Fabrication Of Gratings Research Articles

Directional Amplified Photoluminescence through Large-Area Perovskite-Based Metasurfaces.

Perovskite nanocrystals are high-performance, solution-processed materials with a high photoluminescence quantum yield. Due to these exceptional properties, perovskites can serve as building blocks for metasurfaces and are of broad interest for photonic applications. Here, we use a simple grating configuration to direct and amplify the perovskite nanocrystals' original omnidirectional emission. Thus far, controlling these radiation properties was only possible over small areas and at a high expense, including the risks of material degradation. Using a soft lithographic printing process, we can now reliably structure perovskite nanocrystals from the organic solution into light-emitting metasurfaces with high contrast on a large area. We demonstrate the 13-fold amplified directional radiation with an angle-resolved Fourier spectroscopy, which is the highest observed amplification factor for the perovskite-based metasurfaces. Our self-assembly process allows for scalable fabrication of gratings with predefined periodicities and tunable optical properties. We further show the influence of solution concentration on structural geometry. By increasing the perovskite concentration 10-fold, we can produce waveguide structures with a grating coupler in one printing process. We analyze our approach with numerical modeling, considering the physiochemical properties to obtain the desired geometry. This strategy makes the tunable radiative properties of such perovskite-based metasurfaces usable for nonlinear light-emitting devices and directional light sources.

Optical Fiber Grating-Prism Fabrication by Imprint Patterning of Ionic-Liquid-Based Resist.

We present a method of microstructure fabrication on the tip of the optical fiber using a UV soft-imprint process of polymerizable ionic liquid-based optical resist. Ionic liquid with two UV-sensitive vinylbenzyl groups in the structure was diluted in non-hazardous propylene glycol (PG) to obtain liquid material for imprinting. No additional organic solvent was required. The impact of propylene glycol amount and exposure dose on optical and mechanical properties was investigated. The final procedure of the UV imprint on the optical fiber tip was developed, including the mold preparation, setup building, UV exposure and post-laser cure. As the IL-containing vinylbenzyl groups can also be polymerized by the radical rearrangement of double bonds through thermal heating, the influence of the addition of 1-2% BHT polymerization inhibitor was verified. As a result, we present the fabricated diffraction gratings and the optical fiber spectrometer component-grism (grating-prism), which allows obtaining a dispersion spectrum at the output of an optical in line with the optical fiber long axis, as the main component in an optical fiber spectrometer. The process is very simple due to the fact that its optimization already starts in the process of molecule design, which is part of the trend of sustainable technologies. The final material can be designed by the tailoring of the anion and/or cation molecule, which in turn can lead to a more efficient fabrication procedure and additional functionalities of the final structure.

Fabrication error detection in diffraction gratings with high dynamic range Fourier plane imaging and spatial filtering

We summarize our development of a low-cost instrument for the detection of fabrication errors in diffraction gratings. Our instrument applies a low-cost digital camera and high dynamic range (HDR) imaging in the focal plane of a lens to analyze light reflected by a diffraction grating. A dynamic range close to 1010 is achieved for a spatial frequency range that is relevant for types of errors that occur in the lithographic fabrication of gratings. We also describe a modification of the instrument in which a spatial filter is used to block the large fraction of light that does not carry information on fabrication errors. This “coronagraph” modification reduces measurement times by about an order of magnitude. A unique pseudologarithmic transformation is described for the visualization of wide range data that include zero or negative values, such as HDR images.

Fabrication of nanometre sized gratings via ion irradiation

The damage caused by irradiation of crystalline material with ions results in localized volume changes. Here, swelling is utilized to fabricate nanostructured gratings with heights below 10 nm for extreme ultraviolet radiation. Irradiations were performed through a structured layer of photoresist shadowing parts of the sample from a broad ion beam. This enabled much shorter fabrication times than comparable direct write processes with a focussed ion beam. The study presents results from first systematic investigations regarding the fabrication of nanostructured gratings by irradiation of silicon with a broad beam of helium ions with energies of 30 keV. A smaller, scanned beam is used for comparison. Fluence was varied from 0.4 to 7.5×1016 ions/cm2. Fabricated structures were measured via atomic force microscopy. This yielded a controllable method to fabricate shallow gratings with heights in the range of 0 to 10 nm.

