Blazed gratings and Fresnel lenses fabricated by electron-beam lithography
TL;DR: A blazing technique using electron-beam lithography to achieve higher efficiency of gratings and Fresnel lenses is described, and the experimental results showed high-efficiency performance and nearly diffraction-limited focusing.
Abstract: A blazing technique using electron-beam lithography to achieve higher efficiency of gratings and Fresnel lenses is described. Transmission-type blazed gratings have been formed in polymethyl methacrylate films. As a result of measurement, we found that their diffraction efficiency of the first order in these gratings amounts to as much as 60 to 70% at 0.633 microm. Fresnel lenses of 1-mm diameter and 5-mm focal length, which have a sawtooth relief profile, have been also fabricated, and the experimental results showed high-efficiency performance (about 50%) and nearly diffraction-limited focusing.
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TL;DR: High Contrast gratings (HCGs) as mentioned in this paper are a class of planar optics with a large refractive index contrast, which can be designed top-down based on intuitive guidelines.
Abstract: A new class of planar optics has emerged using subwavelength gratings with a large refractive index contrast, herein referred to as high-contrast gratings (HCGs). This seemingly simple structure lends itself to extraordinary properties, which can be designed top-down based on intuitive guidelines. The HCG is a single layer of high-index material that can be as thin as 15% of one wavelength. It can be designed to reflect or transmit nearly completely and with specific optical phase over a broad spectral range and/or various incident beam angles. We present a simple theory providing an intuitive phase selection rule to explain the extraordinary features. Our analytical results agree well not only with numerical simulations but also experimental data. The HCG has made easy fabrication of surface-normal optical devices possible, including vertical-cavity surface-emitting lasers (VCSELs), tunable VCSELs, and tunable filters. HCGs can be designed to result in high-quality-factor (Q) resonators with surface-normal output, which is promising for wafer-scale lasers and optical sensors. Spatially chirped HCGs are shown to be excellent focusing reflectors and lenses with very high numerical apertures. This field has seen rapid advances in experimental demonstrations and theoretical results. We provide an overview of the underlying new physics and the latest results of devices.
451 citations
TL;DR: In this article, the theoretical performance of blazed binary diffractive elements composed of pillars carefully arranged on a two-dimensional grid whose period is smaller than the structural cutoff was investigated through electromagnetic theories.
Abstract: We report here on the theoretical performance of blazed binary diffractive elements composed of pillars carefully arranged on a two-dimensional grid whose period is smaller than the structural cutoff. These diffractive elements operate under unpolarized light. For a given grating geometry, the structural cutoff is a period value above which the grating no longer behaves like a homogeneous thin film. Because the grid period is smaller than this value, effective-medium theories can be fully exploited for the design, and straightforward procedures are obtained. The theoretical performance of the blazed binary elements is investigated through electromagnetic theories. It is found that these elements substantially outperform standard blazed echelette diffractive elements in the resonance domain. The increase in efficiency is explained by a decrease of the shadowing effect and by an unexpected sampling effect. The theoretical analysis is confirmed by experimental evidence obtained for a 3λ-period prismlike grating operating at 633 nm and for a 20°-off-axis diffractive lens operating at 860 nm.
346 citations
TL;DR: The approach with low-cost, semiconductor fabrication compatibility and high working efficiency characteristics offers a way for establishing a complete set of flat optical components for a wide range of applications such as compact imaging sensors, optical spectroscopy, and high-resolution lithography, just named a few.
Abstract: Metasurface-based components are known to be one of the promising candidates for developing flat optical systems. However, their low working efficiency highly limits the use of such flat components for feasible applications. Although the introduction of the metallic mirror has been demonstrated to successfully enhance the efficiency, it is still somehow limited for imaging and sensing applications because they are only available for devices operating in a reflection fashion. Here, we demonstrate three individual GaN-based metalenses working in a transmission window with extremely high operation efficiency at visible light (87%, 91.6%, and 50.6% for blue, green, and red light, respectively). For the proof of concept, a multiplex color router with dielectric metalens, which is capable of guiding individual primary colors into different spatial positions, is experimentally verified based on the design of out-of-plane focusing metalens. Our approach with low-cost, semiconductor fabrication compatibility and h...
285 citations
TL;DR: By designing the reflectance and the phase of non-periodic HCGs, both focusing reflectors and lenses can be constructed and HCG optics can simultaneously focus the reflected and transmitted waves, with important technological implications.
