Table of contents

Since 2011 the Portuguese Society for Optics and Photonics celebrates Optics and Photonics and its remarkable contribution to the development of our societies and humankind organizing the Applications in Optics and Photonics, AOP, international conferences. Our conferences are designed to foster the establishment of the widest range of cooperation projects and relationships with colleagues and institutions from all around the world while increasing the external visibility of Portugal' Optics and Photonics research.

After two and half years of confinement and major constraints due to the global Covid19 pandemic, the Portuguese Optics and Photonics community and friends from all over the world meet again in-person in another exciting most enjoyable and highly successful AOP conference.

With the renewed and recharged enthusiasm and commitment of the Portuguese Optics and Photonics community and all the over two hundred participants, the 5th International Conference on Applications in Optics and Photonics, AOP2022, toke place July 18 to 22, 2022, at the welcoming UNESCO World Heritage historical city of Guimarães in the beautiful northwest of Portugal.

Five plenary, twenty three keynote and seventeen invited lectures by world renowned researchers and scholars as well as top level young researchers in all fields of Optics and Photonics, set the high quality standard of a varied and exciting scientific program. The proceedings book herein reunites a good number of interesting papers in different fields of Optics and Photonics contributing to assess the state-of-the art on a range of O&P subjects in Portugal and abroad, and to foresee the future of research in Optics and Photonics and of its remarkable contribution to the development of our societies and humankind.

Braga, October 21, 2022.

Manuel Filipe Pereira da Cunha Martins Costa (Editor and chairperson of the AOP2022 conference)

List of AOP 2022 Committees are available in this Pdf.

All papers published in this volume have been reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing Publishing.

1. Type of peer review: Single anonymous

2. Conference submission management system: Morressier

3. Number of submissions received: 62

4. Number of submissions sent for review: 61

5. Number of submissions accepted: 54

6. Acceptance Rate (Submissions Accepted / Submissions Received × 100): 87.1 %

7. Average number of reviews per paper: 1.20

8. Total number of reviewers involved: 28

9. Contact person for queries:

Name: Manuel Filipe Pereira da Cunha Martins Costa

Affiliation: University of Minho/SPOF

Email: mfcosta@fisica.uminho.pt

To achieve high photocatalytic activity, TiO₂ nanoparticles nanoparticles require an excitation source in ultraviolet radiation. Incorporating chemical elements into the TiO₂ lattice can tune its band gap, resulting in an edge-shifted red absorption to reduce energies, improving photocatalytic performance in the visible region of the electromagnetic spectrum. In this research, TiO₂ semiconductor nanoparticles were subjected to a doping process using iron chloride (FeCl₃) powder to activate photocatalysis under visible light and consequently improve pollutant capture. To study the effectiveness of the doping process, the main ratios (1:1), (1:1.622) and (1:3) of TiO₂:FeCl₃ were evaluated using Diffuse Reflectance Spectroscopy (DRS), X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The main results of this research show that doping TiO₂ with FeCl₃ shifted the absorption edge to longer wavelength values, changing the optical properties of the material and decreasing the band gap (E_g) of TiO₂ compared to the undoped TiO₂ (reference). There are no relevant differences between the XRD pattern of the samples with TiO₂-FeCl₃ and TiO₂ nanoparticles (reference). The fraction of the anatase phase in doped TiO₂ nanoparticles has the same magnitude as the reference TiO₂. Regarding FTIR, the Fe-doping process alters the TiO₂ reference spectrum, increasing the intensity of hydroxyl bonds and peaks particularly, indicating the Ti-O-Fe bond vibration.

In this communication, we present a method to estimate the aberrated wavefront at the focal plane of a vectorial diffraction system. In contrast to the phase, the polarization state of optical fields is simply measurable. In this regard, we introduce an alternative approach for determining the aberration of the wavefront using polarimetric information. The method is based on training a convolutional neural network using a large set of polarimetric mapping images obtained by simulating the propagation of aberrated wavefronts through a high-NA microscope objective; then, the coefficients of the Zernike polynomials could be recovered after interrogating the trained network. On the one hand, our approach aims to eliminate the necessity of phase retrieval for wavefront sensing applications, provided the beam used is known. On the other hand, the approach might be applied for calibrating the complex optical system suffering from aberrations. As proof of concept, we use a radially polarized Gaussian-like beam multiplied by a phase term that describes the wavefront aberration. The training dataset is produced by using Zernike polynomials with random coefficients. Two thousand random combinations of polynomial coefficients are simulated. For each one, the Stokes parameters are calculated to introduce a polarimetric mapping image as the input of a neural network model designed and trained for predicting the polynomial coefficients. The accuracy of the neural network model is tested by predicting an unseen dataset (test dataset) with a high success rate.

The colliding laser-produced plasma (CLPP) has a wide range of applications in various contexts, that might start with astrophysical applications or pulsed laser deposition or Laser-Induced Breakdown Spectroscopy (LIBS), which is a powerful analytical technique for elemental analysis and material identification.

In CLPP experiments, the stagnation layer might form at the interface region when two dense laser-induced plasmas collide, and the degree of stagnation can be diagnosed by the collisionality parameter that is used to determine what kind of interaction will take place, i.e., soft or hard stagnation.

Our experimental work presents the results of the temporal, spatial and semi-spectrally imaging of colliding plasmas of aluminium and silicon targets. The analysis is focused on describing the velocity of the expanding plasma front for the interaction zone. The aim of the work presented here is to further advance and study colliding plasma techniques, as well as other methods to realize and control species density and expansion, with a view to a deep understanding of these complex mechanisms and optimising emission in the visible wavelength range.

All investigation sequences were based on a similar experimental setup, where two different focusing lenses were used with an effective focal length (EFL) of approx. 100mm or 125mm to achieve seed separation around 1.66mm or 2.16mm, respectively. Time-resolved emission imaging was employed to track the stagnation layer‛s size and shape, which might act as a signature of hard versus soft stagnation.

The study provides a considerable amount of detailed data related to the expansion velocity of the interaction zone which extends the understanding of the behaviour of particular species within colliding laser-produced plasmas.

Stable colour centre production in lithium fluoride (LiF) crystals can employ as a high-spatial-resolution imaging tool for extreme ultraviolet (XUV) irradiation, as well as the possibility for images of the unfocused beam and the beam focused by a multi-layer mirror.

The LiF crystal sensitivity has sufficient to impress high-contrast photo-luminescent patterns with XUV single-pulse irradiation on an area up to 40mm². The suggested imaging technique, using LiF as a detector, can contribute to reducing the lack of sufficient knowledge for XUV beam characterization and profile featurization which can open a very wide range of XUV metrology and tomography applications.

The experimental results explain the concepts of detection of high-intensity source at13.5nm using a YAG:Ce scintillator crystal embedded with a CMOS camera, additionally using LiF as a 2D high-resolution detector, and the work shows investigations outcomes and improvement procedure and analysis.

The results demonstrate the potential of LiF crystals as a sub-micrometre resolution two-dimensional imaging tool for XUV irradiation applications. Moreover, the research study explains the optimization sequences of the new imaging technique that will play an important role to predict the achievable spot size, geometry, beam profile and intensity distribution, as well as the characterization complexity of XUV source features.

