Optical Sensors 2021

We are reviewing the high-average and high peak-power fs-laser sources and experimental areas currently in operation and preparation for user operation. This includes the 1 kHz, 15fs, 50mJ, Allegra laser based on OPCPA-technology. Short pulse 5ps-CPA thin disc lasers pump a series of OPCPA crystals ensuring a high contrast output. The Allegra laser enters the experimental area E1 with a number of end-stations for user experiments. The HAPLS (sub-30fs, Ti: Sapphire) laser pumped by a high-average power frequency converted DPSSL is currently delivering 500 TW, 3.3 Hz pulses via a stable vacuum beam transport system with a pointing stability around 1rad to the experimental areas for plasma physics experiments (E3) and ion acceleration (E4) with the ELIMAIA station. Both areas are fully equipped with target chambers and focusing optics for experimental operation and user assisted commissioning. The Nd:Glass laser Aton provides 1.5 kJ pulses and is currently being compressed to 10 PW in a large compressor tank. A second oscillator allows shaped pulse ns-operation at kJ level or future combination of 1 PW pulses and kJ shaped ns-pulses for advanced WDM or fusion experiments in the E3 area. A new laser disc liquid cooling technology enables repetition rates of 1 shot/minute allowing a much higher data acquisition for this kind of experiments. Furthermore we will report on the first experiments and the future experimental plans as well as on the prospects for user operation.

The Extreme Light Infrastructure – Attosecond Light Pulse Source (ELI-ALPS), the Hungarian pillar of ELI, is the first of its kind that operates by the principle of a user facility, supporting laser based fundamental and applied researches in physical, biological, chemical, medical and materials sciences at extreme short time scales. This goal is realized by the combination of specialized primary lasers which drive nonlinear frequency conversion and acceleration processes in more than twelve different secondary sources. Any light pulse source can act as a research tool by itself or, with femtosecond synchronization, in combination with any other of the sources. Thus a uniquely broad spectral range of the highest power and shortest light pulses becomes available for the study of dynamic processes on the attosecond time scale in atoms, molecules, condensed matter and plasmas. The ground-breaking laser systems together with the subsequent outstanding secondary sources generate the highest possible peak power at the highest possible repetition rate in a spectral range from the E-UV through visible and near infrared to THz. The facility – besides the regular scientific staff - will provide accessible research infrastructure for the international scientific community user groups from all around the world. The attosecond secondary sources are based on advanced techniques of Higher-order Harmonic Generation (HHG). Other secondary sources provide particle beams for plasma physics and radiobiology. A set of state-of-the-art endstations will be accessible to those users who do not have access or do not wish to bring along their own equipment. Step by step the lasers are now commissioned, trialed and handed over for user operation. References S. Kuhn et al., “The ELI-ALPS facility: the next generation of attosecond sources.”, Topical Review, Journal of Physics B, 50 (2017) 132002

Founded by the European Strategy Forum on Research Infrastructure (ESFRI), three state-of-art laser-based institutes in Romania, Hungary, and the Czech Republic were commissioned in the Extreme Light Infrastructure (ELI). Construction for the three sites started in 2012 and, as of 2020, all sites are operational. ELI-NP (Extreme Light Infrastructure: Nuclear Physics) is located 10km south of Bucharest in Romania. Its flagship installation is two beams of 10 PW, each providing 230 J output energy at a 23 fs laser pulse width. The capability to provide a 10 PW output was recently demonstrated in a live performance. We were able to show that the 10 PW laser shots can be delivered for 10 minutes at a rate of one shot every minute. A total of 230 Zoom participants worldwide, including Prof G Mourou and Prof D Strickland, the Physics Nobel Laureates in 2018, witnessed this breakthrough demonstration. An early experiment at the 100 TW laser station at ELI-NP has already been completed. We successfully demonstrated an electron acceleration of up to 300 MeV, either resulting in monoenergetic or broadband spectra, depending on the well controllable experimental conditions we set. Operations at the 1 PW and 10 PW experimental stations will start soon. External user access will be tested with the early and commissioning experiments and will be formulated coherently within the framework of the IMPULSE project guided by ELI-DC. Reference Current status and highlights of the ELI-NP program research program, KA Tanaka, K Spohr, D Balabanski, et al., Matter Rad. Extremes, 5, 024402 (2020): doi.10.1063/1.5093535

We’ve come a long way since 1609, from spectacle lenses to mirrors in space, from twitching frog legs to the Event Horizon Telescope observing a black hole. But far more is possible. On the ground, a new generation of optical telescopes is under construction, up to 39 m in diameter. Adaptive optics compensates for the turbulent atmosphere, but could work far better with an orbiting reference beacon in space. Bright chemiluminescent emission lines in the upper atmosphere interfere with observations, but could be blocked by fiber optic filters. Energy-resolving photon counting detectors promise far greater sensitivity. New ways of making mirrors offer far better resolution for space X-ray telescopes. Coronagraphs can suppress starlight enough to reveal exoplanets in direct imaging, or starshades can cast star shadows on telescopes to do the same thing. New generations of far IR detectors with large cryogenic telescopes in space can reveal the cool and cold universe. Radio telescopes on the quiet far side of the Moon can overcome the limits of the ionosphere and intense local interference to see events in the early universe as it heated up again after the Big Bang expansion cooled everything. Neutrino telescopes can see stars being shredded by black holes, and gravitational wave detectors see merging neutron stars and black holes. Atom wave gravimeters can measure the internal structure of planets and asteroids, and sample return missions are already bring back distant bits of the solar system. What will happen next? I don’t know but it will be glorious.

The nascent field of semiconductor core fibres is attracting increased interest as a means to exploit the excellent optical and optoelectronic functionality of the semiconductor material directly within the fibre geometry. Compared to their planar counterparts, this new class of waveguide retains many advantageous properties of the fibre platforms such as flexibility, cylindrical symmetry, and long waveguide lengths. Furthermore, owing to the robust glass cladding it is also possible to employ standard fibre post-processing procedures to tailor the waveguide dimensions and reduce the optical losses over a broad wavelength range, of particular use for nonlinear applications. This presentation will review progress in the development of nonlinear devices from the semiconductor core fibre platform and outline exciting future prospects for the field.

X-ray free-electron lasers, delivering x-ray pulses of femtosecond duration, are available for experiments for more than a decade and allow for hitherto unachievable x-ray intensities on sample, reaching up to 1021 W/cm2 for hard x-rays. At these intensities, the probability of a single atom or molecule to absorb a photon of an impinging x-ray pulse reaches unity. Moreover, several interactions of photons and matter within the duration of the x-ray pulse – nonlinear x-ray matter interactions – become possible, opening the pathway to nonlinear x-ray optics. For a macroscopic ensemble of atoms, molecules, nanometer-sized clusters or a solid, the interaction with a strongly focused x-ray beam can create macroscopic, highly excited states of matter, far from equilibrium. In particular, saturated absorption with a high-intensity x-ray pulse can result in transient states, present for roughly one femtosecond, with the characteristic feature, that every single atom in the interaction region is in a population inverted state with missing population in the innermost electronic shell. This macroscopic population inversion can lead to collective radiative decay mechanisms, such as amplified spontaneous emission or superfluorescence. In this presentation I will give you an overview over our experimental and theoretical investigations of these single-pass x-ray laser amplifiers in the x-ray spectral domain. I will address applications of this phenomenon in the area of chemical x-ray emission spectroscopy, a new concept of an x-ray laser oscillator, and will highlight recent theoretical developments to describe collective spontaneous emission in the x-ray spectral domain.

The Matter in Extreme Conditions (MEC) instrument at LCLS pioneered the use of the hard X-ray free electron laser (XFEL) in combination with high-power optical lasers to advance high energy density science. Commissioned in 2012 as an open-access scientific capability, this application of the powerful XFEL diagnostic has driven a rich array of high-profile scientific results, providing new insight into atomic and structural properties of dynamic plasma and high-pressure material states. Aided in part by the success of MEC and other high power laser facilities, there has been a strong call from the research community over the past 5 years for increased national investments in high power lasers combined with existing national lab infrastructure. In response to a mission need statement from the US Department of Energy, Fusion Energy Sciences, SLAC has developed a conceptual design for a project to build a new HED science facility combining high rep-rate (10Hz) petawatt laser systems and high energy (1kJ) long pulse lasers with the LCLS XFEL. Combined with flexible and high efficiency experimental systems, this facility will enable a world-unique set of scientific capabilities complementing the new emerging generation of high-power laser facilities, including the pillars of ELI and new HED end stations at European XFEL and SACLA. In this talk, I will present an overview of the facility conceptual design and place it in the context of the growing field of high-power laser science.

