Phase Gratings Research Articles

Multi-value phase grating fabrication using direct laser writing for generating a two-dimensional focal spot array

As a beam splitter, multi-value phase grating (MVPG) has a higher diffraction efficiency than the traditional Damman grating (DG) due to its increased number of phase values within one period of the grating. In this paper, two MVPGs are numerically designed within a 120 μm × 120 μm area, which generate 4 * 4 and 5 * 5 focal spot arrays in the far field. Both gratings are fabricated by direct laser writing (DLW) technology. Their diffraction efficiencies reach 68.58% and 63.4%, respectively. To compare, DGs with the same size and focal spot arrays are designed and fabricated, whose diffraction efficiencies are tested to be 29.55% and 35.04%, respectively. The results demonstrate the better optical properties of multi-value phase gratings and the capability of DLW in three-dimensional nano-scale diffractive optical element fabrication.

Optimal Design of Surface Relief Grating for High‐Resolution Two‐Photon Interference Lithography

AbstractTwo‐photon interference lithography with an elastomeric phase grating that allows spontaneous conformal contact to the photoresist can be used to fabricate practical‐scale, 3D photonic crystals through a single exposure. In principle, the unit cell symmetry and fill factor of the 3D periodic nanostructures produced using this technique are strongly depend on the structural parameters of the phase grating. However, theoretical approaches to derive the optimal parameters of the phase grating for realizing high‐definition 3D nanostructures are still lacking. Here, the change in the Talbot interference pattern is systematically predicted with the relief height of the phase grating under the conditions in which two‐photon interference lithography is performed through optical simulations. The collective set of results reveals the design error of the relief height of the phase grating, as inferred by the scalar approximation thus far, and presents the optimal condition that satisfies the π‐phase shift inferred by the full‐vectorial numerical solution.

High resolution 2D beam steerer made from cascaded 1D liquid crystal phase gratings

Optical beam steering (BS) has multiple applications in fields like target seeking and tracking, optical tweezers, billboard displays and many others. In this work, a two-dimensional beam deflector based on blaze gratings is presented. Phase-only 1D blaze gratings have been prepared using maskless Direct Laser Writing (DLW) resulting in high-resolution structures in indium-tin oxide (ITO) coated glass wafers. The device is composed of two identical 1D liquid crystal (LC) cells cascaded orthogonally back-to-back, with a resultant active area of 1.1 × 1.1 mm2. The 1D cells have been prepared with 144 pixels each with a 7.5 µm pitch. The total 288 pixels are driven by a custom made 12-bit Pulse Width Modulation (PWM) electronic driver, allowing for an arbitrarily high resolution. The system performance is documented, and the efficiency of the system has been tested. A maximum diagonal steering angle of ± 3.42° was achieved.

Broadband terahertz multi-beam splitters with uniform power distribution based on coding metasurfaces

High efficiency, uniform power distribution, and broadband working of beam splitters are of crucial importance for large format heterodyne array receivers at terahertz frequencies. We present two types of quad-beam splitters (QBSs) based on coding metamaterials, designed to generate 1 × 4 and 2 × 2 beams respectively in the THz range. The designed metasurfaces are composed of a periodic array of metal-dielectric-metal (MDM) scattering unit cells, thus introducing a well-designed phase shift in the electromagnetic wave. For normally incident electromagnetic waves, the simulation results show that the 2 × 2 QBS has higher power efficiency and broader bandwidth in comparison with the 1 × 4 QBS. The 2 × 2 QBS works well in that the power efficiency is larger than 70% and the power distribution difference of the main beams is less than 2.8% in the range of 0.75–1.35 THz, which indicates an ultra-broad frequency range up to 57.1%. Meanwhile, under oblique incidence, the power distribution and the power efficiency among the 2 × 2 quad-beam nearly remain stable when the wave incident is within 40-degree. A prototype is fabricated and the 2 × 2 QBS behavior is experimentally demonstrated at 0.85 THz, where the power efficiency is as high as 70.4% and the power distribution of each beam approximately is uniform under the 20-degree incidence. To further improve the efficiency of astronomical observations, a 36-beam splitter is designed by using a simple two-dimensional addition method, and the power efficiency can reach 89.9% at 0.85 THz, and the working bandwidth is 57.1% from 0.75 to 1.35 THz with evenly distributed main beams. The simulation results show that the beam splitting function can also be well realized under the waves with 20-degree oblique incidence. Compared to conventional Fourier phase gratings, the metasurface-based beam splitters provide broadband performance and a simpler fabrication process, which is very expected in compact heterodyne array receiver systems.