Increasing the size of the smallest features of Photonic Integrated Circuits (PICs) to multi-micron dimensions can be advantageous to avoid expensive and complex lithographic steps in the fabrication process. In applications where extremely reduced chip size is not a requirement, the design of devices with multi-micron dimensions is potential interesting to avoid the need for e-beam lithography. Another benefit is that making the dimensions larger reduces the effect of lithographic imperfections such as waveguide surface roughness. However, the benefits do not come without limitations. Coupling the light in and out of the circuit is more challenging since diffraction gratings are not available when designing for such large dimensions. Circuit bends must have a larger radius of curvature and the existence of multimode propagation conditions can have detrimental impact in the performance of several devices, such as interferometers. In this study we perform simulations of the coupling between a lensed multimode optical fiber and a multi-micron a-SiN:H rib waveguide. Light coupling efficiency is analyzed as a function of distance variations using the FDTD method and compared with coupling to a strip waveguide. Moreover, we use numerical simulations to study the performance of a Mach-Zehnder interferometer sensitive to refractive index variations. Both the interferometer, splitters and combiners are designed with multi-micron dimensions.

Accommodation lag is important factor for normal vision. Higher lag of accommodation may cause various ocular symptoms particularly during near tasks. In this study, the lag of accommodation was assessed in the peripheral retina and it was compared with the central accommodative lag with aberrometer. In this cross-sectional study, fifty-three young subjects with normal visual acuity and without any active ocular disease or past ocular surgery were included. Aberrations in the central and peripheral field of view up to 30° off axis from the centre in horizontal and vertical meridian in 10° steps were measured with Hartmann-Shack aberrometer with stimulation of accommodation by -2.50D lens. Accommodative stimulus and accommodative response were calculated with defocus and hence accommodative lag was obtained. Accommodative lag in the centre and periphery was compared. Repeated measure of ANOVA showed that there were significant differences in lag of accommodation in various eccentricities (F(8.912, 454.514) = 2.372, p = 0.013). Pairwise test showed that lag in the centre was similar with lag on other peripheral field of view (p > 0.05). However, accommodative lag at 10° nasal field was significantly lower than the lag at 20° temporal, 20° nasal, 30° temporaland 30° nasal (p < 0.05). Similarly, lag at 10° superior fixation was lower than lag at 20° temporal, 20° nasal, 30° temporal and 30° nasal fixations (p < 0.05). We found higher lag of accommodation in horizontal off-axis fixations in comparison to that of vertical off-axis fixations (p < 0.05). Lag of accommodation was positive correlated with vertical coma and primary spherical aberrations but negative correlated with secondary spherical aberrations (p < 0.05). Thus, Hartmann-Shack aberrometer was successfully used to assess accommodative lag in the peripheral field of view up to 60° visual field. Peripheral lag of accommodation depends up on eccentricity. Lag was found higher in horizontal off-axis fixation than at vertical fixations. Coma and spherical aberration had association with lag.

Purpose: The aim of the present study was to state a relationship between the meibomian gland loss area (MGLA), eyelid hyperemia and meibomian gland (MG) orifices plugging in a sample of university students. Material and methods: A total of 74 participants were recruited. Meibography images were obtained with the OCULUS® Keratograph 5M and MGLA was calculated using the ImageJ software; also, MGLA was categorized following the Meiboscale into 4 groups: group 1 (<25%), group 2 (25-50%), groups 3 (50-75%), and group 4 (>75%). An exhaustive slit lamp examination of both eyelids was performed. Eyelid margin hyperemia and MG orifices plugging of each eyelid were categorized following Arita et. al grading scales. Results: A significant statistical relationship was found between MG orifices plugging and MGLA for both eyelids (Fisher's exact test; both p < 0.019). Also, correlations were obtained between lower MGLA and lower MG orifices plugging (Cramer-V = 0.583, p ≤ 0.001); and between upper MGLA and upper eyelid margin hyperemia (Cramer-V = 0.418, p = 0.023), and upper MG orifices plugging (Cramer-V = 0.413, Fisher's exact test: p = 0.042). Conclusion: MGLA varies depending on MG orifices plugging in upper and lower eyelids; also, in upper eyelids MGLA was correlated with eyelid hyperemia.

The interrogation of optic fiber sensors usually relies in complex and costly equipment with low portability due to their size such as Optical Spectrum Analyzers (OSA) or high-resolution spectrometers. Because of this, micro spectrometer devices, such as Micro-Electromechanical Systems (MEMS) with Fabry-Pérot tunable filters, are emerging as simpler and compact alternatives capable of being used to acquire spectral information in a wide wavelength band. In this work it is described the development of an interrogation system capable of infrared spectroscopy using a MEMS Fabry-Pérot Interferometer (MEMS-FPI) with a spectral response in the 1350nm to 1650nm range. Its performance is tested with the interrogation of long period fiber gratings both as a refractive index sensor and as a temperature sensor. Deconvolution techniques such as Wiener filtering are used to reduce the impact of the tunable filter's impulse response in the measured signal. Results are comparable to those obtained using a typical OSA which shows the system's potential as a cheaper and more transportable alternative.

Faraday materials based on transparent ceramics are regarded for high power magneto-optical isolators. Pure yttria ceramics with high transmittance were prepared using the raw oxide powders. To enhance the magneto–optical performance of the ceramics, samarium oxide were introduced to yttrium oxide matrix as a paramagnetic ions. The Sm-Y₂O₃ Faraday ceramic was melted above 2700 °C for 10 min. It is noted that as-prepared ceramic presents the highest in-line transmittance above 61.0% at the high spectrum range of wavelengths from 350 to 1110 nm. Physicochemical properties of the sample were characterized by means of numerous techniques. No secondary phase was detected from the sample using X-ray diffraction. The Verdet constant of Sm-Y₂O₃ ceramic at 532 nm is as high as 20 rad/m^*T, which is higher than that of pure Y₂O₃ ceramic. The good optical quality and magneto-optical properties make Sm-Y₂O₃ ceramic an attractive magneto-optical material.

The principal cause of upper limb amputations is due to traumatism. The prosthesis is an assistive device to help in the activities of daily for the amputee person. However, one of the latest reports shows that in developing countries there are around 30 million people without assistive devices. This work presents the development of two kinds of sensors for the PrHand, an upper limb prosthesis based on compliant mechanism and soft-robotics. The sensors are made with polymeric optical fiber (POF), due to their flexibility and low cost, and the working principle is based on intensity variation. The angle sensors are used for monitoring the interphalangeal joint of the fingers, and for the assessment were made cycles of closing and opening each finger. On the other hand, the force sensors are located at the tip of three fingers to track the force made over the objects. Before encoring the sensors were evaluated making five cycles of compressing and decompressing each sensor. The results show a linear behavior between the angle and the voltage variation, one most remarkable angle sensor result was with a sensibility of 0.0357 V/° and an R² of 99 % closing and 0.0483 V/° opening. In the case of the force sensor, a polynomial relation was found between the voltage changes and the pressure over the sensor; in some cases, the relation between voltage changes and pressure could be linear but that depends on the construction of the sensor. Regarding the obtained R² of 99 %, its sensibility was 0.0361 V/N compression and 0.0368 V/N decompression. In conclusion, was successfully developed two kinds of sensors for the instrumentation of PrHand prosthesis. It is expected to use angle and sensor variables as input in algorithms of Machine Learning to improve the detection of objects. One aspect to improve is to control in a better way the sensor construction parameters due to the considerable influence over the sensor behavior.

In the conventional quantum mechanics of conserved systems, Hamiltonian is assumed to be a Hermitian operator. However, when it comes to quantum systems in presence of dissipation and/or noise, including open quantum optical systems, the strict hermiticity requirement is nor longer necessary. In fact, it can be substantially relaxed: the non-Hermitian part of a Hamiltonian is allowed, in order to account for effects of dissipative environment, whereas its Hermitian part would be describing subsystem's energy. Within the framework of the standard approach to dissipative phenomena based on a master equation for the reduced density operator, we propose a replacement of the hermiticity condition by a more general condition of commutativity between Hermitian and anti-Hermitian parts of a Hamiltonian. As an example, we consider a dissipative two-mode quantum system coupled to a single-mode electromagnetic wave, where we demonstrate that the adjoint-commutativity condition does simplify the parametric space of the model.

