This PDF file contains the front matter associated with SPIE Proceedings Volume 11354 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Visible Light Communication (VLC) is currently a research topic under severe development due to the possibility to provide high data rates and handle the general, worldwide demanding need for climbing bandwidth. VLC uses Light Emitting Diodes (LED), operating in the visible part of the electromagnetic spectrum, as optical sources for optical wireless communication. The technology provides dual functions of lighting and communication. Its main advantages are related to high data rates, higher bandwidth, reliability and a secure data transmission compared to other wireless technologies (such as Wi-Fi). This paper explores the use of VLC to establish different optical communication links for bidirectional communication between vehicles and infrastructures, using 3 links, namely Infrastructure-To-Vehicle (I2V), Vehicle-To-Infrastructure and (V2I) communication. The proposed application uses VLC to support autonomous navigation of mobile robots inside a modern, automated warehouse, providing navigation and stock management services. Specific coding schemes are used in each optical link using On-OFF keying modulation. In the I2V link RGB white LEDs are used to allow simultaneous modulation of the emitters embedded in each LED, which enables wavelength division multiplexing of the transmitted optical signals. The detection is based on a based a-SiC:H pin-pin photodetector with tunable sensitivity in the visible range. Different indoors communication scenarios are presented and the system performance on bit error rate is discussed using a bit parity error control methodology. Requirements related to synchronous transmission and flicker mitigation were addressed to enhance the system performance.

Optical wireless communication has been widely studied during the last years in short-range applications. This paper investigates the applicability of an intuitive wayfinding system in complex buildings using Visible Light Communication (VLC). Typical scenarios include finding places, like a particular shop or office, guiding users across different floors, through elevators and stairs. 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. At the receiver side, the modulated light signal, containing the ID and the 3D geographical position of the transmitter and wayfinding information, is received by SiC photodetector with light filtering and demultiplexing properties. Since lighting and wireless data communication is combined, each luminaire for downlink transmission become a single cell, in which the optical access point (AP) is located in the ceiling and the mobile users are scattered within the overlap discs of each cells underneath. The light signals emitted by the LEDs are interpreted directly by the receivers of the users positioned underneath. The effect of the location of the Aps is evaluated and a model for the different cellular networks is analyzed. Orthogonal topologies are tested, 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 calculated. Buddy wayfinding services are also implemented. The results showed that the system make possible to determine the position of a mobile target inside the network, to infer the travel direction along the time and to interact with information received and to optimize the route towards a static or dynamic destination.

The redesign of the trajectories though complex, can be accomplished by the application of methods for navigation, guidance and combination of knowledge of road traffic control of vehicles. In this work the communication between the infrastructures and the vehicles, between vehicles and from the vehicles to the infrastructures is performed through Visible Light Communication (VLC) using the street lamps and the traffic signaling to broadcast the information. Vehicle headlamps and taillights are used to transmit data to other vehicles or infrastructures allowing digital safety and data privacy. 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) devices, with light filtering properties, are used. The primary objective is to control the arrival of vehicles to an intersection and schedule them to cross at times that minimize delays. A further objective is to allocate delays between left-turns and forward movements, moderating the speed and slot between vehicles travelling in these directions, maintaining a safe distance from one to another. Pedestrians and bicycles are incorporated. A Vehicleto-Everything (V2X) traffic scenario is stablished and bidirectional communication between the infrastructure and the vehicles is tested, using the VLC request/response concept. A phasing traffic flow is developed as a proof of concept. The experimental results confirm the cooperative VLC architecture showing that communication between connected cars is optimized using a request/response concept. An increase in the traffic throughput with least dependency on infrastructure is achieved.

In the field of space remote sensing, a visible CMOS detector with a long line of small pixels is needed. In order to meet the requirement of high-resolution earth observation, this paper designs a long-line CMOS detector integrated with PIN detector and readout circuit, based on 0.35 micron process. To reduce the equivalent input noise of the device by true correlation double sampling, CTIA integral amplifier followed by four sampling follow circuit is adopted. In order to meet the requirements of high sampling rate of imaging detection, a four sampling long-line CMOS detector with 10 MHz sampling frequency is designed in this paper. By reducing the width to length ratio of the first stage P-type following transistor to decrease the bus parasitic capacitance and reducing the bias voltage of the P-type following load transistor to increase the driving current, thus the sampling frequency of the read-out circuit is increased from the original 2 MHz to the 10 MHz, which effectively improves the readout frequency of the long-line visible light CMOS detector, In order to achieve true correlated double sampling and reduce the equivalent input noise of the device, the muliti-sampling is used to connect CTIA integral amplifier. Then a low noise and high sampling rate CMOS detector is developed. Through the test, the SNR of CMOS detector can be more than 350, which is twice as that of conventional reading technology. the CMOS detector possesses an equivalent input noise electron less than 50e when the integral time is 200 us and the area of photosensitive is 20 um × 18 um, it can work steadily at the sampling rate of 10MHz, its MTF can exceed 0.5 when it work at 4MHz. The linearity, the output swing and the sensitivity of the detector can meet the requirements of the Aerospace remote system. The development of the CMOS detector has laid an important theoretical foundation and practical value for the future ultra high speed and high definition imaging detection.

In this paper, a novel Field Programmable Gate Array (FPGA) based instrument for Time Correlated Photon Counting (TCPC) is reported which takes advantage of the photon number resolving ability of newer single photon detectors technologies, such as silicon photomultipliers (SiPM). Utilizing the received photon number in the formation of the TCPC histogram will enable faster measurements in comparison to Time Correlated Single Photon Counting (TCSPC) as less information is being discarded per excitation pulse. The concept of (TCSPC) and the differences with TCPC are introduced, as the well as the advantages of using TCPC when using a number resolving photodetector such as a SiPM rather than a traditional Single Photon Avalanche Diode (SPAD). The design and performance of the system is reported. An 8-stop TCPC system is presented along with a hardware solution to handle time correlations in real-time on-chip rather than in post processing. A system accuracy of 42ps RMS has been demonstrated.

The accurate determination of the azimuth of a given direction, e.g., the true (geographic) North, is of fundamental importance in many fields. Just as few examples, it guides buildings construction in civil engineering, supports environmental and cartographic surveys, allows the correct positioning and stability control of concentrating solar power plants, as well as of airport installations, provides the geographic North reference for geomagnetic measurements, contributes to the interpretation of the orientation choices of ancient constructions in archeoastronomy, can be the primary benchmark to calibrate other compasses or gyroscopes. When aiming at reaching azimuth measurements with accuracies well below 1°, magnetic compasses are unreliable: firstly, they indicate the magnetic North rather than the geographic one; secondly, they are heavily influenced by possible surrounding ferromagnetic items.

Lock-in thermography (LIT) is a non-destructive testing technique with a broad spectrum of applications, spanning from detection of manufacturing defects in industrial samples to early diagnosis of diseases in hard and soft tissues. Nevertheless, commercialization and wide-spread adaption of LIT has long been impeded by the cost (usually $10k-$100k) and size of infrared cameras. In this paper, we demonstrate that this cost and size limitation can be overcome using cell-phone attachment infrared cameras/sensors. Developed low-cost and portable LIT systems use an intensity-modulated near infrared light for illumination while detecting thermal signatures by the low-cost cellphone attachment infrared camera (Seek thermal compact; Android). While the nominal frame rate of camera is less than 9fps, we have deciphered the communication protocol and frame information structure of the camera and set up packets of information and send them to the camera’s default endpoint address and, subsequently, acquire frame data from camera through a corresponding pipe. As such, the developed platform can control camera attributes through a simple USB interface while achieving a stable high frame rate of 33fps. To demonstrate performance of developed low-cost and portable system, two types of LIT experiments were conducted: (i) in response to the recent legalizations of marijuana in Canada, we interrogated photothermal responses of commercially available oral fluid latral flow immunoassays (LFAs), demonstrating reliable detection of THC (the psychoactive substance of cannabis) at concentrations as low as 2 ng/ml. (ii) To demonstrate ability of the system in early detection of dental caries, artificially induced early caries were created on healthy enamel surfaces and imaged with the low cost and portable system at different stages of formation. Results, suggest ability of the system in detection of caries at very early stages when neither x-ray nor visual-tactile inspection can detect them. Both sets of experiments clearly demonstrate the promise of the developed low-cost and portable LIT system in producing reliable LIT images, paving the way for translation of this technology to industry.