Quantitative investigation on a period variation reduction method for the fabrication of large-area gratings using two-spherical-beam laser interference lithography.

Gratings produced by two-spherical-beam Laser Interference Lithography (LIL) will have a nonuniform period, and the associated period variation is larger with the increase of the substrate size. This work quantitatively investigates a noninvasive method for improving the period variation on 4-inch silicon wafers. By temporarily deforming the flexible silicon wafer using a customized concave vacuum chuck [J. Vac. Sci. Technol. B19(6), 2347 (2001)10.1116/1.1421558], we show that the fabricated gratings will have improved period uniformity, with the period variation reduced by 86% at the 1000 nm central grating period setting. This process is a simple and efficient way to achieve linear gratings without altering the LIL configuration with two spherical beams. We present experimental results on the impact of a concave vacuum chuck on the chirp reduction at different grating period settings. Then, we compare two different LIL configurations with different wavelength sources concerning their influence on the efficiency of period variation reduction. Finally, the flatness of the 4-inch silicon wafers due to the temporary bending process is verified using optical profilometry measurements.

Cassava Grating Machines, Designs and Fabrication: A Review of Related Literature

Cassava products produced in Nigeria varies, ranging from one product to another, mostly for direct human consumption after harvesting. This is because the emphasis of the promotion of cassava has been on its use as food. The use of the crop as a basic raw material for industrial purposes would improve industry in Nigeria. Cassava products has been diversified ranging from one product to another, such as the use of cassava in livestock feed, means that more maize and other feed materials used in the past can now be available for other uses such as cassava flour products like glucose for pharmaceuticals, food supplements, alcohol and other beverages. The need for improved method of extracting pulp from cassava for economic purposes made researchers to device improved method of achieving these extractions. However, this particular study describes a detailed review of the literature concerning cassava grating machines, design and fabrication in Nigeria. The methodology used in this study was a secondary data collection approach that involves the review of journal and conference paper articles from past authors, internet sources and materials, newspapers and magazines and so on and so forth. Hence, authors in this research reported that to achieve the call for a good design that assures effectiveness and quality of the processed products. The design was made using Autocad professional software while the fabrication was done using locally sourced materials. Findings from existing studies showed that cassava grating machines has been designed to be mechanically operated and in so doing cassava is fed through the hopper for grinding. Authors in this study also reported that the performance evaluation of cassava grating machines were carried out, giving the average collection efficiency of 93.25% and average grating efficiency of 86.1%. Keywords: Mechanical Advantage: Hopper: Grating Unit: Internal Combustion Engine: Shaft: Machineries: Design Calculation: Literature Review: Nigeria.

A Very Fast Single-Step Process for Optical Microfiber Long Period Gratings Fabrication

Optical microfiber long period gratings (MLPGs) with advantages such as low insertion loss, polarization independence, high resonance dip, and simple configuration are broadly involved in different applications, including fiber optics micro-scale components and sensors. However, it is still a grand challenge to fabricate MLPGs by using current long-time multistep processes. Herein, based on the typical arc-discharge fiber heating and pulling technique, a very fast single-step process for MLPGs fabrication is presented. In this process, the applied fiber heating arc-discharge is functionalized by a series of narrow OFF-pulses to simultaneously modulate the being pulled microfibers. Through the developed one-step technique, a low-loss adiabatic optical microfiber with a periodic array of micro-tapers along its waist region is implemented in less than 100 s, which is much faster than current methods. It is shown that the realized single-step MLPGs with the diameter of 20 μm are characterized by high resonance dip (>27 dB), low transmission loss (≤1.2 ± 0.2 dB), narrow FWHM (<20 nm), and high repeatability. The measured external refractive index (RI) sensitivity and temperature dependency of the gratings are 744 nm/RI-unit and 12 pm/°C, respectively. The results of this study could be of interest for the applications of the MLPGs for miniature fiber optics elements and sensors realization.