Coma is one of the most common ocular higher order aberrations and highly affects the quality of image. It is assumed that corneal aberrations are balanced by internal (lenticular) aberrations so that retinal image quality may not have great impact. However, during accommodation, the shape, position, and curvature of the crystalline lens changes which might disrupt this balance between internal and corneal aberration. This study aimed to investigate the effect of accommodation on primary coma (${C}_{3}^{-1}$ and ${C}_{3}^{1}$) and secondary coma (${C}_{5}^{-1}$ and ${C}_{5}^{1}$) in relaxed and accommodated eyes. Zernike coefficients were measured in 53 subjects with Hartmann-Shack aberrometer both at the central and peripheral retina up to 30° off-axis in horizontal and vertical meridians. The process was repeated with 2.50 D accommodation stimulus and comas were compared with and without accommodation. Root-mean-square of total coma was also assessed. With accommodation, vertical comas changed to more negative value and horizontal comas changed to more positive values in most of the off-axis positions. In contrast, the secondary vertical comas became less negative and secondary horizontal comas became more negative with accommodation in most of the off-axis fixations. Thus, the results showed that accommodation affects coma which depends up on position of the fixation.

Modal decomposition of light is essential to study propagation properties of waveguides and photonic devices. Modal analysis can be carried out by implementing a computer generated hologram acting as a match filter in a spatial light modulator. In this work, a series of aspects to be taken into account in order to get the most out of this method are presented, aiming to provide operational procedures. First of all, the influence of the mode normalization in the complex amplitude encoding inherent noise is investigated. Then, a method for filter size adjustment based on the LP-modes symmetry is presented. Finally, a robust method to measure the phase difference between modes is proposed. These procedures are tested by wavefront reconstruction in a conventional few mode fiber.

Techniques for wavefront measurement have many applications as optics systems for astronomy and as verification tests for optical surfaces. The development of large aperture optical systems drives the search for low cost and high-resolution wavefront detection sensors. The Hartman technique and its variations (i.e the Shack-Hartman sensor) are the current standards for the characterization of low-order optical aberrations, such as defocus and spherical. The scanning pentaprism method is presented as a simple and low-cost method for the verification of such aberrations. In this method, a transverse section of a wavefront is scanned and sampled into a series of sub-wavefronts with smaller apertures. The relative positions of the produced centroids are measured relative to a calibrated position. This allows for the determination of the optical path difference along the section and consequently the wavefront error. Both techniques were used as tools for collimating a telescope that is part of the on-ground support equipment of ESA PLATO mission. In this work, the results from both methodologies are compared.

Bloch Surface Waves (BSW) consist of electromagnetic modes generated at the interface between a photonic crystal and an isotropic dielectric. This type of surface mode displays sharp resonances and high sensitivity to external refractive index variations, and thus appears to be an ideal candidate for usage in optical sensors. Nevertheless, design and optimization of photonic crystals is not a trivial task and constitutes an ongoing field of research. The sensitivity of BSW in both refractometric and adsorption sensing is calculated analytically using first-order perturbation theory for TE modes, allowing the understanding of how several physical parameters of the photonic crystal influence the sensitivity. Preliminary experimental results are presented, which aim to use the analytical calculations to allow for both refractometric and adsorption sensing in a single photonic crystal structure.

We present a modal analysis of coupled two-core integrated waveguides fabricated by femtosecond laser writing as a function of the core-to-core distance, illuminating position and input light wavelength. In order to do that we use the correlation filter method, implementing the computer generated holograms in a phase-only spatial light modulator. Due to the two-core waveguide symmetry, we prove it is not necessary to encode the complex amplitude in a phase-only device as long as the cores are not strongly coupled. A comparison between experimental and numerical modal weights is presented, showing that simple phase-only match filters allow the modal decomposition of two-core waveguides output beams.

Optical techniques are used in many applications in the metrology field, namely for high accuracy surface profiling. Although there many techniques are available, a specific measurement methodology must be correctly chosen according to the specifications of the range of measurement, field, and surface characteristics. In this work we simulate and develop a small prototype capable of measuring surfaces of circa 10 by 10 cm with an uncertainty of 20 µm in all directions, using the astigmatic method as baseline. The aim of this paper is then to show a dedicated and optimized optical setup that allow the surface characterization of a sample surface.

Apart from radiation, which constitutes the primary source of information in laser-induced breakdown spectroscopy, the process is accompanied by secondary processes such as shock wave generation and sound emission. In this manuscript, we explore the possibility of relating plasma properties with the sound from the shock waves in multiple materials, from metals to minerals. By analyzing the behavior of shock wave sound from homogeneous reference metallic targets, we investigate the relation between plasma properties and sound signal, demonstrating that distinct materials and plasma characteristics correspond to distinct plasma sound fingerprints.

Reservoir computing is a versatile approach for implementing physically Recurrent Neural networks which take advantage of a reservoir, consisting of a set of interconnected neurons with temporal dynamics, whose weights and biases are fixed and do not need to be optimized. Instead, the training takes place only at the output layer towards a specific task. One important requirement for these systems to work is nonlinearity, which in optical setups is usually obtained via the saturation of the detection device. In this work, we explore a distinct approach using a photorefractive crystal as the source of the nonlinearity in the reservoir. Furthermore, by leveraging on the time response of the photorefractive media, one can also have the temporal interaction required for such architecture. If we space out in time the propagation of different states, the temporal interaction is lost, and the system can work as an extreme learning machine. This corresponds to a physical implementation of a Feed-Forward Neural Network with a single hidden layer and fixed random weights and biases. Some preliminary results are presented and discussed.

The study of the Sun is an area still open in several topics of astrophysics, in a field that has seen an expansion in recent years - therefore, it is critical that collected data is thoroughly traceable and accurate to be used in new study cases or predictive models. A ground based, portable, optimized system, consisting of a Schmidt-Cassegrain telescope coupled to a refractor telescope acting as a pointing telescope, is being designed to provide high resolution imaging of smaller areas on the Sun's surface, being able to obtain disk-resolved, high spectral resolution data, at a relative low cost (compared to large consortium developed instruments). The light collected by the telescope will be fibre-fed to a spectrograph - the injection of light in the fibre is critical and requires an imaging sensor to aid the light guiding process. The goal of the present work was to explore the best candidates for the image sensors, their architectures, requirements, and constraints, as well as their expected performance range and signal noise. The trade-off analysis between CMOS and CCD based sensors was made and it was concluded, that for the intended application, either type of architecture is admissible, provided the sensor is within desired parameters.

In this work, a microfluidic system combined with a fibre-optic extrinsic Fabry-Perot interferometer is proposed to measure refractive index continuously and in real time. A microfluidic platform was designed and created for this purpose through 3D printing. The Fabry-Perot cavity is an integral part of the microfluidic chip and is perpendicular to the sample flow. The light is conducted through a single mode optical fibre and the refractive index measurements were based on the optical power and wavelength shift of the reflected spectra. The developed optofluidic setup was characterised using different concentrations of glucose solutions. A sensitivity of 1102 nm/RIU was obtained when using the wavelength shift, however, when the same solution was analysed over time, the signal for wavelength shift measurements was found to be unstable. The optical power shift was correlated with the refractive index and a sensitivity of -79.6 dB/RIU was obtained, with a good linearity (r² = 0.996). Good results were verified in terms of stability with a maximum standard deviation of 0.028 dB and a sensor resolution of 4.3×10⁻⁴ RIU. This sensor has a great potential for applications in which refractive index real-time measurements are required, such as food and beverages industry process control.

