Diffraction Gratings Research Articles

SIMULTANEOUS COMPENSATION OF SECOND AND THIRD ORDER DISPERSION IN CPA LASER SYSTEMS

This paper presents a theoretical study aimed at solving the problem of compensation for second and third order dispersion in CPA laser systems. We study the propagation of light pulses generated by a Ti-Sapphire master oscillator along the path of a stretcher-amplifiers-compressor. The wave equation and dispersion balance equations are used to analyze various Ti-Sapphire amplifier configurations. The research results include the values of the deviation of the compressor length and the angle of incidence of the light pulse on the input diffraction grating of the compressor. Different versions of amplifiers differ in the number of passes of a light pulse through Ti-Sapphire crystals and in the geometric profile of the crystals. The results obtained are presented in the Table. This research is essential for the development of more efficient CPA laser systems.

Accurate Prediction of Antimicrobial Susceptibility for Point-of-Care Testing of Urine in Less than 90 Minutes via iPRISM Cassettes.

The extensive and improper use of antibiotics has led to a dramatic increase in the frequency of antibiotic resistance among human pathogens, complicating infectious disease treatments. In this work, a method for rapid antimicrobial susceptibility testing (AST) is presented using microstructured silicon diffraction gratings integrated into prototype devices, which enhance bacteria-surface interactions and promote bacterial colonization. The silicon microstructures act also as optical sensors for monitoring bacterial growth upon exposure to antibiotics in a real-time and label-free manner via intensity-based phase-shift reflectometric interference spectroscopic measurements (iPRISM). Rapid AST using clinical isolates of Escherichia coli (E. coli) from urine is established and the assay is applied directly on unprocessed urine samples from urinary tract infection patients. When coupled with a machine learning algorithm trained on clinical samples, the iPRISM AST is able to predict the resistanceor susceptibility of a new clinical sample with an Area Under the Receiver Operating Characteristic curve (AUC) of ∼ 0.85 in 1 h, and AUC > 0.9 in 90 min, when compared to state-of-the-art automated AST methods used in the clinic while being an order of magnitude faster.

Polarization-insensitive EDG demultiplexer combined with a polarization beam splitter.

Polarization dependence is an inherent challenge for wavelength-division multiplexing transceivers on silicon photonic platforms, causing severe problems with polarization-dependent losses and hindering the implementation of monolithic integrated receivers. In this study, we developed a polarization-insensitive demultiplexer on a silicon nitride (Si3N4) platform, which provides a promising solution to the polarization challenge. Comprising an etched diffraction grating (EDG) and a polarization beam splitter (PBS), the demultiplexer can achieve polarization insensitivity by introducing an additional optical path difference for polarization compensation. The fabricated demultiplexers were experimentally measured to have minimum insertion losses of 1.5 dB, cross talks of better than -25 dB, and polarization-dependent losses of better than 0.7 dB. This is the first, to the best of our knowledge, proposed solution for a polarization-insensitive EDG demultiplexer combined with a PBS on a Si3N4 platform.

Optical fiber speckle spectrometer based on reversed-lens smartphone microscope

Smartphones are a potentially powerful platform for scientific instruments. Here, we demonstrate speckle spectroscopy with smartphone-level hardware. This technique promises greater performance thresholds than traditional diffraction gratings. Light is injected into an optical fiber and the emergent speckle patterns are imaged by a reversed-lens smartphone camera. The smartphone then uses an algorithm, running on a mobile computing app, to determine, in less than one second, the (hitherto unknown) input spectrum. We reconstruct a variety of visible-wavelength (470–670 nm) single and multi-peaked spectra using a tunable source. The latter also include a metameric pair, i.e., two spectra that are different, yet represent colors that are indistinguishable to the human eye.

Patterning Complex Line Motifs in Thin Films Using Immersion Controlled Reaction-Diffusion.

The discovery of self-organization principles that enable scalable routes towards complex functional materials has proven to be a persistent challenge. Here reaction-diffusion driven, immersion controlled patterning (R-DIP) is introduced, a self-organization strategy using immersion controlled reaction-diffusion for targeted line patterning in thin films. By modulating immersion speeds, the movement of a reaction-diffusion front over gel films is controlled, which induces precipitation of highly uniform lines at the reaction front. A balance between the immersion speed and diffusion provides both hands-on tunability of the line spacing (d = 10 - 300 µm) as well as error-correction against defects. This immersion-driven patterning strategy is widely applicable, which is demonstrated by producing line patterns of silver/silver oxide nanoparticles, silver chromate, silver dichromate, and lead carbonate. Through combinatorial stacking of different line patterns, hybrid materials with multi-dimensional patterns such as square-, diamond-, rectangle- and triangle-shaped motifs are fabricated. The functionality potential and scalability is demonstrated by producing both wafer-scale diffraction gratings with user-defined features as well as an opto-mechanical sensor based on Moirépatterning. This article is protected by copyright. All rights reserved.

