bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of spatial coherence on photolithographic phase mask performance
Authors: Salik Boaz , Yariv Amnon
Published: February 2023

Since Marc Levenson’s introduction of phase masks to photolithography [1], there have been numerous improvements in their design and fabrication [2-6]. One issue not yet considered is the effect of illumination source spatial coherence on the effectiveness of phase masks in improving resolution and focal depth. As the illumination wavelength has grown shorter (to accommodate the classical resolution limit

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, sources have become more spatially coherent [7], and with the use of excimer laser illumination we approach complete spatial coherence. It has generally been assumed that increased spatial coherence improves the performance of phase masks, since it enhances the destructive interference between adjacent (opposite phase) features. Although this is true for periodic patterns, we show here that more complex images suffer a trade-off between the contrast enhancement of coherent alternating features and the larger effective aperture of incoherent imaging. This effect is particularly pronounced in complex 2-D images where phase conflict is a problem.
Diffractive Optical Elements for Tracking and Receiving in Optical Space Communication Systems
Authors: Blattner P. , Herzig H. P. , Weible K. J.
Published: February 2023

The design of first, generation free space laser communication systems is based on laser diodes with output powers in the order of 100 mW [1]. The data rate transmission is in the order of 100 Mbit/s. This leads to terminals with large transmitter and receiver telescope diameters and, consequently, to high terminal mass and dimensions. The optical systems are usually designed with refractive lenses and reflective mirrors. Alternatives are planar diffractive optical elements (DOEs). By relying on diffraction and interference rather than on reflection and refraction, unique and novel properties can be realized. Almost any structure shape, including non–rotationally symmetric aspherics, can be manufactured, which provides all degrees of freedom for the design. Other interesting aspects of DOEs are their low weight, their strong dispersion, and the possibility to make segmented elements, large arrays of elements, beamsplitters, and polarizers. These properties are useful for many applications of DOEs in space, including: filters for image data processing [2], beam shaping [3, 4], and antireflection structures [5, 6]. Furthermore, the combination of refractive and diffractive surfaces (hybrid elements) offers new possibilities for optical design. The negative dispersion of DOEs can be used to compensate the chromatic aberrations of refractive lenses [7, 8]. Hybrid elements can also be used to compensate the temperature induced variations of their mounting system [9, 10]. Diffractive optical elements for space applications must comply with a number of requirements, including mechanical, thermal and optical stability [8]. Suitable techniques for realizing the microstructures in space qualified materials are based on a variety of high resolution lithographic and optical processes [11].
Scalar Design of Diffractive Elements using Direct and Indirect Optimization
Authors: Mait Joseph N.
Published: February 2023

Although analysis of diffractive optical elements (DOEs) is critical to an understanding of the technology, equally important for their widespread application is an understanding of their design or, in counterpoint to analysis, their synthesis. The problem of design is essentially a casting of a designer's understanding of physics into an optimization problem: the DOE is to be determined so that it achieves some desired performance, preferably optimally, subject to the constraints of fabrication.
Beam-Pointing Stabilization and Ladar Heterodyne Mixing Efficiency Increase Using a Liquid Crystal Phased Array Device
Authors: Missey Mark J. , Dominic Vincent , Watson Edward A.
Published: February 2023

Laser radar imaging systems often require the ability to accurately point the transmitted laser beam as well as the ability to mix the return light with a single mode receiver. An addressable liquid crystal phased array provides the precise spatially dependent phase shifts needed to achieve such beam stability and increased ladar heterodyne mixing efficiency. The device consists of a layer of nematic liquid crystals sandwiched between two substrates. One substrate is uniformly grounded, while the other is etched with narrow, closely spaced individual 1-D electrodes. The liquid crystals underneath a given electrode are rotated by applying an appropriate voltage, thus generating a birefringent phase delay. Two of these writable one-dimensional gratings can be cascaded to implement two dimensional phase profiles.
Programmable Wavefront Generation with Two Binary Phase Spatial Light Modulators
Authors: Yang Guoguang , Broomfield Seth
Published: February 2023

In this paper we propose a programmable wavefront generation system using two binary phase spatial light modulators (BPSLMs). The output of the binary phase hologram has inversion symmetry and is restricted to be space–invariant, if the output of the hologram is viewed in the Fourier plane of a lens. Inversion symmetry may be broken by introducing a fixed binary phase hologram [1,2] but in this case diffraction efficiency ηd is not increased. Alternatively, an asymmetric output may be generated by increasing the number of phase levels [3]. Results obtained in this way increase ηd but the output remains space-invariant.
Reformulation of the Fourier modal method for surface-relief anisotropic gratings
Authors: Li Lifeng
Published: February 2023

