The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

Resonant waveguide gratings (RWGs), also known as guided mode resonant (GMR) gratings or waveguide-mode resonant gratings, are dielectric structures where these resonant diffractive elements benefit from lateral leaky guided modes from UV to microwave frequencies in many different configurations. A broad range of optical effects are obtained using RWGs such as waveguide coupling, filtering, focusing, field enhancement and nonlinear effects, magneto-optical Kerr effect, or electromagnetically induced transparency. Thanks to their high degree of optical tunability (wavelength, phase, polarization, intensity) and the variety of fabrication processes and materials available, RWGs have been implemented in a broad scope of applications in research and industry: refractive index and fluorescence biosensors, solar cells and photodetectors, signal processing, polarizers and wave plates, spectrometers, active tunable filters, mirrors for lasers and optical security features. The aim of this review is to discuss the latest developments in the field including numerical modeling, manufacturing, the physics, and applications of RWGs. Scientists and engineers interested in using RWGs for their application will also find links to the standard tools and references in modeling and fabrication according to their needs.

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Recent Advances in Resonant Waveguide Gratings

Interferometric hologram evaluation and real-time vibration analysis of diffuse objects

Dynamic color tuning is a very important and fascinating direction in the field of structural colorations due to its possible applications in stealth, anticounterfeiting, displaying techniques, etc. However, the most recent work about structural colors either have limitations on dynamic frequency tunability or require special conditions. In this work, a tensile substrate (e.g., polydimethylsiloxane) is introduced into conventional plasmonic structures to demonstrate dynamic tunable structural colors. The proposed idea is experimentally realized by fabricating samples via interference photolithography. The results show that resonance-induced colors can be dynamically tuned from green to fuchsia by stretching the tensile substrate. Moreover, a further thematic analysis of the physical mechanism in the proposed structure is conducted. The authors envisage that their method has potential applications in anticounterfeiting, biometric sensors, and mechanics measurements. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Actively Tunable Structural Color Rendering with Tensile Substrate

Inspired by natural photonic structures (Morpho butterfly, for instance), researchers have demonstrated varying artificial color display devices using different designs. Photonic-crystal/plasmonic color filters have drawn increasing attention most recently. In this review article, we show the developing trend of artificial structural color pixels from photonic crystals to plasmonic nanostructures. Such devices normally utilize the distinctive optical features of photonic/plasmon resonance, resulting in high compatibility with current display and imaging technologies. Moreover, dynamical color filtering devices are highly desirable because tunable optical components are critical for developing new optical platforms which can be integrated or combined with other existing imaging and display techniques. Thus, extensive promising potential applications have been triggered and enabled including more abundant functionalities in integrated optics and nanophotonics.

https://www.mdpi.com/1996-1944/10/8/944/pdf

Artificial Structural Color Pixels: A Review

We design and fabricate efficient, narrow-band, transmission color filters whose operating principle resides in a narrow-band guided-mode resonance associated with a surface-plasmon resonance. The fundamental device consists of an aluminum grating over a 200-nm-thick aluminum oxide film on a glass substrate. Numerical simulations show a sharp resonance-derived spectral profile that is additionally shaped by a neighboring Rayleigh anomaly. Besides the Rayleigh effect, we show numerically that the narrow bandwidth is predominantly due to the low refractive-index contrast between the waveguide film and the substrate. Red, green, and blue filters are fabricated using ultraviolet holographic lithography followed by a lift-off process. The experimental spectral efficiency in transmission exceeds 80% with full-width-at-half-maximum linewidths near 20 nm. We provide color images of the zero-order transmitted spectra, and illustrate the pure colors associated with the modal resonance extracted as side-coupled output light.

Efficient band-pass color filters enabled by resonant modes and plasmons near the Rayleigh anomaly