Biosensors are expected to provide fast, sensitive, and robust detection at low cost. Despite all these constraints which weigh on the development of emerging technologies and conception of new prototypes, the major challenge is still to carry out measurements in complex matrices and hard-to-reach environments. Optical fibers are perfectly suited to fulfill these requirements. In this paper, we investigate the use of tilted fiber Bragg gratings (TFBGs) photo-inscribed in the core of telecommunication-grade optical fibers as biosensors. Thanks to their high refractive index sensitivity, they are able to track molecular interactions happening on their surface. We present different strategies to use them for label-free immunoassays. Bare, gold-sputtered, gold electroless-plated (ELP), and hybrid configurations were functionalized with antibodies, aiming at the detection of cancer biomarkers. We discuss the relative performances of these four configurations and show that each leads to singular key features, driving their own selection as a function of the target application. The optrodes were tested in laboratory settings but also in gelled phantoms and in human resected lung tissues to study the surface plasmon excitation inside complex media, and to discriminate the nature of the tissue through biomarkers detection.

Biogenic amines, such as putrescine are potential indicators of food storage condition and deterioration. The real time measurement of their concentration in food may become an important method of food control. It was found that putrescine diffuses through a thin layer made from a solution of Poly(ethylene-co-vinyl acetate) (PEVA) and maleic anhydride. Poly(ethylene-co-vinyl acetate) is a common non-chlorinated vinyl capable to adsorb specific analytes as putrescine which upon diffusion, reversibly binds to the maleic anhydride causing the polymer swelling resulting in spectral changes from the optical point of view. Long Period Fiber Gratings coated with 30 nm titanium dioxide, a high refractive index material used to increase the intrinsic sensitivity to the external refractive index, were overcoated with a thin layer of maleic anhydride doped Poly(ethylene-co-vinyl acetate). When exposed to solutions containing small concentrations of putrescine the resonant band corresponding to the LP_1,6 cladding mode was found to move to shorter wavelengths. The observed blue shift corresponds to the increasing concentration of putrescine in the fiber sensor structure. Further work is being carried out to improve the sensitivity and the limit of detection of the sensing system as well as to increase range of operation, which is presently limited to 0.3 to 0.5 M.

Long Period Fibre Gratings (LPFGs) were fabricated by femtosecond (fs) laser direct writing in a standard single-mode fibre (SMF-28e) to measure variations in the surrounding refractive index (SRI). The sensing sensitivity of these structures was optimized with the deposition of homogeneous thin layers of titanium dioxide (TiO₂) by physical vapour deposition (PVD) process. A set of LPFGs were coated with different thickness layers of TiO₂, and the spectral features were monitored for different SRI solutions. The wavelength shift and the optical power variation of the LPFG minimum attenuation band were measured achieving sensitivities of ~570 nm/RIU at using SRI near to 1.3600 in the case of the LPFG coated with 60 nm of TiO₂, a 10-fold increase over the corresponding for a bare LPFG. For SRI values higher than the cladding refractive index, a sensitivity over ~3000 nm/RIU was determined for 30 nm of TiO₂ thick film, a region where the bare LPFGs are useless. For 30 nm of TiO₂, the optical power variation follows a quasi-linear function of the SRI, with a range of ~10 dB. Moreover, values as high as 50 and 120 dB/RIU at 1.3200 and 1.4200, respectively, can be obtained by choosing the proper film thickness. Preliminary studies revealed that coating fs-laser direct writing LPFGs with titanium dioxide improves their performance.

Composite materials are finding their way into aerospace applications thanks to their high stiffness-to-mass ratio. Nevertheless, composite components require frequent inspections because of their sensitivity to critical damage. Damage as small as barely visible impact damage (BVID) can grow as result of structural loading, with component failure as possible outcome. Optical fibre sensors (OFS) are considered excellent candidates for permanently installed structural health monitoring (SHM) systems, owing to their many advantages over electrical sensors. Current state-of-the-art BVID detection with OFS has so far however been limited to proof-of-concept demonstrations at low technology readiness levels. In this work, we equipped a total of 16 coupons, made of 5 different state-of-the-art composite materials, with aerospace compatible embedded or surface mounted optical fibre Bragg gratings (FBGs). We impacted each coupon at two locations and acquired the FBG reflection spectra before and after each impact. We first demonstrate how changes in the Bragg wavelength and in the Bragg peak shape can be quantified when the FBGs are exposed to the (non-)uniform strain field of BVIDs. Second, we show that this method was able to successfully detect the BVID in all considered scenarios and that in most cases, it was able to also locate the damage within an uncertainty of ±1 FBG location. Finally, we show the reliability of this method in terms of repeatability and considering the effects of temperature changes and on-ground airplane vibration. To the best of our knowledge, we are the first to use in-flight-compatible embedded and surface mounted FBG-sensors for the detection and location of BVIDs on aerospace-grade composite materials. These results motivate the use of FBG sensors as a permanent sensor network for cost-efficient damage detection in composite aerospace components for locally monitoring damage-prone locations.

We investigate possibilities of using a multicore fiber containing fiber Bragg grating (FBG) in sensing applications. We use the advantages of the femtosecond point-by-point technique to inscribe FBGs in the selected cores of polyimidecoated 7-core fiber. Besides the results on 3D shape sensing we present new approaches for acoustic wave detection and environment refractive index sensing. In particular, we show that spatial division multiplexing with a multicore fiber allows one to create multipoint acoustic sensor based on a single laser source. In addition, to detect the change in environment refractive index by using point-by-point FBG, there is no need in fiber coating removal. Thus, durability of the fiber along with the FBG inscription approach is of great potential for fabrication of next generation multiple parameter sensors.

In this study, we assess the feasibility of highly dense fiber Bragg grating (FBG) arrays for real-time temperature measurement during Nanocomposites (NCs)-enhanced laser ablation (LA) of pancreas tissue. FBG arrays were fabricated with the femtosecond point-by-point writing technology. Each highly dense array contains 25 FBGs with a grating length of 0.9 mm and an edge-to-edge distance of 0.1 mm. As alternative fiber sensors, we used commercially available acrylatecoated FBG arrays containing 5 FBGs. Temperature measurements by the highly dense FBG array were compared to thermal camera readings during laser irradiation of water samples. The augmented thermal effect produced by special NC comprising of a polydopamine matrix embedded with gold and copper was evaluated during the irradiation of an ex vivo phantom. The phantom consisted of a blended porcine pancreas tissue mixed with the NC; tissue mixed with water was used for control. The results clearly demonstrate that the highly dense arrays better detect the peak temperature and temperature distribution. The NC presence increased the maximum temperature reached during LA from 48°C (control) to 90°C (NC) at 2 mm, and from 33 °C to 36°C at 4 mm distance from the laser tip. The low spatial resolution of the commercial arrays produced an underestimation of the peak temperature by 2°C (control), and by 1°C (NC) at 4 mm. These results highlight the importance of the proper selection of the measurement system characteristics, especially when high temperature gradient should be measured in biological tissues undergoing thermal ablation for cancer treatment.