Phenomenon like resonance energy transfer is widely utilized for many bio-detection schemes where biomolecules actively bind to optical donor and acceptor labeled antibodies to form “sandwich complexes” but the large size of these complexes limits the efficiency of energy transfer, preventing sensitive detection which leads to false outcomes of the tests. In our project, we propose to improve the efficiency of energy transfer through the use of solution-phase optical microcavities. We have designed a novel optical donor that should be capable of performing the energy transfer efficiently over larger distances than the traditional resonance energy transfer limit. We have designed structures where colloidal fluorescent quantum dots (QDs) are precisely located inside dielectric microspheres and the fluorescence of the quantum dots is trapped inside the optical cavities via total internal reflections leading to optical resonances known as whispering gallery modes and the tuning of the experimental parameters will allow us to maximize the coupling of the fluorescence emission of QDs to the modes to achieve the best efficiency of the system. Following the fabrication of the optical donor, we have introduced highly absorbing dye nanoparticles as optical acceptors in the evanescent field of the microcavities and characterized the efficiency of the energy transfer through the optical modes. Now we are developing a technique to impart bio-specificity to the microbeads to detect biomolecules of interest with improved sensitivity and simple methodology.

In this work, a cost-effective optofluidic system is propossed and preliminary experimental results are presented. A microfluidic channel monolithically integrated into a photonic integrated circuit technology is used in conjunction with a cyclo-olefin copolymer (COC) substrate to provide fluidic in- and output ports. We report on initial experimental results as well as on the simple and cost-effective fabrication of this optofluidic system by means of micro-milling.

Self-injection locking to an external fiber cavity is an efficient technique enabling drastic linewidth narrowing and self-stabilization of semiconductor lasers. We introduce a simple dual-frequency laser that employs the same external ring fiber cavity for self-injection locking of a standard semiconductor DFB laser and for the generation of the Stokes light via stimulated Brillouin scattering. In contrast to the previous Brillouin laser configurations, the system spliced from standard telecom components is supplied by a low-bandwidth active optoelectronic feedback that helps to maintain the self-injection locking to provide both the DFB laser line narrowing and permanent coupling between the DFB laser and the fiber ring cavity thus enabling the dual-frequency laser operation. The laser performance characteristics are well superior to the on-board laser modules commonly used with BOTDA. In particular, the configuration reduces the natural Lorentzian linewidth of the light emitted by the laser at pump and Stokes frequencies down to 270 Hz and 110 Hz, respectively, and features a stable 300-Hz-width RF spectrum characterizing beating between two laser outputs. In a direct comparison with the commercial BOTDA, we explore the utilization of our low-cost solution for the BOTDA sensing demonstrating distributed measurements of the Brillouin frequency shift in 10-km sensing fiber with 1.5m spatial resolution.

Traditional depth estimation methods based on EPI utilize the texture information of the scene to extract line features, which is effected heavily by weak texture, repeated texture and noise. To overcome these problem, we propose an active light field sensing system (ALF), which is made up of an unfocused light field camera (LFC) and a digital light processing projector (DLP). In this paper, we placed a standard plate moving at multiple position to capture a set of phase information under different depth. At every location of the standard plate, EPI was integrated to extract line features, which is consist of spatial pixel with the same phase information. With this process, we can obtain a set of corresponding slopes and depth values for each spatial pixel in the central viewpoint, and then determine the relationship between the two variables. Another calibration is proposed to obtain distortion coefficients, in order to correct distorted line features in the EPI. The experimental results proved the efficiency for depth sensing.

In this work, we present two micro-opto-fluidic platforms for smart recognition of water-based fluids exploiting absorption spectroscopy. The identification of the samples is based on their absorption properties in the near infrared region from 1165 nm to 1650 nm and, in particular, on the analysis of the absorption band of water located around 1450 nm. In the instrumental setup, the fiber-coupled light emitted by a Tungsten lamp is shone onto the micro-devices and the output radiation is directed to an optical spectrum analyzer. The first platform works in reflection by means of a rectangular glass micro-capillary with integrated reflectors. Thanks to the presence of the double metallization, light can cross the capillary channel multiple times in order to enhance measurement sensitivity. The second platform works in transmission and exploits a commercial device with a micro-fluidic polymeric channel. The performances of the sensing platforms were initially theoretically studied by implementing a MATLAB® model based on geometrical optics and Lambert-Beer formula for absorption. Then, experiments were carried out by testing water-alcohol dilutions, proving results in a good level of agreement with the theoretical predictions. We also successfully employed our platforms for specific measurement of the water content in Scottish whisky and Venezuelan white rum liquor. The proposed readout technique is remote, contactless, non-invasive, and thus totally safe. Moreover, borosilicate glass micro-capillary and polymeric channel are both sterile, biocompatible and low-cost devices. These features make our opto-fluidic-platforms highly suitable also for many other applications, ranging from biology to food analysis.

Nitrogen-vacancy (NV) centers are crystallographic defects which provide diamonds with unique physical properties. The centers are known for their intensive, time-stable fluorescence, and an electron spin, which exhibits long coherence time and may be manipulated using external stimuli. Nanodiamonds containing the NV centers are promising tools in biolabeling, biosensing, and drug delivery due to the aforementioned properties of the defects combined with a chemical inertness of a core and an easily functionalized surface of the diamond. Many biochemical reactions are pH-sensitive, therefore, in order to utilize the NV centers for monitoring of such processes, the pH-dependency of the properties of the nanodiamonds needs to be well-understood. Functionalization of the nanodiamonds’ surfaces with biological molecules undergoing pH-triggered changes of conformation, e.g. poly-L-lysine, could not only increase the particles’ biocompatibility and promote cell adhesion, but also possibly enhance pH-sensitivity. In the present study, an impact of pH on the fluorescence, a zeta potential, and a contact angle of the NV centers-containing nanodiamonds dispersed in liquid media is examined. The suspensions were made of commercially available, fluorescent diamond particles in an as-received, unmodified state, and after the poly-L-lysine had been attached to their surfaces via two different procedures – in aqueous, and anhydrous environment. Values of pH of dispersion media were specifically chosen to induce diverse conformation of the poly-L-lysine: from a fully relaxed conformation, through a state of being neither wholly extended, nor helical, to a complete α-helix conformation. The intensity of the photoluminescence emitted by the NV centers has been found to depend on the pH-triggered conformation of the poly-L-lysine attached to the surfaces of the nanodiamonds. The impact of the conformation of the poly-L-lysine on the electric charge of the nanoparticles has also been analyzed. This study confirms the potential of the nitrogen-vacancy centers for optical sensing of pH-triggered processes.

Detection of analytes in aqueous solution with high specificity and sensitivity is of paramount importance in many fields of science, ranging from bio-medicine, environmental control, and food quality assessment. Surface-enhanced Raman scattering (SERS) has proven to be a cutting-edge analytical technique for this purpose, by combining the high selectivity of Raman features with the high sensitivity deriving from the plasmonic amplification of Raman signals. Herein, we report a facile and quite effective approach to fabricate large-area Ag-based SERS substrates, exhibiting a porous, coral-like nanotexture. Due to their intrinsic large surface-area and high hot-spot density, the produced substrates appear quite promising for the detection of analytes at trace levels. The nanoporous substrates are produced by Solid-State Dewetting (SSD) of thin Ag-films. In particular, ~30 nm tickness Ag-films are first deposited on glass coverslips by magnetron sputtering. Then, marked roughening is induced by exposing the films to an Inductively Coupled Plasma (ICP) discharge, using synthetic air as gas discharge. The formation of the porous film is mainly due to silver etching produced by reactive oxygen species produced in the air-based plasma. As side effect, these species lead to an oxidation of the outer part of the Ag-film, which strongly degrades the plasmonic performance of the SERS substrates. However, the film is restored to its pristine metallic form by a further ICP treatment but in Argon atmosphere, which has the effect to reduce the Ag-oxides (as demonstrated by XRD analysis) without altering the created nanotexture. The performances of our SERS substrates are characterized in terms of enhancement factor and spatial uniformity, and the ultimate sensitivity is evaluated at sub-micromolar concentrations. Globally, the obtained results demonstrate the effectiveness of our proposed method for the production of large area, chip and sensitive SERS substrates.

Spectral sensing in the near-infrared range is of increasing interest for application areas ranging from industrial processes to the agri-food sector, as it allows measuring the chemical composition of organic materials in a fast and non-destructive manner. On-field applications demand spectral sensors with a large spectral range, low angular dependence, robust geometry and small footprint, while being manufacturable on large scale at low cost. To meet these requirements, we developed a multi-pixel array of resonant-cavity enhanced detectors using an InP-membrane-on-silicon platform, where each of the 16 pixels provides an individual photoresponse with a number of resonances, which together cover the wavelength range of 800-1700 nm. The pixels consist of two metal mirrors, which enclose an InP p-i-n photodiode with an InGaAs absorber layer and a tuning layer, which varies in thickness to create the individual photoresponses of different pixels. The multi-pixel arrays are fabricated by adhesive wafer bonding followed by a series of lithography steps to define the tuned pixels and metal contacts for the photocurrent read-out. Despite the limited number of measurement channels with broad spectral response, information on the chemical composition of the sample can be directly retrieved using chemometrics. The sensing capabilities for our spectral sensors are demonstrated with two practical application cases: determination of the nutritional information in raw milk and the classification of different plastic types. For both experiments, the photocurrent measurements from the sensor were used directly in regression or classification algorithms based on partial least squares analysis, leading to convincing prediction performance. This shows that the fabricated spectral sensor can retrieve chemical information for a broad set of sensing problems. Simulations have shown that for a specific sensing problem the prediction performance of the spectral sensor can be further improved by an optimized selection of the available spectral responses.

