Grating Lines Research Articles

Facile fabrication of high-resolution extreme ultraviolet interference lithography grating masks using footing strategy during electron beam writing

The authors demonstrate a method for facile fabrication of transmission grating masks used in extreme ultraviolet interference lithography (EUV-IL) based on a footing strategy during electron beam writing of mask gratings. By modifying the electron beam lithography pattern and dose distribution, a thin footing is generated between the mask grating lines. This thin footing layer effectively prohibits subsequent metal deposition using a standard electroplating setup in the grating region, while outside the grating region metal is electrodeposited freely, absorbing EUV radiation and serving as an EUV-IL mask grating central photon stop layer. The strategy the authors present greatly simplifies the mask fabrication process and increases the yield, as the crucial central stop region can be fabricated directly and without further overlay exposure steps either using electron beam or photolithography.

2N Period submicron grating at the inner wall of a metal cylinder

The aim of the present contribution is to set up and demonstrate the chain of processes leading to the Ni-master of a circular cylinder having an integer number of long grating lines of submicron period at its wall. Microelectronics 2D microstructuring technologies were adapted in order to print a photoresist integer period number on a glass cylinder flank by the projection of a radial planar phase-mask grating. The next step is the galvanic growth of nickel on the photoresist corrugation. Subsequently, the manufacturing of cylindrical gratings will be enabled by an injection moulding process.

A Novel Structured Light Pattern for One-Shot Shape Acquisition

This paper proposes a new one-shot grayscale structured lighting scheme to obtain depth data fast. Its key idea is to code the pattern using modulated sinusoidal gratings along two axes. The features used for matching are the fringe central lines of the vertical grating. The correlation of the intensity profiles is used to measure the similarity of features. Experimental results using a vision system with two cameras and a projector show that the proposed scheme is effective and efficient.

Projection angle dependence in grating-based X-ray dark-field imaging of ordered structures

Over the recent years X-ray differential phase-contrast imaging was developed for the hard X-ray regime as produced from laboratory X-ray sources. The technique uses a grating-based Talbot-Lau interferometer and was shown to yield image contrast gain, which makes it very interesting to the fields of medical imaging and non-destructive testing, respectively. In addition to X-ray attenuation contrast, the differential phase-contrast and dark-field images provide different structural information about a specimen. For the dark-field even at length scales much smaller than the spatial resolution of the imaging system. Physical interpretation of the dark-field information as present in radiographic and tomographic (CT) images requires a detailed look onto the geometric orientation between specimen and the setup. During phase-stepping the drop in intensity modulation, due to local scattering effects within the specimen is reproduced in the dark-field signal. This signal shows strong dependencies on micro-porosity and micro-fibers if these are numerous enough in the object. Since a grating-interferometer using a common unidirectional line grating is sensitive to X-ray scattering in one plane only, the dark-field image is influenced by the fiber orientations with respect to the grating bars, which can be exploited to obtain anisotropic structural information. With this contribution, we attempt to extend existing models for 2D projections to 3D data by analyzing dark-field contrast tomography of anisotropically structured materials such as carbon fiber reinforced carbon (CFRC).

Fabrication and Characterization of Low-Threshold Polarization-Stable VCSELs for Cs-Based Miniaturized Atomic Clocks

Vertical-cavity surface-emitting lasers (VCSELs) with single-mode, single-polarization emission at a wavelength of 894.6 nm have been fabricated for Cs-based atomic clock applications. For polarization control, monolithically integrated surface gratings are employed. Simulated and experimental results show that the longitudinal position of the surface grating has a significant influence on the threshold current. With a grating in the topmost in-phase layer, the threshold currents are reduced to 40% compared to earlier atomic clock grating VCSELs with inverted structure. The output polarization is parallel to the grating lines with a peak-to-peak difference between the dominant and the suppressed polarization modes of 25 dB even at substrate temperatures up to 80 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. Small-signal modulation characteristics of grating VCSELs are presented. The modulation bandwidth exceeds the required 5 GHz at a bias current of only 0.9 mA above threshold at room temperature. A revised chip design with smaller mesa size and thinner passivation layer has been implemented. The VCSELs show similar electrical parasitic bandwidths but require fewer fabrication steps and hence have reduced processing complexity. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factors of less than 0.4 ns corresponding to a maximum 3-dB bandwidth exceeding 25 GHz are obtained at 80 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C ambient temperature.