X-ray phase contrast imaging model: application on tomography with a single 2D phase grating

In this paper, we propose a model dedicated to X-ray phase contrast imaging, which is well adapted to the characterization or inspection of low attenuating samples. We introduce a hybrid approach that combines a ray-tracing step with a wave propagation computation. The mathematical basis of our model is described and we present a comparison of the model to experimental results, for the case of an optical fiber sample, in the framework of a free-propagation phase technique. The extension to the 3D imaging is proposed on simulated data using a grating based technique or more precisely, a multilateral shearing interferometry. This technique uses a single 2D phase grating, which has the advantage of a simpler experimental setup and can be coupled with a standard micro-focus X-ray tube and a high-resolution detector. Our phase model was implemented on the CIVA CT simulation platform and used to generate easily different sets of projection data for any type of sample. While the method for 3D reconstruction has the same basis as the classical CT, we focus mainly on the intermediate processing steps, which are required for the phase retrieval and present the results for a phantom composed of spherical objects in different materials.

Diffraction gratings for spectral devices [Review

Subject of study. This review is intended to acquaint the reader with various types of diffraction gratings and technologies for fabricating them. Method. An information search on the topic, systematization, and analysis are performed. Main results. This paper briefly discusses the areas of application and classification of spectral devices and shows the variety of problems that can be solved by means of spectral devices and that impose various requirements on diffraction gratings. It lists the main characteristics of diffraction gratings used in spectral devices and specifies the stages of their improvement. It discusses classical reflective diffraction gratings—plane (profiled and laminar) and concave. It describes the principles involved in obtaining holographic diffraction gratings and their advantages over ruled ones. It devotes special attention to concave holographic gratings with aberration correction, shows how they are classified, and briefly describes methods of optimizing the parameters of gratings that operate in monochromator systems with simple rotation and flat-field spectrographs with correction of defocusing, astigmatism, and meridional coma, as well as various methods of recording gratings in nonhomocentric beams to expand their correction possibilities. Ruled analogs of holographic gratings are used in a number of cases. It is pointed out that foreign and Russian firms that batch-produce diffraction gratings of the types described here completely satisfy the requirements of the batch-producers of spectral devices. The features of using volume phase gratings in spectral devices are considered, and it is pointed out that, even though these gratings are distinguished by high efficiency, their angular and spectral selectivity have inhibited these gratings from being widely applied in spectral devices. However, there have been active studies in recent years on expanding the regions in which volume phase gratings are used: new system solutions, recording materials, and recording methods have been proposed. Trends to create diffraction elements that combine various functions (cross gratings and grisms) are pointed out. New technologies are proposed for fabricating diffraction gratings: ruled gratings—pendulum-type ruling engines, gratings that reflect with high diffraction efficiency in an expanded wavelength range—“efficiency-achromatization” or double-blaze technologies and volume phase gratings—ultrafast laser inscription and profiled diffraction gratings that operate in the x-ray region—electron-beam lithography, to miniature spectral devices—microelectronic mechanical systems technology used in electronics, composites—concepts of a composite volume phase diffraction grating recorded by integrating several elementary fields. The Conclusion evaluates the modern level and points out development trends. Practical significance. The material presented here can be useful in the development of spectral apparatus.

Impact of compression grating phase modulations on beam over-intensities and downstream optics on PETAL facility

Chirped pulse amplification has been widely implemented in high power laser chains. It consists of a set of diffraction gratings used to stretch and compress short laser pulses. In the case of high power laser chains, the compression stage is followed by the transport mirror in order to carry the laser beam to its final target. In such laser chains, laser beams propagate over a complex set of optical components and understanding the propagation of phase noise turns out to be of crucial importance. Phase modulation can induce laser damage on the final optical components. Here, we study the impact of phase modulation induced by the different diffraction gratings of the Petawatt Aquitaine Laser (PETAL) compressor on the downstream over-intensities, in particular on the transport mirror. This work allows us to quantify the impact of phase modulation for every single grating element in the compression stage, and to estimate the quantity of laser induced damage sites on transport optics for a specific laser shot.

