Diffractive Optical Components Research Articles

Decoupling of Phase and Amplitude Channels with a Terahertz Metasurface Toward High‐Security Image Hiding

AbstractSteganography technology which conceals a message in a carrier to make it invisible is critical for information security. Conventional optical image steganography using diffractive optical components or spatial light modulators suffers from less encoding channel and bulky volume. The emergence of multifunctional metasurface that can manipulate abundant physical dimensions of optical fields allows the multi‐channel image steganography in a compact volume. Here, the image hiding in a metasurface is demonstrated by modulating the amplitude, phase, and polarization states of terahertz (THz) waves completely. Especially, the phase channel can decouple from the amplitude channel based on a Fresnel‐diffraction‐based algorithm. By directly measuring the phase distribution using the homemade THz focal plane imaging system, the number of transmission channels can expand from N to 2N. As a proof of concept, it is shown that the secret images can encode in the phase channel and subsequently extract by using different keys, such as polarization states, detection distances, and its combinations. Moreover, different hiding strategies with different attacker behaviors are also demonstrated. The decoupling of the phase and amplitude channels with a single metasurface may open an avenue toward innovative optoelectronic devices for optical image steganography, data storage, and terahertz communication.

Numerical study of feature-distribution effects foranti-reflection structured surfaces on binary gratings.

Suppressing Fresnel reflections from dielectric boundaries using periodic and random antireflection structured surfaces (ARSSs) has been vigorously studied as an alternative to thin film coatings for high-power laser applications. A starting point in the design of ARSS profiles is effective medium theory (EMT), approximating the ARSS layer with a thin film of a specific effective permittivity, which has features with subwavelength transverse-scale dimensions, independent of their relative mutual positions or distributions. Using rigorous coupled-wave analysis, we studied the effects of various pseudo-random deterministic transverse feature distributions of ARSS on diffractive surfaces, analyzing the combined performance of the quarter-wave height nanoscale features, superimposed on a binary 50% duty cycle grating. Various distribution designs were investigated at 633nm wavelength for TE and TM polarization states at normal incidence, comparable to EMT fill fractions for a fused silica substrate in air. The results show differences in performance between ARSS transverse feature distributions, exhibiting better overall performance for subwavelength and near-wavelength scaled unit cell periodicities with short auto-correlation lengths, in comparison to equivalent effective permittivity designs that have less complicated profiles. We conclude that structured layers of quarter-wavelength depth and specific feature distributions can outperform conventional periodic subwavelength gratings as antireflection treatments on diffractive optical components.

Chiral liquid crystal based holographic reflective lens for spectral detection.

Flat optics based on chiral liquid crystal (CLC) can be achieved using holographic polarization recording with the help of a photoalignment technique to vary the orientation of the optical axis in a thin CLC layer. A variety of reflective diffractive optical components with high efficiency and polarization selectivity can be realized employing this technique. In this work we discuss the use of CLC diffractive lenses in a spectrometer. The functionalities of two mirrors and a linear grating used in a traditional spectrometer are combined into a single holographic CLC component. Circularly polarized light entering through the slit can be reflected and projected onto a linear detector by the CLC component, with over 90% efficiency. This excellent optical functionality can be achieved with a micrometer thin CLC layer, offering the opportunity for device integration.

Spatially microstructured topology of chalcogenide glasses by a combination of the electrothermal process and selective etching for functional infrared media

Chalcogenide glasses exhibit a wide transparency domain spanning from near infrared (IR) to mid-IR and thus, have become highly attractive optical materials in a range of applications. Controlling the topology of these glasses can be seen as a key aspect for the design of optical elements such as gratings, metasurfaces, waveguides, and other diverse refractive and diffractive optical components. Here, we demonstrate the structuring of large, millimeter square areas that have been structured at the micrometer scale employing an easy two-step process, incorporating a micro-poling step followed by immersion in an amine solvent. Ge-Sb-S-Na glasses have been investigated, and the influence of the sulphur and sodium content on the pre- and post-poling material dissolution response has been discussed. Three compositions of varying sulphur and sodium content were selected to study the influence of thermal poling using either a homogeneous or a structured electrode. It was found that either a large difference in dissolution rates of poled and unmodified regions or a large poled layer thickness leads to the generation of significant topological contrast. The origin of the poled region’s selective etching has been explained on the basis of a poling-induced density decrease. Finally, it was demonstrated that when the targeted resolution is micrometric, this rather easy process could be employed as an alternative to classical lithography techniques.