An image domain approach to the interpretation of the visible moiré phenomenon

An approach to the interpretation of the visible moiré phenomenon in the image domain has been proposed. The analysis of the Fourier series expansion presents an initial criterion for distinguishing the real moiré and pseudo-moiré cases. A geometric calculation of the superposed grating lines is utilized to obtain the parameters for describing the real and pseudo-moiré cases. On the basis of the study, the average intensities of the waveforms of the real moiré and pseudo-moiré cases are calculated in order to provide the interpretation. It indicates that different moiré cases result from the garbled discernment of human eyes, which is introduced by the microstructure versus macrostructure effects. The variations of intensity and average intensity in the microstructure result in the confusion of the average intensities of the real moiré and pseudo-moiré waveforms. The interpretation is significant for the visible real and pseudo-moiré effects, both in the multiplicative superposition and in the additive superposition composed from periodic cosinusoidal gratings and binary gratings in the image domain. The approach also considers the coexistence of the real moiré and pseudo-moiré cases. The rule for their coexistence has been summarized in the image domain.

Роздільна здатність і призматична дія мікропризмових елементів Френеля

Розглянуто методи вимірювання гостроти зору та роздільної здатності тестових таблиць в офтальмології та фізиці. Створено експериментальний стенд для вимірювання роздільної здатності зображень з використанням штрихових мір. Досліджено залежність роздільної здатності зображень, що формуються за допомогою мікропризмових елементів Френеля, від величини призматичної діїтаких елементів. Запропоновано алгоритм визначення гостроти зору за роздільною здатністю тестових зображень.

Record high-aspect-ratio GaAs nano-grating lines grown by Hydride Vapor Phase Epitaxy (HVPE)

Nanometric-width GaAs grating lines showing high aspect (height/width) ratio of up to 30, without roughness or shape deviation are reported. They were obtained by HVPE, capitalizing on the near-equilibrium nature of this epitaxial technique. HVPE rapid decomposition of GaCl growth precursors leads to immediate reactivity of the growth reaction to an increase or decrease of the supersaturation of the vapor phase. HVPE growth is also governed by surface kinetics: the morphologies are controlled by the intrinsic growth anisotropy of the crystals. By manipulating surface kinetics and exploiting the fast reactivity of the system, it is demonstrated that HVPE allows to benefit from an enhanced growth anisotropy favoring vertical growth of nanometer-scale grating lines. Unique high-aspect ratios are obtained in one-step short growth time (20min), capitalizing upon the main advantage of the bottom-up approach: the structures are defined by their crystalline properties with no scattering defects as typically introduced by techniques involving dry etching. The role of surface kinetics and mass transport at the nanometer scale is discussed.

Miniaturization of optical spectroscopes into Fresnel microspectrometers

Miniaturized optical instruments have become very important in industry as smart phones and tablet PCs increase in popularity. A chronology of spectrometer development shows that a simple numerical point of view affords important insights. A tiny spectrometer, which is smaller than a few millimeters size, cannot easily rely on the conventional Fraunhofer diffraction due to its optical criterion limit. As an alternate solution to build smaller spectrometers, a Fresnel spectrometer chip with a gradient line grating is attractive. The fabricated Fresnel spectrometers have optical path volumes of about 1 mm3 and spectral resolutions of 10 to 23 nm.

Increased space-bandwidth product in pixel super-resolved lensfree on-chip microscopy

Pixel-size limitation of lensfree on-chip microscopy can be circumvented by utilizing pixel-super-resolution techniques to synthesize a smaller effective pixel, improving the resolution. Here we report that by using the two-dimensional pixel-function of an image sensor-array as an input to lensfree image reconstruction, pixel-super-resolution can improve the numerical aperture of the reconstructed image by ~3 fold compared to a raw lensfree image. This improvement was confirmed using two different sensor-arrays that significantly vary in their pixel-sizes, circuit architectures and digital/optical readout mechanisms, empirically pointing to roughly the same space-bandwidth improvement factor regardless of the sensor-array employed in our set-up. Furthermore, such a pixel-count increase also renders our on-chip microscope into a Giga-pixel imager, where an effective pixel count of ~1.6–2.5 billion can be obtained with different sensors. Finally, using an ultra-violet light-emitting-diode, this platform resolves 225 nm grating lines and can be useful for wide-field on-chip imaging of nano-scale objects, e.g., multi-walled-carbon-nanotubes.