Copper ions (Cu2+) play an essential role in human life as an enzyme co-factor and with a deep involvement in the formation of red blood cells. However, excessive intake of copper beyond the permissible levels, can incite serious health problems such as anemia, kidney failure, neuro- degenerative disorders etc. Due to the advent of industrial revolution, there is an alarming level growth of copper ions in the environment. Therefore, low-cost, eco-friendly, highly selective and rapid detection of copper is of utmost present day interest. The present article discusses a cost effective technique for the detection and quantification of copper ion by using localized surface Plasmon resonance (LSPR) based fiber optic technique. For the purpose, a small portion of a plastic optical fiber is functionalized with gold nanoparticles which are modified with 4-mercapto benzoic acid (4-MBA). The proposed is very successful in the detection of Cu2+ even in trace levels (ppb) in a wide range of real time samples. The results are comparable with the existing detection techniques.

Nowadays, Global Positioning Systems (GPS) are used everywhere for positioning and navigation. However, its use is not suitable in indoor environment, due to power budget constraints and the strong attenuation inside buildings. Therefore, indoors navigation takes advantage of other technologies to infer position. Recently, several Visible Light Positioning (VLP) systems have been reported. Among these technologies, Visible Light Communication (VLC) is one of the most promising, as its operation is based on the use of LED lights, currently widely used in the illumination solutions of most buildings. In this paper, we propose an indoor navigation system based on VLC in an industrial application for automated warehouses, where the navigation of autonomous vehicles (AVG) is supported by VLC. The proposed VLC system establishes bi-directional communication between the infrastructure and the guided vehicles. LED transmitters at the warehouse ceiling support downlink data transmission from the Infrastructure to Vehicle (I2V). This channel provides positioning and navigation of the vehicles, as well as transmission of dedicated messages related to the requested tasks of the management warehouse system to the autonomous vehicles. The uplink channel from the Vehicle to the Infrastructure (V2I) is used to acknowledge the requested tasks and transmit updates on the concluded tasks. Optical transmitters are tri-chromatic white LEDs with a wide angle beam. The characterization of the optical transmitter system is done through MatLab simulations for path loss and VLC channel gain prediction, using the Lambertian model for the LED light distribution. Dedicated receivers based on a-SiC:H/a-Si:H photodiodes with selective spectral sensitivity are used to record the transmitted signal. The decoding strategy is based on accurate calibration of the output signal.

Vehicular Communication Systems are a type of network in which vehicles and roadside units are the communicating nodes, providing each other with information, such as safety warnings and traffic information. In this paper, a traffic controlled intersection is analyzed by using microsimulation. A Vehicle-to-Everything (V2X) communication scenario is stablished and a mesh cellular hybrid network configuration is used. The concept of request/response and relative pose estimation for the management of the trajectory is used, in a two-way-two-way traffic lights controlled crossroad, using Vehicular Visible Light Communication (V-VLC). The connected vehicles receive information from the network and interact with each other and with the infrastructure. In parallel, an intersection manager (IM) coordinates the crossroad and interacts with the vehicles (I2V) using the response distance, the pose estimation and the temporal/space relative pose concepts. The communication between the infrastructures and the vehicles (I2V), between vehicles (V2V) and from the vehicles to the infrastructures (V2I) is performed through V-VLC using the street lamps, the traffic signaling and the headlamps to broadcast the information. Data is encoded, modulated and converted into light signals emitted by the transmitters. Tetra-chromatic white sources are used providing a different data channel for each chip. As receivers and decoders, SiC Wavelength Division Multiplexer (WDM) optical sensor, with light filtering properties, are used. Cooperative localization is realized in a distributed way with the incorporation of the indirect V2V relative pose estimation method. A phasing traffic flow is developed, as Proof of Concept (PoC), to control the arrival of vehicles to the intersection and schedule them to cross at times that minimize delays, A generic model of cooperative transmission based on the graphical representation of indirect relative poses estimation (simultaneous localization and mapping) is analysed.The block diagram expresses that the vehicle’s behavior (successive poses) is mainly influenced by the manoeuvre permission and presence of other vehicles. Results show that the cooperative I2V and V2V messages and the intersection redesigned layout are important issues on traffic control with least dependency on infrastructure.

The sedimentation of solid particles in a liquid is a physical phenomenon that necessitate to be well understood and measured in several cases. In medical diagnosis, a knowledge of the sedimentation speed of red blood cells for example, allows the early diagnosis of various inflammations. In study, optical Micro-Resonators (MRs) are used as sensors to track the dynamical phenomenon of sedimentation of a cloud of nano-particles in water, and the associated consequences on the spectral characteristics of the guided mode are analyzed. A MR is characterized by its eigenvalue, namely the effective index of an optical mode propagating inside. A progressive modification of the environment thus induces a temporal variation of the effective index. Such a variation can be measured by the tracking of the Free Spectral Range (FSR) of the transduced spectra against time. The transduced optical signal is then directed towards an Optical Spectrum Analyzer (OSA) from which spectra are acquired against time. A millimeter tank filled with water is judiciously deposited on the surface of the chip, before the adding of the solution of nano-particles. The spectra are acquired during the whole duration of the process of sedimentation. The data collected this way are then compared to a simple theoretical model describing the sedimentation of a spherical particle in water. Moreover, the sedimentation theory and the derivation of the speed of sedimentation of a spherical particle is presented, plus the presentation of the experimental setup, from the fabrication of the photonic structure by photolithography, to the inclusion of this circuit in an optical characterization platform and the presentation of the data acquisition and treatment program. The experimental results are analyzed and discussed. The differences are around 10% over the theoretical Stokes velocities relating to such sedimentation process. An overall generic curve or spectral response is clearly demonstrated on these sedimentation processes.

Sepsis, defined as the systemic inflammatory response to a confirmed or suspected source of infection, is the most severe infection-related condition and its identification can be particularly difficult in the initial stages. The importance of having a Point-of-care testing platform capable of measuring sepsis biomarkers for a secure early-stage diagnosis is evident to reduce delay in treatment and hence recovery period for the patient. We will report on a simple and cost-effective device which also shows high portability. It is based on the optical detection of labeled essays through a fully-automated fiber probe. Efficient signal collection is obtained by replacing the standard glass substrate with a planar metallo-dielectric multilayer which funnels the emission into a narrow cone around the polar axis [1]. Optical interrogation is implemented with a minimized epi-fluorescence monolithic system directly connected to the fiber. On one hand, optical probes provide the ability to detect low quantities of target molecules without direct contact to the sample; on the other hand, nano-photonics promises to overcome the limitations related to bulk optics with precise and fragile alignment procedures. We will report on preliminary results obtained for a reference dry essays (IgG/anti-IgG) marked with ATTO647N, which demonstrates sensitivity overcoming the requirements for CRP-based sepsis detection. We will also discuss optimization steps which are expected to bring sensitivity beyond the level required for PRC-based sepsis detection. The proposed device is also prone to implementation in microfluidic-based protocols. [1] Checcucci S, Lombardi P., Rizvi S., Sgrignuoli F., Gruhler N., Dieleman F.B.C., Cataliotti F.S., Pernice W.H.P., Agio M., and Toninelli C., Beaming light from a quantum emitter with a planar optical antenna, Light: Science & Applications, Vol. 6, e16245 (2017).

We demonstrate a highly effective method for fibre Bragg grating (FBG) inscription into a seven core fibre (7CF) and its application as an effective vector bending sensor. The development of multicore fibres (MCFs) and enabling the fabrication of FBGs into them result in a solution for multi-parameter measurements such as temperature/strain/bending/twist. The FBG in the central core is on the neutral axis and therefore it is sensitive to thermal but insensitive to deformational changes, whereas the FBGs in the none-central cores can facilitate the measurement of structure deformation, such as bending, loading and twist. Furthermore, the FBGs in different side cores respond to the physical perturbations differently in various orientations, enabling the measurement for both amplitude and direction of the structure change. These MCF-FBG sensors are highly applicable for mechanical structures and flexible medical instruments. The FBGs were successfully UV-inscribed into all seven cores of the 7CF with Bragg reflection strength ranging from 5 dB to 30 dB. The bending response was examined and analysed for the centre core and side cores under bending and also under the twisting at 0, 90, 180 and 270. The results for the FBGs in two cores on the opposite locations respond to the bending differently, as one is blue-shifting with a curvature sensitivity of -68.51 pm/m-1 and the other red-shifting with a smaller sensitivity of 47.37 pm/m-1. The bending response for central core is insignificant as measured only -8.83 pm/m-1. The twists were applied to the 7CF-FBG, the measured curvature sensitivities for one of the 7 cores are -71.79pm/ m-1 at 90, 47.37 pm/m-1 at 180 and 120.68 pm/m-1 at 270 respectively.