Refractive-diffractive hybrid optics array: comparative analysis of simulation and experiments

Hybrid optical elements, which combine refractive and diffractive optical components to enhance optical performance by taking advantage of the optical characteristics of the individual components, have enormous potential for next-generation optical devices. However, there have not been many reports on the simulation methodology to characterize such hybrid optical systems. Here, we present a method for simulating a hybrid optical element realized by attaching an ultra-thin, flexible diffractive optics array onto a refractive optical element. The ultra-thin diffractive optical element is fabricated by direct-laser-writing using a femtosecond pulsed laser as the light source. A systematic investigation of the proposed simulation method, which does not require extensive hardware resources or computational time, but retains resolution and accuracy, is presented. The proposed scheme is validated by comparing simulation and experimental results. The simulation and experimental results on the spot size and focal length for the diffractive Fresnel zone plate (FZP) match well, with typical errors of less than 6%. The aspect ratio of the focal spot sizes at the compound and FZP focal planes of the hybrid optical system from the simulation and experiment also match quite well, with typical errors below 7%. This simulation scheme will expedite the designs for novel hybrid optical systems with optimal optical performances for specific applications, such as microfluidics and aberration-controlled optics.

3D Switchable Diffractive Optical Elements Fabricated with Two‐Photon Polymerization

AbstractDirect laser writing is demonstrated by two‐photon polymerization of multi‐element diffractive optical components that can be switched on and off with an applied voltage. By exploiting the 3D capabilities of the laser microfabrication technique, multiple diffractive optical elements are written into a single liquid crystal (LC) layer. The switching behavior of the diffractive optical elements is controlled by simply changing the write‐voltage of the anisotropic polymer structures during fabrication. Initially, 2D diffraction gratings are written at different depths within the LC layer. Each element is then activated by applying a voltage of sufficient amplitude that causes the second diffractive optical element to become inactive. This is then followed by a demonstration of multi‐element computer generated holograms that are written at different depths within the LC layer. By altering the magnitude of the applied voltage, different images/patterns can be observed in the replay field using a simple electrode configuration. These compact and transmissive LC optical components could excel in applications where a degree of switchability is required but a highly pixelated fully programmable device is excessive.

A Study on Focused Ion Beam (FIB) Milling Machining and Fabrication Technology of Nano-Scale Diamond Tool for Machining Fine-Patterns in a Free-Form Surfaces.

Recently, the technology of the industry has been increasing for diffractive optical elements, holograms, optical components, and next-generation display components. The advanced high value-added industry is designing fine patterns on ultra-precision optical components and applying them to various industries. In the case of the ultra-fine pattern, a contact-type machining technique is required because it requires a precise pattern in nano-scale units. In this paper, the fabrication technology of ultra-precision diamond which is essential in the ultra-precision processing technology was suggested. The material used in the experiment was a single-crystal diamond tool (SCD), and the equipment for machining the SCD used a focused ion beam (FEI COMPANY, system Nova 600) equipment. The back fire method was applied without metal coating in order to carry out the process study and the focused beam of 30 keV Ga+ ions were carried out processing for various fabrication of diamond cutting tools. As a result of applying the backfire method through the process experiment, the cutting edge width of the ultra-precision diamond tool was verified 275 nm.

Roadmap of Terahertz Imaging 2021.

In this roadmap article, we have focused on the most recent advances in terahertz (THz) imaging with particular attention paid to the optimization and miniaturization of the THz imaging systems. Such systems entail enhanced functionality, reduced power consumption, and increased convenience, thus being geared toward the implementation of THz imaging systems in real operational conditions. The article will touch upon the advanced solid-state-based THz imaging systems, including room temperature THz sensors and arrays, as well as their on-chip integration with diffractive THz optical components. We will cover the current-state of compact room temperature THz emission sources, both optolectronic and electrically driven; particular emphasis is attributed to the beam-forming role in THz imaging, THz holography and spatial filtering, THz nano-imaging, and computational imaging. A number of advanced THz techniques, such as light-field THz imaging, homodyne spectroscopy, and phase sensitive spectrometry, THz modulated continuous wave imaging, room temperature THz frequency combs, and passive THz imaging, as well as the use of artificial intelligence in THz data processing and optics development, will be reviewed. This roadmap presents a structured snapshot of current advances in THz imaging as of 2021 and provides an opinion on contemporary scientific and technological challenges in this field, as well as extrapolations of possible further evolution in THz imaging.