Phase change materials (PCMs) have been incorporated into asphalt concrete pavements because they can regulate the temperature by absorbing and releasing heat during physical state changes. This effect reduces temperature gradients of pavements and, consequently, increases its service life. This work presents a systematic review of recent articles published in peer-reviewed journals (available in the Scopus database) involving asphalt mixtures with PCMs and focusing on mechanical characterization. It is observed that most of the selected papers investigated the benefits of polyethylene glycol as a PCM. The most common strategy to avoid leakage during the phase transition involved using a porous material that acts as a carrier matrix for the PCMs. Generally, asphalt pavements with PCMs are systems with favourable thermal transferability, thus demonstrating higher heat absorption and dissipation rates. Finally, the asphalt mixtures containing PCMs showed lower mechanical performance than the control mixtures. However, they still satisfy the required criteria. In any case, it is expected that with the incorporation of PCMs into asphalt pavements, the social and environmental effects (Urban Heat Island) of sunlight in urban areas can be mitigated by the thermoregulation phenomena.

In this work, hybrid optical fiber sensors based on Fabry-Perot (FP) interferometer and Fiber Bragg Grating (FBG) sensors were developed to simultaneously measure two external parameters, pressure, and temperature. The proposed sensor consists of a photosensitive Single-Mode Fiber (SMF), where the FBG is recorded, and spliced to a small section of a Hollow-Core Fiber (HCF). After that, the HCF tip is submerged in a UV-photosensitive polymer (RI = 1.46), creating three cavities, which will create two observable light interferences, allowing the observation of two FP responses in the spectral response. Two sensors with different HCF lengths were created to compare their sensitivities. After curing, the sensors were calibrated to both parameters in the ranges of 0.0 to 4.0 bar (steps of 1.0 bar) and 22.0 to 30.0 °C (steps of 2.0 °C), respectively. By tracking the peak shifts of the FP, it achieved higher sensitivities for the sensor with the shorter HCF tip (182.30 µm of HCF and 28.56 µm of UV-polymer lengths) of around 31.65 nm/bar and 1.53 nm/°C. On the other side, the sensor with the longer HCF tip (318.56 µm of HCF and with 52.17 µm of UV-polymer lengths) achieved 15.65 nm/bar and 1.02 nm/°C. Regarding the FBGs, they achieved 9.65 and 7.86 pm/°C for the longer and shorter sensor, respectively, while presenting insensitivity to pressure. Therefore, the shorter FP cavity produces the more sensitive sensor because, since its length is shorter and possesses a concave shape, it is more susceptible to external changes. Thus, variations of pressure and temperature could be discriminated by using the matrixial method with the FP and FBG sensitivities, given that the determinant of the coefficient matrix results is -0.31, a non-zero value. The developed sensor has the potential to integrate specific applications, such as LiBs to measure and decouple both parameters.

This paper proposes a low-cost portable interrogator for dynamic monitoring of wavelength-based fiber-optic sensors such as fiber Bragg gratings (FBGs) and Fabry-Perrot interferometers (FPIs). The interrogator is based on a compact solution involving a broadband light source and the spectral convolution between the sensor and a tunable filter. The filtered signal is then acquired by a photodetector where the optical-electrical conversion happens. Additionally, a microcontroller performs three actions: (i) controls the filter tuning, (ii) acquires the photodetector signal, and (iii) sends the data to a single-board computer (SBC). Lastly, the SBC performs further signal processing and displays the sensor data on a graphical user interface. The choice for hardware and software development combined allows for a lost-cost solution that supports monitoring of four channels simultaneously, real-time operation, compatibility with Windows and Linux-based operating systems, dynamic inputs for signal processing, wireless communication with low latency, and portability.

Optical trapping is a versatile and non-invasive technique for single particle manipulation. As such, it can be widely applied in the domains of particle identification and classification and thus used as a tool for monitoring physical and chemical processes. This creates an opportunity for integrating the method seamlessly into optofluidic chips, provided it can be automatized. Yet even though OT is well established in multiple scientific domains, a full stack approach to its integration into other technological devices is still lacking. This calls for solutions in tasks such as automatic trapping and signal analysis.

In this manuscript, we describe the implementation of an algorithm seeking autonomous particle location and trapping. The methodology is based upon image-processing, allowing for particle location using real time image segmentation. A local thresholding algorithm is applied, followed by morphological techniques for closing shapes and excluding non-bounded regions - after which only the particles remain on the image. Once the centroid is identified, the stage is translated accordingly by piezo-electric actuators, followed by the laser activation. In this way, trapping is achieved, and one may proceed to analyze the forward scattered optical signal, after which a new particle inside the actuators range may be automatically trapped.

This development, when compared with existent solutions involving holographic optical tweezers, allows for similar capabilities without using a spatial light modulator, thus dramatically reducing the setup costs of autonomous OT solutions. Therefore, when combined with particle classification techniques, this method is well suited for integration into possible optofluidic chips for autonomous sensing and monitoring of biochemical samples.

Nowadays, the diagnosis of Alzheimer's disease is a complex process that involves several clinical tests. Cerebrospinal fluid contains common Alzheimer-related biomarkers that include amyloid beta 1-42 (Aβ1-42) and tau proteins. In this work, we propose vibrational spectroscopy techniques supported by machine learning for the detection of biomarkers in cerebrospinal fluid that are related with Alzheimer's by prediction models. Vibrational spectroscopy provides the entire biochemical composition of the body fluid, and thus, small but typical physiological changes related with the pathology can be ascertained. Within a machine learning framework, Raman and FTIR spectra were analyzed, which were taken from samples of healthy volunteers in comparison with samples from patients clinically diagnosed with Alzheimer's. We find that a logistic regression model can discriminate between healthy control and Alzheimer's patients with a precision of 98%, when the input for the model combines data from both vibrational spectroscopy methods. Our approach shows high discriminative capabilities and constitutes a proof of concept for an alternative and accurate tool for the diagnosis of Alzheimer's disease.

Cerebrospinal fluid contains specific biomarkers of Alzheimer's disease that include amyloid beta peptides and tau proteins. In this work, we present for the first time possible evidence that the formation of the constituents of cerebrospinal fluid during drying is related with Alzheimer's. We use machine learning to examine optical microscope images of dried cerebrospinal fluid patterns from patients with Alzheimer's and healthy controls to create a diagnostic model. To analyze the images, the histogram of oriented gradients is used as a feature descriptor. Each image is mapped into the corresponding feature space, and principal component analysis is applied for dimensionality reduction. A machine-learning prediction model with a sensitivity of 82% was built. These promising preliminary results show great potential for new rapid and low-cost diagnostic pathways in the detection of Alzheimer's disease.