Interferometry by a transparent wedge

In this article we show that a single transparent wedge or a plate with a wedge part can be used as a very simple and useful interferometer with numerous applications. This interferometer permits to modulate phase distribution on interference fringes to evaluate quantitatively the parallelism of a light beam and aberration of a wavefront, to specify the spectral line shape in a wide range, to measure the light wavelength and refractive indices of solids and liquids. In addition, it provides suitable beams for holographic study of phase objects and fabrication of diffraction gratings.

Domain dynamics in coercive-field engineered sub-µm periodically poled Rb-doped KTiOPO4

Nonlinear optical interactions involving counter-propagating photons are of great interest for both classical and quantum optical applications. However, their use is sparsely spread due to the fact that they require quasi-phase-matched devices with sub-µm periods. A recent breakthrough has been the fabrication of bulk sub-µm domain gratings in Rb-doped KTiOPO4 by creating a grating of low- and high- coercive field regions in the crystal via periodic ion exchange, so-called coercive-field engineering. Here, we investigate the physical mechanisms behind this method and study the interplay between the ion-exchanged grating properties and the ferroelectric domain dynamics. Furthermore, we investigate the scalability of the method by studying the domain morphology of sub-µm periodically poled crystals with periods ranging from 755 to 433 nm and correlating it to that of the ion-exchanged regions. We show that the formation of sub-µm domain gratings is governed by the depth, shape, and critical ion-concentration of the ion-exchanged volume and that it is independent of the poling period. These findings are crucial for further scaling the coercive field engineering technique to even shorter poling periods and larger aperture periodically poled crystals.

Exploration of a Flexible Metasurface for Strain Sensors: A Perspective from 2D Grating Fabrication to Spectral Characterization

The flexible plasmonic metasurface is a novel optical device consisting of a large number of subwavelength-sized noble metal (gold, silver, etc.) structures arranged in a specific pattern on a flexible substrate. The usual method for a fabricating flexible metasurface is to build nanostructures on rigid substrates and then transfer them to flexible substrates. However, problems such as structural distortion and structural loss can occur during fabrication. To address these issues, this work improved the process to fabricate and characterize a flexible plasma 2D grating–a type of metasurface composed of gold cubelets with a thickness of 50 nm and a side length of 250 nm. First, an electron beam lithography method modified by proximity effect correction was used to fabricate nanostructures on a rigid substrate. Then, the structures were transferred by a chemical functionalization and a sacrificial layer etching method. In addition, the feasibility of using flexible plasmonic 2D gratings as strain sensors was investigated in this work through a stretching test. Experimental results show that electron beam lithography improved by correcting the proximity effect enabled the fabrication of more precisely shaped nanostructures; the chemical functionalization method significantly improved the transfer yield; and the spectroscopic analysis in the stretching test demonstrated the potential of the flexible plasmonic 2D gratings for sensing applications.

Simulation analysis of high-order high-duty-cycle surface gratings.

High-order surface grating distributed feedback lasers are known to operate with a fundamental mode, narrow linewidth, high power, and high slope efficiency. The adoption of high-order surface gratings can avoid epitaxial re-growth necessary for the fabrication of conventional buried gratings, which simplifies the fabrication process and reduces device cost. It is essential for the design and optimization of device structure to clarify the influence of the change of grating structure parameters on grating characteristics (coupling and loss). Based on Lumerical's Mode Solutions and multiple grating samples, we evaluated the coupling and loss coefficients of surface gratings as a function of duty cycle, order, and V-groove topography. As the order increases, the duty cycle corresponding to the peak value of the grating coupling coefficient increases gradually and approaches one. The grating coupling coefficient decreases with increasing order but increases at some specific orders. At high duty cycles, the width of the grating groove corresponding to the peak of the coupling coefficient remains substantially in the range of 100-150 nm, which is close to the length of a quarter-wavelength in the grating groove filling material. Regarding the grating groove morphology, the fabrication difficulty of the V-shaped groove grating is obviously less than that of the rectangular groove grating, but its coupling coefficient is slightly smaller than that of the rectangular shaped groove grating of the same depth. The larger the V-shaped groove width, the smaller the peak coupling coefficient and the corresponding sidewall inclination will be. Losses decrease with increasing duty cycle and decreasing sidewall inclination of the V-groove.