Josephson Cantilevers for THz Microscopy of Additive Manufactured Diffractive Optical Components

Josephson junctions can be employed as sensors to determine frequency and power of microwave and terahertz (THz) radiation. A Josephson cantilever carries at least one Josephson junction with an antenna structure to be sensitive for THz radiation. In our THz microscope, this cantilever is mounted on a 15 × 15 × 15 mm 3 positioning system in vacuum and is cooled by a cryocooler to operating temperatures between 30 and 85 K. Current-voltage characteristics are measured at every spatial position. The frequency and power of THz radiation are derived from the electrical characteristics for every spatial point and three-dimensional visualizations of the power distribution are evaluated. The THz microscope represents a versatile measuring instrument to characterize many different microwave and THz circuits and components. In this paper, Josephson cantilevers from YBa 2 Cu 3 O 7 on LaAlO 3 bicrystal substrates are employed to characterize additive manufactured diffraction gratings. The diffraction patterns of the gratings are measured and visualized with a far-infrared laser system at a frequency of 762 GHz. The obtained results are matching with calculations from a theoretical model. The presented method is capable of supporting fast prototyping processes for THz components by analyzing diffraction patterns three dimensionally.

Influence of ambient temperature on the modulation transfer function of an infrared membrane diffraction optical system.

In this paper, we present a model that analyzes the influence of the temperature on the modulation transfer function (MTF) of an infrared membrane diffraction optical system. Based on the physical imaging mechanism of diffractive optical systems, the imaging characteristics of the diffraction optical system are characterized by using diffraction efficiency. Then we establish the corresponding calculation model and MTF analysis model based on scalar diffraction theory. In particular, considering the material properties of flexible membrane optical elements and thermal environment effect, the Zernike polynomials are used to establish the thickness distribution model of the membrane diffractive optical components combined with the finite element analysis. After that, we modify the MTF calculation model of diffraction optical system and accordingly propose the model of the infrared membrane diffraction optical system. Finally, we present some experimental results for a 2-m infrared membrane diffraction optical system. The results show that when the temperature is -40°C and wavelength band is 80nm at the center field of view, the diffraction efficiency is reduced to 81%, and MTF at 75 lp/mm is reduced to 0.12. And when the temperature is -40°C at edge field of view, the efficiency at center wavelength is reduced to 71%, and MTF at 75 lp/mm is reduced to 0.02. The established model and method can be used to estimate the imaging performance of a space infrared membrane diffractive telescope and provide theoretical guidance for the processing algorithm and imaging system design.

Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials.

We propose rewritable full-color computer-generated holograms (CGHs) based on color-selective diffraction using the diffractive optical component with the resonant characteristic. The structure includes an ultrathin layer of phase-change material Ge2Sb2Te5 (GST) on which a spatial binary pattern of amorphous and crystalline states can be recorded. The CGH patterns can be easily erased and rewritten by the pulsed ultraviolet laser writing technique owing to the thermally reconfigurable characteristic of GST. We experimentally demonstrate that the fabricated CGH, having a fine pixel pitch of 2 μm and a size of 32.8 × 32.8 mm2, reconstructs the three-dimensional holographic images. In addition, the feasibility of the rewritable property is verified by erasing and rewriting part of the CGH.

Correction: Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials.

Correction for 'Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials' by Chi-Young Hwang et al., Nanoscale, 2018, DOI: 10.1039/c8nr04471f.

Effect of X-ray irradiation on the optical properties of nanostructured thin films TCVA based on structural analysis

Nanocrystalline thin films of 4-tricyanovinyl-N,N-diethylaniline (TCVA) were prepared by the thermal evaporation method. TCVA thin films were irradiated by X-ray radiation at room temperature with different absorbed doses up to 2500 Gy. The structural properties of TCVA pre and post irradiation have been investigated using Fourier-transform infrared and X-ray diffraction. Spectrophotometric measurements were utilized to study the optical transmittance and optical reflectance for TCVA, pre and post irradiation and consequently optical parameters were calculated. At 850 nm, the refractive index of TCVA thin films increases by approximately 16% when the dose increases from 0 to 2500 Gy. It is found that a slight modification in the energy band gap occurred while a significant change appeared in the refractive index. These results are useful for the manufacture of diffractive optical components or integrated optical parts.