Continuum robots are snake-like elastic structures that can be bent anywhere along their length hence representing ideal tools for applications such as minimally invasive surgery. To accurately control these flexible manipulators, 3D shape sensors that are small, sterile, immune to electromagnetic noise, and easy to replace are required. Fiber Bragg Grating (FBG)-based shape sensing is a promising approach for this task. Edge-FBGs are a new generation of fiber-based shape sensors with high flexibility and high spatial resolution that can be monitored using a low-cost interrogation system. In edge FBGs, the amplitude change at the Bragg wavelengths contains the strain information at sensing points. However, such sensors are sensitive to the change in the spectrum profile caused by bending. In practice, the spectrum profile cannot be estimated accurately, making the mathematical model insufficient for predicting the sensor’s shape. Therefore, developing a model that distinguishes the strain signal from the spectrum noise is required. Machine learning techniques are great tools for studying complex problems, making it possible to explore the edge-FBG spectrum and identify patterns caused by undesired bending-related phenomena. In this contribution, we trained a neural network with supervised deep learning to directly extract the shape information from the edge-FBG spectrum, where no referencing was required prior to new measurements. We showed that the model predicts the sensor’s shape with more accuracy than the mathematical approach. Moreover, we studied the feasibility of using a low-cost interrogation system for the edge-FBGs, considering the minimum required signal to noise ratio.

Here, we present a novel label-free biosensor based on fiber optic technology which was tested for the detection of a serum inflammatory marker, the C-reactive protein (CRP). The biosensor is based on a long period grating (LPG) inscribed in a double cladding fiber (DCF) having a W-type refractive index (RI) profile. Such DCF fiber permits to tune the sensor working point to the so-called mode transition region through etching of the fiber outer cladding. Therefore, a significant enhancement of the RI sensitivity, as well as visibility of the grating spectral features were attained, since the mode transition was induced in all-silica fiber structure. Subsequently, the so-prepared LPG was coated with a nano-scale layer of graphene oxide, providing carboxylic functional groups for the covalent immobilization of the biological recognition element for the CRP. As a result, a remarkable limit of detection (LOD) lower than ng/mL levels and a large working range of clinical relevance (ng/mL to µg/mL concentrations) were achieved during the real time detection of CRP in human serum.

Surface-enhanced Raman scattering (SERS) has established itself as powerful tool for molecular sensing in biology and medicine. The integration of SERS systems with optical fiber is a challenging but potentially very rewarding endeavour. However, efforts to transfer the technology from the laboratory to the clinic have been frustrated by the lack of robust stable and sensitive substrates on the fiber tip by using low-cost processes, as well as the complexity of interfacing between sample and the substrate itself. In this work, we proposed the Lab-on-Fiber SERS optrodes, realized directly on the optical fiber tip by nanosphere lithography technique. Three types of highly ordered and reproducible SERS-active substrates have been realized: close-packed array (CPA), CPA after sphere removal (SR) and sparse array (SA) of polystyrene nanospheres, covered by a gold thin layer. In order to optimize the SERS probes, we first compared the SERS performances in terms of Enhancement Factor and reproducibility pertaining to different patterns with different nanosphere diameters and gold thicknesses using the biphenyl-4-thiol (BPT), as target molecule. To determine the most suitable optical fiber probe, in terms of excitation/collection efficiency and Raman background, we selected and tested several optical fibers with BPT solution. Moreover, we have experimentally analysed and compared the SERS spectra of three representative biological probes, BPT (small molecule), bovine serum albumin (BSA, medium molecule) and red blood cells (RBCs), in order to correlate the SERS response to the morphology and hysteric hindrance of the biological target. The SERS analysis indicated that the CPA substrate amplifies the BPT Raman intensity twice as well as the SR and SA substrates, while BSA and RBCs, with the CPA substrate, provide signals comparable to those of SR and SA substrates. Finally, we have optimized a Raman system for SERS optrode operation with efficient lighting and collection via optical fiber.

The report presents the results of research concerning fiber optical sensors based on tilted fiber Bragg gratings. Ease of use, compactness and integrability into measuring systems - these are but a few of a vast list of the advantages of fiber optic sensors. Bragg structure-assisted sensors are widely used in fiber sensorics, but their application is mostly limited to the detection of temperature and mechanical influences. Utilized as the basis of the sensitive element, tilted fiber Bragg gratings inscribed in the core of the optical fiber interacts with the light guided through the fiber, efficiently exciting a set of cladding modes that can be observed in the transmission spectrum of the sensor as a comb-like series of peaks and dips sensitive to the refractive index of the external medium. This concept provides possibilities of creating various direct contact-type fiber sensors, i.e. for measuring humidity and biological molecules’ concentrations in solutions. Functionalization of the surface of such a fiber with a transducer coating, which converts changes in environmental characteristics into changes in the coating’s refractive index, renders it possible to effectively track and measure certain parameters, ensuring high selectivity and measurement accuracy. In the report, a fiber hygrometer is presented as an example of such a sensor design. A technique for creating such a sensor is described, including tested methods for deposition of a functional coating onto the surface of the fiber. Also presented are the results of laboratory tests of experimental samples of fiber hygrometers, which demonstrate the reproducibility of the technique and the feasibility of such sensors as a basis for biomedical application and environmental monitoring systems.

In this work, we present a sensor based on an optical fiber micro ring resonator for water analysis. This kind of sensor is based on Whispering-Gallery mode excitation that arises from light being trapped inside the resonator circumference due to total internal reflection. The circulating light has an evanescent field that extends beyond the resonator into the surrounding medium, enabling changes in the surrounding refractive index to be monitored via the shifts in the resonance wavelengths. WGM resonators can detect molecules such as viruses, proteins, nucleic acids, and even atomic ions.

Conventional RI measuring instruments suffer from limitations due to their voluminous size, inefficiency for remote monitoring and high cost. Evanescent field absorption based POF sensors could be low cost and reliable alternatives for RI measurement. Since the fiber with fluorinated polymer cladding over PMMA fiber core offers better chemical resistance, U-bent probes with their cladding intact can be an alternative. A characteristic study on effect of increase in the number of U-bends of a fiber optic sensor on its RI sensitivity is carried out. The cladded U-bent plastic optical fiber (POF) probes with single, triple and quintuple U-bent regions investigated under this study show a RI sensitivity of 2.7, 3.7 and 2.3 absorbance units/RI units respectively. Triple U-bent cladded fiber optic probe made of 0.5 mm POF with a bend diameter of 2.5 mm show higher RI sensitivity in comparison to single and quintuple U-bent probes. The highest sensitivity obtained here is more than 50% of decladded single U-bent POF probes, however with superior chemical resistance. Further studies on the optimum bend diameter and chemical resistance could potentially give rise to robust and sensitive probes.

We have proposed an experimental study on the effect of the fiber profile parameters on the sensitivity of the tapered optical fiber hydrogen sensors. To study the effects of taper profiles on the sensitivity of the tapered fiber, we divided our study into three experiments where the main parameters of each experiment are tapering angle, waist diameter, and taper length. To examine the effects of taper profile on the sensitivity of tapered fiber, we fabricated eight tapered fibers with varying taper profiles. By controlling the fabrication conditions such as pulling duration, pulling speed, heating length, and temperature, tapered fiber with different shapes and properties can be fabricated. By measuring and comparing the sensitivity of the fibers, we found that tapering angle, waist, and length have a significant effect on the sensitivity of the sensor. According to the first part of our experiments, the sensitivity increases from 2.5% to 7% when the angle was increased from 2° to 4°. The second part of our experiments shows that the sensitivity increases from 7% to 8.5% when the length was increased from 10mm to 20mm. The last part of our experiments shows that the sensitivity increases from 4% to 5.5% when the waist diameter was decreased from 35μm to 15μm. To ensure which parameter is being studied, we fixed all other parameters in our experiments. The results of this research show that increasing the tapering angle and length can both help improve sensitivity. Decreasing the waist diameter can also improve sensitivity. We believe that the tapering angle has the most significant effect on the sensitivity of the sensor.

A novel hyperspectral sensing imaging that takes advantage of engineered all-dielectric metasurfaces supporting bound states in the continuum here is discussed. This approach combines surface-enhanced fluorescence and resonant shift sensing during microscopic raster scanning of cells. The amplification of the optical field on resonance allows increasing the fluorescence emission of a dye as a function of the spatial-variant dielectric environment in the near-field of the structure. We first demonstrate the fluorescence emission amplification by resonant pump matching in microscopy configuration. Then, we take advantage of Fano interference in the fluorescence emission to map the spatially variant environment of biological cells. To demonstrate the real implementation of our BIC-enhanced imaging as a platform for biosensing, hyperspectral maps of prostate cancer cells are experimentally measured.