In this study, we report on the thermal regeneration of Type-I tilted fiber Bragg gratings produced in hydrogen loaded single-mode optical fiber (SMF28). Both 193 nm excimer laser and 266 nm femtosecond pulses were used to inscribe the gratings through phase mask technique. We show that the regenerated cladding modes resist, without degradation, up to 910 ◦C and show the same refractometric properties as in non-regenerated tilted gratings.

We demonstrate a single pixel, compressed sensing (CS) approach for fibre Bragg interrogation. We reduce optical source and detector complexity by employing a broadband ASE source and a single-pixel detector respectively. Reconstruction is aided by convex optimisation, which provides the requisite sampling compression, yielding reconstruction accuracies approaching those of uncompressed measurements.

Plastic solid waste management is a growing field in many countries that is supported by governmental legislation. Plastic recycling is widely concerned since the other methods such as, landfilling and burning, harm the environment and are economically inefficient. Different methods have been proposed in literature based on the physical and thermal properties of the plastic but they are labor intensive and time consuming. The most promising method is based on the optical spectral sensing in the infrared range. It is non-destructive and time-efficient especially when coupled with machine learning models such as chemometrics. However, the infrared spectrometers are bulky, expensive and require building a model for each unit. Micro-electro-mechanical-system (MEMS) Fourier-transform infrared spectroscopy (FTIR) spectrometers are designed to be portable and lower in cost and in power consumption than traditional spectrometers. In this work, we present a classification predictor of two plastic categories Polyethylene Terephthalate (PETE) and Polypropylene (PP) using a portable MEMS FTIR spectrometer. PETE and PP samples are collected with different shapes and surface curvatures and the samples diffuse reflectance spectra are measured at 10 different surface spots per sample. The measurements are averaged and processed to mitigate the physical scatter effects. A multivariate linear classification chemometrics model is built and validated using one sample out cross validation. The classification using one principle component reaches a classification success rate of 100 % opening the door for low cost portable device for accurate plastic sorting.

With the rapid development of industries such as mining activities, metal plating, pesticides and fertilizers manufacture, petroleum refining etc. heavy metal pollution has become a global threat. Unlike organic contaminants heavy metal ions are not biodegradable and tend to accumulate in soil, water and living organisms once being released in the environment. Heavy metal ions accumulated in an organism exceeding their critical level cause various diseases and disorders. That is why it is so vital to monitor the presence and concentrations of heavy metal ions in wastewaters. In this study we propose a new approach to solution of inverse multiparametric problem – determination of concentrations of 5 types of ions (Co²⁺, Ni²⁺, Cu²⁺, SO42-, NO3-) employing Raman and absorption spectroscopy, via adaptive data analysis methods. Such approach beneficially differs from conventional chemical analysis since it allows simultaneous and non-invasive monitoring of all the ions present in the aqueous solution compound in real mode. Aqueous solutions of CuSO₄, NiSO₄, CoSO₄, Cu(NO₃)₂, Ni(NO₃)₂, Co(NO₃)₂ salts were studied. The database consisting of 3854 absorption spectra and 3823 Raman spectra of these solutions was obtained. Adaptive data analysis methods comprise various data-driven methods which don’t require any apriori knowledge about the object of the study. This peculiarity beneficially distinguishes such methods from conventional modal-based approach especially concerning multicomponent aqueous solutions of heavy-metal ions where non-linear interactions take place. In this study artificial neural networks of various architectures as well as partial least squares regression were used in order to solve inverse multiparametric problem of optical spectroscopy. Results of the application of all the methods are discussed in the report. This study has been performed at the expense of the grant of Russian Science Foundation (project No. 19-11-00333, K.A.L., S.A.B., I.V.I, T.A.D., S.A.D. – conducting experiment, processing of spectra, discussion) and was supported by Foundation for the Advancement of Theoretical Physics and Mathematics “BASIS” (project No. 19-2-6-6-1, O.E.S. – application of artificial neural networks).

We present laser-based spectroscopy in the mid-infrared spectral region inside novel anti-resonant (AR) hollow core fiber (HCF). AR-HCF used in this work has small (few dB/m) attenuation near 4 µm and exceptionally small bending losses. This gives perspective for compact all-fiber-based mid-infrared chemical sensors with optical path lengths of several meters. For gas sensing demonstration, a distributed feed-back (DFB) quantum cascade laser (QCL) operating near 4.54 μm and a 3.2-m-long fiber were used to detect nitrous oxide (N₂O) and carbon monoxide (CO) using direct laser absorption spectroscopy (DLAS) and wavelength modulation spectroscopy (WMS).

Global climate change demands better use of energy and stricter limitations on the emission of greenhouse gases. Additionally, due to technological advances, automation in process analytics demand better in-situ sensor technologies. For this Raman spectroscopy is suitable, but the technique itself needs to be enhanced to be viable. Here, we present a first analysis for the suitability of fibre-enhanced Raman spectroscopy (FERS). We studied environmental gases by means of Raman spectroscopy with hollow core photonic crystal fibres (HC-PCF).

The utilization of an external modulation allows the coherence of laser probe pulses launched to the optical fiber to be maintained in coherent optical time domain reflectometry. However, continuous-wave (CW) component product of external modulation could considerably degrade the sensitivity of the system. In this paper, we discuss the effects of finite extinction ratio in different external modulation methods and the attempts that have been made in order to overcome these effects. A model is proposed to analyze the impact of external modulation CW component on backscattered optical signal of probe pulses from optical fiber as a function of extinction ratio, fiber length and pulse widths. External modulation can be achieved by acousto-optic modulation or electro-optic modulation. From the results obtained with the model, the advantages and drawbacks of each technology are discussed, subsequently leading to required prospective developments and refinements.

Optical fibre Fabry-Perot interferometers (FPIs) composed by different ultracompact size cavities were fabricated in SMF-28 fibers by using femtosecond (fs) laser micromachining assisted with hydrofluoric (HF) acid. This is made possible due to the high spatial resolution obtained from a non-linear absorption process triggered by the fs-laser exposure. The proposed structures consist of refractive index modified areas written longitudinally from bottom to top by a fs-laser beam that is focused with a 100× oil immersion lens. Then, the inscribed fiber was immersed in a 10 % HF acid solution for 105 minutes. Different FPI structures were developed in the fiber core region, following the same protocol as before, resulting in single open cavities with optical paths from 15 μm to ~ 23 μm length. Inline dual cavities, each with the same optical path but separated by ~ 8 μm length of unmodified fibre core, and a 23 μm wide single FPI cavity followed by an 8000 μm fibre optic cleaved facet were also fabricated. This last configuration results on a convolution of multiple interferences with high and low frequencies capable to monitor different parameters. All the configurations were tested to gas pressure variation and when submitted to different controlled gaseous environments, namely 100% of N₂ and 50 % of CH₄/N₂ achieving sensitivities in the order of 4 nm/MPa and 4.8 nm/MPa, respectively, in pressure range 0-1 MPa with self-temperature compensation. In conclusion, we presented the simultaneous measurement of gas pressure and temperature in the case of the single FPI cavity followed by an 8000 μm fibre optic cleaved facet. Given the preliminary results presented, further research is necessary to improve the performance of such FPIs sensor, for instance, optimization of the cavities sizes for achieving refractive index measurements is still to be done, as well as a more thorough optical characterization.