Surface-relief gratings made with anisotropic materials are finding more applications. An example is grooved magneto-optic disks as data storage media. The present work is a reformulation of the couple-wave method, for solving the anisotropic grating problem, that is described in Refs. 1-3. [Since the method essentially is a modal method relying on expanding both the electromagnetic fields and the permittivity function into Fourier series, here it is referred to as the Fourier modal method (FMM).] It originated from the work documented in Refs. 4-7. Recently Lalanne and Morris4, and Granet and Guizal5 simultaneously reformulated the conventional FMM for isotropic gratings in TM polarization. As a result, the convergence of the method for highly conducting metallic gratings was greatly improved. Auslender and Hava6 also reported the same reformulation. The findings of these authors were mathematically justified and summarized in the form of three Fourier factorization rules7. The use of these factorization rules has led to improvement of convergence in two other cases: the C method for gratings with sharp edges8 and the FMM for crossed gratings.9 This conference paper briefly reports yet another successful application of the factorization rules. A detailed exposition will soon appear elsewhere.10
Applicability of the method of reduction in the Fourier modal method
Authors: Li Lifeng
Published: February 2023

The Fourier modal method (FMM) is one of the simplest and most effective methods for modeling diffraction gratings. Burckhardt’s paper1, published in 1966, marked the beginning of this method. In Burckhardt’s work, a volume grating of lossless, sinusoidally varying permittivity was considered. Later Kaspar2 extended Burckhardt’s work to lossy and non-sinusoidal volume gratings. Apparently unaware of Burckhardt and Kaspar’s work, Peng et al.3 also proposed the Fourier modal method; however, they refrained from applying it to surface-relief gratings (see next section). Apparently unaware of the concerns of Peng et al., Knop4 extended Burckhardt’s work to rectangular surface-relief gratings. Moharam and Gaylord5 took one step further. They applied the FMM to analyze surface-relief gratings of arbitrary profile.
Perturbation theory - a unified approach to describe diffractive optical elements
Authors: Testorf Markus
Published: February 2023

The conceptual advantage of Kirchhoffs approximation1 for the description of optical elements and systems is the intensive use of the Fourier transformation2. Its simple mathematical relations can be used to predict spatially distributed light signals in any plane of an optical system. An analysis in terms of Fourier optics and, more specific, the paraxial approximation is even appropriate if more rigorous calculations are required to achieve a desired accuracy for the design of the system.
Study of the resonant behavior of waveguide-gratings Increasing the angular tolerance of guided-mode filters
Authors: Lemarchand F. , Sentenac A. , Giovannini H.
Published: February 2023

Studies of anomalies of the reflection and transmission curves of waveguide-gratings have demonstrated unique filtering capabilities of these structures. Vincent and Neviere [1] showed that the excitation of a leaky mode in the system can lead to 100% reflectance at a given wavelength under certain condition of symmetry. A comparative study of guided-mode resonance filters with classical multilayers design shows that the latter requires considerably more layers to yield equivalent narrow-band linewidths [2]. However, contrary to thin-films filters, waveguide-gratings are very sensitive to the angle of the incident wave. Hence, the narrow-band filter suffers significant reduction in the peak reflectance, even if the incident optical beam is wide [3].
Chromatic compensation of free-space light propagation combining diffractive and refractive lenses. Achromatic Fresnel and Fourier applications.
Authors: Andrés P. , Climent V.
Published: February 2023

It is well-known that the propagation of electromagnetic waves in free space is a physical phenomenon that explicitly depends on the wavelength of the light radiation. This fact results in the chromatic dispersion of the field diffracted by an aperture illuminated with a broadband source. For instance, the Fraunhofer diffraction pattern achieved at the back focal plane of a refractive objective is an example of pure lateral chromatic distortion, whereas axial and transversal chromatic blurring may occur at the Fresnel diffraction region.
Substrate-mode polarization-controlled optical switch with sandwich reflection holograms
Authors: Moreau V. , Habraken S. , Renotte Y. , Lion Y.
Published: February 2023

The development of optical communication networks has led to a growing need of optical interconnection to route high data-rate signals without optical-to-electrical conversion.1
Novel multichannel WDM-PON demultiplexer using an AWG and diffractive optical elements
Authors: Pawlowski E. , Ferstl M. , Hellmich H. , Kuhlow B. , Przyrembel G. , Warmuth C. , Salgueiro J. R.
Published: February 2023

In order to increase the capacity of optical transmission systems, it is advantageous to use the high-parallel capability of optical wavelength division multiplexing (WDM) [1] techniques. Key devices for WDM-communication systems are optical demultiplexer. A variety of different devices, such as Mach-Zehnder filters [2], diffractive optical elements (DOE) [3], acousto-optical filters [4], transversal filters [5] and arrayed-waveguide gratings (AWG) [6,7] have been already developed. However, to realize a device with a higher functionality it is usefull to integrate waveguide devices with DOEs. As a special case of WDM functionality upgrade, we have considered a 1.55-μm WDM extension of an existing passive optical net (PON). In this paper we report, for the first time to our knowledge, of the fabrication of a fully integrated multichannel WDM-PON demultiplexer. The device is used to distribute 1.3-μm wavelength signals (1/N power) and to multiplex an 8-channel WDM spectrum at 1.55-μm wavelength with 200 Ghz channel spacing. Planar lightwave circuits (PLC), based on silica waveguides, are very attractive devices for these applications [8]. They allow high reliable and low cost production, due to their suitability for integration of optical components. Furthermore, the silica waveguides show low optical losses.
Planar-integrated optical systems for pulse shaping
Authors: Testorf Markus , Österberg Ulf
Published: February 2023

