Optical Sensors 2023

Development of novel plasmonic nanopatterns is of great interest for various applications, including chemical and biological analysis. Plasmonic properties associated to the nanostructure can be tuned by changing the size and the shape of the nanoparticles or the periodicity or, more in general, the geometry of the nanopattern. In this work we present a study of periodic arrangements of novel plasmonic metamolecular unit cells made of triangular nanoelements. Nanostructures analyzed were fabricated using electron beam lithography technique (EBL) that allows to create patterns with high accuracy and repeatability. Morphological analysis was realized by Scanning Electron Microscopy (SEM) and their plasmonic properties were studied and compared using experimental set-up for Localized Surface Plasmon Resonance (LSPR) and Surface Enhanced Raman Spectroscopy (SERS) measurements. We tested the sensing performance of our nanostructures analyzing a SARS-CoV-2 (COVID-19) Spike Antibody getting its molecular fingerprint. Our results suggest that these plasmonic patterns are promising to develop highly sensitive nanosensors for the detection of biological analytes.

The increasing demand for precise chemical and biological sensing has led to the development of highly efficient plasmonic optical fiber sensors. Therefore, it is essential to optimize and match the operating wavelength region of both the optical fiber configuration and localized surface plasmon resonance of nanoparticles (NPs). This can be achieved by developing NPs that can reach resonance at near-infrared wavelengths, where refractive index sensitivity is enhanced, and silica optical fibers have lower losses. High aspect-ratio bimetallic Au@Ag nanorods and different side-polished fiber structures are tested using numerical simulations. The selected optical fiber configuration was based on a side-polished fiber with a 1 mm polished section. It is compared power losses and power at the NP interface for two configurations: a step-index single-mode fiber (SMF) with core/cladding diameters of 8.2/125 µm and a multimode graded-index fiber (GIF) with 62.5/125 µm at various polishing depths. The results showed that the best performance for both configurations was achieved at similar polishing depths, namely 59.5 and 55.2 µm for the SMF and GIF, respectively. The optical impact of retardation effects due to the proximity with the fiber structure were also observed, which caused a reduction in sensitivity from 1750 nm/RIU to 1500 nm/RIU and a red-shift of around 70 nm.

To achieve single-molecule detection based on enzyme-free and isothermal amplification techniques, we have developed a strategy employing coupled catalytic hairpin assembly reactions and investigated several parameters influencing its yield. We employed avidin-biotin assay using biotin-modified trigger DNA and surface plasmon resonance to excite fluorescence-labeled hairpin DNA captured a surface. Our investigation of association and dissociation of fluorescence-labeled hairpin DNA allows to determine the reaction yield and provide guide to design the involved oligonucleotides.

Circulating Tumor Cells (CTCs) have emerged as an eligible biomarker for liquid biopsy. These cells are released in peripheral circulation at a very early stage from the tumor mass via metastatic or non-metastatic cascade. These cells provide a non-invasive method for cancer detection and monitoring. In this work, Gold Nanoparticle (GNP) decorated U-bent optical fiber was used as a sensor platform. For specific detection of cancer cells, an antibody for nucleolin protein which over-expresses on their surface was employed as a receptor. This Localized Surface Plasmon Resonance (LSPR) based biosensor poses salient features like high sensitivity, ease of fabrication, low cost, and handling. For sensor fabrication, U-bent optical fiber was coated with GNPs and then with cysteamine and glutaraldehyde. Further, the antibody and ethanolamine (blocking agent) was immobilized. The sensor was introduced to 10^4 MCF-7 cells and 10^5 WBCs in PBS buffer and the binding absorbance for 2 hours was monitored. The obtained absorbance for MCF-7 cells and WBCs was around 0.05 and 0.002 O.D. respectively, which indicated a very high specificity of the sensor for cancer cells. The obtained results are promising and pave the way to develop a highly specific and affordable point-of-care device for cancer detection and monitoring.

State-of-the-art multi-Petawatt laser facilities coming online include the Zettawatt Equivalent Ultrashort pulse laser System (ZEUS), a user facility being commissioned at the University of Michigan. The 3-PW pulses will make ZEUS the highest power laser in the USA. This talk will describe the various experimental approaches that can be used to produce ultrashort particle beams and light-sources, as well as their application to study strong-field plasma physics and beyond. One area of interest is to create extremely strong magnetic fields within the hot plasma in the laboratory, so we can study the microphysics likely to be occurring around the most energetic objects in the universe.

Laser Plasma Accelerators (LPA) rely on our ability to control finely the electrons motion with intense laser pulses. Such manipulation allows to produce giant electric fields with values in the TV/m exceeding by more than 3 orders of magnitude those used in current accelerator technology. Controlling the collective electrons motion permit to shape the longitudinal and radial components of these fields that can be optimized for delivering high quality electrons beam or energetic photons. To illustrate the beauty of laser plasma accelerators I will explain the fundamental concepts we recently discovered, and I’ll show the maturity of our approach in delivering particle and radiation beams for societal applications including for radiotherapy with the ebeam4therapy EIC project.

On December 5th, 2022, the National Ignition Facility in Livermore, California, USA performed the first experiment demonstrating controlled fusion ignition in the laboratory. With a 2.05MJ UV laser drive energy delivered to the target, a neutron yield of 3.15MJ was released by the fusion reactions in the capsule, providing a net target gain of ~1.5×. The results of this experiment will be discussed, along with the decades-long developments in optical materials, laser architectures, target fabrication, and target diagnostics enabling this recent accomplishment. We will discuss the next steps for NIF and provide an outlook on future applications and technologies, including the reinvigorated pursuit of Inertial Fusion Energy.

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions. To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy. We use it to exemplify how deep learning can be employed for a broad range of applications, from particle localization, tracking and characterization to cell counting and classification. Thanks to its user-friendly graphical interface, DeepTrack 2.1 can be easily customized for user-specific applications, and, thanks to its open-source object-oriented programming, it can be easily expanded to add features and functionalities, potentially introducing deep-learning-enhanced video microscopy to a far wider audience.

Radiography is the gold standard imaging technique in dental medicine. While every modern X-ray equipment manufacturer strives to obtain the best possible image characteristics, there are certain limitations for the different types of dental radiographs: panoramic, intraoral, cephalometric, and cone-beam computed tomography (CBCT). Such targeted characteristics include especially resolution, field of view (FOV), and dose radiation, with a clear trade-off between them. The aim of a series of studies we have performed was to address such trade-offs of X-ray imaging using a higher-resolution technique, optical coherence tomography (OCT) [https://doi.org/10.3390/ma13214825, https://doi.org/10.3390/s21134554]. The present work focuses on two of the most common types of dental radiographies (i.e., panoramic and intraoral) obtained with Planmeca X-ray units (Planmeca, Helsinki, Finland). The aim of this work is to present protocol elements and results of their OCT-based optimization. The procedure and working steps are described. Radiographs performed before and after the optimization for patients in a dental clinic in Timisoara, Romania, are presented. Statistical analyses of image characteristics (i.e. contrast, brightness, contrast to noise ratio (CNR) and sharpness) are pointed out, in the trade-off with the radiation dose. The way the ALARA (as-low-as-possible radiation dose) protocol is observed, while improving to the highest possible level image characteristics of considered radiographs is discussed. Limitations that can influence the result of the image characteristics improvement are highlighted. The developed protocol can be applied in every dental clinic or radiology center.