The invention of holography by D. Gabor, followed by the works of E. Leith and Upatnieks, made possible to perform nearly arbitrarily wavefront transformations with the aid of optical microstructures fabricated by interference (Gabor, 1948; Leith & Upatnieks, 1962; Denisyuk, 1962; Benton, 1969). The realization by A. Lohmann and co-workers in the mid1960’s that optical holograms can be simulated by digitally generated binary transparencies was another significant step forward in the path towards widespread application of diffraction in optics (Lohmann, 1956; Brown & Lohmann 1966; Lohmann & Paris, 1967). This new approach was called digital holography, or equivalently computer-generated holography. The computer-generated hologram (CGH) is distinguished primarily from its optical cousin by the fact that the computer is able to design a hologram of a non-existent, synthetic or virtual object, and the operation of the diffractive optical element (DOE) can be optimized mathematically rather than experimentally (Turunen & Wyrowski, 1997). This is clear from the words of Professor Lohmann himself, commenting on the shift from classic holography to digital holography (Lohmann, 2008): “we considered images as information, and we applied notions about carriers from communications and information theory [...]. In other words, our approach represented a paradigm shift from physical optics to optical information processing. “ Since the operation of CGH is based on the diffraction of light, this field is also called diffractive optics. Its essence is the control of optical fields by microstructured media (Turunen & Wyrowski, 1997). The DOE is an optical device whose superficial microrelief has a height comparable to the light wavelength used. The DOE may be implemented in the form of a transparency or a reflecting mirror. Throughout this text the terms computer-generated holograms (CGH), diffractive optical element (DOE), or simply hologram are employed with no distinction among each other.

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Digital Holography: Computer-Generated Holograms and Diffractive Optics in Scalar Diffraction Domain

The standard charging process for polymer ferroelectrets, e.g., from polypropylene foams or layered film systems involves the application of high DC fields either to metal electrodes or via a corona discharge. In this often-used process, the DC field triggers the internal breakdown and limits the final charge densities inside the ferroelectret cavities and, thus, the final polarization. Here, an AC + DC charging procedure is proposed and demonstrated in which a high-voltage high-frequency (HV-HF) wave train is applied together with a DC poling voltage. Thus, the internal dielectric-barrier discharges in the ferroelectret cavities are induced by the HV-HF wave train, while the final charge and polarization level is controlled separately through the applied DC voltage. In the new process, the frequency and the amplitude of the HV-HF wave train must be kept within critical boundaries that are closely related to the characteristics of the respective ferroelectrets. The charging method has been tested and investigated on a fluoropolymer-film system with a single well-defined cylindrical cavity. It is found that the internal electrical polarization of the cavity can be easily controlled and increases linearly with the applied DC voltage up to the breakdown voltage of the cavity. In the standard charging method, however, the DC voltage would have to be chosen above the respective breakdown voltage. With the new method, control of the HV-HF wave-train duration prevents a plasma-induced deterioration of the polymer surfaces inside the cavities. It is observed that the frequency of the HV-HF wave train during ferroelectret charging and the temperature applied during poling of ferroelectrics serve an analogous purpose. The analogy and the similarities between the proposed ferroelectret charging method and the poling of ferroelectric materials or dipole electrets at elevated temperatures with subsequent cooling under field are discussed.

Alternating current-generated plasma discharges for the controlled direct current charging of ferroelectrets

Spatial light modulators perform the modulation of wavefront so that the desired light distribution is acquired. They work by diffraction, according to the Huygens-Fresnel principle, and for that they are called Diffractive Optical Elements (DOEs). The focus of this work is the study of light modulators through Scalar Diffraction Theory. The initial objective was to execute the calculation of spatial light modulators through the implementation of the so-called Iterative Fourier Transform Algorithm. The calculation of three phase holograms is made: analog phase, 4 level phase and binary phase. The results are evaluated by calculating the diffraction efficiency and by signal to noise ratio. To verify the calculation, binary holograms were fabricated using photographic film in a simple and low cost way. Simulated and optical reconstructions are presented, showing the viability for the use of the algorithm in the coding of DOEs. Next, the resonance frequencies analysis in open tubular channels ferroelectrets is made through an experimental setup based in the Michelson interferometer. The ferroelectrets present the piezoelectric effect and are continuously produced through new techniques. In optics there is in interest in feroelectrets characterization in order to use them as spatial light modulators. The interferometric setup and the procedure used to measure the resonance frequencies are shown. The obtained results and discussion demonstrate the viability of the use of optical measurements in the characterization of ferroelectrets.

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Aplicação da óptica escalar na modulação de frentes de onda e em medidas de ressonância de moduladores de ferroeletretos

We code and fabricate binary amplitude holograms using the Iterative Fourier Transform Algorithm (IFTA) and a photographic camera, in a simple and low cost way.

Daniel B. Mazulquim

Papers

Efficient band-pass color filters enabled by resonant modes and plasmons near the Rayleigh anomaly

Digital Holography: Computer-Generated Holograms and Diffractive Optics in Scalar Diffraction Domain

Alternating current-generated plasma discharges for the controlled direct current charging of ferroelectrets

Aplicação da óptica escalar na modulação de frentes de onda e em medidas de ressonância de moduladores de ferroeletretos

Binary amplitude holograms: coding and fabrication using photographic film