses, polymers, and photoresists. This significant material‐independence allows FsDLW to combine different materials and manufacturing processes to implement a cross‐platform solution. This review first describes the different optical loss types and suitable measurement methods for different applicable scenes, then summarizes the two fabrication mechanisms and points out the general direction for adjusting the waveguide properties by fabrication processes. Finally, the application fields and development prospects of different materials are discussed by overviewing the characteristics of different materials and the material selection preferences of different devices. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of optical waveguides and processing technology via FsDLW.

CMOS-Compatible Silicon Etched U-Grooves With Groove-First Fabrication for Nanophotonic Applications

We propose a method for process integration to passively edge-couple the optical fibers with on-chip integrated waveguides. By fabricating U-grooves before the waveguide formation, the groove-first process provides a universal platform for hybrid, large-scale fiber-to-waveguide interconnection. This integrated method simplifies the groove formation and avoids unwanted waveguide damage during the conventional groove formation. Besides, the groove-first process can be utilized with the pre-defined layers for cost reduction. The demonstrated groove-first fabrication helps to improve the coupling stability and suppress the power variation. Time-dependent measurements exhibit > 3.5 dB improvement in the power stability. We also show that this groove structure can provide stable coupling with a high-power input up to 300 mW. In addition, a naturally process-induced inverse-taper with sub-micrometer resolution is formed under conventional UV contact lithography, which potentially provides efficient conversion between the fiber-to-waveguide mode. The groove-first method builds a universal, simple, and flexible integration process for silicon photonics.

Rapid automatic waveguide recognition using YOLO and OpenCV for 3D waveguide fabrication

A 3D waveguide is attractive because it has the potential that the waveguides are arranged, not only in plane, into three-dimension. The mosquito method, in which the core and cladding material sources are liquid and will be cured using UV light, is known as one of the ways to fabricate the 3D waveguide. In this method, if multiple waveguides are fabricated, the time until UV cure is different between the first waveguide and the last one and it leads to core position shift because of gravity. To solve the problem, we considered reducing the time from the first waveguide formation to the UV cure using automatic waveguide fabrication with a camera. For the automatic waveguide fabrication, YOLO (you look only once) and OpenCV are exploited as machine learning and an image processor, respectively. As a result, a waveguide recognition time of 10 ms and image processing time of 50 ms, totally 60 ms, are realized.

Formation of channel proton-exchange waveguides in YB3+, ER3+:PPLN

Formation of channel proton-exchange waveguides in YB3+, ER3+:PPLN

Optical properties of He+-implanted and diamond blade-diced terbium gallium garnet crystal planar and ridge waveguides

Terbium gallium garnet (Tb3Ga5O12, TGG) crystal can be used to fabricate various magneto-optical devices due to its optimal Faraday effect. In this work, 400-keV He+ ions with a fluence of 6.0 × 1016 ions/cm2 are irradiated into the TGG crystal for the planar waveguide formation. The precise diamond blade dicing with a rotation speed of 2 × 104 rpm and a cutting velocity of 0.1 mm/s is performed on the He+-implanted TGG planar waveguide for the ridge structure. The dark-mode spectrum of the He+-implanted TGG planar waveguide is measured by the prism-coupling method, thereby obtaining the relationship between the reflected light intensity and the effective refractive index. The refractive index profile of the planar waveguide is reconstructed by the reflectivity calculation method. The near-field light intensity distribution of the planar waveguide and the ridge waveguide are recorded by the end-face coupling method. The He+-implanted and diamond blade-diced TGG crystal planar and ridge waveguides are promising candidates for integrated magneto-optical devices.

Tapered self-written waveguide for a silicon photonic chip I/O.

An optical coupling method with high alignment tolerance by self-written waveguide (SWW) formation is a promising candidate for co-packaged optics (CPO) by silicon photonics (SiPh). However, conventional SWWs cannot be used with Si waveguides because visible light for SWW formation cannot radiate from the waveguide facet. Here, we devised a new, to the best of our knowledge, optical circuit with SiOxNy waveguides for SWW formation from an SiPh chip. With our circuit, we achieved optical coupling between an SiPh chip and a standard single-mode fiber (SSMF) with a tapered SWW (TSWW). The lowest excess coupling loss compared to butt coupling with a high-numerical aperture (NA) fiber is approximately 0.6 dB over the C-band with the TSWW. In addition, our coupling method has higher alignment tolerances than butt coupling with a high-NA fiber (HNF).