Abstract: We propose planar, high numerical aperture (NA), low loss, focusing reflectors and lenses using subwavelength high contrast gratings (HCGs). By designing the reflectance and the phase of non-periodic HCGs, both focusing reflectors and lenses can be constructed. Numerical aperture values as high as 0.81 and 0.96 are achieved for a reflector and lens with very low losses of 0.3 and 0.2 dB, respectively. The design algorithm is also shown to be readily extended to a 2D lens. Furthermore, HCG optics can simultaneously focus the reflected and transmitted waves, with important technological implications. HCG focusing optics are defined by one-step photolithography and thus can be readily integrated with many devices including VCSELs, saturable absorbers, telescopes, CCDs and solar cells.
257 citations
TL;DR: The selected research activities on integrated optics components and devices using periodic structures are reviewed, with emphasis on the authors' works employing the electron-beam writing technique.
Abstract: The selected research activities on integrated optics components and devices using periodic structures are reviewed, with emphasis on the authors' works employing the electron-beam writing technique. The periodic structures include static gratings and dynamic ones produced through acoustooptic (AO) and electrooptic (EO) effects. They provide a variety of passive functions and effective means for guided-wave control. The review is made from the integration point of view, including the most recent results. First, the theoretical fundamentals are outlined and the electron-beam writing techniques, including the writing system, are discussed. Next, passive components (grating deflectors, filters, lenses, couplers, etc.) and elements for guided-wave controlling and detecting (AO and EO grating elements and photodetectors) are described. Then, integrated optic devices, i.e., wavelength demultiplexers, RF spectrum analyzers, optical disk pickup, etc., are presented. Finally, the possibility of future applications is discussed.
257 citations
References
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TL;DR: A new, computer-generated, optical element called a kinoform that operates only on the phase of an incident wave and forms a single image by wavefront reconstruction without the unwanted diffraction orders characteristic of holograms is described.
Abstract: A new, computer-generated, optical element called a kinoform is described. This device operates only on the phase of an incident wave and forms a single image by wavefront reconstruction without the unwanted diffraction orders characteristic of holograms. The kinoform is also more efficient in the use of spatial frequency potential and reconstruction energy and can be synthesized in considerably less computer time than the digital hologram.
636 citations
TL;DR: In this article, the diffraction by thin refractive-index gratings of arbitrary periodic shape is treated, and three analytical approaches are shown to be equivalent for all diffracted orders.
Abstract: Diffraction by thin refractive-index gratings of arbitrary periodic shape is treated. Three analytical approaches are indicated and are shown to be equivalent. Resultant expressions for the diffraction efficiencies are given for all diffracted orders.
156 citations
TL;DR: It was found that ordinary-type Fresnel (zone-plate) lenses and a special-type lens for converting an incident Gaussian intensity distribution into a uniform one have near-diffraction-limited performance.
Abstract: Micro lenses are basic components of micro optics. We have proposed a new fabrication technique for micro lenses that uses electron-beam lithography and have developed an electron-beam lithography system that is specially designed for this purpose. To demonstrate the feasibility of this technique, ordinary-type Fresnel (zone-plate) lenses and a special-type lens for converting an incident Gaussian intensity distribution into a uniform one were designed and fabricated. It was found that these Fresnel (zone-plate) lenses have near-diffraction-limited performance. The fabrication technique and experimental results are discussed.
101 citations
TL;DR: In this paper, a method to synthesize kinoform lenses and aspherical surfaces by optical means is described, using a scanning method to obtain a continuous profile on photographic plates and photoresists.
18 citations
TL;DR: In this article, the use of electron-beam lithography for making micro Fresnel lenses was proposed, which can focus incident plane waves into a nearly ideal diffraction-limited spot with an efficiency of 30%.
Abstract: Microlenses constitute an area of very important components in microoptics. This paper proposes the use of electron-beam lithography for making micro Fresnel lenses. An electron-bean machine developed for this purpose offers great flexibility in their design and fabrication. Micro Fresnel lenses for visible and infrared were made using PMMA as an electron-beam resist. Fabricated lenses with F-numbers above 1 can focus incident plane waves into a nearly ideal diffraction-limited spot with an efficiency of 30%, while theory predicts 40%. A minimum spot size, or intensity half-width, of 0.7 μm was obtained at wavelength of 0.6328 μm using an electron-beam fabricated lens with a very small F-number of 0.65.
8 citations