The ability to influence the temporal shape of short optical pulses1 provides access to many promising applications. For instance, high capacity optical fiber communication systems based on a wavelet decomposition of the available time-bandwidth product rely on a specific shape of the optical wavelets2.
Optical measurement of the global and local geometry of grating structures
Authors: Blattner P. , Traut S. , Herzig H. P.
Published: February 2023

Advancement in the areas of lithography and holography have enabled the realization of very fine surface-relief grating structures in the nanometer to micrometer range. The characterization of such structures is of obvious importance. Different methods exist to determine the optical properties of gratings. The dispersion properties are typically analysed by spectrometers. The wavefront quality is measured by commercially available interferometers. The diffraction efficiency can be determined by scanning the far-field intensity distribution.
Evaluation of a diamond-cut large-groove grating for near infrared spectroscopy
Authors: Goto Miwa , Imanishi Masatoshi , Iwamuro Fumihide , Maihara Toshinori
Published: February 2023

The rapid progress of large format infrared detector arrays enables us to take a fairly wide spectrum with a medium resolution by a single exposure, if a coarsely grooved echelle-type grating can be used. To produce such a spectrum onto a square detector array, it is necessary to fabricate a grating with much larger groove separation than those used in visible spectroscopy, which has so far not been available. For instance, if we envision a spectrograph which produces an echelle spectrogram in the 3 to 4 microns, a realistic solution of spectrograph design would be to employ a large-groove grating usable in the orders ranging from 20-th to 30-th, or even higher. Of course, the width of such grooves is beyond the limit of the usual ruling method. We therefore attempted to produce a grating with a 125 μm groove scale by the high precision cutting of an Aluminum alloy directly with a diamond bite. In this report, we present the test result of the machine-cut grating, and make evaluation of the diffraction efficiency by referring to the result of a numerical simulation software. The grating is now incorporated in an astronomical spectrograph which works mainly in 3 μm region (Imanishi et al 1996).
Micro-jet Printing of Refractive Microlenses
Authors: Cox W. Royall , Chen Ting , Guan Chi , Hayes Donald J. , Hoenigman Rick E. , Teipen Brian T. , MacFarlane Duncan L.
Published: February 2023

The technology for fabricating micro-optical elements for low cost optical interconnects by micro-jet (ink-jet) printing has been under development for over two years [1,2]. This data-driven method of micro-optics fabrication offers the benefits of low cost, flexibility and in-situ, non-contact processing. These features can be used to advantage in applications where increasing the efficiency of optical power coupling as a value-added step is a goal, and they provide unique capabilities for rapid prototyping and customization of microlens arrays. Here we present our latest results in developing this Optics-Jet technology for applications such as collimation of the outputs of LEDs and diode lasers, as well as for increasing the efficiency of focusing of GRIN lenses [3]. Data on printed microlens optical characteristics will be shown, as well as their performance in collimation and astigmatism reduction of optical sources.
Diffraction characteristics of thick phase volume hologram recorded in photo-thermo-refractive glasses
Authors: Dunn S. , Moharam M. G. , Glebov L. , Richardson K. R.
Published: February 2023

Volume holographic optical elements have numerous applications in beam shaping, spectral filters, optical display systems, optical interconnects, and data storage. One of the primary challenges facing the development of applications involving volume holographic optics is the recording media. It must meet a number of requirements including phase volume recording with high efficiency, low scattering, large dynamic range, and high resolution, while exhibiting good thermal, chemical, and mechanical durability, as well as environmental stability. Current recording media include photographic films, dichromated gelatin, photoresists, photopolymers, photochromies, photo-organics, and photoreffactive media. These media meet only a few of the desired requirements.
Diffractive and micro-optics at Centro Ricerche Fiat: implemented technologies and applications in the transport industry and general lighting
Authors: Perlo P. , Repetto P.M. , Sinesi S. , Lambertini V. , Bigliati C.
Published: February 2023

Emphasis on the design methodologies and on the technologies implemented to rapidly manufacture large nonrepeated cluster is given. The development of systems based on diffractive and micro-optics for the motorcycle, automotive and general lighting industries is presented. Considerations on their use over the more conventional approaches conclude the paper.
High efficiency transmission diffractive grating and grating lens of the Megajoule laser final optic assembly
Authors: Adolf Alain , Dulac Arnaud , Journot Eric
Published: February 2023

The French Megajoule laser facility (LMJ) is designed to provide 1,8MJ/600TW of UV light on an X-ray drive target. This performance requirements are given by inertial confinement fusion ignition mission. The LMJ laser will have 30 bundles of 4x2 IR phosphate-glass amplifier chains of 40 cm square aperture. In the target area this bundles are split into 2x2 bundles which are called ≪ quads ≫. These quads are directed around the target chamber, converted into UV light and focused on the target.
Design of diffractive optical elementrs for mode shaping within custom laser resonators
Authors: Barton Ian M. , Taghizadeh Mohammad R.
Published: February 2023

