Blazed Gratings Recorded in Absorbent Photopolymers

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 different spatial periods in different types of photopolymers using a diffusion model. Finally, we analyzed the output and diffraction efficiencies of the 0 and 1st order so as to compare the simulated values with those measured experimentally. We evaluated the effects of index matching in a standard PVA/AA photopolymer, and in a variation of Biophotopol, a more biocompatible photopolymer. Diffraction efficiencies near 70%, for a wavelength of 633 nm, were achieved for periods longer than 300 µm in this kind of materials.This work was supported by the “Ministerio de Economía y Competitividad” (projects FIS2014-56100-C2-1-P and FIS2015-66570-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013)

Adulterant Detection in Peppermint Oil by Means of Holographic Photopolymers Based on Composite Materials with Liquid Crystal

Diffraction gratings are recorded in a holographic photopolymer containing nematic liquid crystal and peppermint oil. The presence of the oil modifies the polymerization and the holographic response. The composite containing oil adulterated with triethyl citrate obtains a diffraction efficiency related to the oil’s purity. The results obtained suggest the possibility of developing a holographic chemical analysis method for quality control of raw materials.Ministerio de Ciencia e Innovación (Spain) under projects; PID2019-106601RB-I00 FIS2017-82919-R; Generalitat Valenciana (Spain) under projects: IDIFEDER/2021/014; (cofunded by European Union through the FEDER Programme) PROMETEO 2021/006

Design and development of an innovative and simple optical sensor for the detection of acetic acid

The technology we are developing consists of the use of coordination compounds with metals to carry out this detection of Acetic acid. This compound normally reacts with acetic acid changing its colour, making it a suitable compound for use as a detector. The proposed method allows detecting acetic acid in any medium, whether in solution, in the gas phase, in the solid phase, or in any combination of these. Upon contact with the acid, a colour change occurs that can be detected visually or through optical means. After its use, the active medium can be regenerated by a simple procedure and be available again for new use. This allows the creation of simple and intuitive detection devices, usable by non-experts and that can be regenerated and reused. The main advantage of this sensor is to allow the specific detection of acetic acid and quantification of its concentration, using coordination compounds with metals that are present in the yellow dye.This work was supported by Ministerio de Ciencia e Innovación (Spain) under project PID2019-106601RB I00,and Generalitat Valenciana (Spain) under projects IDIFEDER/2021/014 (cofunded by European Union through the FEDER Programme), PROMETEO2021/006

Design and development of a simple and innovative Optical detection sensor for acetic acid

The technology we are developing consists of the use of coordination compounds with metals to carry out the detection of acetic acid, which is a harmful substance for human health and some art works.This work was supported by Ministerio de Ciencia e Innovación (Spain) under project PID2019-106601RB-I00, and Generalitat Valenciana (Spain) under projects IDIFEDER/2021/014 (cofunded by European Union through the FEDER Programme), PROMETEO 2021/006

Holographic Lens Resolution Using the Convolution Theorem

The similarity between object and image of negative asymmetrical holographic lenses (HLs) stored in a low-toxicity photopolymer has been evaluated theoretically and experimentally. Asymmetrical experimental setups with negative focal lengths have been used to obtain HLs. For this purpose, the resolution of the HLs was calculated using the convolution theorem. A USAF 1951 test was used as an object and the impulse responses of the HLs, which in this case was the amplitude spread function (ASF), were obtained with two different methods: using a CCD sensor and a Hartmann Shack (HS) wavefront sensor. For a negative asymmetrically recorded HL a maximum resolution of 11.31 lp/mm was obtained. It was evaluated at 473 nm wavelength. A theoretical study of object-image similarity had carried out using the MSE (mean squared error) metric to evaluate the experimental results obtained quantitatively.This research was funded by Universidad de Alicante (UAFPU20-23); Generalitat Valenciana (CIDEXG/2022/60, CDEIGENT/2018/024, IDIFEDER/2021/014, PROMETEO/2021/006); Ministerio de Ciencia e Innovación (PID2019-106601RB-I00, PID2021-123124OB-I00)

Cylindrical diffractive lenses recorded on PVA/AA photopolymers

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 DOE like fork gratings, photonics structures, lenses, sinusoidal, blazed or fork gratings. In these experiments there are different experimental set-ups and different photopolymers. In this work due to the improvement in the spatial light modulation technology together with the photopolymer science we propose a recording experimental system of DOE using a Liquid Cristal based on Silicon (LCoS) display as a master to store complex DOE like cylindrical lenses. This technology permits us an accurate control of the phase and the amplitude of the recording beam, with a very small pixel size. The main advantage of this display is that permit us to modify the DOE automatically, we use the software of the LCoS to send the voltage to each pixel In this work we use a photopolymer composed by acrylamide (AA) as polymerizable monomer and polyvinyl alcohol (PVA). We use a coverplated and index matched photopolymer to avoid the influence of the thickness variation on the transmitted light. In order to reproduce the material behaviour during polymerization, we have designed our model to simulate cylindrical lenses and used Fresnel propagation to simulate the light propagation through the DOE and analyze the focal plane and the properties of the recorded lenses.This work was supported by the “Ministerio de Economía y Competitividad” (project FIS2014-56100-C2-1-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013)