Particle swarm optimizer for the surface plasmon resonance effect on metal gratings.

In this work, the spectral dependence of optimum parameters of the surface plasmon resonance (SPR) effect on metallized sinusoidal diffraction gratings, under normal incidence, was determined using the particle swarm optimization method. The method was chosen due to its simplicity and effectiveness in providing reliable results, relative to direct search or gradient methods. The Rayleigh's hypothesis, which restricts the analysis to the case of shallow gratings, is used to model the diffracted fields across the interface between the sensing medium and metal. A penalty function was applied to avoid the occurrence of singularities and violation of the validity of the Rayleigh hypothesis. Using this procedure, the optimum values of grating periodicity and amplitude that maximized the sensitivity function for gold, silver, copper, and aluminum-metals that yield high quality factor SPR effects-were determined in a wavelength range between 500 and 1600 nm, for both gaseous and aqueous sensing media.

Fabrication and Soft-X-Ray and EUV Range Testing of Au- and Multilayer Mo/Si-Coated Diffraction Gratings with High-Order Blaze

Fabrication and Soft-X-Ray and EUV Range Testing of Au- and Multilayer Mo/Si-Coated Diffraction Gratings with High-Order Blaze

Shaped vibration cutting: A novel fabrication method for mid-infrared relief gratings with controllable profiles

Relief gratings are a particular group of diffractive gratings with a controlled profile, which can precisely modulate the intensity distribution of diffractive lights through its surface structure of depressions and elevations. The mechanical ruling is still one of the most dominant methods for fabricating relief gratings due to its accuracy and capacity to texture free-formed surfaces. However, the ruling has the drawbacks of low material adaptability and inflexible profile adjustability that restrict its wider application. This study invents a novel ruling process, i.e., shaped vibration cutting (SVC), which uses a controllable special-shaped vibration locus of a diamond cutting tool. The tool moves perpendicularly to the cutting plane, enabling the ruling-based fabrication of relief grating on difficult-to-cut materials with flexible control of the grating profile. Slope grooving tests with elliptical and triangular trajectories were performed on aluminum and silicon materials to explore the surface generation and defect formation mechanism comprehensively. The defect-less process window regarding the vibration trajectory, crossfeed, depth of cut, and ruling velocity was identified. Finally, mid-infrared relief gratings were successfully fabricated using the SVC process on aluminum without burrs and silicon in a ductile regime with a maximum depth of 2.3 µm, which outperforms the existing cutting-based texturing technique. To further demonstrate the process capacity of SVC in high material adaptability and flexible profile adjustability, multi-blaze gratings that have spatially varying groove profiles have been fabricated on bulk metallic glass.

A novel method for fabrication of dual-blazed diffraction gratings using mosaicking technique

A novel method for fabrication of dual-blazed diffraction gratings using mosaicking technique

Plasmon-enhanced photostimulated diffusion in a thin-layer Ag–GeSe2 structure

This work studies photostimulated diffusion of silver, enhanced by a plasmon field, into GeSe2 thin films. To ensure the excitation of surface plasmon polaritons (SPP) at the interface between Ag and GeSe2, silver diffraction gratings substrates were used, on which chalcogenide layers were deposited by thermal evaporation in vacuum. The samples were exposed to the p-polarized radiation of a He-Ne laser. The kinetics of photostimulated processes was studied by recording the changes in SPP characteristics with exposure. It has been established that at the initial stage of the photodiffusion process, SPP excitation at the Ag/GeSe2 interface during exposure results in a fourfold increase in the photostimulated flux of silver ions. The concentrations of photodissolved silver in the chalcogenide layer are estimated. The mechanism of photostimulated diffusion of Ag in GeSe2 and its features in such thin-layer structures, as well as a possible mechanism of plasmon-stimulated acceleration of this process, is discussed.

Ultra-compact dual band imaging spectrometer with freeform prisms.

Wide spectrum and miniaturization are the main challenges in the imaging spectrometer design. In this paper, we propose an ultra-compact dual band imaging spectrometer (CDBIS) with cemented freeform prisms, which works at both the visible-near-infrared (VNIR) from 400nm to 1000nm and the shortwave-infrared (SWIR) from 1000nm to 1700nm. The imaging spectrometer is only composed of three cemented prisms, a primary prism and two triangular prisms. And a freeform surface characterized by the Zernike polynomial is introduced in each prism. The CDBIS is dispersed by a diffraction grating, which is designed on the second surface of the primary prism. Based on vector aberration theory (VAT), the relationship among the astigmatism generated by the introduced freeform surfaces, the wavelength, and the field of view is studied. Accordingly, a wideband is realized by introducing the freeform surfaces after the diffraction grating. Furthermore, through optimizing the coefficients of Zernike polynomial terms, residual astigmatism at different wavelengths is well balanced. An imaging spectrometer with a volume of only 100c m 3 is obtained, with a spectral resolution of 1.45nm at VNIR and 2.40nm at SWIR, respectively. It has a huge potential for broadband space exploration.