This paper presents the experimental analysis of the vulcanization process of nitrile rubbers for the diaphragms fabrication used in FBG-based pressure sensors. Tests using diaphragms with different rubber thicknesses (0.5mm, 1.0mm, and 1.5mm), vulcanization temperatures (125°C, 150°C, and 200°C), and vulcanization times (2.5min and 5.0min) were performed to analyse the chemical degradation of diaphragms. Degradation analysis was performed using digital macrography of the diaphragm surfaces and the diaphragms stiffness was analysed by tensile tests. An FBG was embedded in the diaphragm which was vulcanized using the temperature and time which resulted in the lowest rubber degradation, and a compression test was performed. Results of the digital macrography show that diaphragms vulcanized at 125°C presented smaller degradation areas, in which diaphragms with 0.5mm rubbers presented an area degradation mean of 17.5%, whereas 1.0mm rubbers presented 14.5%, and 1.5mm rubbers showed 11.0%. Moreover, greater thickness led to smaller degraded area for the same temperature and vulcanization time. Thus, for the same thickness in the rubber, the higher vulcanization temperature results in a higher material stiffness, where stiffness is directly related to the reduction of cross-links due to the degraded area. Results of the sensitivity test using diaphragms vulcanized at 125°C showed a pressure sensitivity of 11.67kPa/mm and wavelength sensitivity of 456.1pm/mm for 0.5mm rubber thicknesses, 18.04kPa/mm pressure sensitivity, and 112.3pm/mm wavelength sensitivity for 1.0mm rubber thickness and 31.55kPa/mm pressure sensitivity and 913.8pm/mm wavelength sensitivity for 1.5mm rubber thickness. It concludes that the 0.5mm rubber vulcanized diaphragm obtained higher sensitivity when comparing pressure and wavelength.

The biosensor consists of an optical sensing system and an optoelectronic data acquisition system. The sensor's optical system consists of a biochemically functionalized polymer optical fiber (POF-Plastic Optical Fiber) based on Field Evanescent technology. The Evanescent Field technique has been widely adopted in sensing and in this project, it was obtained by bending the fiber in a "U" shape, aiming to increase the sensitivity of the biosensor, through the contact of the curved sensor part with the sample biological. A data acquisition system was developed through an optoelectronic project aiming to increase the sensitivity when compared to a commercial equipment acquisition system. This work presents a biosensor for the detection of Escherichia coli based on an evanescent field with a polymer optical fiber linked to the analog signal acquisition system through an optoelectronic system developed. The interaction investigation of antibodies and antigens in Escherichia coli for computational methods was carried out in order to obtain information about the action of the antibody and in future steps applied in the validation of the diagnostic method.

We will discuss some of main topics in two recent publications on color from the International Commission on Illumination (CIE): CIE 015:2018 and CIE 248:2022. Regarding CIE 015:2018, it is the 4^th edition of the most important CIE general publication on colorimetry, generally known as 'CIE publication 15'. Among main novelties in CIE 015:2018 with respect to its previous 2004 edition, we can mention the introduction of the next four topics: 1) Cone-fundamental-based colorimetric observers; 2) New CIE illuminants (indoor daylight illuminants, smoothed daylight illuminants, illuminant E, and white LED illuminants); 3) The CIE colour appearance model CIECAM02; 4) The CIE 2017 color fidelity index. As a consequence of the active research on color appearance during the past few years, CIE 248:2022 proposed the CIECAM16 color appearance model for related colors and CIE 1931 standard colorimetric observer. In general, color appearance models provide a viewing-condition-specific method for the transformation of the tristimulus values X, Y, Z, to or from perceptual attribute correlates. CIECAM16 replaces CIECAM02 and may be useful for color management systems and image industries. CIECAM16 is simpler and maintains the predictions of experimental visual data made by CIECAM02. Finally, we will discuss advances in two issues related to color included in the current CIE Research Strategy: 1) A roadmap toward a new CIE colorimetry based on cone fundamentals, currently studied by CIE Technical Committee 1-98; 2) Color differences in tri-dimensional object colors and spatio-chromatic complexity, currently studied by CIE Technical Committees 8-17 and 8-14, respectively. In overall, we can conclude that color science is an active inter- and multi-disciplinary research field where optics continues playing a key role.

Label-free bioanalytical methods have been widely employed in biomedical research, in particular, in drug screening and discovery, diagnostics, and proteomics. Photonic crystals (PCs) represent a modern alternative to surface plasmon resonance (SPR) techniques. Imaging of PC surface modes has been demonstrated as a promising label-free approach allowing for multiplexed detection. Surface modification of PC sensors is an important stage determining the effectiveness of the analysis of biomolecule interactions. Here, we describe the results of the development of a label-free PC-based sensor, the key steps of the modification and functionalization of the PC surface with proteins, as well as the evaluation of its suitability for sensing via 2D imaging of binding events. Our data demonstrate the efficiency of the designed PC-based sensor for analysis of proteins interactions and pave the way for the engineering of a label-free biosensing platform based on PCs.

A method based on the photographic recording of the power distribution laterally diffused by cationic electroactive network (CN)-based hydrogel waveguides is first checked against the well-established cut-back method and then used to determine the different contributions to the optical power attenuation along the hydrogel-based waveguide. Absorption and scattering loss coefficients are determined for 450 nm, 532 nm and 633 nm excitation.

Purpose: Anaglyphs, Vectograms and Cheiroscopes are visual therapy materials based on red/green, polarized, or black/white targes that used similar but slightly different images for each eye to train fusion and vergence skills. This study aimed to analyse the differences in the results obtained on those devices on participants with low, normal, or high AC/A ratios. Material and methods: three groups of volunteer participants were recruited based on their recent clinical history among patients attending the Optometry Clinic of the centre: 15 participants with low AC/A, 15 participants with normal AC/A and 15 participants with High AC/A ratios. None of them was under any type of medication, have an ocular or systemic disease, or were performing any kind of visual training plan that could affect the study. In two sessions one week apart, following the manufacturer's instructions, the participants performed in a random order three visual therapy device-based training: one red/green Fixed Demand Anaglyph [FDA], one Variable Demand Polarized Vectogram [VDPV], and one based on the Wheatstone W [WW]. Participants were instructed to indicate the maximum value base-out (BO) where both image fusion and clarity was lost. Results between both sessions were compared with an analysis of differences. Results: There was found higher BO vergences results with the three devices regarding the second to the first session in the Low and Normal AC/A groups (Wilcoxon test, all p ≤ 0.013), but none in the High AC/A group (Wilcoxon test, all p ≥ 0.162). Conclusion: There is an enhancement of BO vergences in Low and normal AC/A participants but not in high AC/A participants by performing visual training with Anaglyphs, Vectograms and Cheiroscopes devices.

The measurement of physical parameters is important in many current applications, since they often rely on these measurands to operate with the due quality and the necessary safety. In this work, a simple and robust optical fiber sensor based on an antiresonant hollow square core fiber (HSCF) is proposed to measure simultaneously temperature, strain, and curvature. The proposed sensor was designed in a transmission configuration where a segment of HSCF, with a 10 mm length, was spliced between two single mode fibers. In this sensor, a cladding modal interference (CMI) and a Mach-Zehnder interference (MZI) are enhanced along with the antiresonance (AR) guidance. All the present mechanisms exhibit different responses towards the physical parameters. For the temperature, sensitivities of 32.8 pm/°C, 18.9 pm/°C, and 15.7 pm/°C were respectively attained for the MZI, AR, and CMI. As for the strain, sensitivities of 0.45 pm/με, -0.93 pm/με, and -2.72 pm/με were acquired for the MZI, AR and CMI respectively. Meanwhile, for the curvature measurements, two regions of analysis were considered. In the first region (0 m⁻¹ - 0.7 m⁻¹) sensitivities of 0.033 nm/m⁻¹, -0.27 nm/m⁻¹, and -2.21 nm/m⁻¹ were achieved, whilst for the second region (0.7 m⁻¹ - 1.5 m⁻¹) sensitivities of 0.067 nm/m⁻¹, -0.63 nm/m⁻¹, and -0.49 nm/m⁻¹ were acquired for the MZI, AR and CMI, respectively.