Improving the Selected Stages of Integrated-Optic Chip Structure Formation and Its Interfacing with Optical Fibers

The paper considers experimental technological regimes at different stages of integrated optical chips creation for modern applications: optoelectronics, fiber-optic sensors, microfluidics. The considered experimental regimes demonstrate not only qualitative, but also quantitative efficiency: at the stage of the ridge waveguides formation, there is a possibility of achieving high etching rates of lithium niobate - up to 950 nanometers per minute in fluorine-containing plasma with an increased consumption of plasma gases without forced thermostating of the sample. Using scanning electron microscope, structural changes in the surface have been demonstrated: clustering of surface etching foci, indicating the uniformity of etching at the macroscale, and changes in the thickness and structure of the near-surface defect layer, indicating the possibility of its complete removal by the plasma-chemical method. The method can be applied both for the manufacturing of ridge waveguides and optical elements based on them, and for microfluidics elements. Then, the efficiency of the waveguides and optical fibers interfacing method has been confirmed with frequency domain reflectometry. The algorithmic details of the interfacing by the modified Newton's method are also described. The modified Newton’s method allowed to simplify the alignment process by performing coarse alignment based on reflections from the far end face of the waveguide, speed up the alignment process at fine mode, and fully automate the alignment of the waveguide and optical fiber at any initial displacements. All the proposed technological process modernization leads to the improvement of technological characteristics and the individual stages production time reduction.

Investigation of near-surface layer dislocation density of lithium niobate single crystal wafers using chemical etching

Using chemical etching it was shown that the density of dislocation in lithium niobate (LN) single crystal wafers is higher near the surface in depth about 20 um than in the depth of crystal. It caused to change of diffusion coefficient during the waveguide formation with proton exchange (PE) method and can increase DC-drift of intensity optical modulators based on PE-waveguides.

Specific features of the formation of optical waveguides, contact pads and electrical interconnections on lithium tantalate substrates

The article considers the formation of titanium channel optical waveguides in LiTaO3 substrates. These structures were obtained by dry etching of grooves in SF6 plasma and magnetron sputtering of titanium film. After that, waveguides were formed by plasma etching using photoresist as mask. Technological features and modes of microstructure production are described. Al contact pads were produced by magnetron sputtering thin metal films on LiTaO3. Aluminum wires were ultrasonically bonded to Al contact pads using Delvotec 5630. The developed technology of formation of contact pads and bonding modes made it possible to obtain a bonded joint with a bond strength of 23-25 Gs.

Persistent, “Mysterious” Seismoacoustic Signals Reported in Oklahoma State during 2019

ABSTRACT We report on the source of seismoacoustic pulses that were observed across the state of Oklahoma (OK) during summer of 2019, and the subject of national media coverage and speculation. Seismic network data collected across four U.S. states and interviews with witnesses to the pulse’s effect on residential structures demonstrate that they were triggered by routine ammunition disposal operations conducted by McAlester Army Ammunition Plant (McAAP). During these operations, conventional explosives destroy obsolete munitions stored in pits through a controlled sequence of electronically timed shots that occur over tens of minutes. Despite noise-abatement efforts that reduce coupling of acoustic energy with air, some lower frequency, subaudible (infrasonic) sound radiates from these shots as discrete pulses. We use nine months of blast log documents, seismic network records, analyst picks, and physical modeling to demonstrate that seismic stations as far as 640 km from McAAP sample these pulses, which record seasonal patterns in stratospheric and tropospheric winds, as well as the dynamic formation of waveguides and shadow zones. Digital short-term average to long-term average detectors that we augment with dynamic thresholds and time-binning operations identify these pulses with a fair probability, when compared with visual observations. Our analyses thereby provide estimates of observation rates for both partial and full sequences of these pulses, as well as single shots. We suggest that disposal operations can exploit existing, composite seismic networks to predict where residents are likely to witness blasting. Crucially, our data also show that dense seismic networks can record multiscale atmospheric processes in the absence of infrasound arrays.