Advanced low blaze angle x-ray gratings via nanoimprint replication and plasma etch.

We developed a new method of making ultra-low blaze angle diffraction gratings for x-ray applications. The method is based on reduction of the blaze angle of a master grating by nanoimprint replication followed by a plasma etch. A master blazed grating with a relatively large blaze angle is fabricated by anisotropic wet etching of a Si single crystal substrate. The surface of the master grating is replicated by a polymer material on top of a quartz substrate by nanoimprinting. Then a second nanoimprinting is performed using the 1st replica as a mold to replicate the saw-tooth surface into a resist layer on top of a Si grating substrate. A reactive ion etch is used to transfer the grating grooves into the Si substrate. The plasma etch provides reduction of the groove depth by a factor defined by the ratio of the etch rates for the resist and Si. We demonstrate reduction of the blaze angle of a master grating by a factor of 5 during fabrication of a 200 lines/mm blazed grating with a blaze angle of 0.2°. We investigated the quality and performance of the fabricated low blaze angle gratings and evaluate process accuracy and reproducibility. The new blaze angle reduction method preserves the planarity of the optical surface of the grating substrate and at the same time provides improvement in the grating groove quality during the reduction process.

Interference, diffraction, and diode effects in superconducting array based on bismuth antimony telluride topological insulator

It is well-known in optics that the spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in Young’s famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator film Bi0.8Sb1.2Te3. In the limit of an extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Therefore, such arrays can be used as sensitive absolute magnetic field sensors. A key finding is that the device acts as a superconducting diode, controlled by magnetic field.

The Talbot effect in oblique observation of a diffraction pattern

Speaking about the oblique Talbot effect, one usually assumes the case when the diffraction grating is illuminated by a plane wave at an angle, while the screen for observing the diffraction pattern is located parallel to the plane of the diffraction grating. At the same time, as the presented consideration shows, if the grating is illuminated at an angle, then in order to observe the Talbot effect, the observation screen must be tilted as well. In the present work, we considered the inclined Talbot effect for a grating with a finite number of slits, when the observation of the diffraction pattern and the illumination of the grating are performed at an angle. The dependence of the Talbot length on the angles of observation and illumination is determined. It is shown that the effect of self-reproduction can be observed only at certain values of these angles. It is proved that the value of the Talbot length does not depend on the parity of the number of lattice slits. At the same time, the number of slits determines the character of the distribution of maximums on the screen. Thus, in the case of a diffraction grating with an even number of slits, a maximum is observed in the center of the screen. In the case of a grating with an odd number of slits, the pattern of maximums is shifted by half the period of the grating compared to the pattern of maximums in the case of gratings with an even number of slits.

Light Out‐Coupling Enhancement of Blue Quantum‐Dot Light‐Emitting Diodes with Internal Diffraction Wrinkle Pattern

Highly efficient blue quantum‐dot light‐emitting diodes (QLEDs) are still a challenge for displays and solid‐state lighting due to light trapping in a device. Herein, an internal diffraction wrinkle pattern is used to demonstrate a spectrum‐independent enhancement strategy for light out‐coupling. The optimized device with wrinkle pattern shows a peak external quantum efficiency of 15.25% and a maximum luminance of 13 134 cd m−2, and the enhancement of those is 23% and 28%, respectively. The improvement of device performance can be attributed to the extraction of waveguide light by the internal wrinkle pattern used as a diffraction grating. Moreover, simulation also shows that wrinkle pattern is an attractive option to improve the performances of blue QLEDs.

UV Photonic-Integrated-Circuits-Based Structured Illumination Microscopy With a Field of View Larger than $100\,\mu \text{m}^{2}$

Photonic integrated circuits (PICs) are expected to add practicality and new functionalities in a considerable number of optical applications, including optical microscopy. Here, we present a PIC design allowing a far-field structured UV illumination pattern with a fringe period as low as 370 nm, a fringe visibility of 0.83 over field of views of more than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$150\,\mu m\times 200\,\mu m$</tex-math></inline-formula> and a radiant intensity as large as 0.49 mW. The circuits include single mode waveguides with propagation losses of 3 dB/cm at a wavelength <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda =360\,nm$</tex-math></inline-formula> , two diffraction gratings for beam shaping out of the chip plane, a beam splitter and a phase shifter. Using fluorescent gratings with pitches longer or shorter than the wavelength, as control objects, and a collecting lens with a numerical aperture of 0.5, the current PICs enable to highlight experimentally the Moiré pattern at the heart of the optical resolution enhancement and to achieve a doubling of the optical resolution in the direction of the illumination.