Purpose: The present study aimed to analyse the influence of absorptive tinted filter lenses on Contras Sensitivity (CS) in healthy participants under three different environmental conditions. Methods: 10 Healthy qualified volunteers who fulfilled the inclusion/exclusion criteria were recruited: refractive spherical error between +2.00 and -4.00D, refractive cylindrical error less than 1.00 D, Best Corrected Visual Acuity (BCVA) ≥ 1.0 and Low Vision Quality of Life (LVQOF) score ≥ 50. Participants were scheduled for three-session under different environmental conditions where CS was measured with a Pelli-Robson chart with and without five (ML Filters 450, 500, 511, 527 and 550) absorptive tinted filters lenses: 1) indoor, 2) outdoor on a sunny day, 3) outdoor on a rainy day. The filters were always introduced in the same order, from the higher absorption filter (ML Filter 550) to the lower (ML Filter 450). Results between filters and environmental conditions were compared. Results: There was a statistical difference in the CS values obtained with and without a filter in the measurements performed in all environmental conditions (Friedman test: all p < 0.001) with no differences in the pairwise analysis between filters (Wilcoxon test; all ≥ 0.009). There was no statistically difference in the CS values between environmental conditions without filters or with any of the filters (Friedman test: all p ≥ 0.097). Conclusions: The present study found that coloured filter lenses between 450 and 550 nm wavelength absorption had minimal impact on CS in healthy participants.

Here, we numerically propose and demonstrate a technique to couple light between two multi-core fibers (MCFs) using long-period gratings (LPGs). The light is coupled from one core of the input MCF to all cores of the output MCF. For that, an LPG is inscribed in the input core of the input MCF and identical LPGs are inscribed in all cores of the output MCF. First, the light is launched into the input core of the MCF and the optical power is transferred to the cladding due to the LPG inscribed in that core. The optical power in the cladding is then transferred to the other MCF cladding by evanescent field coupling. The optical power in the cladding of the output MCF is distributed by all its cores due to the identical LPGs inscribed in them. We optimized the LPGs period, their lengths and offset distance to increase the power transfer at 1480 nm. We achieved a power transfer of 92% of the input power, distributed by all MCF cores, in 10.6 cm of length. We also studied the power transfer sensitivity to the LPGs period.

Purpose: To compare the values of central corneal thickness (CCT), the anterior chamber depth (ACD) and the axial length (AL) on measurements performed with and without contact lenses (CL) in healthy subjects. ACD was measured with two different devices (Visionix 120+ and EchoScan US-800) and the values were also compared between them. Material and methods: 20 volunteer participants (6 men and 14 women, 24.8 ± 2.73 years) were recruited. In a single visit, participants underwent autorefraction, biometry, topography and pachymetry with the naked eye (without CL). Then, biometry and pachymetry were repeated twice wearing two different CL (Somofilcon A and Nesofilcon A) of -3.00D lens power fitted in random order. Data were compared using t-tests for related samples. Results: CCT values wearing CL were significantly higher than those obtained with the naked eye (Paired t-test; both p ≤ 0.001). On the other hand, no significant differences were found between the ACD or AL values with the naked eye versus any of the CL studied (Paired t-test, all p ≥ 0.111). The ACD values comparing Visionix120+ to EchoScan US-800 measurements were significantly different with both the naked eye and with any CL (Paired t-test; all p ≤ 0.001). Conclusion: CCT measurements cannot be performed while wearing CL. In contrast, ACD and AL measurements were not affected by the use of any CL. In addition, it was observed that ACD results from both devices are not interchangeable neither when measured with the naked eye nor using any CL.

The use of concrete has been widespread in our society in housing and infrastructure, despite the environmental cost associated with its production. Its decay poses a social, economic, and environmental problem. Currently, the carbonation of cement paste is monitored through the measurement of its pH, with several optical fiber sensors (OFS) have been produced for this purpose. In the current work the focus is, also, on the carbonation monitoring of cement paste through an OFS, but not through pH measurements. Single fiber reflectance spectroscopy, previously employed to measure cement paste durability, is used to monitor the discoloration of cement paste caused by carbonation. As the carbonation front reaches the fiber tip embedded in the cement paste, the signal reflected onto the fiber increases. The accelerated carbonation of two limestone cement paste samples in an atmosphere of 100% CO₂ was successfully monitored. The applicability of the sensor for operational use with ambient CO₂ was confirmed through the measurement of carbonation at 3% CO₂. The cross interference from water ingress and egress was also evaluated, and it didn't hinder the measurements of carbonation. Therefore, a novel OFS capable of measuring cement paste carbonation and durability, was achieved.

Monitoring the vibration of industrial engines is essential for running diagnostics that can detect faults and point out the feasibility of predictive maintenance. Therefore, this paper describes an optical accelerometer based on a fiber Bragg grating to monitor the vibration of the gearbox of an industrial engine prototype. Experimental tests were performed varying the motor's rotation speed during normal operation. To validate the proposed system, two electronic accelerometers were attached to the motor's gearbox and bearing. The natural frequency response of the optical accelerometer was simulated and good agreement with the experimental results was obtained (0.83% of error). The proposed sensor was able to correctly identify the operation speeds of 20, 25, 35, 40, 45 and 50 rps with a maximum error of 0.05%. The mean signal-to-noise ratio (SNR) of the optical accelerometer was 64.05% higher than the SNR of one of the electronic solutions. The experimental results show that the vibration signals have different characteristics when measured at the bearings and at the gearbox, indicating the feasibility of multi-signals analysis for fault detection.

In Photonic Integrated Circuits (PICs) it is often necessary some sort of mismatch adaptation between waveguides of different cross-sections. There are several instances of such a designing constraint, being the vertical coupling between the PIC and an optical fibre probably the most representative of all examples. Here, the beam of electromagnetic energy inside the PIC must be inserted/extracted through/to an optical fibre. Typical core diameters are approximately 10 μm and 5 μm, for single mode optical fibres operating in the near infrared and visible wavelengths, respectively. On the other hand, the optical interconnects linking individual structures in PICs are usually single mode waveguides, 400 to 500 nm wide and a few hundreds of nanometres thick. This presents a bidimensional mismatch between the optical fibre and the single mode waveguide within the PIC, that requires both lateral and longitudinal beam expansions. In this work, we have approached the lateral expansion of the fundamental mode propagating in a single mode waveguide, at the operating wavelength of 1550 nm and being coupled out into an optical fibre, through a grating structure 14.27 μm wide. To this end, we have designed and simulated a subwavelength metamaterial planar structure, which is able to expand laterally the fundamental mode's profile from 450 nm to 14.27 μm, within 11.1 μm. Furthermore, we will be presenting the results obtained when comparing this structure with several linear inverted taper waveguides, regarding coupling and propagation efficiencies. Namely, we compared the coupling efficiencies of the modes propagating in an 100 μm long waveguide, when being excited by the analytically calculated fundamental mode and the fields obtained at the end of the designed structure. The results obtained for the designed structure 11.1 μm long and the calculated fundamental mode showed a coupling efficiency of -1.53 dB and -1.20 dB, respectively.

In this work, a hybrid sensor based on a silica capillary in a balloon-like shape for simultaneous measurement of displacement and temperature is proposed for the first time, to the best of our knowledge. The sensor is fabricated by splicing a segment of a hollow core fiber between two single mode fibers (SMF) and by bending the fiber in a balloon shape with the capillary at the top-center position. In a transmission scheme, the SMF-capillary-SMF configuration excites an antiresonant (AR) guidance and the balloon shape enhances a Mach-Zehnder interferometer (MZI). The different responses of the interferometers to external displacement and temperature variations are conducive to a hybrid application of the sensor for simultaneous measurement of these parameters. Experimental results show that, for a capillary length of 1.2 cm and a balloon length of 4 cm, AR is insensitive to displacement and its sensitivity to temperature is 14.3 pm/°C, while the MZI has a sensitivity to displacement of 1.68 nm/mm and twice the sensitivity of AR to temperature, of 28.6 pm/°C. The proposed fiber sensor consists of only one sensing element in one configuration exciting two interferometers at the same time, which makes it of simple fabrication as well as low cost.