Acoustic-graphene-plasmons (AGPs) are highly confined electromagnetic modes, which carry extreme momentum and low loss in the Mid-infrared (MIR) to Terahertz (THz) spectra. In this work [1], we demonstrate a new way to excite highly confined AGPs from the far-field, with localized graphene-plasmon-magnetic-resonators (GPMRs). This approach enables the efficient excitation of single AGP cavities, which are able to confine MIR light to record-breaking ultra-small mode-volumes that are about a Billion times smaller than their free-space volume. Our approach provides direct access to record-breaking ultra-small mode-volumes, enabling a new platform for ultra-strong light-matter interactions and efficient AGP-based devices, such as photodetectors and sensors, in the long wavelength spectrum. [1] I. Epstein et al, "Far-field Excitation of Single Graphene Plasmon Cavities with Ultra-compressed Mode Volumes", Science 368, 1219-1223 (2020).

The realization of periodic plasmonic nanostructures featuring macroscopic dimensions and easily controllable in size and lattice spacing, is a challenging achievement for low-cost nanofabrication tools, which has not been completely explored so far. In this work, periodic array of different metal nanostructures have been easily prepared on large-area by exploiting a modified nano-sphere lithography (NSL) fabrication technique. A valuable ability is to couple the versatility offered by NSL with post-processing tools for a properly engineering of plasmonic NPs. The potentiality to obtain dynamic tunability of metal NPs will enable the creation of intense electromagnetic near field distribution upon interaction with light of a desired frequency. A rational design of such singular or collective optical properties can be used to focus and optimize the investigated functional features. Actually metal nano-prism arrays, owing to their proximity and consequently huge electromagnetic field reached at their sharp tips, have been exploited for many applications such as the development of innovative sensing platform, substrates for surface enhanced Raman scattering (SERS) or surface-enhanced fluorescence microscopy, nanopatterning or the realization of new generation plasmonic solar cells. Moreover, their large “sensing volume”, defined as the penetration depth within which changes of the refractive index can be detected, demonstrated their superior performances for biosensing applications.

We developed a simple model to take into account the refractive index effect on optical path change in multi-wavelength Frequency Modulated Continuous Wave (FMCW) Lidar. Then we developed a scheme to use a single optical frequency comb source to perform Dual Comb Spectroscopy (DCS) experiments and finally we extended this scheme for applications of DCS on earth-satellite path using the Doppler induced frequency shift to simulate the second comb source.

GAs in Scattering Media Absorption Spectroscopy (GASMAS) is used to correlate the average pore size within mesoporous alumina samples to the broadening of the absorption lines of oxygen gas and water vapor entrapped within the pores. Collisions of gas molecules cause extra broadening to the absorption linewidths if the average time between collisions is smaller than the inverse of the linewidth of the absorption line. A gas molecule can collide either with another molecule or with the walls of its container. Hence, for a gas entrapped within a porous medium that has an average pore size comparable to the mean free path of intermolecular collisions, collisions of the gas molecules with the walls of the pores can cause extra broadening. This extra broadening is used to estimate the average size of the pores. At atmospheric pressure, the mean free path of intermolecular collision is about 100 nm and thus broadening due to collision with the walls of the pores should be noticeable for pore sizes of order of 100 nm or less. In this work, high resolution tunable single-mode diode lasers at 761 nm and 936 nm are employed to study the absorption from oxygen gas and water vapor, respectively. The samples used are made from porous pure α-alumina with average pore sizes ranging from 50 to 150 nm.

In this work, a temperature tunable capillary-based polymer whispering gallery modes laser was proposed. The WGM laser device was fabricated by filling the liquid polymer into the capillary tubes. Due to the thermal-optic effect of the polymer, the emission wavelength of the laser device can be continuously tuned from 601.4 nm to 581.9 nm with the varying temperature. Moreover, the suppression of modes was observed owing to the two-ring coupling effect in the capillary cavity. The easy-fabricated and very low-cost method of the temperature tunable WGM laser was verified which exhibits the potentiality for applications of photothermic and sensing devices.

It's presented a new method that combines frequency and phase domains-gated reflectometry. This approach can be applied to a fiber with artificial reflectors to measure the absolute values of optical paths between reflection points in the fiber in the full range of signal frequencies, including zero frequency.

This article demonstrates that the combination of all-dielectric metal oxides sol-gel sensitive materials and metasurfaces, prepared by simple sol-gel methods (dip-coating and soft-Nano Imprint Lithography), can lead to nanocomposite systems with high sensitivity for RI variation and VOC concentration in air detection in spectral shift mode: 4500 nm / RIU ; 0.2 nm / ppm, and in direct reflectance mode: FOM* = 17 ; 0.55 10-3 R / ppm. The metasurface is composed of TiO2 high aspect ratio nano pillars array, replicated from a commercial anti-reflective polymer surface, while the sensitive materials embedding the latter are class II hybrid silica microporous materials containing various types of covalently bonded organic functions. These hybrid layers showed relative significant differences in chemical affinity with different VOCs, which can be exploited to eliminate interferences with air moisture and for qualitative analysis of gas mixtures. We also demonstrated that the presence of the TiO2 metasurface is responsible for the signal intensity increase by almost an order of magnitude in simple reflection mode. This improvement compared to simple Fabry-Perot bi-layer is due to the antenna effect, enhancing the interaction of the confined electromagnetic wave with the sensitive medium. This sol-gel nanocomposite system presents many advantages such as high throughput and low-cost elaboration of the elements, high chemical mechanical and thermal stability ensuring a high stability for detection for long period of time.

Benzene (C6H6) is one of the major public health concerns. It is emitted from various natural and anthropogenic sources, like fires and volcanic emissions, petrol service stations, transportation, and the plastics industry. Here, we present our work on developing a new benzene sensor using a widely tunable difference-frequency-generation (DFG) laser emitting between 11.56 and 15 µm (667–865 cm–1). The DFG process was realized between an external-cavity quantum-cascade-laser (EC-QCL) and a CO2 gas laser in a nonlinear, orientation-patterned GaAs crystal. We obtained the absorption cross-sections of the Q-branch of the ν4 vibrational band of benzene by tuning the wavelength of the DFG laser between 14.79 and 14.93 μm (670–676 cm–1). Benzene sensing measurements were performed near 14.84 µm (673.97 cm–1) with a direct laser absorption spectroscopy scheme. The benzene concentration was varied between ppb and ppm levels. Even with a relatively short optical path-length of 23 cm, our sensor achieved a benzene detection limit of about 10 ppb.

This study investigated innovation of detected the intensity of light via Three Dimension Material Rendering the intensity of light entering the eyes to determine the optimized intensity of light. The innovation of detected the optimized intensity of light via three-dimension material rendering (IDOIL-3D) was rendering into glasses by 3D-printing and can be detected intensity of visible light by a sensor-controlled by computer language. The sensor for detected of light was determined variable value to notification when a variable value has over limit, the sensor will alert in form biofeedback. IDOL-3D can be helped the wearer reduce the intensity of light entering the eyes.

A digital counting and display circuit for long distance laser rangefinder is presented. The laser rangefinder uses a pulsed Nd:YAG laser emitting in the near-infrared spectral region at the wavelength of 1.06 micrometer to measure distances to targets with a resolution of 5 m, an accuracy of +/- 1.5 m, and a maximum range of 15 km based on a direct time-of-flight method. The detection is achieved with a probability of detection of 0.99 and a probability of false alarm of 1.5X10^-7. The digital circuit is characterized by its simplicity, versatility and reliability. It is placed at the end of an optoelectronic detection chain formed by a silicon avalanche photodiode, a low-noise and fast multistage amplifier, and a fast analog-to-digital converter.

KlettWelding is a new technology for connecting any components without the need for soldering, gluing or bonding. The basis for this is a process in which a lawn made of very small and thin wires is applied to any surface. By pressing two components together with such a surface, they are connected permanently, mechanically resilient with very high electrical and thermal conductivity. The generation of the surface is based on a galvanic process in which certain factors can cause disturbances. This can lead to imperfections on the surface and the connection does not hold properly. In addition, certain geometric parameters of the wires such as diameter, height, distribution density and coplanarity may only fluctuate to a certain extent and must therefore also be monitored in the manufacturing process. The aim is therefore to carry out a quality assessment of the surface after the galvanic process with the help of suitable optical measurement methods and evaluation algorithms so that defective parts can be identified and sorted out during production. Problems exist not only due to the fact that the wire sizes are in the range of the light wavelength and below, but also that the surface is very rough and slightly reflective only. Therefore, alternative methods were investigated and developed and corresponding evaluation algorithms were implemented. Several methods such as Mirau interferometry, OCT, entropy and gradient methods as well as confocal chromatic microscopy were examined. The detection of wire diameter, height and density could be measured with an SEM or similar technologies, which, however, have too low sampling speeds. For this reason, a method was developed that determines the parameters sought based on the scatter function of the wire surface irradiated with a laser. The resulting images are evaluated using image processing methods and approaches from artificial intelligence (machine learning).