Photoplethysmography (PPG) is a non-invasive optical-based technique used to measure various hemodynamic parameters. State-of-the-art proposed various methods for arrhythmia (premature ventricular contraction (PVC), atrial fibrillation) detection using PPG signals. However, limited research has been carried out for the detection of other life-threatening arrhythmias. In this research work, the detection of atrial flutter (AFl) from Normal, Sinus Tachycardia (ST) and PVC signals has been carried out using PPG signals. The method relies on time-domain and entropy features for characterizing the AFl PPG pulse. A sliding window approach has been applied to extract features, and an artificial neural network has been implemented for feature classification. The ground-truth generation for the PPG signals has been carried out on publically available and prospective data. The comparative analysis of the results obtained from the two datasets is useful in the effective identification of the abnormality.

Esophageal pressure, bile content and pH are important parameters in gastroesophageal diseases. An all-optical technology is described capable to perform simultaneously oesophageal manometry, pH-metry and bilimetry. The three different sensors were integrated in a single optical fibre catheter for the simultaneous measurement of the three parameters. The optoelectronic prototype for the interrogation of the catheter is constituted by two separate optoelectronic modules for the interrogation of the pressure sensor and for the bile and pH sensors, respectively. The prototype and the optical catheter are compliant with European Directives on medical devices in terms of electromagnetic compatibility, electrical safety and biocompatibility.

We designed, fabricated and tested a Vector Diffractive Optical Element (VDOE) to simultaneously determine the Stokes vector of light. It comprises several sectors. Each one is a vector Fresnel zone plate which focuses the light on separate foci and has different polarization properties. The polarization state is calculated from their intensities. From simulations, we could identify the error sources that were analytically removed. The residual uncertainty after applying our corrections was as low as 6x10^(-5). The uncertainty obtained for our fabricated VDOE, 3.33 %, is competitive with the results from state-of-the-art techniques.

We detect a small phase change in one of two correlated frequency combs. These combs are generated in a single Optical Parametric Oscillator (OPO), synchronously pumped by a train of femtosecond pulses at a repetition rate corresponding to half the OPO cavity's round-trip time. A physical quantity to be measured is changing the phase of one of the two circulating pulses. This added phase is converted into a frequency shift by the resonance condition of the cavity. The noise in the beat signal obtained by interfering the two combs from the cavity is so small that a phase difference of less than a nanoradian can be measured. This sensitivity is a consequence of the correlation between the two combs, created in the same cavity at a time interval of few nanoseconds.

A process for the fabrication of sub 10 nm solid-state nanopore is demonstrated, via photocatalytic effect caused by the electromagnetic field enhancement in plasmonic structures on top of dielectric pillars. A metallic ring is prepared on top of a hollow dielectric pillar arrays by FIB lithography, where areas of maximum plasmonic field trigger sites for metal nucleation and growth under illumination. Using this methodology, we fabricated Au-Ag and Au-Au nanorings, with consistent and reproducible shrinkage in pore diameter, applied to large arrays. Numerical simulations were performed in order to support the findings and to show how the obtained plasmonic structures can be used to confine the electromagnetic field enhancing the intensity in a volume in the scale of sub 10 nm.

SARS-CoV-2 pandemic crisis of last two years showed us the urgency to monitor virus presence in a close environment in order to prevent virus transmission. Standard chemical techniques are usually labor intensive and involve a pre-treatment, the use of chemical reagents and a quite long detection time. Therefore, the development of a rapid, selective, label free and unique detection tool could be highly desirable. Ultrasensitive vibrational spectroscopy is a powerful and promising optical detection tool for pathogens monitoring. It exploits molecules vibrational modes and their characteristic energies which generally constitute a univoque fingerprint. In our work, we employ IR vibrational spectroscopy to characterize different viral species from coronavirus family. In particular we considered Spike proteins from SARS-CoV, MERS-CoV, SARS-CoV-2 and some variants. IR absorbance spectra provide us an insight in Spike proteins structural conformations and constitute an effective discrimination tool, thanks to differences in vibrational features.

In this work, we report a novel design of (PC-CWG) based on square lattice of silicon pillars in air with radius of 0.2𝜇m and lattice constant of 1 𝜇m. A waveguide is introduced by removing three columns of silicon pillars, and a microcavity is created by removing a number of silicon pillars forming curved shapes on both sides of the waveguide. The proposed design demonstrates multiple resonances covering a broad spectral range in MID-IR ranging from 2.4 𝜇m to 4.2 𝜇m that represents the bandgap region. Remarkable resonances are observed at operating wavelengths 2.67 𝜇m, 2.88 𝜇m, 3.03 𝜇m, 3.2 𝜇m and 3.5 𝜇m. Moreover, the reported design shows ultra-high sensitivity reaching 2680 nm/RIU with a significant quality factor of Q=6475 giving rise to a figure-of-merit of 5.7×〖10〗^6 at the operating wavelength of (𝜆=3.03𝜇m). The suggested photonic crystal design offers simple fabrication and broad applicability for refractive index sensing applications.

In order to allow for a molecular specific and sensitive detection, surface enhanced Raman spectroscopy (SERS) became a powerful tool in bioanalytics. By application of suited sample preparation protocols or modifications of the sensing surface, even detection in complex biological matrices is available. Within this presentation examples from our lab in detection antibiotics or metabolites in complex matrices, such as pharmaceutical formulations, body fluids or culture supernatants, will be introduced.

We demonstrate a few methods to fabricate plasmonic nanostructures over a large area and implement them as SERS substrates. In one of the proposed methods, self-assembly was carried out. In another method, only batch processes such as spin coating, controlled reactive ion etching, and thin metal deposition were employed to develop the SERS substrates. These processes can be performed on large wafers, resulting in large numbers of SERS substrates in a single run. The study of sensitivity on the optimized SERS substrates was conducted using SERS-active molecules such as pMBA. The SERS substrates thus fabricated were able to detect low molecule concentrations. We also carried out electromagnetic modeling (FDTD, FEM, and RCWA) of the different SERS substrates by modeling the EM field enhancements in the plasmonic nanostructures in these SERS substrates. The fabricated SERS substrates were characterized for uniformity and reproducibility. The SERS substrates were applied to demonstrate detection of pesticides, explosives, as well as chemical and bio agents.

Wire and Arc Additive Manufacturing (WAAM) has become an important technology especially for producing metal components for aerospace structures. We demonstrate the development of an optical system to identify contaminants in a WAAM process for the purpose of real-time quality control. Samples of tungsten wire were attached using two studs fixed into the Ti-6Al-4V substrate and suspended above the substrate. A plasma torch traversed over the tungsten wire and the plasma spectrum was taken to investigate the contamination which if not detected can result in defects in the final component. High-speed data acquisition was applied to obtain optical signals with short integration times (110ms). Results show the detection and identification of tungsten contamination from a short distance (~30cm), in real time during welding.