Diffractive optical elements (DOEs) have been demonstrated that alter the fundamental mode of a laser resonator to a desired profile, notably by Leger et al.1,2 These, so-called mode-selecting elements (MSEs), usually operate within a Fabry-Pérot laser cavity by replacing one, or both, of the mirrors with a reflecting DOE. They have been mainly applied in solid-state laser systems, e.g., Nd:YAG. The advantages of these customised cavities include superior discrimination against higher-order modes,3 enabling single-mode operation and the inherently useful properties of the fundamental mode profiles that they can generate, e.g., flattops. These properties are much in demand for many applications including material processing.
Liquid Crystal Blazed Grating Beam Deflector
Authors: Wang Xu , Wilson Daniel W. , Muller Richard E. , Maker Paul D. , Psaltis Demetri
Published: February 2023

Non-mechanical beam steering devices can play a crucial role in many applications, such as optical interconnects, optical communications and optical data storage.[1] However, current steering devices either require high voltage or complicated fabrication technology. [2] [3] [4] We have developed a non-mechanical beam steering device using liquid crystal as shown in Figure. 1.
Super-resolution in computer-generated holograms
Authors: Takaki Yasuhiro
Published: February 2023

Resolvable points of the CGH’s diffraction image overlap and interfere with one another. By controlling the interference, diffraction intensity distribution can be controlled with high density.
Novel Polarizers Using 2D Photonic Band Gap Structures
Authors: Hamano T. , Izutsu M.
Published: February 2023

Photonic band gap (PBG) structures have been studied due to interests in the control of spontaneous emission as well as due to their applications in optical devices. Some applications of PBG structures have been proposed, such as reflectors [1], cavities [2], waveguides [3] etc. In order to utilize them in these applications, 2-dimensional (2D) PBG structures are required to producing ‘complete’ band gaps. Thus, their necessary band gaps must be wide in any direction on plane and must operate in two orthogonal polarization states which are parallel and perpendicular to the pillars (or holes) of the structures.
Color pseudo-nondiffracting beams generated by diffractive phase elements
Authors: Dong Bi-Zhen , Liu Rong , Gu Ben-Yuan , Yang Guo-Zhen
Published: February 2023

Nondiffracting beam has extensive applications such as optical alignment, surveying, industrial inspection, and optical interconnection. Recently, pseudo-nondiffracting beam (PNDB) has been proposed. All the PNDB’s, a single and two segments, are almost generated in the monochromatic light illuminating system.1-2
Optical Wavelet Transform with Use of A Computer—Generated Hologram
Authors: Yang Guo-Zhen , Zhang Yan , Gu Ben-Yuan , Dong Bi-Zhen
Published: February 2023

The wavelet transform (WT) is a relatively useful and powerful technique in many applications, such as signal processing, pattern recognition, data compression, and so on.1-3 It overcomes the disadvantages of the Fourier transform and the Gabor transform, and provides an explicit representation of a signal in both space and frequency domains. Many configurations have been proposed to implement the wavelet transform, however, most of them are based on optical correlator. In this presentation, we present a new scheme to achieve the WT by a computer-generated hologram (CGH) based on the general theory of optical transform.4-6 The for determining the CGH is derived and a computer simulation is presented.
Spectral calibration of MODIS bands using the SRCA
Authors: Montgomery Harry , Che Nianzeng , Bowser Jeff
Published: February 2023

The Spectra-Radiometric Calibration Assembly (SRCA) is one of the on-board calibrators of MODerate resolution Imaging Spectrometer (MODIS), designed and manufactured by Hughes Santa Barbara Remote Sensing (SBRS). The SRCA has three calibration functions: radiometric, spectral, and spatial.
Photodeposition technique for restoring holographic films of polydiacetylene
Authors: Abdeldayem Hossin , Paley Mark S. , Witherow William , Frazier Donald O.
Published: February 2023

Polydiacetylenes are a very promising class of polymers for both photonic and electronic applications1-3 because of their highly conjugated structures. We, recently, have discovered the possibility of depositing a permanent holographic grating of information, made of polydiacetylene on a glass substrate. A novel technique for obtaining high quality thin films of a polydiacetylene derivative of 2-methyl-4-nitroaniline (PDAMNA) using photodeposition from monomer solutions onto UV transparent substrates was discovered by members of our group a few years back4. This compound was one of several asymmetric diacetylenes that were first studied extensively for their optical and electronic properties by Garito and co-workers in the late 1970s; however, their investigations did not include behavior in solutions5,6. PDAMNA films can be obtained readily from solutions of DAMNA in 1,2-dichloroethane by irradiation with UV light through a quartz or glass window, which serves as the substrate. This simple straightforward process yields transparent films with thickness on the order of 1μm7. To obtain PDAMNA thin films, a solution of DAMNA in 1,2-dichloroethane is placed inside a chamber shown in figure 1. DAMNA monomer strong absorption at 366nm. A hand-held 15W UV lamp placed directly in front of the substrate ( approximate radiation intensity of 800 μW/cm2 at 6 in.), a film of approximately 0.6 μm thickness is obtained after 24 hours of exposure.
Hybridization of Fresnel diffractive microlenses and VCSELs arrays for free space optical interconnections
Authors: Fraces Michel , Churoux Pascal , Bouzinac Jean-Pierre
Published: February 2023