Combustion processes are characterized by a number of informational parameters, including spectroscopic ones. Therefore, it is proposed using the methods of applied optical spectroscopy for solve the problem of monitoring the hydrocarbon gas combustion in this work. While a monitoring device is spectrometer that studies optical radiation as a signal carrying spectroscopic information about the combustion process and can replace most of the control-measuring equipment located at the facility. The proposed in this paper multichannel optical spectrometer carries out the spectrum analysis in predetermined optical ranges using a set of narrow-band optical filters. An optical fiber bundle is used to introduce radiation into N analyzing channels, which contain optical filters set on the certain wavelength. It allows moving spectrometer on a safe distance from the monitoring process. The combustion process of gaseous hydrocarbon fuel consists of chemical oxidation with oxygen. In this case, the air-gas ratio in the mixture entering the flame front is of great importance. The appearance of the flame and, therefore, its spectrum change depending on the speed of air supply. Therefore, an experimental installation was developed as a part of the research that includes a burner and a gas and air supply system. In the framework of the experimental study the analysis of informative signs in the flame radiation spectrum arising from the combustion of hydrocarbon fuel was perform. The experiment was carried out using an OceanOptics USB2000+ spectrometer. The choice of optical filters, which are part of the multichannel optical spectrometer was perform on the basis of this analysis. The laboratory set-up of the multichannel spectrometer was developed and created. The results of the experimental study of this set-up and the results of a comparative analysis with the OceanOptics USB2000+ spectrometer within the framework of solving the problem of diagnosing combustion of gaseous hydrocarbon fuel are presented.

Fast and nearly instantaneous transmission of information around the globe became a fundamental need in our daily life. However, fiber-optic transmission typically suffers from many impairments. Stochastic-based effects such as the polarization mode dispersion (PMD) are often in the center of attention, where high data rate fiber-optic communication link is deployed. The PMD becomes relevant for transmission systems operating at speeds beyond 10 Gbps. This, however, prevents optical link scaling’s towards faster systems. In-line PMD tests is thus of great relevance within the recently used optical fibers. PMD effects are vastly sensitive to environmental variations and they may significantly reduce the link quality. Our work provides an insight to experimental characterization for PMD-based effects in optical fibers that are influenced by wind gusts. The study was performed under different weather conditions on commercial 111-km-long fiber link with 88 spectral channels as a part of optical power ground wire cables. Differential group delay (DGD) parameter enabled sensitive characterization of wind-related link changes. Maximum DGD’s of 4 and 10 ps were measured under low and strong wind conditions, respectively. Measured data were used in the model to evaluate the optical link quality. For a low wind condition, the optical link quality maintained a reliable operation for bit rates of 10, 40, and 100 Gbps. For strong wind condition, the link transmission was degraded for bit rates of 40 and 100 Gbps. Our results show prospects for effective monitoring of environmental variations and their impact on polarization-based fiber link propagation effects, which can also allow an instant link quality evaluation.

Alkali alumina-borate glass containing different concentrations of chromium, antimony, lithium and crystallization impurities were synthesized by the melt-quenching technique at a temperature of 1400°C in alumina crucibles for 1 hour. The initial glass absorption spectra obtained after the synthesis contain two broad absorption bands, one of which located in the region of 590 nm corresponded 4A2 → 4T2 transition, and the other in the region of 420 nm corresponded to 4A2 → 4T1 transition. After two-stage heat treatment of glass samples at temperatures 450°C and 600°C the chromium-doped borate glass-ceramics was obtained. The two bands of the glass absorption spectra shifted towards small wavelength region after the heat treatment with changing the glass color, which demonstrates that chromium ions are in crystalline surrounding. The XRD studies revealed the LiAl7B4O17 nanocrystals nucleation. For the sample series the mean crystal size increases with increasing lithium concentration and heat treatment temperature of the initial glass. The glass-ceramics photoluminescence spectra possessed three intense bands with maxima at 685 nm, 700 nm, and 715 nm indicating high symmetrical environment around the chromium ions. The maximum value of the quantum yield was 90% under excitation of a wavelength of 532.8 nm. Photoluminescence decay curves are characterized by a sum of two exponential functions with the decay time τ1 = ~1 ms and τ2 =4 – 10 ms. However, there are three components in cathodoluminescence decay curves with τ1= ~1 ms, τ2 = 4 – 6 ms, τ3 =12 – 16 ms (accuracy ~0.001 ms), when excited by a flow of electrons with nanoseconds pulse duration. The presence of shallow traps in the bandgap is the possibly the main reason for the difference between CL and PL decay time of the alkali alumina-borate glass-ceramics. Perspective of light source design using UV, blue and green LED and a material under study as a luminescent filter was reviewed. The main application field for such devices is greenhouse plant irradiators that have lack of near IR component, because mostly they are based on manganese and europium-doped materials. The near IR light activates growth processes in plants and its prevalence in irradiation spectrum will help to improve the greenhouse productivity.

Precise time and stable optical frequency transfers over fibre are currently deployed more and more often as it is clearly presented. This is happening not solely on national but also on pan-European scale. Within European level, there has just started CLONETS-DS research and innovation action intended to facilitate the vision of a sustainable, pan-European optical fibre based network for precise time and optical frequency dissemination by bringing together expertise from national metrology institutes (NMI), academic groups and research infrastructures (RI), research and education networks at both the national and European level (NREN, GÉANT), and innovative high-technology small and medium enterprises (SME). Such a project brings together and combines expertise from national metrology institutes (NMI), academic groups and research infrastructures (RI), research and education networks at the national and European level (NREN, GÉANT) and innovative high-technology small and medium enterprises (SME). The project aims to establish a pan-European time and frequency reference system as a European Research Infrastructure to serve the European science community. It is based on transmitting ultra-precise time and frequency signals via optical fibres. On national level, fibre based infrastructure has been continuously being developed and operated since 2009 year, overspreading from the Czech Republic to Austria (Vienna) and to the border with Poland. The infrastructure is developed by CESNET association (mainly transmission layer and time standards) and the Institute of Scientific Instruments of CAS (optical frequency standards, optical clocks and transmission instruments) in cooperation with the Institute of photonics and electronics of CAS (Laboratory of the national time and frequency Standard) and Department of Measurement, Faculty of Electrical Engineering, Czech Technical University (time standards). In contribution we will present recent state and plans of the infrastructure development on national and international level, including achieved parameters of provided precise time and optical frequency. We will also share the experience we gained in the above mentioned field.

The operation of one of the types of diffraction optical spectral devices, which is an optical spectral device based on an acousto-optic tunable filter, is considered. In such a spectral device, an acousto-optic modulator is used as a dispersing system, which is a grating-like structure. There are two modes of operation of an optical spectral device based on an acousto-optic tunable filter, one of them is based on a linear change in the instantaneous frequency of the control signal, the second mode is based on a frequency-hopping change of the control signal. In this work, the second mode is investigated, as little studied and very promising. The mode based on a frequency-hopping change of the control signal is quite adequate for the use of optical spectroscopy methods in control systems for physical and physicochemical processes, which are accompanied by electromagnetic radiation in the optical range. Based on the use of the Heaviside step function, a mathematical expression is obtained for the control signal formed during one period in the form of a radio pulse, consisting of a sequence of partial radio pulses with a frequency-hopping change, as well as an expression for the temporal spectral frequency variable in time, which is the argument of the spectrum of the analyzed optical radiation. The obtained mathematical expressions are the basis for studying the operation of an optical spectral device based on an acousto-optic tunable filter with a frequency-hopping change of the control signal. This research is carried out in two stages. In the first stage, linear transformations of optical radiation are considered, here a complex spread function of the spectral device based on the acousto-optic tunable filter with a frequency-hopping change of the control signal is obtained. Keywords: optical signal, optical spectrum, spectrum measurement, acousto-optic interaction, bilinear spectral conversion, spectral device based on acousto-optic tunable filter, hopping, control signal, complex hardware function.

This work reports the performance improvement of the CZTSSe solar cell by using a back surface field (BSF) layer. Firstly, a cell model with Cadmium (Cd) free buffer structure (Mo/CZTSSe/Zn(O, S)/ZnO/ITO) is developed using SCAPS-1D software. To improve the performance parameters namely open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF) and the power conversion efficiency (PCE) for irradiation under normal working conditions, thickness and composition ratio of the absorber (CZTSSe) and buffer (Zn(O, S)) layer are optimized through simulations. PCE of 14.15% is achieved for a Sulphur content is 40% and 70% in CZT(SxSe1-x)4 and Zn(O1-x Sx) respectively. Further performance improvement is attempted by reducing the Voc deficit by using a back surface field (BSF) layer between the back contact and the CZTSSe absorber layer. BSF layer helps in increasing the conduction barrier height, thereby significantly reducing the recombination at the back contact and helps in increasing the Voc. The P+-MoSe2, P+ - Si0.75Ge0.25 and SnSe layers are used as BSF layers and their performance is compared. Simulation results indicate that for these BSF layers, there is an improvement in the PCE by 15%, 9.68 % and 14.27% respectively. Inclusion of the BSF layer gives further scope for optimization of the thickness of the absorber layer. Through simulations, an increase in the PCE is observed for a reduction in absorber layer thickness, leading to higher performace and lower cost. These findings will be helpful for the research community working in the area of CZTSSe-based solar cells and novel optical sensors.