Perfect Chirped Echelle Grating Wavelength Multiplexor: Design and Optimization

A new method for designing an echelle-type diffraction grating for wavelength division multiplexing (WDM), which is tuned to a single stigmatic point, is introduced. The new grating is defined by the mode and wavelength of operation in a slab waveguide, the position of the waveguides, the order of diffraction, and an arbitrary path, which is called the grating line, upon which individual facets are positioned, blazed, and curved via the outlined algorithm. A systematic design process for echelle gratings (EGs) is presented, covering all the key aspects of this device. A series of rules to improve the performance of any EG WDM device is outlined. A simulated comparison between this device, a standard Rowland grating, and a two stigmatic point grating, was undertaken with the new design performing better and comparably in each case, respectively.

Effect of Text Type on Near Work–Induced Contrast Adaptation in Myopic and Emmetropic Young Adults

Contrast adaptation has been speculated to be an error signal for emmetropization. Myopic children exhibit higher contrast adaptation than emmetropic children. This study aimed to determine whether contrast adaptation varies with the type of text viewed by emmetropic and myopic young adults. Baseline contrast sensitivity was determined in 25 emmetropic and 25 spectacle-corrected myopic young adults for 0.5, 1.2, 2.7, 4.4, and 6.2 cycles per degree (cpd) horizontal sine wave gratings. The adults spent periods looking at a 6.2 cpd high-contrast horizontal grating and reading lines of English and Chinese text (these texts comprised 1.2 cpd row and 6 cpd stroke frequencies). The effects of these near tasks on contrast sensitivity were determined, with decreases in sensitivity indicating contrast adaptation. Contrast adaptation was affected by the near task (F2,672 = 43.0; P < 0.001). Adaptation was greater for the grating task (0.13 ± 0.17 log unit, averaged across all frequencies) than reading tasks, but there was no significant difference between the two reading tasks (English 0.05 ± 0.13 log unit versus Chinese 0.04 ± 0.13 log unit). The myopic group showed significantly greater adaptation (by 0.04, 0.04, and 0.05 log units for English, Chinese, and grating tasks, respectively) than the emmetropic group (F1,48 = 5.0; P = 0.03). In young adults, reading Chinese text induced similar contrast adaptation as reading English text. Myopes exhibited greater contrast adaptation than emmetropes. Contrast adaptation, independent of text type, might be associated with myopia development.

Effect of substrate overetching and heat treatment of titanium oxide waveguide gratings and thin films on their optical properties

We investigate subwavelength titanium oxide (TiO2) resonance waveguide gratings (RWGs) and TiO2 thin films of thicknesses ~200 nm fabricated by atomic layer deposition (ALD), in both amorphous and crystalline phases on fused silica substrates. The TiO2 RWGs are fabricated by electron beam lithography, reactive ion etching, and ALD. The thin films and RWGs are characterized structurally by x-ray diffraction and scanning electron microscopy. The optical characterization of RWGs and optical constants of TiO2 films are studied by an ellipsometer. RWGs are designed for TE and TM modes in such a way that an overetch effect of the fused silica substrate can be investigated. Various RWG samples are prepared by gradually increasing the overetch depth and subsequently measuring the performance of the RWGs. A close agreement between the calculated and experimentally measured resonance wavelength spectral shifts is obtained; however, the magnitudes of the measured shifts are greater than calculated ones. A parallel study related to the measurement of the refractive indices and remeasuring the optical shifts of RWGs is carried out after a heat treatment of all the samples under study. The RWGs do not reveal significant spectral changes after the heat treatment; this is primarily due to a change in the surface chemistry by the redeposition of the reaction byproducts on the grating lines.

Holistic Method for Evaluating Large Area Transparent Conducting Electrodes

Nowadays, specifying the quality of a transparent conducting electrode (TCE) using a figure of merit (FoM) is considered nearly mandatory. However, not much attention is paid to the local variations in the FoM itself across the large area of the TCE. This calls for the definition of a local FoM (LFoM), particularly relevant with regard to several new generation TCEs which have been and are being proposed recently. A LFoM based on local measurements of transmission and sheet resistance, pixel by pixel, would be a Herculean task. The present article addresses this central issue by defining a LFoM based on the diffraction efficiency (DE) of a calibrated high-resolution transmission grating overlaid with a given TCE. The DE value, which critically depends on the periodic nature of the grating material, is shown to be highly sensitive to the various nonuniformities in the TCE overlaid on the grating, with length scales comparable to the grating period. The effectiveness of the so-defined LFoM was demonstrated using a pointer laser and a photodiode in combination with a transmission grating with ∼μm periodicity by taking ITO/glass and ITO/PET as case examples. A metal grating pattern of Cu deposited on seed Pd grating lines was fabricated as an example of new generation TCE and examined for FoM and LFoM, however, without the aid of the external grating. The LFoM based on DE presented here should serve as an excellent screening method for both conventional and emerging TCEs.

