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In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material because they have been proven to be well-suited for the intended see-through application: the capability to provide a virtual image without compromising the information about the surrounding environment. Moreover, holography fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced reflection holographic gratings exhibit the correct properties to work as a coupler, where the sensitivity of the material and its properties are studied and examined.

It is well known that Spatial Light Modulators (SLM) are of great interest and used in many different areas because of their continuous capability of light modulation and their potential as a linear variable retarder. However, high-definition SLM devices face the challenge of providing high performance under the influence of different phenomena, such as crosstalk between adjacent pixels, fringing fields, and diffraction effects arising from the finite pixel grid pattern. In this work, a numerical analysis that computes the director orientation as a function of the retardance across specific voltages (gray level) is compared to experimental results. More specifically, this work is focused on analysing how previously mentioned phenomena affect the interpretation of the residual twist angle in parallel-aligned (PA) on SLM. This twist angle is computed from the Stokes parameter and compared to the actual orientation of the director distribution.

Estimating the actual parameters of real holographic volume gratings from diffraction efficiency measurements is challenging. The natural formation of the grating provides different phenomena, such as shrinkage, bending of the fringes, or non-homogeneous modulation as a function of the thickness, amongst other issues. This work proposes a deep learning Convolutional Neural Networks (CNNs) and Feedforward Neural Networks (FNNs) hybrid architecture capable of predicting the grating parameters from theoretical and experimental diffraction efficiency patterns. For the training set of this regression problem, Kogelnik’s Coupled Wave Theory simulated data has been employed. Our best model has been trained with an 8000-sized dataset of 80 points of diffraction efficiency patterns simulated from a range of values for the normalized grating wavelengths, index modulations, and optical depths. It achieves test losses under one per cent (mean absolute error) for predicting the normalized grating wavelengths, index modulations and optical depths.

Devices based on liquid crystal (LC) exhibit a great interest in Optics due to their capability to set up applications with variable properties. Some examples of these elements are spatial light modulators (SLM) based on parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplays. Other applications of LC in diffractive elements are based on polymer-dispersed liquid crystal devices (H-PDLC), e.g. diffraction lenses, optical data storage, and image capture devices. These examples share one of the most exciting features of LC, which is the capability to change the optical properties with an external voltage. Here, a review of the latest developments in estimating the director distribution in LC-based devices is summarised. The results here summarised show the potential of the approach for rigorously analysing the fringing field and crosstalk polarimetric impact on PA-LCoS devices, the bending in H-PDLC fringes, and the application of machine learning on the estimation of the LC director distribution in this kind of devices.

It is a fact that augmented reality or virtual reality has burst into society with force: allowing the creation of programmed video games to be played with virtual reality glasses or the manufacture of glasses that act as mobile devices connected to the Internet ("Google glasses"). Augmented reality devices generally consist of a headset and a display system to show the user virtual information in addition to the real one. The systems used are the transparent optical screen and the mixed video screen. In this way, virtual images can be used that are shown to the user, mixed with reality or projected directly on the screen. On the other hand, the "glasses" have some advantages in relation to a direct viewing mobile screen, for example, hands-free and high privacy character. Among the different models of glasses proposed, transparent glasses are especially important for mobile use because they are safer and easier for the public to accept. However, combining high-quality images with clear visibility throughout the system remains a challenge. In this work, holographic waveguides will be manufactured in photopolymers and the experimental results will be contrasted with the numerical simulations carried out using the RCW models. An important fact that must be taken into account in the recording of the holographic waveguide is the possible recording of noise reflection gratings. In general, noise gratings in other devices extract a small amount of energy from the diffracted order, without any other spurious effects. However, in this particular device it will be shown that noise reflection gratings could create an unwanted afterimage. Since the reconstruction is performed at a different wavelength than the recording, the reflection noise grating may or may not be "visible" during the reconstruction, so it is possible to control the appearance of the gratings, for example, by controlling the thickness of the final waveguide. The gratings to performed the study were recorded

Holography is a broad field of research that interacts with a wide range of disciplines, from physics and chemistry to art through engineering, as shown by the large number of publications that can be found on the subject. Holography is integrated into our daily lives, often associated with the rainbow-like effect on banknotes, credit cards, and ID cards. Let us also consider that holography involves many optical phenomena (coherence, diffraction, interference, analogue and digital recording devices, lasers, materials, etc.). Therefore, holography is an extraordinarily productive and attractive field as a research area. Furthermore, holographic devices facilitate the development of many applications, some of which are reviewed in the present paper.

