1,720,952 research outputs found
Integrating Photonics into Fab Labs
No full textAn ambitious project teams up local photonics organizations with creative facilities to promote European photonics innovation.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Optic
Limits of realizing irradiance distributions with shift-invariant illumination systems and finite etendue sources
No full textWhen redistributing the light emitted by a source into a prescribed irradiance distribution, it is not guaranteed that, given the source and optical constraints, the desired irradiance distribution can be achieved.We analyze the problem by assuming an optical black box that is shift-invariant, meaning that a change in source position does not change the shape of the irradiance distribution, only its position. The irradiance distribution we can obtain is then governed by deconvolution. Using positive-definite functions and Bochner s theorem, we provide conditions such that the irradiance distribution can be realized for finite etendue sources.We also analyze the problem using optimization, showing that the result heavily depends on the chosen source distribution.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Adam groupImPhys/Urbach grou
Diffractive optical elements are all you need: Designing an optical system using physics-informed and data-driven methods
No full textIn this work, we consider how to optimize an optical system, specifically one with diffractive optical elements (DOE). We start by describing optical theory called Fourier optics also known as wave optics. This type of optics is found by making assumptions from the Maxwell equations for magnetic and electrical fields. This leads us to the Rayleigh-Sommerfeld diffraction integral, which we need to propagate light. To optimize an optical system, we introduce the standard optimization methods used when gradients are available and also dive into data-driven methods. Two wellknown algorithms in each category: the Adam optimization method, which is an extension of normal gradient descent methods, and the UNet convolutional neural network. To make the optimization methods work with our physics simulation, we use an automatically differentiable implementation which gives the gradients for the optimization. Combining the two optimization methods with our optics engine, we optimize optical designs such that the resulting intensity on the sample plane resembles some target intensity. We are able to optimize systems with single and multiple DOE and for high and low resolution DOE designs. We find that more lenses makes the optimization better and increases the variability in the created projection. We also find that increasing the resolution severely slows down the optimization with the Adam method. Although, the optimization method Adam is well suited for this optimization task. It becomes computationally very expensive on high resolution due to the physics simulation at every optimization step. Some physical simulations require high resolution to make sure the simulation does not contain to much artefacts. We show that the data-driven approach has potential to solve this issue. We train a network that takes as input a target intensity and outputs the lens that produces that intensity. Combining these results, we conclude that modern optimization methods are well suited for optical system optimization and we find that there is a large untapped potential for data-driven methods in optics.Applied Mathematic
Review of Near-Field Terahertz Measurement Methods and Their Applications: How to Achieve Sub-Wavelength Resolution at THz Frequencies
No full textIn the last decades, many research teams working at Terahertz frequencies focused their efforts on surpassing the diffraction limit. Numerous techniques have been investigated, combining methods existing at optic wavelength with THz system such as Time Domain Spectroscopy. The actual development led on one side to a resolution as high as ?/3000 and one the other side to a video-rate recording. The purpose of this paper is to give an overview of the history of the field, to describe the different approaches, to give examples of existing applications and to draw the perspective for this research area.Imaging Science and TechnologyApplied Science
An exact solution for dipole fields inside optical multilayer structures
No full textIn this report, we derive some tools that can be used to construct semi-analytical solution for the electromagnetic field of a dipole in an arbitrary multilayer system. The proposed methods consist of a recursive determination of electric fields -- using the mathematical principle behind a Fabry-Perot interferometer -- and two different derivations for the decomposition of the electric field of a resonating dipole into plane waves -- using dyadic Green functions and two dimensional Fourier transforms respectively. These decomposition methods are not analytic, since the resulting integrals can only be computed numerically. The results of these tools are compared to known results from other literature and seem to nicely match, making them useful tools for the combination into a method for computing the dipole field in the multilayer. This merge is not completed in this project. However, some suggestions on how to perform this combination are done.Applied SciencesApplied MathematicsApplied Physics and Applied Mathematic
BSc Optics