The concentration of energy from Edge Lasers by Diffractive Optical Component

The aim of this paper is to design a diffractive optical element based on the laser junction numerical model. We assumed a ?long? laser junction emitting quasi-monochromatic, spatially incoherent light that corresponds to the high power laser. Diffractive optics approach can be used due to the narrowband illumination. The especially designed numerical junction model was experimentally verified. Then a numerically designed diffractive focusing element was manufactured and tested in the experimental setup. This paper includes theoretical investigations, numerical modeling as well as experimental data. Full Text: PDF ReferencesE. Wolf, "New theory of partial coherence in the space?frequency domain. Part I: spectra and cross spectra of steady-state sources", J. Opt. Soc. Am. 72, 343 (1982). CrossRef E. Wolf, "Coherence theory of laser resonator modes", J. Opt. Soc. Am. A 1, 541 (1984). CrossRef A. Naqwi and F. Durst, "Focusing of diode laser beams: a simple mathematical model", Appl. Opt. 29, 1780 (1990) CrossRef J. Yang, T. Chen, G. Ding and X. Yuan, "Focusing of diode laser beams: a partially coherent Lorentz model", Proc. SPIE 6824, 68240A (2007); CrossRef X. Zeng and A. Naqwi, "Far-field distribution of double-heterostructure diode laser beams", Appl. Opt. 32, 4491 (1993). CrossRef Y. Li and J. Katz, "Nonparaxial analysis of the far-field radiation patterns of double-heterostructure lasers", Appl. Opt. 35, 1442 (1996). CrossRef X. Zeng, Z. Feng, and Y. An, "Far-field expression of a high-power laser diode", Appl. Opt. 43, 5168 (2004) CrossRef J. Tervo, J. Turunen, P. Vahimaa, and F. Wyrowski, "Shifted-elementary-mode representation for partially coherent vectorial fields", J. Opt. Soc. Am. A 27, 2004 (2010). CrossRef J. Turunen, "Elementary-field representations in partially coherent optics", J. Mod. Opt. 58, 509 (2011). CrossRef H. Partanen, J. Tervo, and J. Turunen, "Spatial coherence of broad-area laser diodes", Appl. Opt. 52, 3221 (2013) CrossRef M. Sypek, "Light propagation in the Fresnel region. New numerical approach", Opt. Commun., 116, 43 (1995) CrossRef Z. Jaroszewicz, A. Kolodziejczyk, M. Sypek, C. Gomez-Reino, "Non-paraxial analytical solution for the generation of focal curves", J. Mod. Opt., 43, 617 (1996) CrossRef M. Sypek, C. Prokopowicz, M. Gorecki, "Image multiplying and high-frequency oscillations effects in the Fresnel region light propagation simulation", Opt. Eng., 42, 3158 (2003) CrossRef C. Prokopowicz, "Numerical calculation of light propagation in off-axis region", Proc. SPIE, 5484, 482 (2004). CrossRef A. Sobczyk, Z. Jaroszewicz, A. Kolodziejczyk, A. Kowalik, Cz. Prokopowicz, M. Sypek, "Nonparaxial anamorphic diffractive lenses", J. Opt., 15, 025702 (1-5) (2013) CrossRef

Optical probing of long-range spatial correlation and symmetry in complex biophotonic architectures on transparent insect wings

We experimentally probe the structural organization of complex bio-photonic architecture on transparent insect wings by a simple, non-invasive, real-time optical technique. A stable and reproducible far-field diffraction pattern in transmission was observed using collimated cw and broadband fs laser pulses. A quantitative analysis of the observed diffraction pattern unveiled long-range quasi-periodic order in the arrangement of the microstructures over mm scale. These observations agree well with the Fourier analysis of SEM images of the wing taken at various length scales. We propose a simple quantitative model based on optical diffraction by an array of non overlapping microstructures with minimal disorder which supports our experimental observations. We observed a rotation of the original diffraction profile by scanning the laser beam across the wing sample which gives direct signature of organizational symmetry in microstructure arrangements at various length scales. In addition, we report the first optical detection of reorganization in the photonic architecture on the Drosophila wings by various genetic mutations. These results have potential for the design and development of diffractive optical components for applied photonics and may open up new opportunities in biomimetic device research.