Multi-level electronic integration of massively parallel computers leads to latency effects and I/O bottlenecks. Free space optical interconnections might be a good alternative to interconnect processors located on face to face PC boards.
New Theoretical Method For Nonuniform Gratings Investigation
Authors: Karapetyan G.G.
Published: February 2023

Uniform Fiber Bragg Gratings are wavelength selective reflectors obtained by a periodic modulation of core refractive index along the fiber. They have many applications as narrow-band elements in optical fiber systems. Recently the NG are used for many purposes [1]. For their investigations the numerical solutions of coupled mode are used traditionally. This appoach requires a much machine time, and is not convenient for NG design. Therefore the analytical formulaes for characteristics of NG will be of benefit in NG design, syntezing, and optimization. The first step in solving this problem has been undertake in [2] where the WKB- approximation for solving coupled mode has been used. The drawback of this approximation is that it is not uniform in all frequency interval and is not valid near so called turning points. Then, an unknown phase shift occurs in formulaes which can not be determined within the WKB- approximation, and one needs to evaluate this unknown parameter from qualitative estimations. To avoide these drawbacks of WKB- approximation we elaborated another more suitable method which is valid uniformely in all frequency interval. This method, called R-approximation is the generalization of asymptotic solution of second order differential having one turning point [3] for the case when there are two or more turning points, in the result the analitical formulaes for characteristics of arbitrary NG obtained. R-approximtion is more exact and common than WKB-approximation. The last come to R-approximation by removal from turning points. As an uniform asymtotic formulaes R-approximation has a relative error ~ O(1/H) in all frequency interval, where H=πμN describes the gratings strength, μ-is the depth of effective permittivity modulation, N-is the number of grating periods (for uniform grating the maximum reflectivity is |R|2=th2(H/4)). On the basis of obtained common formulaes a special case of linearly chirped gratings (LCG) is investigated in detail and a designing software “LCG” is created. This software provides all characteristics of LCG versus strength, detuning, and chirping rate, and is a powerfull and convinient tool for designers.
Reconfigurable optical interconnects in free-space optical processing modules based on polarization-selective diffractive optical elements
Authors: Thienpont H , Nieuborg N , Goulet A , Kirk A , Koczyk P , Heremans P , Kuijk M , De Tandt C , Ranson W , Vounckx R , Veretennicoff I
Published: February 2023

Free-space optical interconnects have been widely used in parallel optical information processing systems [1]. The growing complexity of the desired routing configurations has created an urgent need for data transparent, reconfigurable and flexible interconnections. Polarization has always played an important role in the realization of such interconnects, because of the possibility to route the optical data via an electro-optic control of its state of polarization.
Binary high-efficiency single order gratings for beam switching
Authors: Bartelt Hartmut , Glaser Tilman , Schroeter Siegmund
Published: February 2023

Grating structures with a grating period in the range of the illumination wavelength differ in their diffraction properties considerably from conventional diffraction structures. In this case diffraction properties are sensitive in a complex manner to illumination direction, structure thickness, illumination wavelength or polarization. For modeling of the diffraction properties rigorous solutions of the wave have to be used [1]. Specific examples of the properties of such gratings include highly efficient single order gratings or polarization dependent beam splitting structures [2]. Although theoretical modeling of such gratings is known for a long time, practical realization of such gratings was limited until recently by the structuring technology. After first investigations based on an interferometric technique now also more flexible techniques based on direct e-beam writing in the submicrometer range become available [3]. In the following we want to describe at first results for the design of an efficient single order binary phase grating structure. Then the combination of two single order gratings for achieving beam switching properties with small mechanical shifts in the sub micrometer range will be discussed.
Diode laser illuminated automotive brake lamp using a linear fanout diffractive optical element
Authors: Remillard J.T. , Marinelli M.A. , Fohl T. , O'Neil D.A.
Published: February 2023

Marinelli and Remillard discussed the design and fabrication of diode laser illuminated automotive signal lamps.1 The optics are made from thin (~5 mm) plastic sheets that manipulate light using reflection and refraction from edges, surfaces, and shaped cut-outs. The resulting lamps can be well under 1 inch in thickness providing functional and styling advantages not attainable with conventional automotive lighting systems. Functionally, the sheet optic consists of a section that receives, divides, and expands the laser light (the manifold), and a section that directs it out of the lamp into the appropriate beam pattern (the kicker). The kicker is the visible part of the lamp optic, and the most efficient use of space is realized by maximizing the ratio of kicker to manifold area. Here we describe the design and fabrication of a thin, laser illuminated brake lamp that uses a diffractive optical element (DOE) at the entrance of the manifold. The DOE provides a compact way of uniformly spreading the light exiting the fiber, and allows for smaller manifolds than those discussed in the previous work.
New Convex Grating Types Manufactured by Electron Beam Lithography
Authors: Maker Paul. D. , Muller Richard E. , Wilson Daniel W. , Mouroulis Pantazis
Published: February 2023

