Sergi Gallego

• Professor Fellow SPIE
• University of Alicante

In this work we present a formalism based on scalar Green’s functions to deal with electromagnetic scattering problems. Although the formulations of the Mie theory and Born approximations in terms of electromagnetic scattering are well known and relevant, they have certain disadvantages: complexity, computational time, few symmetries, etc. Therefor...

In this work a three-dimensional diffusion model is used to model photopolymers as a recording media. This model allows us to predict the properties of the Diffractive Optical Elements (DOEs) once we recorded into the photopolymer. This model had never been tested with more complex elements, such as multifocal diffractive lenses, as presented in th...

In this work we present a formalism based on scalar Green’s functions to deal with electromagnetic scattering problems. Although the formulations of the Mie theory and Born approximations in terms of electromagnetic scattering are well known and relevant, they have certain disadvantages; complexity, computational time, few symmetries, etc. Therefor...

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 co...

The response of three of the most used commercial polymers (poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET) and polypropylene (PP)) under irradiation with high repetition rate (1 kHz–1 MHz) femtosecond (450 fs) multi-pulse (N = 10–1500) laser at λ = 343 nm, 515 nm (1.40 J/cm² for both former wavelengths) and 1030 nm (1.70 J/cm²) is r...

In the present work, a 3-Dimensional diffusion model is proposed to predict the main properties of Diffractive Optical Elements (DOEs), recorded in photopolymers, including refractive index modulation and the evolution of the transverse intensity distribution. The model enables the selection of appropriate material characteristics based on the inte...

The response of three of the most used commercial polymers (poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET) and polypropylene (PP)) with different thermal properties under irradiation with high frequency (1 kHz-1 MHz) femtosecond (450 fs) multi-pulse (N=10-1500) laser at λ=515 (1.34 J/cm²) and 1030 (1.70 J/cm²) is reported. Thermal a...

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 e...

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 sp...

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...

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 an...

Nowadays augmented reality, 3D Image, mixed reality and see-through applications are very attractive technologies due to their great potential. Holographic optical elements can provide interesting solutions for injection and extraction of the image in the waveguides that are part of the see-through devices. We have developed a coupled waveguide sys...

Aguirregabiria et al (2022 Eur. J. Phys. 43 035603) obtained the Lorentz transformations by assuming the invariance of Maxwell’s equations in vacuum under inertial transformations. However, they do not initially assume that these transformations must be linear. Later, Redzic (2022 Eur. J. Phys. 43 068002) indicates that it is necessary to explicitl...

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,...

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.

A numerical formulation based on the precise-integration time-domain (PITD) method for simulating periodic media is extended for overcoming the Courant-Friedrich-Levy (CFL) limit on the time-step size in a finite-difference time-domain (FDTD) simulation. In this new method, the periodic boundary conditions are implemented, permitting the simulation...

This work shows the redesign of an elemental experience based on the Helmholtz resonator using 3D printing. A Helmholtz resonator is based on a volume and at least one opening that can include a tube or not. The air column inside the tube can be considered the mass of the system, whereas the volume represents the system’s stiffness. Due to these an...

Photopolymers have become an important recording material for many applications, mainly related to holography. Their flexibility to change the chemical composition together with the optical properties made them a versatile holographic recording material. The introduction of liquid crystal molecules in a photopolymer based on multifunctional monomer...

In this work, we test a nondestructive optical method based on the Fresnel–Kirchhoff integral, which could be applied to different fields of engineering, such as detection of small cracks in structures, determination of dimensions for small components, analysis of composition of materials, etc. The basic idea is to apply the Fresnel–Kirchhoff integ...

Spatial light modulation with liquid crystal on silicon microdisplays is at the heart of a wide range of modern optics and photonics areas. We show how to model these devices with a focus on applications.

Polymer nanocomposites are designed and engineered on a nanometer scale with versatile applications including optics and photonics [...]

Precise characterization of parallel-aligned liquid crystal on silicon microdisplays has an important impact in many advanced photonics applications. We show liquid crystal on silicon (LCoS) modeled as a non-absorbent reciprocal device. Combined with time-average Stokes polarimetry, LCoS enables us to demonstrate robust measurements across the whol...

In the processes related to the development of cancer, there are different genetic and epigenetic events involved that result in structural changes of the affected cells. In the early stages of the disease, these changes occur at the nanoscale, remaining undetectable by conventional light microscopy, due to diffraction-limited resolution (∼250 - 55...