The combustible gas sector requires for instrumentation capable to determine the composition and the quality of the gas mixtures present in the transport and distribution networks. The gas parameters need to be monitored in a wide interval, since mixtures are found within an extremely variable range. A compact, fast and highly sensitive instrument based on Raman spectroscopy has been developed with the specific aim to operate directly on-line. This approach is intrinsically non-invasive and multi-species sensitive. The Raman scattering is stimulated by a multi-mode laser diode centered at 455 nm with 1,5 W optical power. The system is able to determine the main components of the natural gas: methane, heavier hydrocarbons, nitrogen, carbon dioxide and hydrogen. The Heating Value (HV) is finally calculated using the ISO6976:2016 standard. Several certified gas mixtures have been tested with the instrument operated at different temperatures in the range from -20°C to 50°C, to prove the capability to operate in a wide industrial temperature range. The calculated HV value lies in the ±0.5% error range.

In this work, we have demonstrated the application of plasmonic quasi crystal (PlQC) as SERS active substrate. SERS, an offshoot of Raman spectroscopy, is a powerful analytical technique that provides chemical information about molecules or molecular assemblies adsorbed or attached to nanostructured metallic surfaces. We have demonstrated the detection of urea (20μL), up to 10-5 M concentration using PlQC as SERS substrate. Urea, a biomolecule, is irradiated by a laser source (λ=785nm), and Raman spectra are collected using the Raman setup (Renishaw). All Raman peaks of urea were distinctly visible for further analysis. The proposed PlQC can be used as a SERS active substrate for on-site narcoanalysis, forensic study, explosive detection, bio-diagnostics, detection of adulterants in food/water etc.

In this work, we present the development of a full-Stokes imaging polarimeter that provides the 2D map of the polarization state of a scene in a single acquisition working in the complete visible band. The vectorial nature of polarization makes it impossible to measure it with the intensity-based detectors. Stokes parameters describe the state of polarization of light and provide the amplitudes of the electric field and the phase difference of both components using simple experiments that measure the time-averaged intensity of the waves. Our camera can transform the input polarization into intensity I by using polarization-sensitive elements to recover the complete Stokes vector S at each pixel of the camera. The states used for measuring the input polarization are claimed to be the optimal polarization states for a fast acquisition in a single shot immunized to Gaussian and Poisson noise. The acquisition errors for full-Stokes parameters are demonstrated to be lower than 10% demonstrating the capability of the system to perform Stokes imaging both in indoor and outdoor scenes. The camera has great potential in computer vision and deep learning applications due to the complementarity of the information provided when compared to intensity data.

In this paper we investigate the use of photopolymer material as the sensor medium. This research will focus on the creation of self-written waveguides with the photopolymer and the interaction with the environment. This SWW can be used to measure direction of propagation and angle of incidence upon the polymer material. Under environmental force new SWWs can be measured and recorded within the PVA/AA on a 3D plane. These newly created SWWs, from numerical modelling, can represent the interaction with the surrounding environment. This can be used to measure force and direction of movement.

A freeform-curved sensor is presented here to demonstrate its highlights in off-axis optical system design. First, we take the extremely demanding TMA telescope as an example, the introduction of the freeform sensor makes the imaging performance reach the diffraction limit, and the PV sag departure of the mirror surface is reduced by 71% compared with the traditional design using flat sensor. Next, we performed finite element analysis on the silicon die with freeform shape to ensure that the stress distribution of the curved sensor is within a safe range when bending. Finally, the prototype of freeform-curved sensor will be manufactured, and its surface shape will be tested in the laboratory.

Photoacoustic microscopy (PAM) plays a vital role in label-free microscopic imaging of the optical absorption contrast in tissues. It usually combined single ultrasound transducer to receive the acoustic waves converted from absorbed optical energy by transient thermoelastic expansion. The opaqueness of conventional ultrasound transducers makes the system to misalignment, complicated and bulky. However, recent developed transparent transducer has lower bandwidth as lack of appropriate matching and backing, which will cause lower axial resolution for imaging. Hence, developing 30-MHz transparent transducer with a -6 dB bandwidth higher than 50% will bring more feasibilities to achieve photoacoustic imaging with higher resolution. And this study indicated the potential of developing new transparent ultrasound transducer for photoacoustic imaging, which will bring more possibilities to develop a fast, compact, and, hand-held PAM imaging device.

This contribution presents a Permeable Diffractive Optical Element (PDOE) for the continuous monitoring of physical and/or chemical parameters in running fluids. The design of our PDOE is based on Fresnel zone plates, with holes drilled on a rigid substrate. The PDOE maximizes the irradiance at its focal plane, maintaining an appropriate permeability ratio. We use two optimization methods: Particle Swarm Optimization, that generates all the holes simultaneously; and an iterative method where the holes are added successively. The remaining PDOE surface is treated to provide sensing capabilities. A proposal for the optoelectronics of the device is also presented.

In every field of science, new techniques for target molecule detection are increasingly required. This work presents itself as a method for developing new sensors that can detect target molecules even in samples with low concentrations. The aim of the current research project is to create an optical sensor substrate that is precise and specific for fluorescent or fluorescently marked targets. We produced nanostructured surfaces on bulk silver substrates using a femtosecond pulsed laser (Laser Libra Ti:Saphira from Coherent). These surfaces have a larger superficial area, which increases the fluorescence of molecules nearby by due to the surface plasmon resonance, in the effect of metal-enhanced fluorescence (MEF). The COVID virus spike antibody (SARS-CoV-2(2019-nCoV)) and a secondary fluorescently marked antibody (Alexa Fluor™ 633 goat anti-human IgG (H+L)) was used to functionalize the nanostructures. Initial results indicated that the functionalization process was successful in achieving our initial goals, presenting the proposal's methods as an effective route for the development of biosensors. The primary antibody was initially detected in a very low concentration (0.0525 ng/uL), and the fluorescent signal was enhanced on the nanostructured portion of the surface by 6.3 times more than it was on the surface without modification.

The interest in LiDAR imaging systems has recently increased in outdoor ground-based applications related to computer vision, in fields like autonomous vehicles. However, for the complete settling of the technology, there are still obstacles related to outdoor performance, being its use in adverse weather conditions one of the most challenging. When working in bad weather, data shown in point clouds is unreliable and its temporal behavior is unknown. We have designed, constructed, and tested a scanning-pulsed LiDAR imaging system with outstanding characteristics related to optoelectronic modifications, in particular including digitization capabilities of each of the pulses. The system performance was tested in a macro-scale fog chamber and, using the collected data, two relevant phenomena were identified: the backscattering signal of light that first interacts with the media and false-positive points that appear due to the scattering properties of the media. Digitization of the complete signal can be used to develop algorithms to identify and get rid of them. Our contribution is related to the digitization, analysis, and characterization of the acquired signal when steering to a target under foggy conditions, as well as the proposal of different strategies to improve point clouds generated in these conditions.