Azimuthal controlling of electromagnetically induced phase grating in five-level quantum systems

In this paper, we suggest a theoretical model for creating a two-dimensional (2D) electromagnetically induced phase grating in a five-level quantum system interacting with a weak probe light, two coupling standing light in the x and y directions and a Laguerre–Gaussian (LG) field. By derivation of the Maxwell’s wave equation, we obtain the dynamic response of the probe light in the quantum system. Then, we perform the analytical solution of the probe susceptibility for obtaining the linear and nonlinear properties of the medium. By numerical calculations, we discuss the amplitude and phase modulations and Fraunhofer diffraction patterns of the probe light in different parametric conditions. We show that by adjusting the orbital angular momentum (OAM) of the LG light a 2D grating is observed. Moreover, we find that the probe energy can be transferred from zero order to high order of direction when we change the OAM number of LG light. Our proposed model may have potential applications in fundamental research and quantum information processing based on OAM light in quantum systems.

Electrically tunable metasurface by using InAs in a metal–insulator–metal configuration

Abstract The ability of modulating optical properties at a lateral subwavelength scale is of crucial importance due to its potential applications for wide-angle holographic displays, optical communications, and interferometric sensors. Here, we present an electrically tunable metasurface whose optical properties can be element-wise controlled at the lateral subwavelength scale in the mid-infrared wavelength regime. Our proposed device facilitates an n-doped InAs layer as a dynamic-tunable layer, and the charge carrier concentration inside the InAs layer is tailored by external gate biases. This InAs active layer is sandwiched between top aluminum strip antennas and a bottom gold substrate, forming the metal–insulator–metal configuration. The change of the charge carrier concentration gives rise to modulation of the amplitude and phase of reflected light in a mid-infrared regime. Numerical investigations show the reflectivity contrast of 44%P with biases of −2.5–0 V and the phase change of 236° with biases of −15 V to +15 V at the wavelength of ∼5 μm. Versatile wavefront shaping such as beam focusing with Fresnel Zone plate and beam steering with saw-tooth phase grating is also provided.

Spontaneous emission induced grating in a Rydberg quantum system

In this paper, we study the electromagnetically induced grating via spontaneous emission induced coherence (SIC) in a four-level quantum system consisting of a Rydberg state. The quantum system interacts with a weak probe light and a strong coupling light with standing wave pattern. We find that under presence of SIC, the amplitude and phase modulations of the medium can be controlled when we tune the detuning of the coupling light. Here, we realize that by tuning the amplitude and phase modulations of the medium, the energy of probe light can be transferred from zero order to high order of grating, respectively. In this case, the switching from amplitude grating to phase grating is possible when we adapt the optical parameters of the medium. Our proposed model may have potential applications in quantum information processing.

A method for spatio-temporal characterization of pulse beams with an all-optical image sensor

A method for analyzing the spatio-temporal intensity distribution of pulse beams, such as photons, electrons and other particles, with an all-optical image sensor has been developed. The image sensor measures the photon or particle intensity by probing the induced refractive index change due to their excitation in the semiconductor. In order to prove this scheme, the interaction of the electron beam with the image sensor has been simulated, indicating that the transient phase grating can be created in the semiconductor. The transient phase grating can be probed with a laser to evaluate the spatio-temporal intensity distribution of the incident electrons. In addition, an InP-based image sensor has been established for analyzing pulse laser beams. A pump-probe technique has been utilized to record images with varying delays between the analyzed and probe lasers and a differential method has been developed to improve the temporal resolution to be less than the duration time of probe lasers. Sequential images, representing the spatio-temporal distribution of the analyzed laser beams with several hundreds of picoseconds temporal resolution, have been obtained, indicating the ability of this scheme for analyzing the spatio-temporal distribution of pulse laser beams and paving the way for promising applications in characterization of pulse particle beams.

Study of Phase Grating Induced by Spontaneous Coherence in Different Three-Level Systems

Study of Phase Grating Induced by Spontaneous Coherence in Different Three-Level Systems

Design Method of Phase Grating Mark in Resonance Domain

Design Method of Phase Grating Mark in Resonance Domain

Quadriwave Lateral Shearing Interferometry Quantitative Phase Imaging Based on 2D Ronchi Phase Grating

Quadriwave Lateral Shearing Interferometry Quantitative Phase Imaging Based on 2D Ronchi Phase Grating

Tunable laser induced periodic surface structures in Ge2Sb2Te5 thin films

Planar photonic structures, such as gratings and metasurfaces, are routinely used for beam steering, waveguide coupling, and light localization. However, conventional fabrication techniques that involve lithography are demanding in terms of time and cost. Much cheaper and simpler methods for surface patterning and formation of periodic surface structures are enabled by direct laser processing. Here, we demonstrate low-cost rapid fabrication of high-quality phase gratings based on the formation of laser induced periodic surface structures (LIPSS, or ripples) in Ge2Sb2Te5 (GST) thin films. Due to unique phase change properties of GST, the structures demonstrate strong modulation of refractive index with period controlled by the wavelength of laser irradiation. We study the formation of phase change LIPSS in a broad range of excitation wavelengths and observe transition between regimes with different orientations of generated ripples with respect to laser polarization.