D-dimer is a useful diagnostic biomarker for deep vein thrombosis or pulmonary embolism, collectively referred to as venous thromboembolism (VTE). The ability to detect in real-time the amount of D-dimer with a fast and reliable method is a key step to anticipate the appearance of these diseases. The combination of fiber-optic–based platforms for biosensing with the nanotechnologies is opening up the chance for the development of in situ, portable, lightweight, versatile, reliable and high-performance optical sensing devices towards lab-on-fiber technology. The generation of lossy mode resonances (LMRs) by means of the deposition of nm-thick absorbing metal-oxide films on special geometric-modified fibers allows measuring precisely and accurately surface refractive index changes, which are due to the binding interaction between a biological recognition element and the analyte under investigation. This approach enhances the light-matter interaction in a strong way, thus turning out to be more sensitive compared to other optical technology platforms, such as fiber gratings or surface plasmon resonance. Here, the results of a highly specific and sensitive biosensor for the detection of D-dimer based on LMR in fiber-optics are presented by monitoring in real-time the shift of the LMR related to the biomolecule interactions thanks to a conventional wavelength-interrogation system and an ad-hoc developed microfluidics. A detection limit of 100 ng/mL, a value 5-fold below the clinical cutoff value, has been attained for D-dimer spiked in human serum. The comparison of the results achieved with proteomics-based methodologies, which allows for the identification of betaand gamma-chains of fibrinogen, demonstrates the ability of our platform to specifically (<90%) recognize D-dimer.

An optical fibre dosimeter based on a terbium-doped gadolinium oxysulphide (Gd₂O₂S:Tb) inorganic scintillating detector (ISD) was recently proposed for external beam radiation therapy (EBRT) dosimetry applications. Although it has demonstrated many promising characteristics, an energy dependence was found during percentage depth dose (PDD) measurements. In this study, the response of a Gd₂O₂S:Tb based ISD to superficial x-ray energies and 6 MV EBRT photon beams has been measured and compared to absorbed dose values generated using a Monte Carlo (MC) model of a superficial x-ray treatment unit and a clinical linear accelerator treatment head. The relationship between beam energy and the response of the scintillating phosphor was investigated for depth dose and beam profile measurements. An overresponse was observed during physical measurements in the kV range that is indicative of an energy-dependent variation in scintillation efficiency of the Gd₂O₂S:Tb. This study indicates that this intrinsic energy dependence may result in a significant increase in signal at kV energies relative to MV irradiation, which was not accounted for in the MC model.

In the field of radiation therapy, optical fiber dosimeters (OFD) offer several advantages over conventional dosimeters for real-time dosimetry. Their sensing tips can be small in size affording them the potential for high spatial resolution capabilities. In previous work, a novel inorganic scintillating detector (ISD) based on Gadolinium Oxysulfide (gadox) was fabricated for in vivo optical fiber dosimetry of conformal small animal irradiators. The performance of this detector was evaluated for 40 and 80 kVp imaging beams and the 220 kVp therapy beam of the Small Animal Research Platform (SARRP). The purpose of this study was to use a validated Monte Carlo (MC) model of the SARRP to investigate (i) dose absorption in the ISD active volume and (ii) dose perturbation by the inorganic scintillating phosphor volume. A comparison was also drawn between the perturbation by the gadox phosphor and a ZnS-based phosphor. The gadox-based detector was seen to cause high levels of dose perturbation in the radiation field, leaving significant dose shadows in the irradiated media. The use of ZnS:Ag phosphor reduces the perturbations with just over half as much dose absorbed relative to the gadox phosphor. An optimized ISD design which utilizes the higher light yield of the less perturbing ZnS:Ag phosphor to allow for a smaller high-density active volume, and significantly mitigating kV dose perturbation, has been proposed.

This study forms the first part of research into enhancing the forward and back scattering of light in an optical fibre using nanoparticles (NPs). This approach has the potential to enhance the sensitivity of optical fibre sensing by increasing the signal-to-noise ratio. The work described in this paper is focused on understanding the scattering of light by a suspension of NPs in refractive index matching liquid. It was noted early in the experimental work that rheological effects related to the viscosity and flow of the liquid affect the scattered light measured and therefore these effects are considered in the analysis. Gold nanoparticles in the tens to hundreds of micrometre size range were selected as the scattering particles based on their optical properties. These are suspended in a refractive index liquid with a similar refractive index to the optical fibre core. Effort was needed to transfer the NPs from their aqueous sodium citrate solution to the paraffin based solution. We investigated two types of interaction with the optical fibre: (i) dropping the NP suspension onto the end of a single-mode optical fibre and (ii) using the NP suspension as an interface between two single-mode optical fibres. It was noted that the surface tension of the liquid, the diameter of the fibre and the spacing between the fibres in case (ii) influence the reflected and transmitted light. In case of excess liquid, droplets flowed down the fibre and interestingly in case (ii) modified the reflected and forward transmitted light as it passed across the fibre interface. Our initial findings are that the influence of the gap between two optical fibres decreased after dropping refractive index liquid into the gap after fibre collimation, which is a beneficial result for understanding the influence of scattered light from a liquid containing NPs. Note, the position between the two fibres can also change due to the weight of the droplet and the fibre ends had to be re-collimated to investigate the influence of the moving droplets. These results will be expanded by additional experiments and modelling of the scattering from the nanoparticales and droplets.

The funding landscape in Europe is complex and potentially overwhelming with a multitude of pan-European and national funding mechanisms available. This presentation explores some of the options available by the European Union and Research Council as well as presenting more detail on Research Funding in the UK around BREXIT.

We present a suspended-element silicon photonic crystal membrane sensor with a diaphragm area of 12 μm by 15 μm suitable for free-space ultrasonic acoustic measurements. The sensor is based on the position-dependent directional coupling between neighbouring photonic crystal edges and exhibits compatibility with broadband optical sources, low insertion loss, and more freedom in the mechanical design. By tuning the wavelength such that both time-averaged outputs of the directional coupler were balanced, a differential detection scheme was implemented where common noise sources were suppressed while enhancing the sensor signal without additional photonic components. Using a coiled speaker, the dynamic acoustic response of the sensor from 10 kHz to 80 kHz was measured and we report a peak system response in the difference signal at 40 kHz with a sensitivity of 40 μV/Pa. The compact size and improved mechanical frequency response of these integrated photonic sensors make them suitable for array applications, particularly for the study of fluid dynamics involving high Reynolds number phenomena.

Significant enhancement of the longitudinal magneto-optical effect accompanied with high transmission was demonstrated by experimental measurements and confirmed by numerical simulations for small angles of incidence. The work was led with a subwavelength resonant structure consisting of a 1D dielectric grating structured on top of a magneto-optical waveguide. The simplicity of the fabricated structure associated to the significant achieved magneto-optical effect, make the structure a promising tool for applications like magnetic field sensors or in non-destructive testing.

This paper studies two different approaches for evanescent wave optical sensing: an horizontal one and a vertical one. In horizontal waveguides, the evanescent wave is distributed on the upper cladding. While in a vertical configuration, the evanescent wave is distributed on the left and right sides of the waveguide. In an horizontal configuration the evanescent wave can be also on both sides of the waveguide in order to increase the optical energy for sensing if the substrate under the waveguide is locally removed. However, in this configuration to achieve sensitive devices, the layers have to be freestanding and thin [1] limiting practical implementations of such approaches. Furthermore, very few materials can be defined as tall and thin in the case of a vertical configuration, as the deposition techniques often used (PECVD/LPCVD) are meant for films in the couple of micron range. In the following we will investigate the properties of the materials used but also the fabrication feasibility for both configurations.

Development of sensors for detection of volatile organic compounds (VOC) have a high demand in food storage applications, medical industries and in detection of leaks in industrial distribution lines. In this work, theoretical and experimental studies of a sensor based on transmission volume and surface holograms functionalized with MFI type nanozeolites studies towards different VOCs such as methanol, ethanol, toluene and acetone are presented. The gas sensing response of the different hologram configurations has been investigated using a custom-designed optical gas sensor setup suitable for different gas exposure conditions. The role of the zeolite nanoparticles has been studied by measuring the spectral response and diffraction efficiency changes under exposure to analytes with different molecular size and polarizability. This allows an optimum sensitivity, response time, selectivity, repeatability and reversibility of the sensors to be achieved.

