LightWave 3D is a 3D computer graphics software developed by NewTek. It has been used in film, television, motion graphics, digital matte painting, visual effects, video games development, product design, architectural visualizations, virtual production, music videos, pre-visualizations and advertising. Wikipedia.
Asli B.H.S.,Lightwave |
Flusser J.,Czech Institute of Information Theory And Automation
Information Sciences | Year: 2014
The paper describes the calculation of the Krawtchouk Moments (KMs) from an image, which is a computationally demanding task. We present two original methods that use the outputs of cascaded digital filters in deriving KMs. The first approach uses the digital filter outputs to form geometric moments (GMs) and the KMs are obtained via GMs. The second method uses a direct relationship to obtain KMs from the digital filter outputs. This is possible thanks to the formulation of Krawtchouk polynomials in terms of binomial functions, which are equivalent to the digital filter outputs. In this study, the performance of the proposed techniques is compared with other existing methods of KMs calculation. The experimental study shows that the first and the second proposed techniques perform 57% and 87% faster than the recurrence method for a real image of a size 128 × 128 pixels, which performs a significant improvement. © 2014 Elsevier Inc. All rights reserved. Source
Bhattacharya J.,Iowa State University |
Chakravarty N.,Iowa State University |
Pattnaik S.,Iowa State University |
Dennis Slafer W.,Lightwave |
And 2 more authors.
Applied Physics Letters | Year: 2011
We describe a photonic-plasmonic nanostructure, for significantly enhancing the absorption of long-wavelength photons in thin-film silicon solar cells, with the promise of exceeding the classical 4n2 limit for enhancement. We compare identical solar cells deposited on the photonic-plasmonic structure, randomly textured back reflectors and silver-coated flat reflectors. The state-of-the-art back reflectors, using annealed Ag or etched ZnO, had high diffuse and total reflectance. For nano-crystalline Si absorbers with comparable thickness, the highest absorption and photo-current of 21.5 mA/cm2 was obtained for photonic-plasmonic back-reflectors. The periodic photonic plasmonic structures scatter and reradiate light more effectively than a randomly roughened surface. © 2011 American Institute of Physics. Source
Lightwave | Date: 2011-01-06
A VCSEL structure is provided. The VCSEL structure comprises a substrate. The structure may also include one or more conducting layers positioned on the substrate. There may be void spaces positioned between portions of the conducting layers to electrically isolate the portions. A method for fabricating the VCSEL structure is also provided.
Agency: Cordis | Branch: FP7 | Program: BSG-SME | Phase: SME-1 | Award Amount: 1.45M | Year: 2009
Europe has suffered in the last years a large number of forest fires that has caused enormous losses in terms of human life and environmental damage. During 2007, more than 3376 square kilometres of forest and agricultural fields disappeared in smoke, causing the loss of more than 64 lives and more than 1.6bn Euros .These figures meant an increase of a 50% in southern European countries such as Greece in relation to the impact by forest fires in the previous years. The burnt area represented a 14% of the total forest mass in the European Union, and an 25% for the southern European countries (Spain, Portugal, Italy and Greece), in danger of desertification . Despite of the use of the latest technologies, such as satellite monitoring, the situation has not significantly improved for the last 25 years. Even more, it seems that the risk and number of forest fires are increasing each year due to a combination of human (smokers, campers and picnickers or tourists) and environmental factors (earthquake, erupting volcanoes, drought, lightning, etc). FORFIRE aims to develop an outdoors fire detection system using a new camera sensor only sensible to VUV part of the spectrum. This feature provides a set of advantages comparing with current sensors. Developing this new sensor will provide the capability of early fire detection with a very low rate of false alarm (0.1%). This can be achieved by focusing on the spectral characteristics of flames in the Vacuum Ultra Violet (VUV) area (at wavelengths between 140 to 240 nm) of the electromagnetic spectrum. The objective of the project is to develop each of the components necessary for the integration and validation of FORFIRE product to place SMEs in a position for successfully differentiation from abroad competitors.