In this paper, an external cavity diode laser (ECDL) in Littrow configuration with narrowband emission is presented. The laser system is based on a commercially available GaN Fabry-Perot laser diode. Longitudinal mode selection is performed using a reflective holographic grating. Tuning range over 3.4 nm is achieved with a short linewidth of 0.02 nm at the rated current. The ECDL system is integrated into an optical sensor for remote detection of Nitrogen Dioxide (NO2) gas.

This work presents a simple and non-contact method to determine the angular displacement of a target measured with a bifurcated Optical Fiber Displacement Sensor (OFDS). Target angular displacements are estimated from the intensity-modulation variations of the reflected light. The OFDS consists of a central single-mode optical fiber (OF) and two concentric multimode OF rings. The method has been validated to analyze the alignment stability of a mechanical structure, such as the blades of an aircraft. Results reveal that theoretical model and experimental data are in good agreement, and that the rotation angle of the target is a trade-off value since increasing it enhances the sensitivity of the sensor, at the cost of decreasing its linear working area. In fact, compared to the results when the target and the OFDS are at 90º, results indicate that the sensitivity of the device can be enhanced 4 times by positioning the target at an incident angle of 10º, although in return, its linear working region decreases 60 %. Moreover, the blind region decreases to 50 %.

We present an emerging material with a novel photodiode structure designed for monitoring of substances in the SWIR detection range. Refined detection designed for industry standards unlocks consumer electronic applications such as continuous non-invasive blood glucose monitoring and easy air quality detection. At the current state of optimisation, D* is 9.4×10^10 Jones at 0 V bias and 2.0 μm which is comparable to the much more mature extended InGaAs technology with the same cut-off wavelength range. Resolution of optical powers down to 40 pW has been demonstrated, without temperature stabilisation or phase-sensitive detection, indicating the photodiode’s potential.

We demonstrate an integrated on-chip whispering gallery mode (WGM) ring resonator tested for humidity sensing. When developed, SU-8 is chemically and mechanically stable, as well as optically transparent above 400 nm wavelength and it has high refractive index. Therefore, it is a suitable material for optical WGM resonator. When light is coupled in the resonator, it circulates along the surface for prolonged periods of time interacting with the surrounding environment. Resonance wavelength depends on the refractive index and/or the radius of the resonator. Polymers, including SU-8, are sensitive to gas and temperature changes in the environment. We tested the ring resonators in changing relative humidity (RH). Due to changes in RH, the refractive index of SU-8 changes, and we observed a shift in the resonance wavelength. While the sensitivity was average compared to similar studies using other materials or geometries, the ring geometry showed high response and recovery time.

Here, we report the use of yeonnokjam silk, one of the characteristic varieties in Korea, as a smart fabric chemo-sensor. Various races of colored silks were investigated, and we found out that the yeonnokjam silk stood out as a highly fluorescent material when compared to other colored silks such as golden silk, daehwangjam, and juhwangjam. The yeonnokjam silk cocoons were exposed to the HCl vapor for different time intervals, corresponding to low (5 ppm) to lethal (3000 ppm) HCl exposures. Fluorescence peak intensities for these colored silk cocoons deteriorated with time as exposing samples to the HCl vapor. Even very weak HCl-exposure could induce a drastic decrease of fluorescence, indicating that the silk cocoon itself could be extremely sensitive chemo-sensors. Although more studies are required to know and understand the intrinsic light-emitting trait of the natural material, our study proves that the natural material has strong potential as a high technological material in optics applications.

In the last decade, commercial fibre-optic sensors, often based on gratings, have emerged as a popular contender to conventional electronic sensors, with numerous advantages especially in mechanical, civil and aeronautical engineering applications. However, the ever-increasing demand has fuelled higher device performance requirements, which can only be achieved by introducing novel operating mechanisms and fabrication techniques. In our presentation, we demonstrate theoretically and experimentally a new approach to designing and fabricating high-performance analog output optical sensors. An ad hoc fabricated asymmetric Fabry-Perot cavity allows to control the coupling coefficient parameter. In our transducer, this parameter depends on temperature. An important feature of our proposal is that it does not require a spectrometer to obtain the signal, an economic voltmeter is sufficient. This solution can be used to achieve the highest performance for instrumentation, industrial, or clinical applications; or to optimize a solution to achieve the lowest power dissipation at a given performance level for battery powered and portable applications. Furthermore, it has the advantages of high repeatability, low-cost, straightforward and reproducible fabrication, and does not show signs of hysteresis.

Due to their superior properties in single-molecule detection, plasmonic and nanopore-based sensors have attracted research interest. In recent times, they have been combined in a single device, resulting in plasmonic nanopores-based sensors. These solid-state devices featured unprecedented enhancements in single-molecule and nanoparticle detection, optical spectroscopies and trapping, control of local temperature. In this context, we have investigated two kinds of nanostructures: plasmonic nanopores and plasmonic nanoantennas, both of which were fabricated on free-standing Si3N4 membranes. As regards the nanopores, we were able to prove that their plasmonic coating enhanced their conductance when illuminated at 631 nm. On the other side, antenna-shaped nanopores (i.e., nanoantennas) were fabricated via plasmonic photochemical deposition. At this regard, we demonstrated that it was possible to fabricate nanoantennas with different internal diameters by different time of plasmon-induced photochemical deposition of metal precursors at the free tip of the nanoantenna. In conclusion, we proved that it was possible to use each nanoantenna (i.e., each decreasing internal diameter) to detect the translocation of nanoparticles with correspondingly decreasing diameters or of DNA.

Magnetic fluid is a very interesting material that changes its optical properties such as refractive index, optical transmittance, and birefringence when under influence of a magnetic field. In the contribution, we present the design of a probe responding to the presence of a magnetic field, consisting of a capillary filled with magnetic fluid and connected to polarization-maintaining fibers on both sides. If we place a capillary with a magnetic fluid in a transverse magnetic field (field lines are perpendicular to the axis of the capillary), this field causes a birefringence in the magnetic fluid. As a result of the birefringence of the magnetic fluid in the capillary, there will be a change in the polarization state of the optical wave passing through the fluid in the capillary, and this change is registered using a fiber linear polarizer placed between the fiber coming out of the capillary and the optical spectrum analyzer. A relationship between the magnitude of the magnetic field flux density and the spectral change of the signal detected by the optical spectrum analyzer is observed. The result indicates a strong potential of a magnetic fluid in the field of the optical fiber sensors of magnetic fields.