In this work, in addition to the sensor application of coated optical microresonator, we show the phase transition of Pd-H system using WGMs. WGMs are propagating on a cylindrical microresonator which is based on a single mode optical fiber coated with a desired metal thickness and desired morphology. Light coupling is achieved by tapered fiber connected to a tunable laser working in the infrared wavelength. WGMs are observed and tracked by transmitted laser light. The sensor consisting of the resonator and a tapered fiber is placed in a metal chamber that is connected to the gas tanks. Desired concentration of the gas is achieved by mixing the carrier gas (nitrogen) and hydrogen. By increasing or decreasing of the hydrogen concentration in the sensing chamber, palladium layer expands or contracts. The change in the radius of the resonator translates in to shifts in spectral positions of the WGMs. However, these expansion or contractions rates are different for different phases of the Pd – H system. For instance, solid solution of hydrogen in palladium, represented by α has the lowest expansion or contraction. In contrast β phase has the highest rate. These phase transitions and intermediate phase are shown using the WGMs.

The sensitive, selective and real-time detection of odors, in the form of volatile organic compounds (VOCs), remains an important challenge in modern science. As a result, in the field of artificial olfaction, subsequent advances in sensor technologies have given rise to a variety of gas sensors spanning to address a large plethora of applications such as medical diagnostics, quality control, environmental monitoring and etc. Currently, however, the development of electronic nose (eN) technology has garnered the most attention with its biomimetic approach of multi-sensor systems. This study focuses on such an opto-eN system, which utilises Surface Plasmon Resonance Imaging (SPRI) as its transduction technique, operating in gas phase. The immediate requirement, therein, lies on the robustness of these system, especially in their ability to produce reliable measurement during in situ/on field applications. In this regard, temperature and humidity variations, regionally and seasonally, have shown to cause the most significant impact. Their influence on the signal is integrated, with chemical and physical contributions arising from both the immobilized sensing receptors and the metallized SPRI prism, responsible for the plasmonic behavior. Accordingly, we began by optimizing the prism metallization through a complete numerical study on metal layer configurations and thickness choices. The chosen structures were then experimentally compared for optimum performance and stability. Finally, the selected Chromium/Gold (Cr/Au) prism sample was used to test the effect of humidity and temperature. The developed numerical model was demonstrated to be a useful technique, which was experimentally coupled at various temperatures to obtain a fundamental understanding of the adsorption of water on gold surfaces. We believe that the comprehension of this phenomenon and its possible implications will be transferable and thereby useful for sensors beyond the opto-eN application.

We describe a combination of Tunable Diode Laser Spectroscopy and Range Resolved Interferometry that enables multipoint gas detection using a single laser and photodetector. Tunable Diode Laser Spectroscopy (TDLS) permits gas detection via the measurement of its optical absorption while a diode laser is tuned through an absorption line. Range Resolved Interferometry (RRI) employs a signal processing technique previously used for position sensing and vibrometry. The principle of operation is the sinusoidal modulation of the emission wavelength of a laser which is coupled into a network of interferometers. The detected signal is demodulated to give the signal amplitude within each interferometer. Signals from different interferometers can be distinguished based on the optical path length difference, enabling continuous interrogation of multiple measurement channels simultaneously. In this work, a number of gas cells are combined with optical fibre to create systems of nested interferometers, including a combination of gas cells and a common local oscillator. The laser wavelength was modulated with a combination of fast sinusoidal (49kHz) and slow (2Hz) ramp wave forms, the ramp sweeping the central wavelength of the laser through the methane absorption line at 1653nm. The intensity signal for each cell was extracted using the RRI technique in order to measure the methane concentration within each cell A Mach-Zehnder topology allows the measurement of methane at concentrations as low as 200ppm. We discuss the potential performance of other topologies that are more suitable for field deployment.

A multi gas analyzer for in line composition evaluation has been developed and optimized for the detection of fuel gas main components. The system has been designed for unmanned and remote operation on natural gas pipelines and biogas production plants as a low cost and low maintenance alternative to current industry standard gas chromatographic methods which are used to evaluate the mixture heating value as well as to detect undesired contaminants. The system does not require any consumable supply and could also be considered as a competitor of most available non-analytical techniques for the determination of heating value, which in our case can be obtained from actual gas composition through application of the relevant calculation as described by ISO 6976 norm. A high-power, lighting grade multimode laser diode pump has been used to reduce both manufacturing and operation costs as well as power supply requirements. Sample gas is flowing in a cell rated for high pressure operation and the spectral analysis is performed by a custom design, high throughput lens based spectrometer developed for this application featuring an industrial CMOS camera as a low cost, high sensitivity and low noise focal plane array. The use of a multimode pump operating over a wide temperature range and a non-cooled detector array are the source of several issues in the recorded spectra which have been addressed with the developement of custom image processing and fitting software routines to cope with broadened, drifting Raman spectra. This approach has been lab calibrated against the single components (such as methane, ethane, propane, n-butane, iso-butane, nitrogen, oxygen, water vapour, carbon dioxide, carbon monoxide, hydrogen) and tested with certified gas mixtures made to simulate the concentration levels commonly found during field operation at total absolute pressures ranging from 1 to 6 bar.

A theoretical study of a new sensing concept based on Bloch surface waves (BSWs), which utilizes a onedimensional photonic crystal (1DPhC) represented by a multilayer structure, is presented. 1DPhCs have a number of useful features, including physical and chemical robustness. We model the response of a BK7 prism/multilayer/analyte system in the Kretschmann configuration for s- and p-polarized waves. We show that the 1DPhC supports surface electromagnetic waves at frequencies within the forbidden transmission band of the multilayer structure. A dip in the reflectance spectrum for s-polarized wave represents the excitation of the BSW and this is demonstrated for air and gaseous analytes.

The optical determination of oxygen partial pressure is of great interest in numerous areas, like medicine, biotechnology, and chemistry. A well-known optical measuring approach is based on the quenching of luminescence by the oxygen molecules. The conventional approach consists in measuring the intensity decay time and relate it to the oxygen concentration through a multi-parametric model (Stern–Volmer equation). The parameters of this equation are, however, all temperature-dependent. Therefore the temperature needs to be known to determine the oxygen concentration and is measured separately, either optically or with a completely different sensor. This work proposes a new approach based on a multi-task learning (MTL) neural network. Using the luminescence data of one single indicator, which is sensitive to both oxygen and temperature, the neural network achieves predictions of both parameters which are comparable to the accuracy of commercial senors. The impact of the new proposed approach is however not limited to dual oxygen and temperature sensing, but can be applied to all those cases in which the sensor response is too complex, to be comfortably described by a mathematical model.

In this work, we study the nonlinear dynamics of two elastically coupled micro-membranes. These MHz-resonators are capacitively driven by a pair of integrated interdigitated electrodes. Each membrane is suspended over a 350 nm air gap constituting a Fabry-Pérot cavity used to optomechanically read-out its displacement with a 633 nm laser. The linear regime analysis of the system reveals a strong constitutive difference of the resonators natural frequencies as well as a weak coupling regime. The system is strongly driven to reach a nonlinear regime that is described with a two coupled Duffing resonators model. We report the emergence of classical chaos when the resonant driving force is modulated with a low frequency (kHz) pump. The experimental bifurcation diagrams corresponding to the change of low frequency pump and amplitude of this modulation are numerically reproduced. We discuss the dissipative aspect of the problem that plays a crucial role in the pump frequency range allowing the chaotic regimes to be reached. This system constitutes an interesting base for the fundamental investigation of the collective dynamics of an array of nonlinear resonators. Additionally, our bifurcation diagrams exhibits several brutal dynamical changes often referred as “extreme events”. We consider using these highly sensitive points in the parameters space as working points for chaos based sensing applications.