We print a tunable photopolymer (photopolymer dispersed liquid crystal -PDLC), using the laser-induced direct transfer technique without absorber layer, which was a challenge for this technique given the low absorption and high viscosity of PDLC, and which had not been achieved so far to our knowledge. This makes the LIFT printing process faster and cleaner and achieves a high-quality printed droplet (aspheric profile and low roughness). A femtosecond laser was needed to reach sufficiently peak energies to induce nonlinear absorption and eject the polymer onto a substrate. Only a narrow energy window allows the material to be ejected without spattering.

En este trabajo presentamos diferentes características que debemos tener en cuenta cuando queremos evaluar el retardo de una lámina retardadora variable, o de cualquier dispositivo que se pueda comportar como una de estas láminas. En nuestra experiencia, y debido a que están involucradas diferentes funciones trigonométricas, hemos encontrado que siempre aparece cierta incertidumbre en el retardo medido que está limitado por los valores obtenidos de dichas funciones. Intentaremos contextualizar los resultados con los diferentes modos de desenrollado que podemos utilizar y ver en qué punto se produce dicho enrollado, así como las consideraciones que deberemos tener en cuenta para evaluar el retardo para que se ajuste a lo que realmente estamos midiendo., In this work we present different aspects that we have to manage when we want to evaluate the retardance introduced by a variable waveplate, or any device that behaves in that way. In our experience, and due to the trigonometric functions that are involved, we have find that we always appears some uncertainty in the measured retardance that are limited by the values obtained by the used trigonometric functions. We will try to contextualize the results with the different methods of unwrapping that we can use and at what point the wrapping occurs. We will make some considerations to consider making the evaluated retardance closer to the real retardance introduced by the waveplate.

The study of liquid crystal (LC) director distribution is an important area of research in materials science and technology. Parallel-aligned liquid crystal (PA-LC) devices have been extensively studied due to their applications in liquid crystal displays, optical devices, and sensors. Estimating the LC director distribution is a critical step in designing and optimising PA-LC devices. This work shows the results derived from apply- ing novel optimisation techniques to estimate the liquid crystal (LC) director distribution in parallel-aligned liquid crystal (PA-LC) devices. Moreover, the genetic algorithm (GA) has been applied and compared with the minimisation of the Frank-Oseen free energy through the Euler-Lagrange equations. The GA is a stochastic optimisation technique that can effectively explore the search space and find the global optimum. Overall, this study’s results demonstrate the GA’s effectiveness in estimating the LC director distribution in PA-LC devices. This approach can improve the performance and design of liquid crystal displays, optical devices, and sensors. Furthermore, it can be extended to other fields where the optimisation of complex systems is required. Further research is needed to optimise the GA parameters and to explore its potential in other applications.

In this work, the impedance response of a set of trombones is analysed in order to find correlations between their sound and timbre and the main characteristics of the impedance curves. For this specific application, an impedance tube has been designed and manufactured to measure the different trombones' impedance curves. A plastic trombone (P-Bone) has been considered in the experiments to determine the importance of the material used to fabricate the instrument. In order to parametrise the trombones considered here, the instrument profile has been theoretically studied using a conical approach. More precisely, the tube and bell cone of the trombone has been discretised along its length in a set of small conical segments. Also, the influence of the mouthpiece is considered in the analytical formalism, and all these factors are optimised by employing a genetic algorithm to find the physical parameters that fit the experimental impedance curves. The experimental results are also compared with the opinions obtained from a survey about the subjective assessment of the same music passage recorded with the different instruments considered here. The results show that the impedance curve and some of the fitted parameters obtained correlate with the assessment of trombones in the blind survey. Moreover, the quality of the impedance tube here designed reveals that it is an excellent option to find leakages or dysfunction in this instrument.

The phase-shift exhibited by liquid crystal on silicon devices (LCoS) depends on the voltage applied and the illumination wavelength. Most of the LCoS used in the labs are digitally addressed using a binary pulse width modulated signal. Usually, these devices are characterized for a very small range of the available binary voltage values and for specific wavelengths. In this work, we consider a commercial parallel-aligned liquid crystal on silicon device (PA-LCoS) in which the binary voltages are accessible through the software of the vendor. We perform a complete averaged Stokes polarimetric characterization of the device where we are able to obtain the absolute unwrapped retardance values for a wide range of voltage parameters and across the visible spectrum. This provides a practical approach to evaluate the whole range of phase modulation possibilities, and to analyze some issues related with the physics of the device.

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material, as they are well-suited for the intended see-through application. Moreover, Kogelnik’s theory fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced gratings exhibit the correct properties to work as a coupler.