Swept-source optical coherence tomography (SS-OCT), benefiting from its high sensitivity, relatively large penetration depth and non-contact and non-invasive imaging capability, is ideal for human skin imaging. However, limited by the size and performance of reported optical galvanometer scanners, existing portable/handheld OCT probes are still bulky, which makes continuously handheld imaging difficult. Here we reported a miniaturized electrothermal-MEMS-based SS-OCT probe that only weighs about 25 grams and has a cylinder with a diameter of 15 mm and a length of 40 mm. The SS-OCT probe can achieve a lateral resolution of 20 μm, an imaging speed of 5 frames/s, and an effective imaging field of view (FOV) of 3×3 mm2. OCT imaging of leaves, dragonfly, and human skin has been successfully obtained, showing the imaging performance and potential applications of this SS-OCT probe.

Nanoimprint lithography is the simple method using stamp and UV or thermal curable resins for nano-structures/patterns with low cost, high-throughput, and high resolution. Residual-layer free NIL provides good performance of micro/nano-scale structures functional arrangements with 2/3D layouts. We demonstrated nanohole patterns of 200 nm pore size using residual-layer-free NIL without further process for removing residual layers for reflectance biosensor. The reflectance peaks of gold substrate are enhanced to 8 times using the hexagonal hole patterns of diameter 200 nm, and pitch 400 nm. So, this substrate can be applied for immune reflectance biosensor with magnetic nanoparticles for pre-treatment.

Non-Hermitian systems with varying loss-gain profiles are receiving significant attention due to their exotic behavior at a certain point called the exceptional point (EP). EPs are singularities of non-Hermitian systems where the eigenfrequencies as well as the associated eigenstates coalesce. These EP singularities are ultrasensitive to small perturbations. A conventional system follows a linear relation with perturbation whereas these singularities follow a square root dependence for small perturbations.

This work presents a novel biosensor platform combining plasmonic and electrochemical methods in a single platform. The proposed biosensor integrates four independent flow channels equipped with individual three-electrode systems and thus allows for the simultaneous monitoring of four different processes by both surface plasmon resonance and electrochemical methods. The biosensor was characterized (channel-to-channel and chip-to-chip variability, long-term stability, potential stability, and sensitivity). Finally, a proof-of-concept model biosensing experiment was performed to demonstrate the applicability of the developed biosensor for bio-detection.

The article evaluates a surface plasmon resonance (SPR) sensor that uses a graphene microribbon (GMR) array on a silicon waveguide to detect benzoic acid in terahertz (THz) frequencies. The graphene micro-strips are periodically spaced to excite SPR in THz efficiently. The application of planar waveguide technologies enables the development of miniature and compact multisensor devices that can connect to instrumentation using optical fibers, providing remote operation. Here, the impact of modifying variables such as ribbon width (r_w) and the number of ribbons (num_rib) are examined for a specific structure of GMR, tuned to E_F = 0.45 eV and Γ = 3.7 meV with periodicity λ = 4 µm, deposited on a silicon waveguide of h = 15 µm and SiO_2 substrate. The results show that manipulating these variables enhances the plasmon formation but also highly affects the plasmonic modal distribution along the array. The article concludes that the balance between these features can lead to the sensor's performance optimization. Therefore, changing the analyte refractive index with the acid concentration, a very high sensitivity sensor of 8658 nm/RIU is presented for r_w = 3 µm and num_rib = 200.

Microfluidic devices have the capability to assist in the development of basic miniaturized devices. Optical measurements are powerful in the application of sensors. Optofluidic, or the integration of optics with microfluidics, provides an appealing framework for the implementation of optical devices with a wide range of characteristics and functions. We provide a manufacturing approach for optofluidic devices by integrating a microfluidic channel made of PDMS with silicon nitride substrate to enable optical measurements. The SiN thin film was prepared by the means of plasma-enhanced chemical vapor deposition (PECVD), such that SiN was deposited on a Si wafer using only SiH4 and N2 pre-courses to reduce the hydrogen content. The SiN thin film thickness is in the range of 300 nm to 350 nm. A microfluidic channel was prepared by casting PDMS on a fabricated mold patterned on a silicon wafer. The device was composed by integrating the SiN substrate with the microfluidic channel and tested for optical measurements.

Cost-effective narrow-band laser sources are of great demand for applications in distributed fiber sensing. Self-injection locking to an external fiber cavity is an efficient technique enabling drastic linewidth narrowing and self-stabilization of semiconductor lasers. The main drawback of this technique is its high sensitivity to fluctuations of the configuration parameters and environment noise. In the proposed laser configuration, the self-injection locking mechanism is used in combination with an external high-Q ring fiber cavity and a simple active optoelectronic feedback circuit ensuring a stable mode-hopping free laser operation at a single longitudinal mode. Specifically, the laser configuration is fully spliced from the polarization maintaining (PM) single-mode optical fiber that has significantly improved the laser stability against the environment noise. Drastic narrowing of the DFB laser linewidth down to ~300 Hz and a phase noise less than –100 dBc/Hz (>30 kHz) are achieved with the PM fiber ring cavity built from a single fiber coupler. We have explored key features of the laser dynamics revealing stability and tunability of the laser linewidth as an additional benefit of the proposed technique.

Theoretically, a multimode optical fiber supports excitation and propagation of a single optical mode, i.e., a field pattern that satisfies the boundary conditions and does not change along the fiber. When two counterpropagating optical modes are excited, they could interact through the stimulated Brillouin scattering (SBS). Here, we present a simple theoretical formalism describing SBS interaction between two individual optical modes selectively excited in an acoustically uniform multi-mode optical fiber. Employing a weakly guiding step-index fiber approach we have built an analytical expression for the spatial distribution of the sound field amplitude over the fiber core and explored the features of SBS gain spectra responsible for the interaction between modes of different orders. On this way we give a clear insight into the sound propagation effects accompanied SBS in multimode optical fibers and demonstrate their specific contributions to the SBS gain spectrum.

In this work we examine the use of state-of-the-art distributed sensing systems to extract temperature information from the optical fibre infrastructure already existing in the EAC power distribution network in Cyprus (~25-year-old installation); as a means of optical fibre distributed sensing in the underground and overhead (OPGW) cables. The optical fibres are collocated with existing power distribution cables, for the purpose of power line monitoring cable joints that are prone to failure, along with general monitoring for unusual behaviour and potential cable fault conditions. Detection is achieved using DTS: Distributed Temperature Sensors (Silixa Ltd) that use RAMAN-based measurements in combination with OTDR (Optical Time-domain Reflectometry) for high-precision temperature detection. We examine the correlation between the temperature of the power cable with the power consumption provided by the EAC and the weather conditions. Furthermore, our data will give an indication of how important is uniform spacing between power and optical cables. The real-time and continuous monitoring of the temperature of the optical cables through the distributed sensing systems may help identifying abnormal cable behavior (hot spots) and possible future network failures in the power network.