机械刻划光栅的刻线弯曲与位置误差对平面光栅性能影响及其修正方法

机械刻划光栅的刻线弯曲与位置误差对平面光栅性能影响及其修正方法

Power‐scaling properties of apertured microchip vertical external‐cavity surface‐emitting lasers

Presented is the power-scaling characteristics of microchip vertical external-cavity surface-emitting lasers which include grating apertures for mode selection. Multi-Watt multi-lateral-mode emission at a wavelength of 1060 nm is obtained with sub-linear increase in maximum output power with aperture-size. It is also shown that the polarisation is only set by the grating lines for high-order modes which interact sufficiently with the grating.

Femtosecond laser damage of broadband pulse compression gratings

The fabricated gratings used for an 800-nm compressed laser pulse have more than 90% diffraction efficiency in the -1st order for TE polarization within 760-860 nm, and the maximum value is 94.3%. The laserinduced damage threshold (LIDT) of the gratings increases from 0.53 to 0.75 J/cm2 in the normal beam in a pulse width \tau of 40-100 fs. The LIDT of the gratings is observed a \tau^{0.25} scaling in the pulse width region. The damage morphologies of the gratings indicate that the initial damage of the gratings locates at the grating lines, a position that coincides with that of the electric field maximum.

Reversible Full‐Color Generation with Patterned Yellow Electrochromic Polymers

A different light: The yellow electrochromic copolymer, propylenedioxythiophene phenylene P(ProDOT-Ph) is patterned by the micromolding in capillaries (MIMIC) process to fabricate line gratings. Under illumination by white light, colors are generated by diffraction and can be changed by applying an external voltage (see picture). The diffracted color is blue shifted by electrochemical doping, a process that is completely reversible.

Formation of surface relief grating in polymers with pendant azobenzene chromophores as studied by AFM/UFM

We studied peculiarities of the structural reconstruction within holographically recorded gratings on the surface of several different amorphous azobenzene-containing polymers. Under illumination with a light interference pattern, two processes take place in this type of polymer. The first process is the light-induced orientation of azobenzene units perpendicular to the polarization plane of the incident light. The second one is a transfer of macromolecules along the grating vector (i.e. perpendicular to the grating lines). These two processes result in the creation of a volume orientation grating (alternating regions of different direction or degree of molecular orientation) and a surface relief grating (SRG)—i.e. modulation of film thickness. One can assume that both orientation of molecules and their movement might change the local mechanical properties of the material. Therefore, formation of the SRG is expected to result also in modulation of the local stiffness of the polymer film. To reveal and investigate these stiffness changes within the grating, spin-coated polymer films were prepared and the gratings were recorded on them in two different ways: with an orthogonal circular or orthogonal linear polarization of two recording light beams. A combination of atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) techniques was applied for SRG development monitoring. We demonstrate that formation of the phase gratings depends on the chemical structure of polymers being used, polymer film thickness, and recording parameters, with the height of grating structures (depth of modulation) increasing with both the exposure time and the film thickness. UFM images suggest that the slopes of the topographic peaks in the phase gratings exhibit an increased stiffness with respect to the grating depressions.

Solving the inverse grating problem by white light interference Fourier scatterometry

Scatterometry is a well-established, fast and precise optical metrology method used for the characterization of sub-lambda periodic features. The Fourier scatterometry method, by analyzing the Fourier plane, makes it possible to collect the angle-resolved diffraction spectrum without any mechanical scanning. To improve the depth sensitivity of this method, we combine it with white light interferometry. We show the exemplary application of the method on a silicon line grating. To characterize the sub-lambda features of the grating structures, we apply a model-based reconstruction approach by comparing simulated and measured spectra. All simulations are based on the rigorous coupled-wave analysis method. Combining white light interferometry with Fourier scatterometry provides an optical metrology tool for characterizing subwavelength structures. Valeriano Ferreras Paz and co-workers from Stuttgart University in Germany have experimentally shown that this approach is capable of accurately measuring the profile of a silicon line grating, which has a height of around 75 nm, a critical dimension of 200 nm and a pitch of 400 nm. The technique uses a CCD camera to image interfering pupil images that are generated by mixing white light travelling down a reference arm with white light that has illuminated a sample. The profile of the sample is reconstructed by comparing the measured and simulated pupil images for each position of a scanned mirror in the reference arm until the best match is found.