Morphology and diagnostic potential of the ionospheric Alfvén resonator

The layering of the ionosphere leads to the formation of resonators and waveguides of various kinds. One of the most well-known is the ionospheric Alfvén resonator (IAR) whose radiation can be observed both on Earth’s surface and in space in the form of a fan-shaped set of discrete spectral bands (DSB), the frequency of which changes smoothly during the day. The bands are formed by Alfvén waves trapped between the lower part of the ionosphere and the altitude profile bending of Alfvén velocity in the transition region between the ionosphere and the magnetosphere. Thus, IAR is one of the important mechanisms of the ionosphere-magnetosphere interaction. The emission frequency lies in the range from tenths of hertz to about 8 Hz — the frequency of the first harmonic of the Schumann resonance. The review describes in detail the morphology of the phenomenon. It is emphasized that the IAR emission is a permanent phenomenon; the probability of observing it is primarily determined by the sensitivity of the equipment and the absence of interference of natural and artificial origin. The daily duration of the DSB observation almost completely depends on the illumination conditions of the lower ionosphere: the bands are clearly visible only when the D layer is shaded. Numerous theoretical IAR models have been systematized. All of them are based on the analysis of the excitation and propagation of Alfvén waves in inhomogeneous ionospheric plasma and differ mainly in sources of oscillation generation and methods of accounting for various factors such as interaction of wave modes, dipole geometry of the magnetic field, frequency dispersion of waves. Predicted by all models of the cavity and repeatedly confirmed experimentally, the close relationship between DSB frequency variations and critical frequency foF2 variations serves as the basis for searching ways of determining in real time the electron density of the ionosphere from IAR emission frequency measurements. It is also possible to estimate the profile of the ion composition over the ionosphere from the data on the IAR emission frequency structure. The review also focuses on other results from a wide range of IAR studies, specifically on the results that revealed the influence of the interplanetary magnetic field orien tation on oscillations of the resonator, and on the facts of the influence of seismic disturbances on IAR.

Морфология и диагностический потенциал ионосферного альвеновского резонатора

The layering of the ionosphere leads to the formation of resonators and waveguides of various kinds. One of the most well-known is the ionospheric Alfvén resonator (IAR) whose radiation can be observed both on Earth’s surface and in space in the form of a fan-shaped set of discrete spectral bands (DSB), the frequency of which changes smoothly during the day. The bands are formed by Alfvén waves trapped between the lower part of the ionosphere and the altitude profile bending of Alfvén velocity in the transition region between the ionosphere and the magnetosphere. Thus, IAR is one of the important mechanisms of the ionosphere-magnetosphere interaction. The emission frequency lies in the range from tenths of hertz to about 8 Hz — the frequency of the first harmonic of the Schumann resonance. The review describes in detail the morphology of the phenomenon. It is emphasized that the IAR emission is a permanent phenomenon; the probability of observing it is primarily determined by the sensitivity of the equipment and the absence of interference of natural and artificial origin. The daily duration of the DSB observation almost completely depends on the illumination conditions of the lower ionosphere: the bands are clearly visible only when the D layer is shaded. Numerous theoretical IAR models have been systematized. All of them are based on the analysis of the excitation and propagation of Alfvén waves in inhomogeneous ionospheric plasma and differ mainly in sources of oscillation generation and methods of accounting for various factors such as interaction of wave modes, dipole geometry of the magnetic field, frequency dispersion of waves. Predicted by all models of the cavity and repeatedly confirmed experimentally, the close relationship between DSB frequency variations and critical frequency foF2 variations serves as the basis for searching ways of determining in real time the electron density of the ionosphere from IAR emission frequency measurements. It is also possible to estimate the profile of the ion composition over the ionosphere from the data on the IAR emission frequency structure. The review also focuses on other results from a wide range of IAR studies, specifically on the results that revealed the influence of the interplanetary magnetic field orien tation on oscillations of the resonator, and on the facts of the influence of seismic disturbances on IAR.

The study of the birefrigence modulator based on lithium niobate

This work investigates a lithium niobate X-cut birefringence modulator with a titanium diffusion channel waveguide. The wave voltage of the modulator depends on the growth and processing conditions of the lithium niobate crystal and on the technology of waveguide formation. The tolerance for determining the length of the electrodes and the gap between them exceeds 1 %. In this regard, the calculated values of the wave voltage can differ significantly, and an experimental measurement of the wave voltage is required for practical use. The authors present an experimental refinement for the value of the wave voltage of the modulator and perform a comparison of the value with the theoretical one. In the experiment, the wave voltage was determined using a scanning Michelson interferometer. It is shown that the experimentally measured value of the wave voltage diverges from the calculated one by more than 26 %. This difference is based on the assumption that the vector of the electric field inside the crystal is directed perpendicular to the axis of propagation of optical radiation, and the magnitude of the electric field does not change over the depth of the crystal. In this case, the overlap integrals of the ordinary and extraordinary waves are equal. In real modulators with a channel waveguide formed by titanium diffusion technology, these assumptions are not fulfilled. The refractive index of lithium niobate and the electro-optical coefficient may vary for different crystal samples, depending on the conditions of their growth, processing and waveguide formation technology. The results of the work can find application in the field of interferometric measuring devices, in which a birefringence modulator is used, since the value of the wave voltage is necessary for the design of control electronics.