Metallic nanostructures allow for strong enhancement of field intensity by plasmonic effects and offer efficient means for the amplification of weak optical spectroscopy signals. Typically, the metallic nanostructures are made static. A possible route to expand the spectrum of applications and performance of plasmon-enhanced spectroscopy tools is pursued, based on responsive hydrogel materials that act as artificial muscles and provide on-demand, reversible reconfiguration of plasmonic hotspots. Hydrogels are three-dimensional polymer networks with the ability to intake large amounts of water. Some classes of responsive hydrogels can be reversibly toggled between two states – swollen and collapsed – by modulating their temperature T. In this work, we use poly(N-isopropylacrylamide)-based responsive terpolymers (pNIPAAm) and we disperse polystyrene (PS) nanoparticles in the hydrogels, allowing precise control on the temperature-induced changes of the swelling ratio and allowing for a mechanically more rigid structure . This controlled actuation mechanism finds various applications in plasmonic nanomaterials. Here we present the concept of a microscopic responsive hydrogel structure that allows the modulation of the distance between metallic nanoparticles and a flat metal surface, for reversible near-field coupling and formation of a gap mode. The plasmonic coupling can be exploited for probing of molecules, by plasmonically-enhanced optical spectroscopy.

Monitoring pH and extracellular acidification in biological samples containing live mammalian cells can provide valuable information on the glycolytic activity and bioenergetic status of cells. Compared to pH electrodes, optochemical pH sensors look more advantageous, since they allow rapid, non-invasive parallel analysis of multiple samples with stable readout of pH. We have developed new fluorescent pH sensors based on hydrophobic protonable metal-free porphyrins (OEP and OEPK) embedded in a proton-permeable polymeric matrix together with a proton transfer agent. These pH sensors provide internally-referenced calibration-free operation, both in ratiometric intensity and lifetime based detection modes. Sensor development included optimization of the indicator dye and its photophysical characteristics, screening of different proton transfer agents to minimize sensor toxicity, tuning of protonation range and pKa, long-term storage stability and response time studies. Optimised pH sensor coatings were then deposited on plastic substrates (96-well microplates) and used for real-time monitoring of Extracellular Acidification Rate (ECAR) for cultured cancer cells and 3D spheroid structures on standard laboratory equipment (multi-label plate reader and confocal FLIM microscope). The advanced pH sensors tailored for use with biological samples have high potential for cell analysis and related applications.

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.

A lens-less optical fiber designed for enhanced-fluorescence biosensor applications is presented. In order to obtain the enhanced sensor performances, two elements are essential: a planar antenna that redirects fluorescence emission into a narrow cone and an automated fiber-based optical system for multi-spot analysis. In particular, the potential early diagnosis of sepsis via C-reactive protein (CRP) detection is here demonstrated, reaching a limit of detection of 1.5 ng/mL), which is in the clinical range of interest for such biomarker. Upon the combination with other sepsis biomarkers, the presented sensor can become relevant for the early diagnosis of sepsis. These results validate the developed prototype as a simple, affordable, easy-to-operate, plug&play device with fast turnaround times, compatible with standardized micro-well arrays, and potentially suitable for POC applications with respect to the diagnosis of sepsis. It is also suitable for implementation with other biomarkers and liquid environments.

Optical Oxygen sensing is a convenient approach for monitoring and imaging molecular oxygen (O2) in biological samples, however existing intracellular O2-sensing probes still have some limitations. This study describes a new phosphorescent hetero-substituted derivative of Pt(II)-tetrakis(pentafluorophenyl)porphyrin (PtPFPP) obtained via a two-step thiol click-modification. Particularly, 1-thio-b-D-glucose (Glc) and thio-methyl-polyethylene-glycol (mPEG) moieties were covalently attached to PtPFPP, producing the trans-di-glucosylated-di-PEGylated derivative, PtGlc2PEG2 (trans). Previously, we demonstrated that such short PEG oligomers drastically reduce the translocation of the tetra- or tri-PEGylated derivatives across cell membrane. However, the new trans-di-PEGylated-di-glucosylated derivative provided efficient intracellular staining and O2 sensing (IcO2) of murine embryonic fibroblast (MEFs) cells.

Rolling circle amplification (RCA) serves as enzymatic enhancement for the detection of low concentrated cancer biomarkers on the plasmonic sensor surface, probed by surface plasmon resonance and surface plasmon-enhanced fluorescence. Single binding events can be imaged by fluorescence microscopy. The bio-architecture is improved by antifouling polymer brushes for the reduction of unspecific binding. The demonstrated platform shows great potential for reaching low limits of detection, applicable for various protein biomarkers.

Ferritin is an important biological iron-complex. Its detection is of great clinical significance to screen various diseases. While low concentration of ferritin indicator of Iron deficiency (Anemia), it’s elevated concentrations indicate diseses like diabetes,alcohol abuse and liver disorder. The portable sensor systems for ferritin assumes diagnostic values. The present research work deals with the development of a surface plasmon resonance (SPR) optical fiber sensor for the detection of ferritin in a broad range (i.e,. 10 ng to 1000 ng). The attachment of antibodies over the sensor has been facilitated by modifying the gold film with 2-D MoS2 layer over etched optical fiber surface. Different stages of the biosensor fabrication have been investigated with appropriate characterization techniques like electron microscopy and vibrational spectroscopy. A robust conjugation of antibodies over MoS2-gold surface has allowed a good sensor sensitivity and an effective complex free protocol to target a broad range of ferritin . Based on the SPR wavelength shifts measurements, it has been possible to analyze ferritin with a low detection limit of… The sensor is also found selective to ferritin and it does not yield any response to non-specific analytes, e.g. IgG,BSA and other analytes found in human serum. The main advantages of the sensor can be highlighted as a stable response, detection of ferritin over a wide concentration range, a low limit of detection, specificity, and rapid analysis time.

The article describes a modification of the fiber-optic sensor based on a Bragg grating, which is implemented in oxygen glasses, which are commonly used in real medical practice. This type of experimental fiber-optic sensor can be used to monitor the respiratory activity of the human body over time. Modifications primarily consist of the design improvement of the Bragg grating implementation itself in using conventional oxygen glasses for better transfer of measured parameters to the Bragg grating itself. The practical part also describes the experimental verification of the functionality and the subsequent evaluation of the measured data. The experimental measurement was carried out on a group of 5 volunteers in laboratory conditions.

Water salinity analysis is critical for water quality monitoring and evaluation in order to guarantee water safety. Unregulated salinity may be harmful to human health, crops, industry, and the ecosystem. The salinity levels in water sources are constantly changing as a result of natural and anthropogenic ecological change. Exceeding specific salt levels might endanger human health, particularly through drinkable water. In this work, we present a simulation of an optofluidic sensor to measure the water’s salinity. We built a design to measure the change in the refractive index in a microfluidic channel based on the dielectric grating. The generated design was modelled to alleviate the manufacturing process of the microfluidic sensor of the saline water. The design was optimized for the range of measurements of the refractive index of saline water by the selection of the material of the sensor.