We present a prototype light detection and ranging (lidar) system that compressively samples the scene using our deep learning optimised sampling basis and reconstruction algorithms. This approach improves scene reconstruction quality compared to an orthogonal sampling method, with reflectivity and depth accuracy improvements for one frame per second acquisition rates. This method may pave the way for improved scan-free lidar systems for driverless cars and for fully optimised sampling through to decision-making pipelines. The requirement for 3D imaging is a challenge across a range of sectors including gaming, robotics, health-care and automotive industries. Mature technologies such as radar and ultra-sound sensing are effective at long and short ranges respectively. With lidar capable of millimetric depth precision, with good spatial resolution at ranges of around 100 m, it has become a key technology in this area, with depth information typically gained through time-of-flight photon-counting measurements of a scanned laser spot. Single-pixel imaging (SPI) is an alternative imaging modality for recovering spatial information. SPI methods offer an alternative approach to spot-scanning, which allows a choice of sampling basis. Unlike scanning systems, the freedom to choose the sampling basis in SPI provides the opportunity to use compressed sensing techniques, where a high-quality image can be reconstructed from a number of measurements that is fewer than the number of pixels in the image. Compressed sensing has been demonstrated using an optimised imaging basis and reconstruction algorithm derived from a trained convolutional neural network. This deep learning approach achieves a 4% compression ratio, enabling lidar imaging using 25 times less measurements such that faster acquisition times can be used.

We present a low-cost stand-alone AI based wavefront sensor (AIWFS) trained only with synthetic data. A simple defocused image of a source provides non-ambiguous phase retrieval competing with traditional wavefront sensors such a Shack-Hartmann (SH) sensor. An artificial neural network (ANN) is trained to output the Zernike coefficients, or any other relevant figures of merit, exclusively from synthetic data. The synthetic data typically contains random Zernike coefficients or wavefront, noise, as well as a defocus error to avoid any stringent accuracy requirement. Once trained, the AIWFS can be used directly on many other applications without any retraining. In its simplest form, the AIFWS’s hardware is just a camera taking defocused images of a point source, like a star. However, with the proper synthetic data, many types of source and optical layouts can be accommodated, such multi-point, or extended, sources to simultaneously determine both on-axis and field-dependent wavefront performance, from a single measurement. In applications using actual stars, the NN also provides the Fried’s parameter as an estimation of atmospheric turbulence. The ANN outputs are computed directly there is no numerical iteration nor any convergence consideration. The system can run at video rates, in real time, and therefore is suitable for analyzing systems with vibrations or moving parts. The AIWFS only requires a single camera making it a simple cost-effective solution that can take advantage of an existing camera that may already be in an optical system. This paper shows results using AIFWS for telescopes with both actual and artificial stars.

In this study, we developed modified photonic Doppler velocimetry (PDV) measurement system which can measure a wide range of flight velocities of ejecting debris. Using a utilized collimated probe with an iris, we can measure a target with a wide movement range and enhance the signal to noise ratio (SNR) by eliminating unwanted scattering light. The Doppler interference signal can be detected and recorded with an InGaAs photodetector and a high-speed oscilloscope. We found the beat frequency to be proportional to the detected velocity so that we could measure the flight velocity of ejecting debris. In order to localize the Doppler interference signal temporally, we used a continuous wavelet transform (CWT) to obtain a three-dimensional (3D) mapping of frequency, magnitude and time. The velocity line tracing algorithm (VLTA) was developed based on image processing algorithms to retrieve the flight velocity curve from the corresponding scalograms. Using a confocal microscope, our surface morphology observations, along with simulations, were used to verify the velocities measured on our PDV system.

Three-dimensional (3D), in vivo and in live imaging of living samples with a sub-micrometer resolution is a current necessity for biomedical researches which corresponds to a hot topic for microscopy engineers. It is likely that the role of computational approaches is yet underestimated and underused in 3D-microscopy. This paper is an illustration of the fundamental role that could be played by such strategies. Usual imaging depths in biomedical microscopy reach few hundreds of micrometers in optimal conditions when multiphoton approaches are favored. However, light scattering and absorption still damage image quality, especially as imaging depth increases. Our approach rests on the multi-parametric 3D-PSF estimation of the true 3DGaussian model of the PSF along multi-millimeter depth. Image acquisition in MPM generates stacks of 2D images constituting an overall 3D-image. 3D-volumes of images containing a single object are selected and isolated all along the depth using automatic morphological tools. Finally, our computational 3DGaussian shape-fitting algorithm named FIGARO is applied on each individual PSF and quantify PSF full-width at half maximum (FWHM) in the 3 dimensions simultaneously with PSF tilt angles. FWHM evolution in the 3 dimensions along the 2 mm depth highlights a highly significant effect of spherical aberrations. Starting from standard values of PSF measured at sample top compared to what expected in MPM, we show an increase with a factor three of the PSF FWHM in axial plane when the sample bottom is reached, and no modification of PSF dimensions in lateral plane all along the depth. The main direction of the PSF shows a convergence toward a focal point that will be discussed

In this study, we compare the hyperspectral imaging capabilities of a custom-built visible light OCT with those of a commercial grade hyperspectral camera. Using the Short-Time-Fourier-Transform algorithm on the OCT signal, we estimate the variation in the surface spectral response from two paint pigments. Our study aims at comparing the spectral measurements obtained from calibration samples and to estimate an optimal working point for OCT-based hyperspectral processing.

We have evaluated the performance of a range of retroreflective tapes for their potential to improve detection of casualties in maritime search and rescue (SAR). The potential for cockpit distraction in the visible region was also evaluated. Different material samples were placed at a representative distance from an operational UK SAR aircraft under different illumination conditions. Footage was recorded from pilot night-vision goggles (NVGs) and from the different cameras on board operating in the visible, near IR and mid IR regions. Six materials were tested. Two silver coloured, SOLAS approved materials were tested with broadband visible retroreflection, one with microsphere construction, the other with microprismatic construction. Three microprismatic materials were tested that included overlaid filters to colour them red, orange and yellow. Finally, a reflective microprismatic tape was tested that incorporated a visible-light-blocking filter that rendered it black in the visible but reflective in the near infrared. These tests confirmed that pilot perception of the microprismatic silver, orange and yellow materials was highest in both the visible and near IR (700nm - 2.5μm) regions. Cockpit reflectance tests showed that, when applied to an orange suit, colour-matched retroreflectors provide minimal visual distraction from reflection.

With the continuous development of ultraviolet technology, the working band of UV detector is more controllable and optional, and the sensitivity has been greatly improved, so it has been widely used in ultraviolet camera, flame detection, welding detection and other fields with its unique advantages, it is of great significance to study the performance of ultraviolet detector parts. In this paper, we designed a set of evaluation and testing devices for detecting the signal-to-noise ratio, resolution, dynamic range and other parameters of ultraviolet ICCD (intensified charge-coupled device) detector after carrying out theoretical evaluation of ultraviolet detection and imaging photoelectric system and studying its related testing technology. In this paper, firstly we analysed the definition and the testing principle of the ultraviolet ICCD detector’s relevant parameters, such as signal-to-noise ratio, resolution, dynamic range, and designed the relevant algorithm model on the basis of that, then designed the supporting related hardware such as: Uniform light source system, test target, dark box, video processing acquisition system, etc. Secondly, based on LabVIEW platform, the software of related data acquisition and analysis is developed, and the video real-time display is realized, and finally the test experiment of signal-to-noise ratio, resolution and dynamic range is carried out to evaluate the performance of UV ICCD detector.