Geometric Phase Flat Optical Gratings with High Diffraction Angle Based on Dual‐Frequency Nematic Liquid Crystal

AbstractDiffractive optical elements (DOEs) are increasingly used as lightweight and compact solutions in photonic devices. Steering of light and manipulation of the polarization can be efficiently obtained with the help of photo‐aligned liquid crystal (LC) devices. 1D LC diffraction gratings are studied that are based on the geometric phase principle and demonstrate that the optical functionality can be substantially broadened by using dual frequency LC. Switching between a highly efficient diffractive and a transmissive state is obtained by adjusting the frequency of the applied electric field. Compared to commonly studied 1D nematic LC diffraction gratings, the steering efficiency over large diffraction angles is strongly increased. By using an appropriate electric‐field treatment, the efficiency for first‐order diffraction of red light over an angle of 12.6° increases from 60% to 90%. Moreover, additional switching phenomena are observed at intermediate voltage treatments, leading to enhanced tunability of the DOEs. The origin of this behavior is explained with the help of finite element Q‐tensor simulations for the director configuration.

Towards Two-Photon Polymerization-Compatible Diffractive Optics for Micro-Mechanical Applications.

Diffractive optics are structured optical surfaces that manipulate light based on the principles of interference and diffraction. By carefully designing the diffractive optical elements, the amplitude, phase, direction, and polarization of the transmitted and reflected light can be controlled. It is well-known that the propagation of light through diffractive optics is sensitive to changes in their structural parameters. In this study, a numerical analysis is conducted to evaluate the capabilities of slanted-wire diffraction gratings to function opto-mechanically in the infrared spectral range. The slanted wire array is designed such that it is compatible with fabrication by two-photon polymerization, a direct laser-writing approach. The modeled optical and mechanical capabilities of the diffraction grating are presented. The numerical results demonstrate a high sensitivity of the diffracted light to changes in the slant angle of the wires. The compressive force by which desired slant angles may be achieved as a function of the number of wires in the grating is investigated. The ability to fabricate the presented design using two-photon polymerization is supported by the development of a prototype. The results of this study suggest that slanted-wire gratings fabricated using two-photon polymerization may be effective in applications such as tunable beam splitting and micro-mechanical sensing.

Surface-acoustic-wave-driven graphene plasmonic sensor for fingerprinting ultrathin biolayers down to the monolayer limit

Surface plasmon polaritons in graphene can enhance the performance of mid-infrared spectroscopy, which is key for the study of both the composition and the conformation of organic molecules via their vibrational resonances. In this paper, a plasmonic biosensor using a graphene-based van der Waals heterostructure on a piezoelectric substrate is theoretically demonstrated, where far-field light is coupled to surface plasmon-phonon polaritons (SPPPs) through a surface acoustic wave (SAW). The SAW creates an electrically-controlled virtual diffraction grating, suppressing the need for patterning the 2D materials, that limits the polariton lifetime, and enabling differential measurement schemes, which increase the signal-to-noise ratio and allow a quick commutation between reference and sample signals. A transfer matrix method has been used for simulating the SPPPs propagating in the system, which are electrically tuned to interact with the vibrational resonances of the analytes. Furthermore, the analysis of the sensor response with a coupled oscillators model has proven its capability of fingerprinting ultrathin biolayers, even when the interaction is too weak to induce a Fano interference pattern, with a sensitivity down to the monolayer limit, as tested with a protein bilayer or a peptide monolayer. The proposed device paves the way for the development of advanced SAW-assisted lab-on-chip systems combining the existing SAW-mediated physical sensing and microfluidic functionalities with the chemical fingerprinting capability of this novel SAW-driven plasmonic approach.

Wavefront measurements using the Ronchi test for high-NA lithography projection lenses.

The Ronchi test is widely used for wavefront measurements in advanced lithography tools, and a physical optics explanation of the Ronchi test based on scalar diffraction theory can be found in numerous publications. However, for high-numerical aperture (high-NA) lithography projection lenses, the vector nature of light should be considered when performing wavefront measurements, especially the effect of polarization aberrations on the wavefront test results. In this paper, a vector model for describing shearing interferometry for high-NA lithography projection lenses is established. In addition to considering the vector nature of light, the vector model also calculates the Ronchigram on the screen of a detector at any distance from a diffraction grating, as opposed to the distance restriction for the Fraunhofer diffraction approximation used by the existing methods. Using the developed mathematical model of the Ronchi test, the Ronchigrams of high-NA lithography projection lenses under non-polarized illumination are simulated, and the effect of the distance between the diffraction grating and the detection screen on the wavefront measurement accuracy are discussed.