The advantages of spectrometer forms utilizing concentric surfaces have been recognized for some time.1,2 In order to realize these advantages in practice, a reliable and flexible method of generating gratings on curved substrates is needed. Concave gratings are commonly manufactured using both ruling and holographic techniques. However, it is difficult to produce well-blazed curved gratings.3,4,5 These difficulties are exacerbated in concentric spectrometer designs in which the grating must typically cover an arc that is greater than the blaze angle itself.
Fabrication of blazed holographic optical elements on oxygen free copper by ultrahigh precision cutting
Authors: Morita Shin-ya , Yamagata Yutaka , Higuchi Toshiro
Published: February 2023

A holographic optical element (HOE) is a kind of diffractive optical element. An HOE can substitute an optical system with multiple optical components like lenses, mirrors, beam-splitters, prisms and so on. So it is expected to reduce the number of its optical parts, improve a performance of various optical systems, such as optical storage systems[1] like CD or DVD systems, optical instrumentations, fiber optics and etc., and make an optical system simple, small and light weighted.
Single-step etching fabrication of diffractive microlens on high-energy-beam sensitive glass
Authors: Wang Michael R. , Su Heng
Published: February 2023

Diffractive microlens has a variety of applications including spot array generation, optical or hybrid opto-electronic interconnections, Fourier transformation, imaging, focusing, collimating, coupling, and beam shaping.[1-4] Diffractive microlens is also important for printing, optical data storage, and display applications. High lens efficiency is often required to minimize unwanted zero-order non-diffracted light beams that are responsible for optical crosstalks and background noises. High diffraction efficiency can be achieved by increasing number of phase levels of surface relief diffractive microlens structures.
A new approach to correct chromatic aberrations utilizing a hybrid surface
Authors: Blough C. Gary
Published: February 2023

A diffractive surface provides a unique method of achromatizing an optical system. Conventional techniques of achromatization with refractive elements utilize the balancing of optical powers and lens material properties to provide a corrected system.1 This requires the introduction of more refractive power than necessary in the system to satisfy the first-order requirements. The addition of more optical power typically requires steeper surface radii and the general correction of the system performance becomes more difficult. A diffractive surface provides a more natural method of achromatizing a system because refractive and diffractive surfaces of the same sign of optical power provide an achromatic solution.2 Hence, the need to introduce excess amounts of optical power to satisfy the first-order properties is eliminated. The diffractive surface can also be utilized to provide aspheric correction, although the wavelength range must be limited to reduce the effects of spherochromatism. In addition, the potential operating wavelength range is limited because of loss in diffraction efficiency introduced from wavelength detuning.
Super resolution and Dammann gratings
Authors: Lohmann Adolf W. , Mendlovic David , Zalevsky Zeev
Published: February 2023

The resolution of a system is defined as the finest detail that can pass through the system without being distorted. The motivation of the super resolution field is to handle the non resolved details using a given apriori information about the input signal [1], e.g. apriori knowledge on: object shape, temporal behavior, wavelength behavior, dimensions and polarization. The super resolution effect is achieved by exchange of degrees of freedom. For instance, let us assume that the spatial aperture of a system is small and some of the signal's information is lost due to this fact. If it is also apriori known that the signal's information is monochromatic, one may convert part of the spatial information into wavelength information, in such a way that the aperture of the system is synthetically expanded. Based on the distinction between the signal information and system's capabilities one may adapt the space bandwidth function (SW) of the signal to the SW function of the system using the Wigner chart [1].
Design of holographic optical beam splitters based on thin grating sequential diffraction technique
Authors: Wang Michael R.
Published: February 2023

Bragg diffractions by superimposed transmission phase gratings are important schemes for the realization of optical beam splitters for optical fanout interconnection, neural network implementation, data storage, and parallel optical processing and computing. The theory of optical beam diffractions by superimposed transmission phase gratings have been developed by several authors [1-13]. However, the existing techniques are limited to 2-D diffraction geometry, suffering from numerical problems when the superimposed grating number increases, and/or restricted to small-angle diffractions. For 3-D diffractions by superimposed transmission phase gratings, required for holographic beam splitting applications, there is no simple theoretical model to treat such problem. Complete modal analysis [6,7] already yields complicated results for single-grating diffraction, because the grating vector can have an arbitrary orientation with respect to the plane of incidence. As a consequence the s- and p-polarized field components become coupled inside the grating region and can no longer be treated separately by conventional coupled-wave theory [14]. The coupled 3-D diffraction is much more complicated than the single-grating case. It is, so far, hard for a design engineer to determine suitable grating index combinations prior to device implementation. As a result, superimposed gratings are often recorded through trial and error in hoping on getting a desired energy distributions for splitted beams.
Confocal microscopic and spectroscopic investigation of autofluorescence of Dictyosphaerium pulchellum wood
Authors: Joshi N.V. , Medina H. , Vielma Maria
Published: February 2023