The performance of a luminescent solar concentrator (abbreviated LSC) is based on the principle of solar light entering a homogeneous medium containing a fluorescent species absorbing it. The light subsequently emitted is trapped by total reflections, concentrated by the geometrical shape, and reemitted into waveguide modes for collection by the solar cells. The main task is to find a suitable luminescent material with good characteristics for this application. Borogermanate glasses based on 43GeO2-27B2O3-6ZnO-7Na2O system with the addition of Pb2+, Cs+, Hal- (Hal=Br, I) ions were synthesised by melt-quenching technique at 1000°C in air atmosphere using quartz crucibles and a platinum stirrer. The glass transition temperature (Tg) was measured with a STA6000 (PerkinElmer) differential scanning calorimeter and was found to be 440°C. The glass samples were heat-treated at temperatures above the Tg for different time to promote the nucleation of the perovskite quantum dots in glass matrix. The initial glass was transparent in the whole visible spectral range from 350 nm to 800 nm. After heat treatment the absorption band near 500 nm and 700 nm occurred for bromine and iodine containing glasses correspondingly. It corresponds to the exciton absorbance in perovskites nanocrystals that were formed during the heat treatment. Herewith the heat-treated samples of bromine-containing glass got a yellow color. In addition, it should be noted that an exciton band position slightly shifts to the large wavelengths from 505 to 515 nm while the heat treatment duration increases. While heating the glass with cesium lead halide perovskite nanocrystals from the room temperature to the glass transition temperature the intensity of the first exciton maximum decreased till its full disappearance at 500-520°C. The decrease in exciton absorbance intensity was due to the thermal splitting of an exciton associated with the planned melting of nanocrystals isolated in the glass matrix. The melting point of nanocrystals can be defined as the temperature of the complete disappearance of the first exciton maximum, since exciton absorption is inherent only in the crystalline phase. The melting point increased with an increase in the mean size of the nanocrystals. The temperature dependence of exciton absorption upon heating and subsequent cooling had the form of a hysteresis curve, which is typical for semiconductor nanocrystals with sizes within 20 nm.

This paper discusses aspects of the experimental research on the inhomogeneity of the spatial distribution of the absolute sensitivity of multi-element photoreceivers based on CCD and CMOS sensors. The expediency of this research is linked to the need to operate calibrated optical radiation receivers, which guarantee optimal conditions for operation in precision instruments, in particular the signal/noise ratio to achieve the specified detection, recognition or measurement characteristics of objects of observation and control. If the distribution of the technological parameters of the optical systems within individual pixels and active regions of the photosensitive matrix is obtained, it will be possible to obtain the distribution of the sensitivity along the working area of the sensor, simplify the algorithm for correcting geometric distortions, improve the calibration, reduce the load on the digital processor. The work considers the main factors influencing the uneven sensitivity of multi-element photodetectors, the results of the systematization on existing methods and technical solutions for the research of optical and electrical characteristics of spatially distributed sensitive photovoltaic transducers are presented. The selection and the arrangement of the installation for carrying out experimental researches of the absolute sensitivity scatter on the working area of the photodetector is justified. The results of the researches could be applied to the metrological validation of optical radiation receivers based on solid-state, multi-element photovoltaic converters from the point of view of their unevenness, as well as the influence of the structure of the photodetectors on the results of measurements and digital image processing.

Recently cylindrical microresonators based on optical fibers were proposed as a promising platform for a variety of photonic devices. The manufacturing accuracy of standard telecommunication optical fibers and the quality of their surface appeared to be high enough to excite high-quality whispering gallery (WGM) modes in their cladding. In addition, the ability to control the WGM propagation along the fiber axis by introducing controlled radius variations allows creating fundamentally new photonic devices based on microresonators, such as delay lines, or optofluidic sensors. Thus, it was proposed recently that triangularly shaped axial variations of effective radius would play a role of a sensor that determines the position of a particle moving inside a fiber-like capillary. In this work, we consider the sensitivity of a similar sensor based on an optical fiber in the task of detecting position of a single microparticle. We study numerically how the dynamics of the whispering gallery modes (WGM) circulating on the surface of an standard optical fiber with removed plastic cladding is affected by a small particle. To be specific, we consider a single molecule of fibrinogen that is put in contact with the surface of the fiber. We have studied both temporal dynamics of optical pulses propagating at the WGM as well as changes in the spectrum of WGM due to impact of the particle. Variations of the effective radius introduced by the particle turned out to be too small to considerably change the dynamics of the optical pulses – no reflection from the particle could be detected. At the same time, spectral measurements appeared to provide possibility to detect particle position.

To support people’s wayfinding activities in crowded buildings minimizing the risks of contamination this paper proposes a method able to generate landmark route and alert instructions using Visible Light Communication (VLC). The system is composed of several transmitters (ceiling luminaries) which send the map information, alerts and the path messages required to wayfinding. The system informs the users, in real time, not only of the best route to the desired destination, through a route without clusters of users, but also of crowded places. An architecture based on a mesh cellular hybrid structure was used. Data from the sender is encoded, modulated and converted into light signals emitted by the transmitters. Tetra-chromatic white sources are used providing a different data channel for each chip. The modulated light signal, containing the ID and the 3D geographical position of the transmitter and wayfinding information, is received by a SiC optical sensor with light filtering and demultiplexing properties. Each luminaire for downlink transmission is equipped with one two type of controllers: mesh controller and cellular controllers do forward messages to other devices in the vicinity or to the central manager services. The light signals emitted by the LEDs are interpreted directly by the receivers of the positioned users. Bidirectional communication is tested. The effect of the location of the Access Points (APs) is evaluated and a 3D model for the cellular network is analyzed. In order to convert the floorplan to a 3D geometry, a tandem of layers in an orthogonal topology is used, and a 3D localization design, demonstrated by a prototype implementation, is presented. Uplink transmission is implemented, and the 3D best route to navigate through venue is calculated. Buddy wayfinding services are also considered. The results showed that the dynamic VLC navigation system enables to determine the position of a mobile target inside the network, to infer the travel direction along the time, to interact with received information and to optimize the route towards a static or dynamic destination, avoiding the threat of contamination in crowded regions.

The article discusses the possibility of using a two-position onboard optical-location system for detecting, classifying and determining the coordinates of the trajectory of objects in the video stream installed on the small aircraft. Every year the requirements for new monitoring systems are becoming more stringent. The data obtained from a single, albeit high-quality, optical sensor can no longer meet the assigned tasks, such as performing search and rescue operations in remote areas, as well as solving problems of finding people in disaster zones. and environmental disasters in a complex noise environment. The system considered in the article includes optical-location sensors, each of which is capable of forming a high-resolution image and classifying the observed objects, as well as, when used together using stereo vision methods, to obtain estimates of the coordinates of the object's trajectory. observed objects. It is shown that combining information in an optical location system allows detecting, classifying and determining the parameters of motion of objects, including people and animals. The article presents the operating modes of the system, and the corresponding restrictions on the conditions for its effective operation.

In this paper we present an optofluidic Fabry-Perot resonator based on polymeric materials. The resonator consists of two plane parallel Bragg mirrors formed by multi-layer optical polymeric films with high reflectivity. The mirrors are based on a commercially available (3M) high performances DBR mirror based on thin polymeric film. The cavity, the mirrors and the substrates are assembled by a lamination process. This approach simplifies the fabrication procedure while retaining high optical surface quality, resulting in a compact and low-cost device. For the optical characterization, white light from a supercontinuum optical source was used to illuminate the FP cavity at normal incidence. The measurements were performed at room temperature when the cavity is filled with water (n=1.3315). Typical reflection dips in the in the optical spectrum have be observed, which correspond to resonances of the FP cavity. The optical resonances have been fit to a Lorentzian curve. We measured a full width at half–maximum of about Δλ=0.023 nm and the resulting quality factor is Q=λ0/Δλ =30300 @ λ0≈697 nm. In order to evaluate the refractive index sensing performance of the device, fluids with different refractive indices has have been injected into the FP cavity by a syringe pump using the integrated microfluidic inlet/outlet. From measurements, the wavelength of the FP resonance shifts toward longer wavelengths as the refractive index of the fluid increases. It is observed that the resonance dip shift has a linear relationship with the fluid refractive index. From the slope of the linear fit we have calculated a bulk refractive index sensitivity of about S= Δλ/Δn ≈ 319 nm/RIU, resulting in a detection limit of about LOD≈1.44×10-6 RIU.