Thermochromic materials change their optical response to temperature reversibly. This study explores the application of thermochromism to road engineering, which is still incipient in this area, from two perspectives. The first one is about the development of functionalized road markings (FRM) working as thermochromic sensors to alert the presence of ice on the road and, in this way, to improve road safety. The second one concerns the functionalization of asphalt pavements for reversible color change at high temperatures to reduce energy absorption in the form of heat and, in this way, mitigate Urban Heat Islands (UHI) effect. For the development of the FRM, thermocapsules were added into acrylic ink, applied to an AC10 asphalt mixture, submitted to high and low temperatures, and visually characterized. For the functionalization aiming for UHI reduction, thermochromic solutions (TS) containing thermocapsules, dye, and resin were superficially sprayed at an AC10, and the Quick Ultraviolet Accelerated Weathering Test (QUV) was performed with subsequent Colorimetry Analysis, where the color coordinates defined by the Comissione Internationale de l' Éclairage (CIE) were measured. The results show that it is possible to functionalize road marks to work as a thermochromic sensor. Also, this property can be improved by synthesizing or using thermocapsules with TT closer to the water melting point. The results also indicate that the asphalt pavement functionalization with surface spraying of TS points out to higher luminosity results in terms of color coordinate, which is intended for the mitigation of heat energy absorption, consequently mitigating the UHI.

Optical trapping provides a way to isolate, manipulate, and probe a wide range of microscopic particles. Moreover, as particle dynamics are strongly affected by their shape and composition, optical tweezers can also be used to identify and classify particles, paving the way for multiple applications such as intelligent microfluidic devices for personalized medicine purposes, or integrated sensing for bioengineering. In this work, we explore the possibility of using properties of the forward scattered radiation of the optical trapping beam to analyze properties of the trapped specimen and deploy an autonomous classification algorithm. For this purpose, we process the signal in the Fourier domain and apply a dimensionality reduction technique using UMAP algorithms, before using the reduced number of features to feed standard machine learning algorithms such as K-nearest neighbors or random forests. Using a stratified 5-fold cross-validation procedure, our results show that the implemented classification strategy allows the identification of particle material with accuracies up to 80%, demonstrating the potential of using signal processing techniques to probe properties of optical trapped particles based on the forward scattered light. Furthermore, preliminary results of an autonomous implementation in a standard experimental optical tweezers setup show similar differentiation capabilities for real-time applications, thus opening some opportunities towards technological applications such as intelligent microfluidic devices and solutions for biochemical and biophysical sensing.

Safe self-driving vehicles require precise 3D Object Identification. LiDAR sensors are key in accomplishing such a task, as LiDARs produce high-definition point clouds. Such point clouds are then processed by 3D Object Detection models to finally detect objects.

Most Object Detection models require massive amounts of data to be trained. Gathering and processing this data is an expensive and time-consuming task, which is why the information taken from each sample must be fully harnessed. Such can be done through Data Augmentation. Data Augmentation contributes significantly for improving performance, being at least as relevant as the advances in the Object Detection models themselves.

A few studies have been reported regarding the effectiveness of Data Augmentation. However, the role played by original and augmented samples has been neglected. This work reports the first-ever detailed quantification of the impact that the inclusion of original and augmented samples in a dataset has in 3D Object Detection in the context of autonomous driving. The obtained results show that although a good augmentation strategy is crucial to the model's performance, it is only as good as the quality of the original samples allows it to be.

One of the challenges in using integrated optical biosensors is their ability to operate in environments outside laboratories. This occurs, among other reasons, because suitable source coupling components are not considered at the design stage. In this work, a highly selective, compact and efficient in-coupling method is proposed with the aim to develop a genuine Point-of-care (PoC) platform. The proposed configuration consists of a single-mode fiber core placed in parallel and centered above an inverted non-linear taper, which can also be seen as a pigtailed input stage. These components are separated by the cladding of the taper that acts as a gap. In this setup, light is coupled from the fiber to the taper, which then becomes the core of a multimode waveguide. The coupled modes depend on the position of the fiber and the geometry of the taper. For interferometric biosensors, the power distribution between the modes is very important because each one reacts differently to the sample placed on the optical transducer. Therefore, the selectivity of the coupling stage affects the interferometric pattern and, consequently, the detection process. In the model presented in this work, the input is set as the fundamental mode (LP₀₁) of the fiber. Since it is centered, only the even modes are excited in the taper. The width of the taper varies from 2 µm to 3 µm, in order to select only high-order modes, due to their large evanescent tails lead to highly sensitive biosensors. The non-linear format optimizes the design by dividing the entire taper into a cascade of linear sections. Those in which the coupling of the desired modes occurs are prioritized by increasing their lengths, thus making the transition smoother. Instead, the other sections maintain a reduced length. To select other modes or change the power distribution between them, one may just simply change the width of the taper and the length of the prioritized sections. In this work, a fiber-to-taper configuration of 8 mm length is presented, which couples 48% and 17% of the input power to TE₈ and TE₁₀ modes, respectively.

The possibility to map the element distribution on a sample surface is one of the interesting applications of laser-induced breakdown spectroscopy that has been extensively explored in recent years. In this manuscript, we explore the combination of photogrammetry and LIBS techniques for the creation of a three-dimensional model of the map of the elements on the surface of the sample. Using a dedicated photogrammetry solution and software, we reconstruct the three-dimensional model of the mineral sample whose mesh is later exploited for the interactive interpretation of the results. Then, making use of Paraview software, which integrates production algorithms and computing performance in a unified solution for scientific purposes, we establish a process pipeline that allows the creation of an interactive three-dimensional model with the spatial distribution of the target elements on top of the sample surface. Our results demonstrate that combining these two techniques can give us a valuable resource for better qualitative analysis and insight, providing an innovative three-dimensional modeling solution that may open the door to a new range of possibilities, from quality control technology involving alloys and mechanical parts to interactive teaching environments for geo and biosciences, just to name a few examples.

Spike-based neuromorphic devices promise to alleviate the energy greed of the artificial intelligence hardware by using spiking neural networks (SNNs), which employ neuron like units to process information through the timing of the spikes. These neuron-like devices only consume energy when active. Recent works have shown that resonant tunnelling diodes (RTDs) incorporating optoelectronic functionalities such as photodetection and light emission can play a major role on photonic SNNs. RTDs are devices that display an N-shaped current-voltage characteristics capable of providing negative differential conductance (NDC) over a range of the operating voltages. Specifically, RTD photodetectors (RTD-PDs) show promise due to their unique mixture of the structural simplicity while simultaneously providing highly complex non-linear behavior. The goal of this work is to present a systematic study of the how the thickness of the RTD-PD light absorption layers (100, 250, 500 nm) and the device size impacts on the performance of InGaAs RTD-PDs, namely on its responsivity and time response when operating in the third (1550 nm) optical transmission window. Our focus is on the overall characterization of the device optoelectronic response including the impact of the light absorption on the device static current-voltage characteristic, the responsivity and the photodetection time response. For the static characterization, the devices I-V curves were measured under dark conditions and under illumination, giving insights on the light induced I-V tunability effect. The RTD-PD responsivity was compared to the response of a commercial photodetector. The characterization of the temporal response included its capacity to generate optical induced neuronal-like electrical spike, that is, when working as an opto-to-electrical spike converter. The experimental data obtained at each characterization phase is being used for the evaluation and refinement of a behavioral model for RTD-PD devices under construction.