Heterogeneous III-V/silicon photonic integrated circuits promise to integrated dissimilar materials without compromising their own properties. InP-based high-power and high-speed In_0.53Ga_0.47As modified uni-traveling carrier photodiodes(UTC-PDs) heterogeneously integrated on silicon-on-insulator waveguides have been demonstrated. In this paper, we will propose a novel GaAs_0.5Sb_0.5/InP type-II waveguide UTC-PD. The p-type In_0.53Ga_0.47As absorption layer is replaced by a p-type GaAs_0.5Sb_0.5 layer. Due to the type-II interface between p type GaAs_0.5Sb_0.5 absorber and InP collector, photo-generated electrons generated in the absorption layer are injected into the collection layer with enhanced kinetic energy, which aids their transport toward the collector and minimizes the current blocking effect. Our device shows a significant improvement in the responsivity (1.14A/W) and bandwidth(40.3GHz) compared with that of waveguide UTC-PD with the same thickness of pure In_0.53Ga_0.47As absorber. The demonstrated type-II PD offers a record overestimated saturation current-bandwidth product 4473.3 mA.GHz. These promising results suggest that our proposed GaAs_0.5Sb_0.5/InP type-II waveguide UTC-PD structure can fundamentally overcome the trade-off among bandwidth, responsivity, and length of high-speed waveguide PDs.

A 2D hot spot diffusion model for describing the superconducting nanowire response to single photon is presented. We develop the 1D hot belt model to 2D hot spot model and can capture the initial stage of the hot spot evolution after photon absorption, this is helpful to comprehensive understand the origins and underlying physics of time jitter in superconducting nanowire-based single-photon detectors. Furthermore, the developed model can qualitatively explain the asymmetry and photon wavelength dependent probability density function (PDF) of the delay time. We find that the left and right half of the PDF distributions respective exhibit the Gauss and non-Gauss shape as increasing the excitation wavelength or decreasing the bias current, and the origins are discussed and analyzed in the framework of newly developed 2D model. The proposed 2D hot spot diffusion model will not only sheds light on the origin and influence of the timing jitter but will also reveal the work principle of the superconducting nanowire devices.

Laser scanners with Risley prisms have the potential to perform a faster scanning in comparison to other twodimensional (2D) laser scanners, for example galvanometer-based. However, in contrast to the (constant speed) raster scanning produced by the latter, scan patterns of Risley prisms are highly non-linear, have intersection points, and are performed with variable speeds. The aim of this study is to build upon the novel, graphical method we have, to our knowledge, introduced for the study of these scan patterns. In contrast to complex analytical methods and to approximate ones, this graphical method is easy-to-apply and it provides exact scan patterns, respectively. In this study examples of experimental results are obtained to validate simulation results obtained using simple prisms equations and a commercially-available mechanical design program, CATIA V5 (Dassault Systèmes, Paris, France). Several characteristics of the laser scanner with a pair of rotational wedges are considered, with a focus on one of Marshall’s parameters, i.e. the ratio M of the rotational speeds of the prisms. An experimental validation is demonstrated for all characteristic graphs of the scan patterns for two pairs of values, M equals 2 or -2, as well as 8 and -8. The contrast between positive and negative values of M, as well as between lower and higher absolute values can be thus observed. As this is but a step in this study, directions of current work are also pointed out.

A Distributed Fiber Optic Sensing (DFOS) system has been successfully developed by RC Integrated Systems LLC (RISL). The DFOS system is capable of providing simultaneous measurement of multiple parameters such as temperature, strain, and pressure for harsh environment applications. DFOS sensors are based on fiber Bragg gratings (FBGs) and coating of a unique high-temperature-resistant (HTR) material on the surface of silica optical fibers. DFOS sensors have been tested to withstand temperatures up to 1,100°C and have great potential for high temperature environment applications. In this work, we were focused on the application of DFOS FBG sensor for strain measurement. A numerical model was established to simulate the FBG response to the applied strain. To verify the modeling result, a simple experimental setup was assembled to measure the sensor’s sensitivity for strain measurement at room temperature. Experimental testing shows that the FBG sensitivity for strain measurement is 1.1957 pm/με which is consistent with the numerical modeling results. The difference between the measured sensor sensitivity and the modeling result is only about 0.33%.

The complexity of treating cancerous cells in patients using radiotherapy, requires precision in terms of the total dose received by the patient. The use of scintillating materials at the tip of the fibre for real time dosimetry dominate the current development of optical fibre dosimeters, however, they are limited to single point sensing. The changes in the structural and chemical properties in optical fibres on exposure to radiation gives rise to attenuation of the optical signal i.e. Radiation Induced Attenuation (RIA). This has proven to be a useful feature in monitoring radiation from gamma sources (Cobalt60 sources) using PMMA (polymethyl methacrylate) fibres and perfluorinated graded-index polymer optical fibre (Cytop). The aim of this study is to investigate the performance of Cytop fibre in monitoring low doses of X-ray radiation (up to 10 Gy), produced by clinical linear accelerators (linac) for real time monitoring. The radiation induced attenuation (RIA) were measured across a 1 m length of Cytop fibre when the fibre was exposed to different radiation energy (6 MV, 10 MV) from the linac. The result of this study shows that the sensor has a good sensitivity of 0.0693 ± 0.004 dB/m/Gy and 0.0711 ± 0.004 dB/m/Gy at the wavelength of 695 nm and 817 nm respectively, for a radiation energy of 6 MV. Preliminary results demonstrate the potential of the Cytop fibre as a dosimeter for radiation treatment. The Cytop fibre sensor also exhibits a higher sensitivity, in the order of 3, when compared to PMMA optical fibres.

Fiber Bragg grating (FBG) based sensors are widely used in very diverse fields ranging from health structural monitoring in civil and aerospace areas to more recent medical applications in the field of diagnosis in different specialities such as cardiology and biomechanics, among others. Their intrinsic properties of strain and temperature sensitivity and their ease of use make FBGs high potential sensors for research purpose. The proposed study aims to evaluate and assess the temperature increase due to heating at the tip of an electrosurgical knife subject to current at high voltage and high frequency in different conditions and verify the feasibility of using FBGs as temperature sensor in this application. For this purpose, an electrosurgical knife composed of a metal conductor and a plastic shaft on top of which 3 FBGs are placed is used. The latter ones are situated and fixed on the circumference of the shaft equally distributed at 120° from each other. To avoid strain interference in the measurements of the shift in Bragg wavelength, the metal conductor is kept fixed. After calibrating the FBGs, different experiments are conducted where the knife is used to heat a specific biological material using a high voltage generator and a thermal camera for measurements verification. The tests showed promising results which demonstrate that FBGs are easy to calibrate in temperature and robust to measure variation of temperature in the surrounding of an electrosurgical knife.

We present the technique and experimental laboratory setup for measuring and analysis of diffuse reflectance spectra. The Experimental spectra obtained by tunable infrared quantum cascade laser with average power of 15 mW. Using causality relations for real and imaginary parts of reflectivity we can calculate the extinction coefficient. We use dumped harmonic oscillator (DHO) model to calculate synthetic spectra and test KramersKronig relations for spectra calculations. Using experimental setup and numerical methods of spectra analysis we could identify the diethyl phthalate (DEP). The proposed method can be used in routine laboratory analysis to complement the ATR and DRIFTS methods of IR spectroscopy.

Emission spectra were obtained for various types of aerosol: aqueous (distilled water, NaCl aqueous solution, seawater aerosol), dust aerosol (aqueous solution of silicon nanoparticles, aqueous solution of atmospheric dust of various concentrations), and the elemental and molecular lines common for these types of aerosol were compared. Experimental data on the elemental composition of water aerosol were obtained by the method of filament-induced emission spectroscopy.