Dictyosphaerium pulchellum Wood, a typical a fresh water alga, is known for photosynthesis and expected to have photoluminescence also. We have, therefore, carried out a confocal fluorescence microscopic and spectroscopic study of this species. 3-D image constructed from 50 optical sections clearly reveals that fluorescence is originated from only the outer layer and not from the central core. Spectral investigation shows that a strong and sharp peak is located at 684 nm. At this peak value, the power measurement was carried out and the number of photons emitted by alga in the solid angle 48.59 Ω was calculated and found to be 3.4*1010/ sec.

The other significant feature of the responsible fluorophore is that the present photoluminescence has a very low quenching rate and hence the emitted radiation is observed for a very long time (512 sec.). This directly suggests that this fluorophore could have direct applications in dye related industries.
Changes in optical properties of cells and tissue after induction of apoptosis
Authors: van der Meer Freek J. , Faber Dirk J. , de Bruin Riëtte , Aalders Maurice C. , Perrée Jop , van Leeuwen Ton G.
Published: February 2023

Apoptosis is the effector of regulated cell death and plays a role in many physiologic and pathologic processes. It is characterized by a highly regulated condensation and fragmentation of the cell nucleus, and breakup of the entire cell into vesicles, (apoptotic bodies) containing cell organelles and fragments of the nucleus. Previous experiments indicate that changes in optical properties after induction of apoptosis might be detected using optical imaging systems, such as optical coherence tomography (OCT), due to an increase in scattering of apoptotic cells. The previous in vitro experiments are extended to ex vivo and in vivo experiments. A nearly two-fold increase in attenuation coefficient is observed in a tissue culture of porcine carotid artery, in which apoptosis is induced by balloon dilation, and a significant 20 % increase in an in vivo setup. The preliminary results of this study indicate that the apoptotic process may also be detected ex vivo and in vivo using optical imaging systems, such as optical coherence tomography (OCT), due to an increase in scattering by the typical disintegration of cellular material.
The Radiosity Diffusion Model in 3D
Authors: Riley Jason D. , Arridge Simon R. , Chrysanthou Yiorgos , Dehghani Hamid , Hillman Elizabeth M. C. , Schweiger Martin
Published: February 2023

We present the Radiosity-Diffusion model in three dimensions (3D), as an extension to previous work in 2D. It is a method for handling non-scattering spaces in optically participating media. We present the extension of the model to 3D including an extension to the model to cope with increased complexity of the 3D domain. We show that in 3D more careful consideration must be given to the issues of meshing and visibility to model the transport of light within reasonable computational bounds. We demonstrate the model to be comparable to Monte-Carlo simulations for selected geometries, and show preliminary results of comparisons to measured time-resolved data acquired on resin phantoms.
Hybrid Monte Carlo-Diffusion method for light propagation in tissue with low scattering layer
Authors: Hayashi Toshiyuki , Kashio Yoshihiko , Okada Eiji
Published: February 2023

Near infrared spectroscopy is increasingly being used for monitoring cerebral oxygenation and haemodynamics. Since the light in the head is strongly scattered, it is necessary to modelling the light propagation in the head to obtain the volume of tissue sampled and partial optical path length in the brain. The serious problem to calculate the light propagation in the head is the heterogeneity of tissue especially the presence of low scattering CSF layer. Since the diffusion no longer holds in the low scattering layer, the light propagation in the head model with low scattering layer should be analysed by Monte Carlo method or light transport In this study, we propose a new approach “Hybrid Monte Carlo-Diffusion Method” to calculate the light propagation in the adult head model with a low scattering CSF layer. The light propagation in a high scattering medium is calculated by the diffusion theory and that in a low scattering CSF layer is predicted by Monte Carlo method. The results of detected intensity and mean time of flight in a simplified adult head model by the Hybrid Monte Carlo-Diffusion method agree well with those predicted by Monte Carlo method.
Analysis of light propagation in neonatal head model by finite difference method
Authors: Fukui Yuichi , Yamamoto Tsuyoshi , Okada Eiji
Published: February 2023

The light propagation in a simple layered ellipse model and more complex neonatal head model are calculated by the finite-difference method. The finite-difference method has advantage of simple algorithm and fast calculation time however has been successful under restricted condition for a heterogeneous medium. The light propagation in the both models is predicted by Monte Carlo simulation to validate the results of the finite-difference method. The detected intensity and partial optical path length calculated by the finite-difference method agree with those by Monte Carlo simulation. The boundary of the grey and white matter in the neonatal head model is more complex than the simple ellipse model. However, the tendency of spatial sensitivity profiles in the neonatal head model is scarcely affected by the effect of heterogeneity of the brain tissue.
Correction for in-homogeneously distributed absorbers in spatially resolved diffuse reflectance spectroscopy
Authors: van Veen R.L.P. , Sterenborg H.J.C.M.
Published: February 2023