Theoretical study of sub-wavelength gratings fabrication by TM0 mode interference in symmetric metal-cladding dielectric waveguide

Theoretical study of sub-wavelength gratings fabrication by TM0 mode interference in symmetric metal-cladding dielectric waveguide

Design and Fabrication of Silicon-Blazed Gratings for Near-Infrared Scanning Grating Micromirror

Blazed gratings are the critical dispersion elements in spectral analysis instruments, whose performance depends on structural parameters and topography of the grating groove. In this paper, high diffraction efficiency silicon-blazed grating working at 800–2500 nm has been designed and fabricated. By diffraction theory analysis and simulation optimization based on the accurate boundary integral equation method, the blaze angle and grating constant are determined to be 8.8° and 4 μm, respectively. The diffraction efficiency is greater than 33.23% in the spectral range of 800–2500 nm and reach the maximum value of 85.62% at the blaze wavelength of 1180 nm. The effect of platform and fillet on diffraction efficiency is analyzed, and the formation rule and elimination method of the platform are studied. The blazed gratings are fabricated by anisotropic wet etching process using tilted (111) silicon substrate. The platform is minished by controlling etching time and oxidation sharpening process. The fillet radius of the fabricated grating is 50 nm, the blaze angle is 7.4°, and the surface roughness is 0.477 nm. Finally, the blazed grating is integrated in scanning micromirror to form scanning grating micromirror by MEMS fabrication technology, which can realize both optical splitting and scanning. The testing results show that the scanning grating micromirror has high diffraction efficiency in the spectral range of 810–2500 nm for the potential near-infrared spectrometer application.

Bragg grating in a flexible and stretchable coreless polymer optical fiber.

In this Letter, we propose and experimentally demonstrate fiber Bragg grating (FBG) fabrication in a flexible and stretchable coreless polymer optical fiber. The flexible polymer optical fiber is prepared with polydimethylsiloxane (PDMS). Femtosecond laser direct writing and slit beam shaping are used to form periodic grating structures in the fiber. The fabricated FBG exhibits a large strain measurement range and a blueshift response to temperature. Moreover, it offers low humidity sensitivity due to its low permeability toward water vapor. Taking advantage of the unique sensing performances of the PDMS fiber, the proposed FBG has considerable advantages over the traditional silica FBG devices for strain and temperature sensing.

Femtosecond Laser Densification of Hydrogels to Generate Customized Volume Diffractive Gratings.

Inspired by nature’s ability to shape soft biological materials to exhibit a range of optical functionalities, we report femtosecond (fs) laser-induced densification as a new method to generate volume or subsurface diffractive gratings within ordinary hydrogel materials. We characterize the processing range in terms of fs laser power, speed, and penetration depths for achieving densification within poly(ethylene glycol) diacrylate (PEGDA) hydrogel and characterize the associated change in local refractive index (RI). The RI change facilitates the fabrication of custom volume gratings (parallel line, grid, square, and ring gratings) within PEGDA. To demonstrate this method’s broad applicability, fs laser densification was used to generate line gratings within the phenylboronic acid (PBA) hydrogel, which is known to be responsive to changes in pH. In the future, this technique can be used to convert ordinary hydrogels into multicomponent biophotonic systems.

Long-Period Fiber Gratings Coated with Poly(ethylene glycol) as Relative Humidity Sensors

Relative humidity is an important parameter in controlled environments and is typically monitored using low-cost electrochemical sensors with low resolution and accuracy. This kind of sensors cannot not be implemented in harsh or explosive environments (as in pyrotechnic facilities) due to electrical discharges, or in marine structures where the oxidation of the sensing probe materials changes the sensing response). In these cases, fiber optic sensors can provide solutions due to their intrinsic properties, such as immunity to electromagnetic interference and resistance in harsh environments. This work presents preliminary results regarding the steps of the fabrication of Long-Period Fiber Gratings, the coating processes with a thin layer of poly(ethylene glycol) (PEG) and its sensing performance to relative humidity, displaying a from 60 to 100%sensitivity of 0.6 nm/%RH in the range of 80 to 100%RH.