In the last decades, new technology fabrication developments have permitted increased resolution and reduced pixel size of Liquid crystal on silicon (LCoS) microdisplays. However, the pixel size reduction triggers the microdisplay performance degradation due to different phenomena, such as the cross-talk between neighbouring pixels, fringing fields, out-of-plane reorientation of the liquid crystal director, and diffraction effects due to the pixelated grid pattern of the microdisplay. In this work, a full 3D simulation model has been applied to predict the liquid crystal director orientation as a function of space and external voltage. The scheme here considered provides the complete vectorial information of the electromagnetic field distribution produced by one single pixel illuminated by plane waves circularly polarised. This analysis is carried on for several pixel and gap sizes for different external voltages. This research focuses on S2 and S3 Stokes parameters and how their behaviour is affected due to the cross-talk phenomena previously presented.

This doctoral thesis presents the research carried out in developing and applying numerical methodologies to forming images by volume elements. The validity of the theoretical models used has been analysed by comparing the results obtained with the models generated with the results obtained using theoretical models that are well established in the scientific community. Furthermore, this knowledge has been applied to fabricating diffractive optical elements (DOEs) in PVA/AA photopolymers and the corresponding experimental validation with the developed theoretical models., En esta Tesis Doctoral se estudió la formación de imágenes en holografía de volumen. En primer lugar se desarrollaron diferentes modelos teóricos para simular el comportamiento de medios dieléctricos de volumen. En particular, se implementó un método no destructivo basado en la integral de Fresnel-Kirchhoff. Además del desarrollo de modelos teóricos que permitieron predecir el comportamiento de la radiación electromagnética en medios dieléctricos en esta Tesis se obtuvo también una contrapartida experimental. En ese sentido se fabricaron elementos ópticos difractivos mediante técnicas holográficas. En particular se fabricaron guías de onda holográficas con aplicaciones en la Realidad Aumentada.

Liquid crystal on silicon (LCoS) microdisplays are an element commonly found in advanced photonic applications. Phase-only modulation and spatial light modulators (SLMs) use parallel-aligned LCoS (PA-LCoS) microdisplays due to their large resolution and small pixel size. However, the crosstalk between neighbouring pixels induces several phenomena, i.e. the smoothing of the electric field in the interpixel region known as fringing fields, out-of-plane reorientation of the liquid crystal director, and diffraction effects due to the finite pixel grid pattern. These effects degrade the performance in SLM applications. Therefore, a rigorous numerical analysis is carried out based on a full 3D model that estimates the LC director distribution of the PA-LCoS microdisplay through uniform applied voltages. Once the LC director distribution is known, a numerical finite-difference scheme simulates light propagation across the structure. Here, the impact of crosstalk is analysed from the polarimetric point of view for different pixel and interpixel sizes. It has been found that the finite-patterned pixel scheme induces the phenomena previously addressed, degrading the responses of the Stokes vector components S0, and S1 and also the degree of polarization (DOP). Furthermore, the impact over these parameters is generally inversely proportional to the fill factor. To isolate the influence of diffraction, out-of-plane, and fringing fields effects is challenging since all phenomena are mixed in both time and space, however we have found some useful trends.

A model describing the parameter and wavelength dependencies not only of retardance, but also its flicker in liquid-crystal-on-silicon spatial light modulators (LCoS SLMs), is presented. We provide results for different digital addressing sequences producing different levels of flicker.

The new technological developments and their impact on both the increase of the resolution and the reduction of the pixel sizes on parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplays have made PA-LCoS a promising candidate for phase-only modulation and spatial light modulators (SLMs) applications. The pixel grid pattern on PA-LCoS induces several phenomena, i.e. the electriceld crosstalk in the interpixel region, also known as fringing fields, out-of-plane reorientation of the liquid crystal director, and diffraction effects due to interpixel region. Here, a rigorous numerical methodology has been applied to avoid simplified models that neglect these kinds of phenomena.

The Precise-Integration Time-Domain (PITD) formulation permits to break through the Courant- Friedrich-Levy (CFL) condition, which limits the accuracy, stability, and indirectly the applicability of the traditional Finite-Difference Time-Domain (FDTD) method. This characteristic permits considering larger time steps than the largest one fixed by the CFL condition. As the conventional FDTD scheme, PI also takes the spatial derivatives through the central finite-difference scheme. This step sets up a set of ordinary differential equations (ODEs) that are solved using the PI Technique. Here, the technique is applied to different periodic and anisotropic optical media. More precisely, to anisotropic polarization gratings (PG). PG is based on a periodically patterned, uniaxial birefringence in the grating plane that modulates the polarization of light instead of its amplitude.

An advanced polarimetric model for liquid crystal devices is presented and the sources of uncertainty to determine the values of its parameters are evaluated using a Monte-Carlo approach.