Broadband and Efficient Diffraction

Surface topography dictates the deterministic functionality of diffraction by a surface. In order to maximize the efficiency with which a diffractive optical component, such as a grating or a diffractive lens, directs light into a chosen order of diffraction, it is necessary that it be "blazed". The efficiency of most diffractive optical components reported so far varies with the wavelength, and blazing is achieved only at a specific nominal energy, the blaze wavelength. The existence of spurious light in undesirable orders represents a severe limitation that prevents using diffractive components in broadband systems. Here we experimentally demonstrate that broadband blazing over almost one octave can be achieved by combining advanced optical design strategies and artificial dielectric materials that offer dispersion chromatism much stronger than those of conventional bulk materials. The possibility of maintaining an efficient funneling of the energy into a specific order over a broad spectral range may empower advanced research to achieve greater control over the propagation of light, leading to more compact, efficient and versatile optical components.

Optical Manipulation with Plasmonic Beam Shaping Antenna Structures

Near-field optical trapping of objects using plasmonic antenna structures has recently attracted great attention. However, metal nanostructures also provide a compact platform for general wavefront engineering of intermediate and far-field beams. Here, we analyze optical forces generated by plasmonic beam shaping antenna structures and show that they can be used for general optical manipulation such as guiding of a dielectric particle along a linear or curved trajectory. This removes the need for bulky diffractive optical components and facilitates the integration of optical force manipulation into a highly functional, compact system.

A polychromatic approach to far-field superlensing at visible wavelengths

Breaking the diffraction barrier in the visible part of the electromagnetic spectrum is of fundamental importance. Far-field subwavelength focusing of light could, for instance, drastically broaden the possibilities available in nanolithography, light-matter interactions and sensing at the nanoscale. Similarly, imaging with a nanometric resolution could result in incredible breakthroughs in soft matter and biology. There have been numerous proposals in this regard based on metamaterials, structured illumination methods or diffractive optical components. The common denominator of all these approaches resides in their monochromatic nature. Here we show that using polychromatic light in dispersive metamaterials allows us to circumvent many limitations associated with previous monochromatic approaches. We design a plasmonic metalens based on metallic nanorods that, when used with broadband light fields, can beat the diffraction limit for imaging and focusing from the far field.

Integrating Diffractive Optomechatronic System Models in Modelica-based Simulation Environments

AbstractThe performances of optomechatronic systems are generally characterized by optical imaging phenomena and the proper operation is fundamentally affected by changes of the relative geometry caused by thermal influences, mechanical displacements and vibrations. Extrinsic and intrinsic disturbances can be compensated by active control of optical elements like lenses, diffraction gratings or laser sources. In the context of system design and performance analysis tasks it is big challenge to model and simulate the coupled optomechatronic behavior including closed-loop control and disturbances properly on a representative level. A promising approach is the integration of diffractive optics models in the well established physical object oriented modeling environment Modelica®, which offers already a broad support of multi-domain libraries, e.g. electrical, mechanical and thermal. The current paper describes the basic modeling requirements for diffractive optical components and discusses the solution for a computationally efficient implementation of two-dimensional spatial optical interfaces and components for Modelica-based simulation environments. The basic diffractive optical functionality in Modelica is shown by simulation results of a basic Fourier system and a MEMS Micro Mirror Array.

Fabrication of transmission phase gratings on porous anodic alumina

The transmission phase grating on anodic alumina membrane (AAM) was fabricated by a lithography and chemical etching method to demonstrate the feasibility of fabricating diffractive optical elements on AAM matrix. The monochromatic light diffraction property of the sample grating was tested using lasers with wavelengths of 532 and 650 nm, respectively. The measured diffraction efficiencies of zeroth and first orders were in good agreement with the calculated results. This method may offer an approach to prepare surface pattern on alumina and could be used in fabricating diffractive optical components such as linear gratings.