Plasmonic nanostructures are widely studied for the construction of affinity-based biosensors. In these biosensors, the plasmonic resonances in visible (VIS) and near-infrared (NIR) regions are used to probe the vicinity of the nanostructure, where the molecules of interest (an analyte) are bound to the surface. Although biosensing is limited to the VIS/NIR regions in conventional plasmonic sensors, sensing in the ultraviolet (UV) region provides the capability of detecting proteins or biological compounds which are fluorescent or have absorption bands in the UV region. In this work, we report on the novel approach that employs plasmonic nanostructures with multiple modes supported in UV and VIS regions to provide high-performance biosensing. The UV mode is spectrally tuned to the targeted biomolecules, and the VIS mode provides high refractive-index sensitivity. Using numerical electromagnetic simulations, we analyzed two bimetallic (aluminum and gold) nanostructures. We demonstrated that optimizing the geometrical parameters of these nanostructures allows us to tune the short-wavelength resonance to a region suitable for UV fluorescence/absorption while providing sufficient electromagnetic field overlap with the long-wavelength resonance in the VIS region for high-performance biosensing. The designed plasmonic nanostructures thus can be employed to identify and quantify the biomolecules simultaneously.

Surface plasmon polariton (SPP)-based methods enable the investigation of biological objects, such as biomolecules and cells, with high sensitivity and spatial resolution. These methods employ various types of SPPs to match the size of the investigated biological object with the penetration depth of an SPP. Large penetration depths are provided by long-range SPPs that are supported by dielectric-metal-dielectric structures with dielectric materials of similar refractive indices (RIs). However, the development of such structures for biosensing is difficult due to the limited availability of dielectrics with a RI close to that of water and desired properties, such as stability and compatibility with relevant fabrication techniques. Here, we describe the development of diffractive structures supporting long-range SPPs. The described structure consists of a low RI dielectric grating with a sine profile with a thin layer of gold. The geometric properties of the structure are optimized using rigorous coupled wave analysis to achieve high sensitivity of the SPPs to bulk RI change and to allow for the excitation of SPPs from both sides of the structure under the normal incidence of light. The laboratory prototypes of the structure were fabricated by creating a grating using soft lithography in a low RI polymer (CYTOP) layer on a glass slide and then coating it with a layer of gold using vacuum deposition. The fabricated structures were characterized experimentally and sensitivity to bulk RI changes was determined and compared with the theoretical predictions. The potential of such structures for SPP biosensing and imaging is also discussed.

A Brillouin Optical Time-Domain Analysis (BOTDA) Lorentzian data fitting method to estimate the Brillouin Frequency Shift (BFS) is proposed. Data is obtained from an experimental setup used to conduct the temperature and strain measurements. Before Lorentzian fitting the noisy data is averaged and filtered. The proposed method attempts to lower computational complexity in determining the Brillouin frequency. The resulting parameters of a completed BGS curve fitting are used as initial set of parameters for the next location point BGS fitting. Completion of the Lorentzian fitting using the Levenberg-Marquardt nonlinear curve fitting algorithm is achieved in a small number of iterations which improves the performance in obtaining the Brillouin frequency shift.

In this study, the performance of the experimental laser speckle imaging system and image processing algorithm for early evaluation of microbial activity in a noisy environment was tested. The proposed sub-pixel correlation algorithm was applied to recognize useful signals attributed to the microbial colony forming units in solid media

Photonic quantum technologies are a promising platform for a large variety of applications ranging from secure long-distance communications to the simulation of complex phenomena. Among the material platforms under study, semiconductors offer a wide range of functionalities opening several opportunities for the development of integrated quantum photonic circuits. AlGaAs is particularly attractive to monolithically integrate active and passive components since it combines high second order nonlinearity, electro-optic effect and direct bandgap. In this talk, I will present the work of our team on the generation of quantum states of light in the telecom range with nonlinear AlGaAs chips working at room temperature. The talk will review recent developments on monolithic and hybrid integrated devices, describe the versatility of these systems for the generation and manipulation of quantum frequency states and show their potential for the implementation of flexible entanglement-distribution networks for secure communications.

Photonic crystal fibres (PCFs)—thin strands of glass with an intricate array of hollow channels running along their length—offer both hollow and solid glass cores, and allow unprecedented control over dispersion and birefringence, ushering in a new era of linear and nonlinear fibre optics, for example: chiral PCF is circularly and topologically birefringent, supporting optical vortices and in some cases strong circular dichroism; through pressure-adjustable dispersion, gas-filled hollow-core PCF provides an elegant means of compressing pulses to single-cycle durations, as well as underpinning a range of unique sources of tunable deep and vacuum ultraviolet light; microparticles optically trapped inside hollow core PCF van be used to sense physical quantities with high spatial resolution; and strong optomechanical effects in solid-core PCF permit stable timing-modulated high harmonic mode-locking at few-GHz repetition rates.

Optochemical sensor based systems for cell analysis are well established and continue to grow providing valuable and detailed information on cell bioenergetics, metabolic signature and ability to withstand stress and drug treatments. The area is currently dominated by the Seahorse / Agilent XF (eXtracellular Flux) and Luxcel/Agilent MitoXpress platforms, which provide accurate measurement of Oxygen Consumption (OCR) and Extracellular Acidification (ECA) rates under different physiological conditions (with substrates, drugs, stressors), by means of dedicated pH and O2 sensors or probes. The XF system, which uses solid-state sensors and specialized microplates, is highly integrated and user-friendly, however outdated sensor chemistry and simple intensity readouts limit its performance (unstable sensor calibrations, cross-talk) and make it expensive. The MitoXpress platform uses stable and accurate lifetime based sensing of O2 and pH (internally-referenced, no cross-talk), but its DIY (design it yourself) assay approach using soluble probes, standard microplates and detectors result make it less sensitive and user-friendly. Several new sensor systems are emerging, which can potentially address these issues of the current systems. Such candidates include the systems: i) based on a substituted Pt-porphyrin dye (meso-Schiff base), which senses pH and O2 via phosphorescence intensity and lifetime signal readouts; ii) with near-infrared fluorescent pH-indicator and phosphorescence O2 indicator dyes and phase measurements at multiple frequencies; iii) the fully-referenced solid-state dual sensor based on a pH-sensitive fluorescent porphyrin dye and an O2-sensitive phosphorescent Pt-porphyrin dye . We will discuss merits and limitations of these different sensor based systems for cell analysis.

A newly developed colorimetric immunosensor based on gold-coated magnetic nanoparticles (Fe3O4@Au) is presented, and its application for the detection of human immunoglobulin G (IgG) in water is demonstrated. By taking advantage of both the localized surface plasmon resonance (LSPR) phenomenon of gold nanoparticles and the magnetic property of the core, the Fe3O4@Au immunosensor provides a fast and effective method for detecting analytes. In a sandwich scheme, Fe3O4@Au nanoparticles are used to enhance the response of the nanostructured gold surface made of gold nanoparticles randomly placed onto a glass coverslip. Specifically, the detection of the target analyte (human IgG) occurs when Fe3O4@Au nanoparticles bind to the target from the top in the presence of a magnetic field, leading to a change in the absorption spectrum of the nanostructure. Preliminary results have shown that the colorimetric immunosensor can achieve a limit of detection of 1 ng/mL, with a measurement carried out in only 10 minutes. The use of gold-coated magnetic nanoparticles in conjunction with the plasmonic surface offers great potential for the sensitive and specific detection of analytes. This could pave the way for future applications of the immunosensor in rapid testing and mass screening.