This work presents recent results derived from the rigorous modelling of holographic polymer-dispersed liquid crystal (H-PDLC) gratings. More precisely, the diffractive properties of transmission gratings are the focus of this research. This work extends previous analysis performed by the authors but includes new features and approaches. More preci...

Photopolymers can be used to fabricate different holographic optical elements, although maximization of the phase-shift in photopolymers has been a challenge for the last few decades. Different material compositions and irradiation conditions have been studied in order to achieve it. One of the main conclusions has been that with continuous laser e...

In this work, we study the imaging characteristics of an optical see-through display based on a holographic waveguide. To fabricate this device, two transmission holograms are recorded on a photopolymer material attached to a glass substrate. The role of the holograms is to couple the incident light between air and the glass substrate, accomplishin...

We study the recording of complex diffractive elements, such as achromatic lenses, fork gratings or axicons. Using a 3-D diffusion model, previously validated, we are able to predict the behavior of photopolymer during recording. The experimental recording of these complex elements is possible thanks to a new generation spatial light modulator capa...

We demonstrate a complete semiphysical and analytical model describing the angular and wavelength dependencies not only of retardance, but also its flicker, in parallel aligned liquid crystal (PA-LC) devices. It relies on the fitting of the molecules’ equivalent tilt angle as a function of applied voltage. The wide range of calculations it offers w...

The possibilities that offer the holographic optical elements for photovoltaic and “see through display” applications open new windows for holographic recording materials. In this sense, some specific characteristics are required for each particular application. Waveguides are one of the key elements for these applications. Photopolymers are one of...

In this paper, we present a method to characterize a complete optical Holographic Data Storage System (HDSS), where we identify the elements that limit the capacity to register and restore the information introduced by means of a Liquid Cristal on Silicon (LCoS) microdisplay as the data pager. In the literature, it has been shown that LCoS exhibits...

We study the behavior of a nanoparticle-polymer composite (NPC) material, based on a thiol-ene monomer system, working with long grating spacing. Thus, we evaluate the suitability of the NPC for storing complex diffractive optical elements with sharp profiles, such as blazed gratings. Using holographic methods, we measure the “apparent” diffusion o...

In recent works, we demonstrated the accuracy and physical relevance of a highly simplified reverse-engineering analytical model for a parallel-aligned liquid crystal on silicon devices (PA-LCoS). Both experimental measurements and computational simulations applying the rigorous split-field finite difference time domain (SF-FDTD) technique led to t...

In this work, an accurate numerical modeling of the diffraction properties of transmission holographic polymer dispersed liquid crystal (H-PDLC) gratings is presented. The method considers ellipsoid geometry-based liquid crystal (LC) droplets with random properties regarding size and location across the H-PLDC layer and also the non-homogeneous ori...

Simplified analytical models with predictive capability enable simpler and faster optimization of the performance in applications of complex photonic devices. We recently demonstrated the most simplified analytical model still showing predictive capability for parallel-aligned liquid crystal on silicon (PA-LCoS) devices, which provides the voltage-...

Holographic polymer dispersed liquid crystals (HPDLCs) are the result of the optimization of the photopolymer fabrication techniques. They are made by recording in a photopolymerization induced phase separation process (PIPS) in which the liquid crystal molecules diffuse to dark zones in the diffraction grating originated. Thanks to the addition of...

In this work, we present a method of manufacturing an optical see-through display based on a holographic waveguide with transmission holograms that couple the incident light between air and the glass substrate, accomplishing total internal reflection. The holograms (slanted transmission gratings with a spatial frequency of 1700 lines/mm) were recor...

Schiff's bases with specific π-electron system have been synthesized and used as additives in holographic polymer-dispersed liquid crystals. It was observed that these substances modify different parameters such as current intensity, voltage, and diffracted light intensity. In addition, the maximum diffraction efficiency obtained in the reconstruct...

The improvements made in diffusion models simulating phase image recording in photopolymers enable the optimization of a wide range of complex diffractive optical elements (DOEs), while the miniaturization of spatial light modulators makes it possible to generate both symmetric and non-symmetric DOEs. In addition, there is increasing interest in th...

Multiplexed diffraction gratings were recorded in 300 μm thick layers of Biophotopol photopolymer by using peristrophic multiplexing schema. Thirteen sinusoidal phase gratings were stored in a low toxicity recording medium. The diffraction efficiency conservation of the multiplexed diffraction efficiency obtained was studied along the time.

The parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay has become a widely used device for the photonics community. It is a very versatile tool that can perform several tasks which transforms it into a key element in many different photonics applications. Since our group is interested in holography, in this chapter, we want to use th...