A computationally efficient theoretical approach is used to assess the performance of novel devices with directly emitting optical vortex modes. With the increasing amount of information that travels in telecommunication systems, single-mode fiber-based infrastructures are no longer sufficient, and there is a continuous need to improve the transmission channel capacity. Among the approaches currently being explored, mode-division multiplexing is one of the most appealing. In this technique—because modes with different topological charge (ℓ) are orthogonal—an additional degree of freedom (i.e., the spatial dimension) can be added to the well-established time, wavelength, polarization, and coding schemes.1–4 Although this new dimension has already been successfully implemented in architectures that are based on digital signal processors (DSPs),1, 2 the huge amount of data still leads to an extremely high power consumption. A passive, full-optical solution would therefore minimize DSP usage and the related power requirements, and would fit well within a ‘green technology’ paradigm. Mastering the orbital angular momentum (OAM) of light is currently one of the most popular topics in the field of optics. Since the OAM of light was first described with simplified mathematical models of laser beams (Laguerre–Gaussian beams),6 several researchers have exploited the concept in a large variety of applications. These applications include optical manipulation,7 imaging,8, 9 single-photon detection,10 and mode multiplexing/demultiplexing.11, 12 Indeed, one of the most critical aspects of realizing a passive, full-optical approach for the enhancement of the telecommunication channel capacity is the generation of OAM light modes in optical fibers. Such modes are usually obtained from standard laser beams with the use of a mode converter. Several conversion techniques—based on bulky optical components—have been extensively described in the literature, e.g., hologram-based techniques that exploit computer-programmed spatial light modulators,13, 14 as well as modal filters that are based on the use of spiral-phase plates (SPPs) and that impress the azimuthal angular momentum onto the beam.15 Although these methods are well-established for bulk optics systems, light sources that directly emit OAM modes have yet to be realized and they would represent a major leap toward the implementation of fully integrated high-capacity networks. In our work we have conducted a parametric investigation of the modal performance of single-mode single-polarization vertical-cavity surface-emitting lasers (VCSELs) that are loaded with a micro-SPP. Our theoretical work, for which we used our in-house VCSEL electromagnetic (VELM) simulator,16 was designed to complement previous experimental work (by another group) in which the commercial VCSEL loaded with a micro-SPP was proposed (see Figure 1).17 VCSELs are axisymmetric semiconductor lasers that radiate orthogonally to their constituent layers. These layers serve as high-reflectivity mirrors and define the 1λ cavity (where λ is the wavelength) of the VCSEL resonator.18 In addition, the circular radiation feature of VCSELs makes them optimal for fiber coupling. In aluminum gallium arsenide VCSELs, an oxide aperture acts as a guide for the optical field and the electric current. This feature, combined with the high reflectivity of the mirrors, means that low threshold currents (at the milliamp level) and high efficiencies can be achieved. Furthermore, the radiation from these devices is emitted at a wavelength of about 850nm, i.e., where the electrically pumped gallium arsenide quantum wells that compose the active region exhibit the maximum material gain. Figure 1. Schematic diagram of a vertical-cavity surface-emitting laser (VCSEL), loaded with a spiral-phase plate (SPP), which can be used to generate an orbital angular momentum (OAM) beam. The sub-wavelength (SW) grating and axes are not shown to scale. Schematic diagram of a vertical-cavity surface-emitting laser (VCSEL), loaded with a spiral-phase plate (SPP), which can be used to generate an orbital angular momentum (OAM) beam. The sub-wavelength (SW) grating and axes are not shown to scale. 5 The experimentally produced SPP-VCSEL was obtained by growing a pillar of silicon nitride on the emitting aperture, and a focused ion beam manufacturing process was used to obtain the SPP.17 In the experimental study, it was also shown that the device could directly emit OAM modes. This SPP-VCSEL device is thus an extremely interesting prospect owing to its compactness, low power consumption, and low cost. Our theoretical work is based on expanding the unknown VCSEL field, in terms of cylindrical wave functions. In our approach, the expansion coefficients are propagated by means of a generalized transmission matrix formalism, which is based on coupled-mode theory. The condition of a mode repeating itself after a full-cavity round-trip is rephrased in terms of an eigenproblem. Its solutions provide the modal wavelengths, the corresponding threshold gains, and field topographies. Our technique is computationally efficient and finds the modes of complex 3D structures (not axisymmetric) within a few minutes on a modern PC.19, 20 As an example, the simulated field profiles for an unprocessed