CCD and Hartmann-Shack wavefront sensor to analyse holographic lens resolution

Nowadays, the study and optimization of volume holographic lenses (HLs) stored in low-toxicity photopolymers have a great interest. HLs are now a component of optical imaging systems that are mostly used in head-mounted displays for virtual and augmented reality or as non-image systems in light deflectors and concentrators. One of the most important parameters used when working with imaging systems is the resolution of the optical system. In this work, the similarity between the object and image of negative asymmetrical HLs stored in a low-toxicity photopolymer named Biophotopol has been evaluated theoretically and experimentally. For this purpose, the resolution of the HLs was calculated using the Convolution Theorem. A USAF 1951 test was used as an object and the impulse responses of the HLs were obtained with two different sensors: CCD and Hartmann-Shack (HS) wavefront sensor. In addition, the resolution of the HLs has been obtained by two different methods: one using the Convolution Theorem, using both the CCD and the HS wavefront sensor, and the other by forming the USAF test image on the CCD sensor. Finally, a theoretical study of object-image similarity was carried out using the MSE (mean squared error) metric to evaluate the quantitative experimental results.This research was funded by Universidad de Alicante (UAFPU20-23); Generalitat Valenciana (CIDEXG/2022/60, IDIFEDER/2021/014, PROMETEO/2021/006); Ministerio de Ciencia e Innovación (PID2019-106601RB-I00, PID2021-123124OB-I00)

Shrinkage measurament for holographic recording materials

There is an increasing demand for new holographic recording materials. One of them are photopolymers, which are becoming a classic media in this field. Their versatility is well known and new possibilities are being created by including new components, such as nanoparticles or dispersed liquid crystal molecules in classical formulations, making them interesting for additional applications in which the thin film preparation and the structural modification have a fundamental importance. Prior to obtaining a wide commercialization of displays based on photopolymers, one of the key aspects is to achieve a complete characterization of them. In this sense, one of the main parameters to estimate and control is the shrinkage of these materials. The volume variations change the angular response of the hologram in two aspects, the angular selectivity and the maximum diffraction efficiency. One criteria for the recording material to be used in a holographic data storage application is the shrinkage, maximum of 0.5%. Along this work, we compare two different methods to measure the holographic recording material shrinkage. The first one is measuring the angle of propagation for both diffracted orders ±1 when slanted gratings are recorded, so that an accurate value of the grating vector can be calculated. The second one is based on interference measurements at zero spatial frequency limit. We calculate the shrinkage for three different photopolymers: a polyvinyl alcohol acrylamide (PVA/AA) based photopolymer, one of the greenest photopolymers whose patent belongs to the Alicante University called Biophotopol and on the last place a holographic-dispersed liquid crystal photopolymer (H-PDLC).This work was supported by the “Ministerio de Economía y Competitividad” (projects FIS2015-66570-P and FIS2014- 56100-C2-1-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013)

Efficient split eld FDTD analysis of third-order nonlinear materials in two-dimensionally periodic media

In this work the split-field finite-difference time-domain method (SF-FDTD) has been extended for the analysis of two-dimensionally periodic structures with third-order nonlinear media. The accuracy of the method is verified by comparisons with the nonlinear Fourier Modal Method (FMM). Once the formalism has been validated, examples of one- and two-dimensional nonlinear gratings are analysed. Regarding the 2D case, the shifting in resonant waveguides is corroborated. Here, not only the scalar Kerr effect is considered, the tensorial nature of the third-order nonlinear susceptibility is also included. The consideration of nonlinear materials in this kind of devices permits to design tunable devices such as variable band filters. However, the third-order nonlinear susceptibility is usually small and high intensities are needed in order to trigger the nonlinear effect. Here, a one-dimensional CBG is analysed in both linear and nonlinear regime and the shifting of the resonance peaks in both TE and TM are achieved numerically. The application of a numerical method based on the finite- difference time-domain method permits to analyse this issue from the time domain, thus bistability curves are also computed by means of the numerical method. These curves show how the nonlinear effect modifies the properties of the structure as a function of variable input pump field. When taking the nonlinear behaviour into account, the estimation of the electric field components becomes more challenging. In this paper, we present a set of acceleration strategies based on parallel software and hardware solutions.This work was supported by the Ministerio de Economa y Competitividad of Spain under project FIS2014-56100- C2-1-P and by the Generalitat Valenciana of Spain under projects PROMETEOII/2015/015, ISIC/2012/013 and GV/2014/076

Registro de hologramas en películas de Biophotopol de 300 μm

En este trabajo se ha optimizado la composición y el proceso de fabricación del fotopolímero Biophotopol con el fin de obtener redes de difracción por transmisión en películas con espesores de 300 μm. Los resultados obtenidos muestran valores de rendimiento en difracción del orden de los obtenidos anteriormente en películas de 1 mm de espesor.Financiado por Ministerio de Economía y Competitividad (FIS2011-29803-C02-01 y FIS2011-29803-C02-02) y Generalitat Valenciana (PROMETEO/2011/021, ISIC/2012/013 y GV/2014/076)