Laser Direct Writing of Silver Clusters‐Based Subwavelength Periodic Structures Embedded in Mid‐Infrared Gallo‐Germanate Glass

The direct laser writing (DLW) using femtosecond lasers allows for the inscription of 3D microstructures embedded inside optical materials. Based solely on the silver ions photochemistry, the DLW in silver‐containing glasses enables to locally induce inside glasses a unique combination of optical properties. The physical modifications of the material encompass not only a refractive index change, but also new physical properties like fluorescence, second‐ and third‐harmonic generations, and surface plasmon resonance. Numerous efforts are deployed to develop the DLW‐assisted silver photochemistry in phosphate glasses. However, this glass family is suffering from its near‐infrared optical cutoff as opposed to the silver‐doped gallo‐germanate glasses. With an extended mid‐infrared (mid‐IR) transmission, these glasses are synthesized via the melt‐quenching technique. Depending on the glass composition, either a glass matrix‐based single track (Type I) or a silver cluster‐based double track (Type A) of refractive index change is produced. By enabling an order of magnitude smaller structures than with Type I, Type A modification is further expanded to embed, for the first time, periodic structures below the inter‐track spacing. Demonstrated with a pitch down to 400 nm, these Type A–based periodic structures bring new insights through the fabrication of 3D diffractive gratings in mid‐IR glasses.

Generation of sub-micrometer surface relief gratings in an azobenzene-containing material using a 355 nm laser

Controlled effective fabrication of surface relief gratings (SRG) of different periods and dimensionality in an azobenzene-containing polyelectrolyte material using an UV-laser operating at 355 nm was demonstrated for the first time. The application of an UV-laser in combination with Lloyd's interferometer allows the accurate control of grating period and the generation of gratings with small period down to 180 nm. The SRG formation is related to the kinetics of the steady state of the trans-cis photoisomerization of a PAZO film at UV exposure. The replication of the manufactured gratings using soft lithography is demonstrated as well.

Envelope modulated x-ray grating interferometry

X-ray dark-field and phase contrast imaging using grating interferometry (GI) have demonstrated great potential for medical and industrial applications. GI relies on the fabrication of high-quality absorption gratings, which has revealed to be quite challenging. This paper proposes an interferometer for dark-field and differential phase contrast imaging using a single phase-shifting element. This proposal simplifies the setup without penalizing the image quality. The proposed interferometer consists of a single dual-period phase grating having two distinct periods, which generates intensity modulation with a period large enough to be resolved directly by the detector. This makes the proposed GI system easily adaptable as there are no stringent alignment requirements. We show the utility of this method for a possible diagnostic task by imaging smoked murine lung samples. The simplicity of the proposed setup compared to a conventional Talbot(-Lau) interferometer suggests that it could be easily and widely used for a variety of applications.

Photodesign and fabrication of surface relief gratings on films of polyimide-based supramolecular systems obtained using host-guest strategy

New supramolecular structures were attained by an original approach based on mixing the concepts of polyamidic acid (PAA) host and an azochromophore guest with hydrogen bonding intermolecular interactions. The materials have been obtained and characterized for use as liquid crystal (LC) alignment layers. The azochromophore was introduced in the PAA solution in different ratio followed by casting on glass plate and thermal treatment to realize a film with imide structure, confirmed by Fourier-transform infrared spectroscopy (FTIR). Thermal analyses indicated that the dye loading in the polymer host slightly reduces the temperature of thermal decomposition from 508 to 466 °C, while glass transition temperature ranges between 244 and 213 °C. UV–Vis data proved that the samples exposure at the wavelengths of 355 nm is beneficial for surface relief gratings (SRGs) formation. Atomic force microscopy (AFM) evidenced the surface structuring of the samples and the changes in the spatial and functional contact area characteristics as a function of azo-dye amount. The attained grating periodicity was about 1 μm, while the depth ranged between 35 and 100 nm depending of the system composition. Surface anisotropy, bearing properties and fluid retention are enhanced upon chromophore incorporation. LCs anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 , which is desirable for LC display applications. • Supramolecular structures, based on a polymer matrix and an azo-dye, are achieved. • Transparent flexible polyimide films with heat resistance up to 466 °C are attained. • As the azo-dye loading increases LASER-made SRGs depth increases from 37 to 81 nm. • Anisotropy, bearing and fluid retention are enhanced upon azo-dye incorporation. • LC anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 .