Absorption and reduced scattering coefficients calculated from spatially resolved diffuse reflectance measurements are usually assumed to be unreliable for wavelengths lower than approximately 600 nm. A correction factor was developed for non-homogenous distribution of absorbers concentrated in discrete cylindrical blood vessels. The concept of an effective absorption coefficient extends the applicability of diffusion theory too much lower wavelength regions.
Dual-wavelength time-resolved optical mammograph for clinical studies
Authors: Cubeddu Rinaldo , Giambattistelli Eleonora , Pifferi Antonio , Taroni Paola , Torricelli Alessandro
Published: February 2023

An instrument for time resolved optical mammography working in the compressed breast geometry was constructed. The system operates with pulsed laser sources emitting simultaneously at two different wavelengths. Time-correlated single-photon counting is used for acquisition. The breast is slightly compressed between two plates and scanned along the X and Y directions. Continuous acquisition and on line display of the processed images permit optimal measurement efficiency and control of the operation. Phantom tests and preliminary in vivo measurements on healthy volunteers demonstrate capability to distinguish between scattering and absorption contributions, as well as discrimination of key breast structures. The equipment is about to be tested in a clinical study on time-resolved optical mammography.
High count rate multichannel TCSPC for optical tomography
Authors: Becker Wolfgang , Bergmann Axel , Wabnitz Heidrun , Grosenick Dirk , Liebert Adam
Published: February 2023

An improved Time-Correlated Single Photon Counting (TCSPC) technique features high count rate, low differential nonlinearity and multi-detector capability. The system has four completely parallel TCSPC channels and achieves an effective overall count rate of 20 MHz. By an active routing technique, up to eight detectors can be connected to each of the TCSPC channels. We used the system to record optical mammograms after pulsed laser illumination at different wavelengths and projection angles.
Use of backprojection algorithms of filtered shadows for optical tomography of strongly scattering media
Authors: Kalintsev Alexander G. , Konovalov Alexander B. , Kravtsenyuk Olga V. , Kutuzov Igor I. , Lyamtsev Oleg V. , Lyubimov Vladimir V. , Murzin Alexander G. , Soms Leonid N.
Published: February 2023

The applicability of backprojection algorithms of filtered shadows that have been earlier developed for computer tomography is shown for the case of optical tomography of strongly scattering media. This opportunity is based on the presence of a long rectilinear part in the approximation of the statistical Photon Average Trajectories of photons propagating through the scattering medium. The results of numerical experiments showed that the quality of reconstruction using filtered backprojection algorithms do not surrender to that for multi-iterative algorithms, at much shorter reconstruction time.
Application of Photon Average Trajectories Method for separate mapping of absorbing and scattering macroinhomogeneities using time-domain measurements technique
Authors: Golubkina Olga V. , Kalintsev Alexander G. , Konovalov Alexander B. , Kravtsenyuk Olga V. , Lyamtsev Oleg V. , Lyubimov Vladimir V. , Mordvinov Gennadiy B. , Murzin Alexander G. , Soms Leonid N. , Tokareva Natalie O. , Yavorskaya Luydmila M.
Published: February 2023

Theoretical analysis and numerical experiments show a significant difference in a temporal dynamics of shadows caused by absorbing and scattering macroinhomogeneities. This difference is especially noticeable at the leading front of the pulse passed through the scattering medium. This makes it possible to image absorbing and scattering inhomogeneities separately using shadows obtained at subsequent time moments.
Instrumentation for Real-Time Dynamic Optical Tomography
Authors: Schmitz Christoph H. , Pei Yaling , Graber Harry L. , Lasker Joseph M. , Hielscher Andreas H. , Barbour Randall L.
Published: February 2023

Presented are the operating characteristics of an integrated CW-near infrared tomographic imaging system capable of fast dam collection and producing 2D/3D images of optical contrast features that exhibit dynamic behavior in tissue and other highly scattering media in real time. Results of preliminary in vivo studies on healthy and cancerous breast tissue are shown.
Investigation of the Optical Diffusion Coefficient in Turbid Media by the Added-Absorber Method
Authors: Reich Oliver , Schael Frank
Published: February 2023

The dependence of the optical diffusion coefficient D on the absorption coefficient μa was investigated. The spatial intensity distribution of light emitted by a low frequency intensity-modulated diode laser was studied in aqueous suspensions of pmma latex beads. The absorption coefficient of the suspensions was gradually increased by adding the dye isosulfan blue (isb) up to a ratio between the absorption and the effective scattering coefficient of the mixture of 3.6. Conventional transmission measurements showed that the absorption coefficient of the mixture increases linearly in the entire concentration range employed. The measurements were evaluated in the framework of photon diffusion theory. The results obtained indicated that for the suspensions investigated the optical diffusion coefficient does depend on absorption.