VCSEL and for three micro-SPP geometries (used to obtain OAM beams with different topological charges) are shown in Figure 2. Figure 2. Modal profiles of four VCSEL devices. (a) A bare device and three devices loaded with SPPs that have topological charge (ℓ) of (b) 1, (c) 2, and (d) 3. The maps in the top part of the figure show a 30 ×30μm2area, at a distance of 100μm from the outcoupling section. The images in the middle row are cross-sectional cuts—in the x (transverse coordinate) and z (longitudinal coordinate) directions—through the field intensity. The transverse geometries of the devices (with the SPPs in red) are shown at the bottom. Ox. aper.: Oxide aperture. E: Electric field. Ex: Component of the electric field in the x-direction. Re(Ex): Real part of Ex. Modal profiles of four VCSEL devices. (a) A bare device and three devices loaded with SPPs that have topological charge (ℓ) of (b) 1, (c) 2, and (d) 3. The maps in the top part of the figure show a 30 ×30μmarea, at a distance of 100μm from the outcoupling section. The images in the middle row are cross-sectional cuts—in the x (transverse coordinate) and z (longitudinal coordinate) directions—through the field intensity. The transverse geometries of the devices (with the SPPs in red) are shown at the bottom. Ox. aper.: Oxide aperture. E: Electric field. Ex: Component of the electric field in the x-direction. Re(Ex): Real part of Ex. 5 We present the results of a preliminary, qualitative comparison between the modes of the SPP-VCSEL device (ℓ of 1) and their ideal (i.e., Laguerre–Gaussian) counterparts in Figure 3. From our VELM results it is also possible to compute a more quantitative estimate of the OAM mode's purity and to thus evaluate the modal performance of the device.5 The simulated mode purities agree with the measured values previously reported.17 For instance, we obtain results of 85, 86, and 78% for the fields in Figure 2(b–d). These results compare well with the experimental data for the corresponding fields, i.e., 89, 84, and 78%, respectively. In an extended simulation campaign, we proved the robustness of the SPP-VCSEL design for most variations. We found only one exception, which was the SPP misalignment with respect to the VCSEL axis. From our results shown in Figure 4, a degradation of the far-field patterns can be observed. In addition, the decreasing efficiency trend, with increasing misalignment, is illustrated. Figure 3. (Left) Far-field (E ) intensity and (right) phase maps of (top) an ideal Laguerre-Gaussian mode and (bottom) the mode emitted by the ℓ=1SPP-VCSEL. revs: Revolutions. (Left) Far-field (E) intensity and (right) phase maps of (top) an ideal Laguerre-Gaussian mode and (bottom) the mode emitted by the ℓ=1SPP-VCSEL. revs: Revolutions. 5 Figure 4. The effect of misalignment (the distance between the SPP and VCSEL axes) on ℓ=1SPP-VCSEL mode. Far-field intensity maps are shown on the left, where the misalignment (Mis) and mode purity (Pur) are given in nm. (Right) The relationship between mode purity and misalignment. The effect of misalignment (the distance between the SPP and VCSEL axes) on ℓ=1SPP-VCSEL mode. Far-field intensity maps are shown on the left, where the misalignment (Mis) and mode purity (Pur) are given in nm. (Right) The relationship between mode purity and misalignment. 5 In summary, we have developed a theoretical approach to assess the modal performance of VCSELs. In particular, we have used our computationally efficient technique to verify a previously experimentally proposed device that is loaded with a spiral-phase plate. The effectiveness, speed, and reliability of our VELM simulator also open up the possibility of exploring other implementations of SPP-VCSELs. In our future work, supported by technological affordability studies, we hope to further develop these devices, improve the purity of the emitted OAM modes, and reduce the manufacturing costs associated with the VCSELs. Department of Electronics and Telecommunications Polytechnic University of Turin Department of Electronics and TelecommunicationsPolytechnic University of Turin Department of Electronics, Information and Bioengineering Polytechnic University of Milan Department of Electronics, Information and BioengineeringPolytechnic University of Milan 1. P. J. Winzer, Spatial multiplexing in fiber optics: the 10× scaling of metro/core capabilities, Bell Labs Tech. J. 19, p. 22-30, 2014. 2. R. Ryf, S. Randel, A. H. Gnauck, C. Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, et al., Mode-division multiplexing over 96km of few-mode fiber using coherent 6 × 6 MIMO processing, J. Lightwave Technol. 30, p. 521-531, 2012. 6. L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, J. P. Woerdman, Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes, Phys. Rev. A 45, p. 8185-8190, 1992. 7. H. He, M. E. J. Friese, N. R. Heckenberg, H. Rubinsztein-Dunlop, Direct observation of transfer of angular momentum to absorptive particles from a laser beam with a phase singularity, Phys. Rev. Lett. 75, p. 826-831, 1995. 19. P. Debernardi, B. Kogel, K. Zogal, P. Meissner, M. Maute, M. Ortsiefer, G. Bohm, M.-C. Amann, Modal properties of long-wavelength tunable MEMS-VCSELs with curved mirrors: comparison of experiment and modeling, IEEE J. Quant. Electron. 44, p. 391-399, 2008.