A Digital Micromirror Device (DMD) is a technology developed by Texas Instruments, that consists in a two-dimensional array of micromirrors, which can be individually tilted between two positions. It has been used as a digital video and image processing solution, commonly found in Digital Light Processing (DLP) video projectors. Over the years, DMDs have become popular in different fields: industrial, automotive, medical, government and home user solutions. In the astronomy field, it has been also considered in on-ground space instrumentation and it has been proposed for the development of some astrophysical space instruments. In order to evaluate the actual impact of such device in the instrument optical design, it is important to know how the light behaves when it interacts with a DMD, namely in what regards to the diffraction process when a light beam is reflected by a periodic array of micromirrors. In this study we describe how we simulate the diffraction patterns produced by a periodic array of micromirrors, for coherent and incoherent sources of light. The results from simulations are verified against laboratory experiments, described also in this study.

Dynamic speckle imaging (DSI) of areas with different speed of processes ongoing in industrial or biological objects relies on statistical processing of a large number of images of the speckle patterns formed on the objects surface under laser illumination. The DSI visualizes the speed spatial distribution as an activity map. We propose compression of the raw DSI data by applying singular value decomposition (SVD). A specific feature of speckle images for DSI is lack of a structure with areas of close intensity values. The gain from the direct SVD application may be modest in cases when a great number of non-zero singular values is needed to build an activity map comparable in quality to the ground truth map from bitmap images. For higher compression, we propose SVD to be applied to the 2D arrays containing the differences between the successive images. The SVD compression has been verified by using synthetic and experimental data.

In this work, optical fiber Bragg grating (FBG) sensors were used to evaluate the thermal performance of an 18650 Li-ion battery (LiB) operating under normal and abusive conditions while positioned in horizontal and vertical orientations. In total, three FBG sensors were used to track in real-time the temperature variation of the cathode, middle, and anode of the LiB. Tests for each orientation were performed, where each of them consisted of two cycles: the first one with normal charge/discharge conditions, operating between 2.75 V and 4.20 V, and another in abusive conditions, operating between 2.00 V and 4.95 V. The battery was submitted to constant current charge and discharge steps, with rest intervals between each operation. The results suggest that, in general, the temperature variation while operation in vertical orientation is lower when compared to the horizontal one, mainly in the anode, while the LiB is submitted to the abusive charge procedure, where the temperature variation difference achieved 3.4 ± 0.2 °C. In addition, the FBG sensors were able to track in real-time the temperature variation of three different locations of the battery simultaneously. The temperature variation registered for each sensor is shown and discussed.

Multifunctional nanosystems are capable to carry one or more therapeutic agents (thermal and/or targeting agents and chemotherapeutic drugs), offering the capability to concurrently perform different treatment modalities using a single nanosystem. Cluster nanostructures, consisting of densely packed aggregates of magnetic nanoparticles, have shown enhanced heating capabilities. Their combination with plasmonic nanoparticles enable synergistic behavior between dual hyperthermia (magneto-photothermia), allowing overheating cancer cells while increasing drug toxicity. In this work, multicore magnetic nanoparticles (NPs) of MnFe2O4 were prepared using oxamide and melamine as clustering agents. The multicore NPs prepared with oxamide were covered with a gold shell, resulting in multicore magnetic/plasmonic NPs with an increased SAR of 173.80 W/g, under NIR light. Liposomes based on these magnetic/plasmonic NPs were prepared and the model drug curcumin was loaded in these nanocarriers with a high encapsulation efficiency. The fusion between the curcumin-loaded magnetic/plasmonic liposomes and models of cell membranes (labelled with Nile Red) was confirmed by FRET, pointing the magneto/plasmonic liposomes as promising for dual cancer therapy (combined hyperthermia and chemotherapy).

New paths to increase the sensing performance of plasmonic sensors have been reported in recent years. There are several methodologies to achieve such purpose, namely by optimizing the nanostructure, nanomaterial and even the sensing platform. Recently the use nanoparticles over plasmonic thin films have been reported and shown sensitivity enhancement, when compared to a bare thin film. Nevertheless, a nanomaterial combination between NP and thin film has not been studied. In this work it was studied such plasmonic materials in order to optimize not only refractometric sensitivity but also decrease the resultant plasmonic band width. It was found that for Au, Ag and Cu thin films, the deposition of plasmonic nanoparticles resulted in an overall refractometric sensitivity and figure of merit (FOM) increase. The larger FOM increase was obtained for the Ag thin film, from 42 to 162 when coupled to Si nanoparticles. The greater sensitivity increase was achieved for a Cu thin film coupled to a Si nanoparticle, with an increase from 1745 to 3230 nm/RIU.

While laser-induced breakdown spectroscopy is often used as a standalone technique, recent years saw an increasing interest in their combination with additional techniques towards multimodal sensing solutions capable of enhancing the capabilities of this technological solution. In this work, we try to identify possible synergies that arise from merging the analysis of laser-induced breakdown spectroscopy with that from a hyperspectral scanning of the sample, comparing it with the performance of standalone solutions. Having investigated the multimodal approach for a case study involving the identification of lithium minerals, our preliminary results demonstrate that while both solutions can provide reasonable results for qualitative mineral identification, they feature advantages and disadvantages that shall be taken into further consideration. Nevertheless, when working in collaboration, the results enclosed suggest that an integrated tandem solution can be an interesting tool for material analysis for research and industrial applications, combining the best of both instruments.

Photonic researchers have increasingly exploiting nanotechnology. Due to the advent of numerous prevalent nanosized manufacturing methods that enable adequate shaped nanostructures to be manufactured and investigated as a method of exploiting nano-structured. Owing of the variety of optical modes, hybrid nanostructures that integrate dielectric resonators with plasmonic nanostructures also offer enormous potentials. In this work, we have explored a hybrid coupled nano-structured antenna with stacked lithium tantalate (LiTaO₃)/Aluminium oxide (Al₂O₃) multilayer operating at infrared ranging from 400 nm-2000 nm. Here, the sensitivity response has been explored of the hybrid nano-structured array made up of the gold metal elliptical disk placed on the top of a quartz substrate and excite the different modes in both materials. It shows large electromagnetic confinement at the separation distance (d) of the dimers due to strong surface plasmon resonance (SPR). The influence of the structural dimensions is investigated to optimise the sensitivity of stacked elliptical dimers. The designed hybrid coupled nano-structure with the combination of gold (Au) and Lithium tantalate (LiTaO₃) /Aluminium oxide (Al₂O₃) with h₁ = h₂ = 10 nm each 10 layer exhibits bulk sensitivity (S), which is the spectrum shift unit per refractive index (RI) change in the surrounding medium was calculated to be 730 and 660 nm/RIU with major axis, (a) = 100 nm, minor axis, (b) = 10 nm, separation distance (d) = 10 nm, height, (h) = 100 nm (with or without stacked). The outcomes from the proposed hybrid nanostructure have been compared with a single metallic (only gold) elliptical paired nano-structure to show a significant improvement in the sensitivity using hybrid nano-structure. Depending on these findings, we demonstrated a roughly two-fold increase in sensitivity (S) by utilising a hybrid nano linked nano-structure with respect to identical nano structure, which competes with traditional sensors with the same height, (h) based on localised surface plasmon resonances. Our innovative plasmonic hybrid nanostructures provide a framework for developing plasmonic nanostructures for use in various sensing applications.