Simple method to evaluate the pixel crosstalk caused by fringing field effect in liquid-crystal spatial light modulators

In this work we provide a simple experimental method to measure and evaluate the pixel crosstalk in phase-only liquid-crystal displays caused by the fringing field effect. The technique is a reverse engineering method that does not require information about the microscopic physical parameters of the liquid-crystal material or details of the fabrication and electronics of the display. Instead, it is based on the overall effect on the diffraction efficiency of displayed binary phase gratings as a function of the addressed gray level. We show how the efficiency of the zero (DC) and first diffraction orders provides valuable information enough to identify and quantify the pixel crosstalk. The technique is demonstrated with a modern phase-only liquid-crystal on silicon (LCOS) spatial light modulator (SLM), illustrating the limitations that this effect imposes to the spatial resolution of the device and providing quantitative measurement of the impact on the diffraction efficiency.

Analysis of period and visibility of dual phase grating interferometer

Dual phase grating interferometer may simultaneously achieve large field of view and high x-ray dose efficiency. Here, we develop a simple theoretical method to better understand the imaging process of the dual phase grating interferometer. The derivation process of fringe period and the optimal visibility conditions of the dual phase grating interferometer are given in detail. Then, we theoretically prove that the fringe period and optimal visibility conditions of the dual phase grating interferometer include that of the Talbot interferometer. By comparing our experimental results with those of other researchers, we find that when the positions of phase gratings are far away from the positions where the fringe visibility is optimal, the fringe period of the dual π-phase grating interferometer is twice the theoretical results under the illumination of polychromatic x-ray. This conclusion may explain the contradictory research results of dual phase grating interferometer among different researchers.

Laser induced tunable Ge2Sb2Te5 phase-change gratings

Periodic photonic nano- and microstructures are routinely used for light manipulation at the nanoscale. However, their fabrication process is demanding in terms of time, cost and facilities. Here we demonstrate a rapid laser-assisted method for fabrication of gratings in Ge2Sb2Te5 (GST) thin films, based on the formation of laser induced periodic surface structures (LIPSS). LIPSS formation mechanisms dependent on the wavelength of the operating laser, lead to high flexibility of the process, producing gratings with tunable period and orientation with respect to the initial laser polarization. The phase-change properties of GST, on the other hand, allows to fabricate phase gratings with strong modulation of refractive index, which are rewritable in nature.

Machine Learning Framework Combining Radial Phase Grating and Channel Information-Assisted Underwater Wireless Optical OAM Communications

In this letter, an enhanced machine learning (ML) framework combining radial phase grating (RPG) and channel information has been proposed for underwater wireless optical orbital angular momentum (OAM) communications. The optical irradiance profile and diffraction pattern are simulated by the combination of split-step angular-spectrum propagation and Monte Carlo methods, then they were embedded by the convolution and fully connected layers. The transfer learning-based ML architectures are trained by the image features and the embedding channel information with fine-tuning. The impacts of oceanic turbulence, seawater types, and transmission distance are considered. Results show that the transfer learning-based OAM detectors could achieve the order-of-magnitude gain in the bit error rate. Besides, the proposed ML framework could combine with a variety of state-of-the-art methods and thus improve the system performance. This work indicates transfer learning-based ML frameworks have great potential in ML-based OAM communication systems.

Spectral, Morphological and Dynamical Analysis of a Holographic Grating Recorded in a Photo-Mobile Composite Polymer Mixture.

We report on the morphological, spectral and dynamical characterization of one-dimensional transmission holographic volume phase gratings, whose refractive index contrast and nanometric pitch are dynamically controlled by an incident laser light. The grating is obtained by the photo-polymerization of a recently developed photo-mobile holographic composite polymer material. The observed changes in the refractive index contrast and grating pitch strongly suggest that the reversible all-optical real-time modulation of the obtained diffraction efficiency is induced by nano-fluidics.