The development of powerful sources with wide spectral coverage is important for many sensing applications. In this paper, various superfluorescent fiber sources (SFS) at 1µm Wavelength using Ytterbium doped (Yb-doped) fiber is studied. Different configurations such as single pass forward (SPF), single pass backward (SPB), double pass forward (DPF), double pass backward (DPB), are compered in terms of spectral bandwidth, power, central wavelength stability and power stability. Double-pass bi-directional sources are employed using loop mirrors. For all cases, maximum power is compared at various laser diode power. Mean wavelength stability is measured between temperature of -40/+60°C to assess potential applications.

Light emitting diodes (LEDs) are opto-semiconductors that convert electrical energy into light energy. Compared to laser diodes, LEDs are less expensive and have longer service life. Primarily fabricated for lighting applications, nowadays are considered also for optocoupler emitter in high-density power electric modules. In this contribution, blue LED based on gallium nitride GaN are evaluated. Generally, manufacturing of electric modules is a very complex procedure. During and after processing of integrated circuits, mechanical stress develops in the materials, especially in the interconnections. Voids, cracks delamination, non-unifom underfill, and misalignments are typical problems related to thermomechanical stress. These become more acute with the constantly increasing complexity and miniaturization of the devices. Therefore, it is crucial to develop strategies to investigate the stress phenomena. Due to stress and strain, deformations in the interconnecting materials alter lattice spacing, and cell parameters of the crystal structures. As a consequence, the energy of phonons associated with certain vibrational modes change. Therefore, the phonon spectrum of the materials changes and each shift of peaks can be compared to the corresponding position in the spectrum for the native original stress-free sample. Raman spectroscopy is an effective technique for stress measurements. In particular, micro-Raman spectroscopy is a powerful tool to unravel localized stress patterns, because a spatial resolution of less than 1 μm may be obtained. In this contribution, a Raman study on interconnections made via soldering and sintering and correlations with physical-chemical properties of both the interconnecting materials and the interconnecting process parameters are presented. Assemblies are realised using GaN-LED and Cu substrates. Stress patterns were first evaluated obtaining Raman line scans along diagonals of the GaN layer. Additionally, full point-by-point hyperspectral mappings of the surface were performed and analyzed. Plastic deformations and creep within the interconnections are observed by the analysis of the Raman signals.

Faraday effect is an optical phenomenon which enables the optical fibre-based plasma current measurement in ITER. Polarimetric optical fibre sensors measure the plasma current (0-17 MA) by exploiting the Faraday effect-induced state of polarization (SOP) rotation of a polarized light propagating in the sensing fibre (placed on the outer surface of the ITER vacuum vessel (VV) section). The Verdet constant serves as a proportionality constant between the SOP rotation and the axial magnetic field induced by the current. However, the presence of unwanted birefringence in the sensing fibre will degrade the measurement accuracy. In this paper, we analyse the effect of the birefringence induced by the fibre bending and twisting as well as and the effect of the temperature dependence of Verdet constant on the plasma current measurement. A polarization-OTDR is employed to interrogate the light; spun fibre is used as sensing fibre. Owing to the difficulty in taking measurements in the ITER representative conditions, a simulation approach is developed—using Jones formalism—to show that the performance of the sensing fibre in terms of plasma current measurement can be characterised by the ratio of precursor fibre linear beat length (LB) over its spun period (SP) i.e., LB/SP. Finally, we propose the minimum required LB/SP ratio of the sensing fibre needed to satisfy the ITER plasma current measurement specifications

The k-wave toolbox is used to construct a compressed-sensing-based photoacoustic imaging model. And the image is reconstructed by the Jacques Hadamard Observation Matrix and the two reconstruction algorithms (OMP and ROMP). The restored image contains the main information of the original image from the visual and PSNR value, it means that the original image can be restored by the combination of Compressed Sensing theory and suitable de-noising method. Compared with Nyquist's sampling method, the amount of data collected by our compressed sensing theory is greatly reduced, which saves resources and space to a great extent. This theory has a great advantage for the photoacoustic imaging of big data, and also can provide the convenience of time for the following image analysis. By the way, it's been experimentally determined that the ROMP reconstruction algorithm has a better reconstruction effect than OMP reconstruction algorithm does.

In turbomachinery, it is very important to monitor vibrations as they may lead to a fast component degradation, lowering the performance and ultimately yielding to fatigue damage. For these reasons, there is a high demand for measurement methods to monitor the behavior of the engine shaft adequately. It is possible to obtain shaft information indirectly from blade tip clearance. Among the different methods used to measure the blade tip clearance, the turbomachinery industry has been working on various non-contact methods. In this work, optical sensors are used to measure the blade tip clearance. Two optical sensors installed circumferentially around the casing to determine the tip clearances of the blades whenever they pass in front of each sensor. These values are then postprocessed using the full spectrum technique to calculate the orbital behavior of the engine shaft. All the data used in this work has been obtained from previous tests at military facilities, where an engine was tested. The optical sensors used consist of a central emitting fiber and two independent concentric rings of receiving fibers. The spreading laser beam emitted by the central emitting fiber hits the target (i.e. the blades) and, then, reflects back to the concentric rings of receiving fibers. The ratio of the light gathered by each ring is then linked to the distance between the target and the sensor. As these sensors rely on optical technology, they do not suffer from any magnetic effect that may arise because of the proximity of the sensor to the target. Nevertheless, it requires a specific software in order to process the gathered data and to provide an interpretation of the events. The key element of this software is the design of a customized algorithm for the detection and tracking of the tip clearance of each blade, which is a necessary step prior to determining the shaft behavior.

UV radiometers are used in many areas. There are many kinds of UV light sources with different peak wavelength and different wavelength range. The broadband UV radiometers are wildly used due to easy to use and low cost. However, there are some obvious disadvantages for the broadband radiometers. They cannot distinguish the spectral characteristics of UV sources. That will cause the spectral mismatch measurement error for the UV broadband radiometers calibration. Recently, the fiber spectroradiometer plays a more and more important role in this area. The fiber spectroradiometer is more portable and low cost compared to the double grating spectroradiometer. We can obtain the spectral characteristics and any UV irradiance using the fiber spectroradiometer. However, for most fiber spectroradiometers, we cannot use them to replace the UV broadband radiometers for the absolute irradiance measurement. There are four key effects for that. The first one is the stray light. Stray light effect is obvious for the fiber spectroradiometer, especially in the UV wavelength range. The second one is the temperature effect. The third one is the non-linearity effect. The fourth one is the bandwidth effect. This effect will cause the measurement error for the spectral distribution of the UV source. In this paper, we research the four factors that reduce the measurement accuracy of the fiber spectroradiometer in UV wavelength range.

With the development of optical frequency comb [1] and ultra-stable laser systems [2], the performance of optical frequency standards have been improved significantly over the past 20 years. The optical clocks based on neutral atom lattice hold excellent stability due to the large signal-to-noise ratio, while those based on trapped ions occupy great uncertainties. The apparatus of the optical ytterbium ion clock includes the physics package and the optical system. Due to the single ion’s weak fluorescence signal and its influence on the signal-to-noise ratio (SNR), the clock’s short-term stability is limited by the quantum limit noise. Therefore, the effective uncertainty evaluation needs the optical clock to operate for a long time, which requires high stability of the optical system. In this paper, the long-term stabilization of the laser system is realized by locking the cooling and re-pumping lasers to the optical frequency comb.

This paper presents the process of creating a gold surface modified by periodic structures by femtosecond laser radiation by two different geometry. The refraction processes of s- and p-polarized light on the gold structured surfaces with the changes in the dielectric permittivity function were studied and compared in this paper. The presence of surface plasmon generation on the rough gold surface in visible region at two frequencies has been established in this work.

GaAs is the basic material used as a substrate for semiconductor architecture for mid- and far-infrared operation. However, due to the high refractive index (n = 3.3) determining high reflectance, the presence of GaAs substrate in infrared detectors generates numerous problems related to (i) Fresnel reflections, (ii) the formation of the etalon effect, (iii) optical crosstalk. Several solutions decreasing these effects were investigated both theoretically and experimentally: AR coating, detectors geometry and surface structurization. The best reflection reduction and at the same time repeatability and low manufacturing cost were obtained for GaAs structurization. These functional surfaces were based on the principles of diffraction gratings and gradient materials and were produced using ion coupled plasma. The fringing effect in 5um-optimized IR photodiode has been reduced up to 4 times in comparison with standard flat detector.

The original image is reconstructed with the help of the compressed sensing based on the k-wave photoacoustic imaging model. The Hadamard matrix is selected as the observation matrix, and the GPSR reconstruction algorithm is used to restore the image of some selected regions. The results show that the noise exists but the reconstructed image contains the main information of the original image. It indicates that when the transverse noise is removed, the original image can be reconstructed well with the help of compressed sensing theory. Only a small amount of data will be collected through the compressed sensing theory, and it means that the pressure on storage devices can be greatly alleviated. And it also saves time for follow-up processing of images. This is of great significance for photoacoustic imaging with high resolution and high data volume. In addition, the simulation experiment verifies the superiority and reliability of the k-wave simulation platform.