Optical elements with ultrahigh spatial-frequency surface corrugations.
TL;DR: The properties of optical elements fabricated by holographically recording an ultrahigh spatial-frequency pattern in a photoresist mask followed by reactive ion etching to transfer this pattern into the surface of a quartz substrate are discussed.
Abstract: In this paper we discuss the properties of optical elements fabricated by holographically recording an ultrahigh spatial-frequency pattern in a photoresist mask followed by reactive ion etching to transfer this pattern into the surface of a quartz substrate. Such optical elements are environmentally durable, potentially easy to replicate, and exhibit diffraction efficiencies in excess of 85%. In addition, two other properties are reported for the first time. Such elements at normal (0°) incidence are antireflective, with broadband reflection coefficients as low as 0.035%. Also, the elements exhibit artificially produced birefringence making them useful as wave plates. These results may be particularly significant in the UV and IR, where damage-resistant antireflection coatings and transparent birefringent materials may not exist.
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TL;DR: In this paper, the basic concepts and strategies adopted to minimize reflectance of anti-reflective coatings (ARCs) are described in greater detail and state-of-the-art fabrication techniques have been fully illustrated.
Abstract: Anti-reflective coatings (ARCs) have evolved into highly effective reflectance and glare reducing components for various optical and opto-electrical equipments. Extensive research in optical and biological reflectance minimization as well as the emergence of nanotechnology over the years has contributed to the enhancement of ARCs in a major way. In this study the prime objective is to give a comprehensive idea of the ARCs right from their inception, as they were originally conceptualized by the pioneers and lay down the basic concepts and strategies adopted to minimize reflectance. The different types of ARCs are also described in greater detail and the state-of-the-art fabrication techniques have been fully illustrated. The inspiration that ARCs derive from nature (‘biomimetics’) has been an area of major research and is discussed at length. The various materials that have been reportedly used in fabricating the ARCs have also been brought into sharp focus. An account of application of ARCs on solar cells and modules, contemporary research and associated challenges are presented in the end to facilitate a universal understanding of the ARCs and encourage future research.
1,047 citations
01 May 1985
TL;DR: In this article, an exact formulation of the grating diffraction problem without approximations is presented, using a series of fundamental assumptions, which reduces to the various existing approximate theories in the appropriate limits.
Abstract: Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.
989 citations
TL;DR: In this article, a review of state-of-the-art anti-reflecting (AR) techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field are presented.
Abstract: Optical reflection, or in other words the loss of reflection, from a surface becomes increasingly crucial in determining the extent of the light-matter interaction. The simplest example of using an anti-reflecting (AR) surface is possibly the solar cell that incorporates an AR coating to harvest sunlight more effectively. Researchers have now found ways to mimic biological structures, such as moth eyes or cicada wings, which have been used for the AR purpose by nature herself. These nanoscopic biomimetic structures lend valuable clues in fabricating and designing gradient refractive index materials that are efficient AR structures. The reflectance from a selected sub-wavelength or gradient index structures have come down to below 1% in the visible region of the spectrum and efforts are on to achieve broader bands of such enhanced AR regime. In addition to the challenge of broader bands, the performance of AR structures is also limited by factors such as omnidirectional properties and polarization of incident light. This review presents selected state-of-the-art AR techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field.
565 citations
529 citations
TL;DR: Sub-wavelength structures with a subwavelength pitch have been known since Hertz conducted his first experiments on the polarization of electromagnetic waves as discussed by the authors, and their applications include anti-reflective coatings, polarization rotators, high-efficiency fiber-chip cou-plers, spectrometers, highreflectivity mirrors, athermal waveg- uides, multimode interference couplers.
Abstract: Periodic structures with a sub-wavelength pitch have been known since Hertz conducted his first experiments on the polarization of electromagnetic waves. While the use of these structures in waveguide optics was proposed in the 1990s, it has been with the more recent developments of silicon photonics and high-precision lithography techniques that sub-wavelength structures have found widespread application in the field of pho- tonics. This review first provides an introduction to the physics of sub-wavelength structures. An overview of the applications of sub-wavelength structures is then given including: anti-reflective coatings, polarization rotators, high-efficiency fiber-chip cou- plers, spectrometers, high-reflectivity mirrors, athermal waveg- uides, multimode interference couplers, and dispersion engi- neered, ultra-broadband waveguide couplers among others. Particular attention is paid to providing insight into the design strategies for these devices. The concluding remarks provide an outlook on the future development of sub-wavelength structures and their impact in photonics.