The Advanced Infrared Detection Assembly Dual Band (AIDA-2B) project, part of the Skyward instrument, is an imager that consists of a main Aluminium alloy metallic frame attached to the Sensor Head Unit (SHU) chassis by means of thirteen screws. The imager features several subassemblies among which the FOV change & focusing mechanism. This mechanism has two separately actioned trolleys that allow the FOV change and focusing movement. Each trolley moves on two linear ball slides and is actuated by a lead screw. In order to achieve challenging optical performance target in the infrared range, the introduction of chalcogenide glass is required. IG4 is the material selected for the lens installed on one of the two trolleys of the focusing mechanism. Such material features excellent thermal properties (such as almost constant refraction index in the whole temperature range), but suffers from an extreme fragility and very weak mechanical properties. In order to employ such material in a challenging mechanical environment such as an airborne IRST instrument a 'floating' design is necessary, with the glass attached to the mechanical mounting by means of adhesive pads, and no metal-glass contact. A description of the design solutions developed, manufactured and qualified for the most critical optical mount inside the Instrument is presented. This paper contains a collection of mechanical results obtained on the optical mount breadboards, including a description of environmental tests performed. Three configurations for the lens mounting have been designed and tested: 1. C-shaped profile; 2. Thin ring; 3. Crown ring. The comparison between these high stability optical mounts based on adhesive joints, as well as the acceptance criteria derived in order to establish the flight worthiness of the manufactured and assembled hardware, are presented in this paper.

We present a study on the application of machine learning to optical fibre distributed sensing, with data recovered using a state-of-the-art, commercial BOTDR distributed sensing system; temperature information extracted from the power line distribution networks part of the Electricity Authority of Cyprus. A machine learning approach was implemented for the prediction task of finding points that are likely to get damaged, mimicking the behavior of power cable joints that are prone to failure, along with general monitoring for unusual behavior and potential cable fault conditions; the task is a binary classification one. Labels “0/1” were assigned to the BOTDR measurements, with “1” corresponding to data points in space and time for which the signal showcased a problematic scenario, such as the collocated fibre’s temperature rising to dangerously high values, and “0” to the rest. The algorithm’s base is a variation of the state-of-the-art transformer architecture, which depends solely on attention mechanisms. The field data recovered show the potential of the algorithm to predict spatiotemporally problematic points, using the temperature measurements of the collocated fibre.

Passive athermalization techniques for optical systems combine materials in the mounting structure with different coefficients of thermal expansion (CTE) to minimize thermally driven shifts. However, such an approach requires complex structures to be manufactured with multiple high-precision opto-mechanical components. Our concept utilises a monolithic and additively manufactured mounting structure and a housing made of a second material to generate mechanical stresses caused by temperature fluctuations. The difference in coefficients of thermal expansion induces these mechanical stresses during temperature changes, resulting in elastic deformations of the inner monolithic structure. The magnitude of the local deformation of the monolithic structure is adjusted via the stiffness between the optical elements. This allows to control the displacement for each optical element such that their positions remain unaffected by a thermal load and thus passively athermalizes the optical system.

Recent development in the field of advanced driver assistant system (ADAS) has shown that Light Detection and Ranging (lidar) sensors are essential for 3D object detection. One of the key parameters of automotive lidar is the maximum detection range, which is dependent on background light as well as the lidar signal itself. To make lidar sensors widely accessible for the automotive market, high-volume series production becomes a necessity. Since today's sensors have a maximum detection range far beyond a hundred meters it is neither economically nor logistically viable to build a long-range setup for series production. In this work we will present a table-top setup with a length no longer than one meter, directly measuring the maximum detection range of a lidar sensor - with similar precision (about two meters for one sigma) compared to the long-range distance measurement. Our setup mainly consists of a triggerable laser and a background light source. Using the fact that the intensity of the back-scattered light is inversely proportional to the distance squared, it is possible to imitate a far-away object by tuning a laser to a reduced intensity.

In this work, a highly sensitive sensor made of SiN is proposed that can be used in gas or biological sensing, where the choice depends on whether a marker is used or not. The whole sensor is subjected to water cladding. The proposed device is based on a Mach-Zehnder Interferometer (MZI) where the reference arm is fixed with exposure to the reference, while the sensing arm is used for sensing the change in the refractive index of the analyte

Conventional sensing techniques including electrochemical, voltammetric, colorimetry, and non-enzymatic are widely used for the detection of chronic diseases. However, such techniques suffer from poor selectivity, complexity, low sensitivity, monofunctional, and expensive development procedures, which limits its widespread and accessibility across the medical field. Replacing these techniques with localized surface plasmon resonance (LSPR) based optical sensors can be much more beneficial as these are real-time, label-free devices, highly reproducible, cheap, and hold higher sensitivity to changes in the refractive index of samples. The plasmonic nanoparticles like - Ag, Au and Cu are highly sensitive to their local environment and undergoes spectral response due to their strong scattering or absorption. The easy monitoring of these light signals paves the way for its utilization in the sensor market. This work studies the influence of morphology of Au on optical tapered fibers for sensing applications.

Covid-19 detection has become of outstanding importance since the pandemic. The usual detecting techniques such as PCR are effective but need a lot of time and a trained laboratory. Thanks to their versatility and the ability to overcome the drawbacks of more classical methods photonics-based optical sensors have proven to be an excellent technology for designing and fabricating biosensors. Here, we present a biosensing platform containing a Fabry-Perot Cavity at the external face of the optical fibre. This external face was later functionalized with peptides developed ad-hoc for the detection of the Spike protein. According to our results, we have been able to detect spike protein starting from 10 ppb.

This investigation proposes and experimentally validates a method to increase the sensitivity of a bending fiber optic sensor based on anti-resonant reflecting optical waveguide (ARROW) guidance. The sensing device is fabricated by splicing a small piece of capillary hollow-core fiber (CHCF) between two single-mode fibers (SMF), then, this structure is placed on a steel sheet to measure different curvature values. The sensor by itself shows a low curvature sensitivity in a curvature small range. However, if half of the CHCF length is covered with polydimethylsiloxane (PDMS), the curvature sensitivity increases, even in a bigger curvature range. Furthermore, the coated device reveals a really small temperature sensitivity, proving that temperature variations do not have an influence on the bending fiber optic sensor operation. The ARROW sensor created with this method is cost-effective and can be used for real sensing applications like structural health monitoring.

The use of femtosecond laser pulses is becoming more widespread for the micro/nano-machining of various materials. Femtosecond lasers are used in several applications, among them, the creation of sensors. Our work aims to create an optical structure, within silica glass, capable of transmitting a signal that limits the loss of signal quality. In the current situation, we report the results obtained using a Femtoprint machine for the creation of waveguides. The parameters that were used to produce them in planar substrates are reported in this text.