No full textThis book treats optics at the level of students in the later stage of their bachelor or the beginning of their master. It is assumed that the student is familiar with Maxwell’s equations. Although the book takes account of the fact that optics is part of electromagnetism, special emphasis is put on the usefulness of approximate models of optics, their hierarchy and limits of validity. Approximate models such as geometrical optics and paraxial geometrical optics are treated extensively and applied to image formation by the human eye, the microscope and the telescope.Polarisation states and how to manipulate them are studied using Jones vectors and Jones matrices. In the context of interference, the coherence of light is explained thoroughly. To understand fundamental limits of resolution which cannot be explained by geometrical optics, diffraction theory is applied to imaging. The angular spectrum method and evanescent waves are used to understand the inherent loss of information about subwavelength features during the propagation of light. The book ends with a study of the working principle of the laser.TU Delft OPEN TextbookImPhys/OpticsImPhys/Adam groupImPhys/Stallinga grou
Focusing light through a free-form scattering medium
No full textImaging and transport light through scattering opaque media is a hot topic pursued in multiple fields, ranging from nanotechnology to life sciences. A promising technique to do this is wavefront shaping (WFS), where the light propagation through a scattering medium is controlled by interference [1] [2]. Recently, the potential of WFS was even extended to, for instance, time-varying samples [3] [4]. In most cases to date, WFS has been done on the quintessential scattering sample geometry, namely in slabs.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Optic
Designing interactive demonstrations of optics phenomena
No full textThe United Nations and Unesco have declared 2015 to be the international year of light. The Optics department of the faculty of Applied Physics from the TU Delft has decided to contribute to this effort by designing optics experiments to be displayed at the Science Center Delft. The goal of this project was to manage first year students that helped design and explain these experiments. Another part was to design an experiment involving lithography. The students were split into three groups, each with a different subject, polarization, cloaking and light emitting diodes. The management part of the subject went well; ten experiments were designed and the principle behind them were explained on posters. I have learned that communication is very important in teamwork and that the group members need to be motivated in order get the proper results.OpticsImaging Science & TechnologyApplied Science
A compressive sensing with photonic crystals enabled spectrometer for trace gas observation
No full textRecently a spectrometer concept has been invented which uses compressive sensing in combination with photonic crystal filters. Here we present an adaption of this concept in push-broom configuration for earth observation. This implementation allows for a compact design, while maintaining a high spatial resolution and high signal-to-noise ratio compared to other traditional implementations. The photonic crystals have a unique transmission profile and act as a spectral filter, which allows for the computational reconstruction of the input spectrum with a limited number of filters. We show, using simulations, that our approach is able to reconstruct input radiance spectra with high accuracy and assess the performance for different number of filter sets. We furthermore show proof-of-principle measurements of the transmission profile of a manufactured photonic crystal. Future research will focus on the effect of noise on the reconstruction algorithm as well as further filter set optimization by combining the filter selection process with trace gas concentration retrieval.ImPhys/Adam grou
Designing free-form optics for multiple-source illumination using differentiable ray-tracing and neural networks
No full textDifferentiable ray-tracing is an exciting new development in computer graphics to approach all sorts of 3D scene design problems by obtaining gradients of renders produced by ray-tracing with respect to parameters that define the scene. These gradients can then be incorporated in a gradient-descent type optimization pipeline.One such type of design problem is caustic design with free-form lenses. This is the process of obtaining the geometry of lenses in an optical system such that the light that passes through this system forms a desired illumination distribution on a target screen. A typical application of this is distributing the light from streetlights or car headlights in a pleasing and efficient way over the street.The non-imaging optics literature offers many methods to design free-form lenses for caustic design, but differentiable ray-tracing is largely unknown in this field. Therefore this thesis proposes a method of optimizing free-form lenses for caustic design with differentiable ray-tracing. The optimization pipeline starts with a multi-layer perceptron neural network which outputs parameters that define one free-form lens side in the form of a B-spline surface. A specially implemented ray-tracer then produces a caustic render by tracing through this lens from either a plane wave or a (grid of) point source(s). Back-propagation and optimization takes place using automatic differentiation in PyTorch and the Adam optimizer.The results, which are verified with LightTools, show great promise for this technique, especially for the plane wave optimizations. The point source grid optimizations proved to be more challenging, but also here the optimization was able to achieve improvement. This shows that the proposed technique also has potential in positive etendue optimizations.Applied Mathematics | Computational Science and Engineerin
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