496 citations
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01 Jan 1973TL;DR: CRC handbook of chemistry and physics, CRC Handbook of Chemistry and Physics, CRC handbook as discussed by the authors, CRC Handbook for Chemistry and Physiology, CRC Handbook for Physics,
Abstract: CRC handbook of chemistry and physics , CRC handbook of chemistry and physics , کتابخانه مرکزی دانشگاه علوم پزشکی تهران
52,268 citations
TL;DR: In this article, a dielectric surface-relief grating is analyzed using rigorous coupled-wave theory and the analysis applies to arbitrary grating profiles, groove depths, angles of incidence, and wavelengths.
Abstract: Diffraction by a dielectric surface-relief grating is analyzed using rigorous coupled-wave theory. The analysis applies to arbitrary grating profiles, groove depths, angles of incidence, and wavelengths. Example results for a wide range of groove depths are presented for sinusoidal, square-wave, triangular, and sawtooth gratings. Diffraction efficiencies obtained from the present method of analysis are compared with previously published numerical results. To obtain large diffraction efficiencies (greater than 85%) for gratings with typical substrate permittivities, it is shown that the grating profile should possess even symmetry.
967 citations
TL;DR: A survey of the characteristics, technology and applications of holographic optical elements (HOEs), considered as general elements in an optical system, can be found in this paper, where the authors show that HOEs provide unique system functions and configurations, show a rapid variation of optical power and image characteristics with wavelength, have relatively large amounts of astigmatism and coma, and require special consideration of optical efficiency during system design.
Abstract: This article is a survey of the characteristics, technology and applications of Holographic Optical Elements (HOEs), considered as general elements in an optical system HOEs function by diffraction of light from a generalized grating structure with nonuniform groove spacing HOEs provide a system of thin film optics They are capable of unique system functions and configurations, show a rapid variation of optical power and image characteristics with wavelength, have relatively large amounts of astigmatism and coma, and require special consideration of optical efficiency during system design Comparison of the aberrations of specific, f/33 elements shows that the on-axis HOE and the conventional glass lens element have similar aberration levels, while the off-axis HOE has four times as much astigmatism and twice as much coma We show that these grating aberrations, which appear for conjugate points that are different from the HOE construction points, are proportional to the average surface grating spatial frequency of an off-axis HOE HOE technology is similar to conventional optics technology, but is less developed The relative complexity of optical systems with HOEs, and the lack of a suitable aberration theory, produce a relince on computer-based raytracing for system design and development We give the basic raytracing equations and discuss the special requirements for hologram recording appara-tus and materials In applications, HOEs will usually provide unique capabilities rather than replace conventional elements, and will usually operate over narrow spectral bandwidths The use of HOEs in several types of laser optical systems, and in visual displays, appears to be not only advantageous, but also technically and economically feasible
145 citations
TL;DR: In this paper, a 2.6 μm-thick organic layer was used to generate steep profile patterns for photo and electron lithography, which reduced the need for thick resist patterns for the lithography step and ensured high resolution combined with good step coverage.
Abstract: High resolution and steep profile patterns have been generated in a 2.6 μm thick organic layer which conforms to the steps on a wafer surface and is planar on its top. This thick organic layer (a photoresist in the present experiments) is covered with an intermediate layer of SiO2 and a top, thin layer of x‐ray or photoresist. After exposure and development of the top resist layer, the intermediate layer is etched by CHF3 reactive ion etching. The thick organic layer is then etched by O2 reactive ion etching. Submicron resolution with essentially vertical walls in the thick organic material was achieved. The technique is also applicable to photo and electron lithography. It reduces the need for thick resist patterns for the lithography step and, at the same time, ensures high resolution combined with good step coverage.
116 citations