Multiplexed diffraction gratings were recorded in 300 μm thick layers of biophotopol photopolymer by using two peristrophic multiplexing schemes separately and in combination. In addition, it was shown that riboflavin may be used as polymer initiator in acrylamide photopolymer films and the holographic properties of these films such as diffraction...

Photopolymers are appealing materials for many optical applications. For most of them, shrinkage plays an important role in the final properties of the display, especially in holographic data storage applications. In this paper, we demonstrate that to quantify correctly the shrinkage, it is mandatory to measure the angle of propagation for both dif...

We introduce a polyvinil alcohol/acrylamide (PVA/AA) photopolymer compound in a holographic memory testing platform to provide experimental results for storage and retrieval of information. We also investigate different codification schemes for the data pages addressed onto the parallel-addressed liquid crystal on silicon (PA-LCoS) device, used as...

Photopolymers are classical holographic recording materials. Recently their chemical composition and the fabrication techniques have been optimized for many new applications such as interconnectors, solar concentrations, 2-D photonic structures, or wave-guides. Their potential usefulness has been drastically increased by the introduction of dispers...

Holographic data storage systems (HDSS) have been a promising and very appealing technology since the first laser developments in the sixties. Impact of ongoing advances in the various components needs to be explored in its specific application to HDSS. In this sense, continuous progress is being produced in spatial light modulator (SLM) technology...

Photopolymers are optical recording materials appealing for many different applications such as holography, data storage, interconnectors, solar concentrations, or wave-guides fabrication. Recently the capacity of photopolymers to record diffractive optical elements (DOE’s) has been investigated. Different authors have reported proposes to record D...

Phase diffractive optical elements, which have many interesting applications, are usually fabricated using a photoresist. In this paper, they were made using a hybrid optic-digital system and a photopolymer as recording medium. We analyzed the characteristics of the input and recording light and then simulated the generation of blazed gratings with...

In order to obtain a highly environmentally compatible photopolymer to replace the well-known acrylamide photopolymer we optimized the previously developed Biophotopol composition to obtain volume transmission gratings in 300 μm layers, at a recording wavelength of 488 nm. The results obtained show an improved energetic sensitivity with similar dif...

Photopolymers can be appealing materials for diffractive optical elements fabrication. In this paper, we present the recording of diffractive lenses in PVA/AA (Polyvinyl alcohol acrylamide) based photopolymers using a liquid crystal device as a master. In addition, we study the viability of using a diffusion model to simulate the lens formation in...

Parallel aligned liquid crystal (PA-LC) devices are widely used in many optics and photonics applications to control the amplitude, phase and/or state of polarization (SOP) of light beams. Simplified models yet with a good predictive capability are extremely useful in the optimal application of these devices. In this paper we propose and demonstrat...

Phase-only modulation is necessary in a great number of modern spatial light modulation applications, and the spatial light modulator (SLM) technology of choice is usually the parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay. Various degradation effects have been analyzed in the literature which may be introduced by SLMs and whose...

One of the most promising phase optical recording mediums are photopolymers. In these materials, the use of an index matching component permits a better conservation of the stored information and, additionally, the study of the molecules migration and shrinkage/swelling phenomena separately. In general, the transmitted beam has the information of t...

We focus on the novelty of three elements in holographic data storage systems (HDSS): the data pager, where we introduce a parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay; the recording material, where we consider the highly versatile PVA/AA photopolymer; and also in the architecture of the object arm, where a convergent correlato...

The adaptation to the European Space of Higher Education has meant a deep change in University education in many aspects, such as the degree organization, subject contents and teaching methodologies. The aim of this work is to show the coordination work on the Bachelor's Degree in Sound and Image in Telecommunications and the Master's Degree in Tel...

Photopolymers as recording media are widely used in optical applications. In such materials, changes in the phase of the transmittance function are generated during exposure due to refractive index and thickness modulations. These changes arise primarily as a consequence of photopolymerization and mass transport processes. Characterizing polymers’...

Free-radical photopolymer materials can be fabricated using a wide range of monomers, binders, dyes, etc. It was shown that in some photopolymers the surface and the internal diffusion for acrylamide materials are very different and also it was demonstrated the viability of acrylamide materials to achieve 2π phase depth for low spatial diffractive...

Photopolymers present appealing optical properties for holographic and diffractive applications. They enable modulation of the electrical permittivity and thickness and are self-processing, and layers with a wide range of thicknesses and properties can be fabricated on demand. In order to obtain a complete characterization of the material, low spat...