The problems of the formation and output of the measurement results of the energy spectrum of the optical signal in a spectrum analysis system based on a device with a diffraction grating and fiber-optic transmission system (FOTS) of the analyzed signals are considered. The use of FOTS allows implementing a contactless method of spectrum analysis. A mathematical model has been developed for obtaining reference values of the energy spectrum by linear CCD sensor detection. A method for correction reading results allows us to take into account the nonuniformity of the spectral sensitivity of the linear CCD sensor, the frequency response of the attenuation of the optical fiber, and also the features of the formed spectra in different diffraction orders is proposed.

A design and application of distributed microresonator-based systems for biochemical sensing are discussed. Two different configurations of the distributed sensors based on integration of the spherical glass microresonators and fabrication of the toroidal microresonators via two-photon polymerization have been demonstrated. The performance of both configurations for biochemical sensing has been analysed.

We present the results of modeling and simulation of heat propagation processes taking place in SiO₂/W/CeB₆/W fourlayer detection pixel of a thermoelectric single-photon detector after absorption of one photon or simultaneous absorption of more than one photon with energy 8 eV (UV) and 0.8 eV (NIR) at different distances from each other. We use the detection pixel model with a surface of 10 μm × 10 μm and layers thicknesses of 0.1 μm and 0.01 μm. Calculations were carried out based on the equation of heat propagation from a limited volume using the three-dimensional matrix method for differential equations. We have shown that a thermoelectric detector is able to count the number of absorbed photons up to four.

In this work we present a scheme to enhance the spectral resolution of the MEMS FTIR spectrometer by cascading it with a reflection-type Fabry-Perot (FP) cavity. In this scheme, we use the different FP longitudinal modes in the reflection response within the FTIR spectrometer range simultaneously to scan the entire spectrum of the measured material, while at the same time the FTIR discriminates between the contributions of those different modes. This discrimination can only be made successfully given that the resolution of the FTIR engine is smaller than the free spectral range (FSR) of the reflection FP. A DSP algorithm is developed to decode the correct spectrum of the measured material using the presented spectrometer. The suggested architecture is implemented experimentally using a reflection FP cavity, consisting of a micromirror and a Bragg coated multimode optical fiber, with a scanning MEMS Michelson interferometer having a resolution of 16 nm at 1550 nm. A 50/50 optical splitter is used to cascade the reflection FP cavity and the MEMS Michelson interferometer. The system was used to resolve two laser lines at 1548 nm and 1554 nm achieving a resolution of 6 nm at 1550 nm leading to about 2.6 times enhancement in spectral resolution. The system was also used to measure the absorption lines of a references material in the wavelength range of 1450 nm to 1750 nm. The result was compared to the measurement of a bench top spectrometer with a good agreement.

A multilayered fiber SPR sensor is studied with graphene multilayers for ethanol detection. The sensor design variants (graphene mono-, bi-, tri-, and quadra-layer) are simulated and analyzed at 1310 nm and 1550 nm wavelengths. The dynamic radiation damping in terms of variable temperature and Ag layer thickness is enforced on the sensor variants to lead to possible sensing performance enhancement. At an optimum radiation damping (ORD) condition (317.8 K temperature and 35.1 nm thick Ag layer at 1550 nm wavelength), the figure of merit (FOM) of the fiber (ZBLAN core and NaF clad) SPR sensor with graphene monolayer has the potential to reach to an ultrahigh magnitude of 27164.89 RIU^-1 . The proposed sensor can be an important milestone in developing highly sensitive and accurate fiber optic chemical sensors.

We investigate an all-fibered frequency-shifting loop (FSL) that includes an electro-optic intensity modulator (EOM) and an optical amplifier, and is seeded by a continuous-wave laser. At variance with frequency-shifted feedback lasers that contain an acousto-optic frequency shifter (AOFS), the EOM creates at each round-trip two side-bands that recirculate inside the loop. We experimentally and theoretically investigate the time response of the FSL in the fractional Talbot condition. Experimental results show that the intensity-modulating FSL generates short pulses with a repetition rate multiplication. We observe pulses at repetition rates tunable between 5.867 MHz and 715.8 MHz. The system is also modeled by a simple linear interference model that takes the amplitude modulation function and loop delay into account. The model predicts the fractional Talbot property as in AOFS-based systems, but with an additional amplitude modulation of the pulse train, in good agreement with the experimental results. This experiment shows an alternative approach to AOFS loops, taking advantage of the inherent bandwidth and tunability of the EOM. This fractional Talbot laser may find applications in optical sampling, THz generation and ultrafast data processing systems.

A phase detection method is proposed and demonstrated to measure the response of surface plasmon resonance (SPR) in the spatial domain. In an experimental setup comprising a laser source, a launching optics, a gold coated SF10 glass plate, a coupling prism, a Wollaston prism and a CCD camera, a spatial interference fringes are recorded. Two such spatial interferograms, one including interference of p- and s-polarized waves from the SPR structure for air when the SPR phenomenon does not occur, and the other one for an analyte when the SPR phenomenon occurs, are used to detect the SPR phase shift at the source wavelength. The interferometry setup is used to measure the SPR phase shift for aqueous solutions of ethanol. The measurements are accompanied by theoretical modeling of the SPR responses using the material characteristics, that is, the refractive index of the SF10 glass, the complex refractive index of gold, and the refractive index of the analyte.

Singe event effect (SEE) simulation in modern integrated circuits (ICs) by femtosecond laser irradiation through the substrate allows eliminating a lot of problems connected to the presence of multiple opaque metal layers above the IC active layer. With this irradiation geometry, the proper wavelength of laser radiation should be chosen to generate sufficient amount of nonequilibrium charge in the active layer on the one hand, and to avoid significant laser energy losses in the thick substrate on the other hand. In this paper several typical microelectronic ICs were selected to investigate the dependence of SEE generation effectiveness on the laser wavelength when irradiating through the substrate of various thickness. It was found, that the most appropriate laser wavelength for the silicon substrate thicknesses of 300 to 800 μm lies in the 1030 to 1070 nm range

The influence of β-radiation exposure (the total dose up to 41.1 MGy and dose rate of 2.5 kGy/s) on the spectral characteristics of high and low reflective FBGs inscribed using femtosecond laser radiation in Ge-doped and pure-silica core fibers with polyimide and metal coating is presented. The largest Bragg wavelength induced shift (BWS) of +55 pm is observed in the case of weak reflective FBG (type I) inscribed in Ge-doped fiber. A comparable red shift in wavelength of + 50 pm is observed in the case of high reflective FBG (type II), which is explained by an increase in the concentration of GeE’-centers and, accordingly, an increase in the effective refractive index. Moreover, a significantly smaller BWS of -10 pm was obtained in the case of high reflective FBGs inscribed in pure-silica core fibers.

This work reports the optimisation of a plasmonic waveguide sensor based on amorphous silicon compounds (a-SiC:H, a-SiN:H or a-SiCN:H) using the FDTD method and modal decomposition. The sensor consists of an array of parallel surface plasmon interferometers with different propagation lengths, each one comprising a thin layer of metal embedded into an amorphous silicon waveguide. In order to reduce the complexity and hardware, we have proposed a structure consisting of an array of parallel surface plasmon interferometers with different propagation lengths, such that at the end of the plasmonic structure the modes can interfere constructively or destructively depending on the refractive index of the sampling medium and the propagation length. The variation of the output intensity at the end of each waveguide element provides a convenient interrogation scheme. In this work we analyse different solutions for splitting the input fundamental mode into the different parallel waveguides, including multi-mode interference structures and directional coupler splitters. By exploring amorphous silicon compounds that can be deposited by Pressure Enhanced Chemical Vapor Deposition (PECVD) at low temperatures, we aim to achieve a low-cost process that is compatible with back-end CMOS processing and wavelengths in the visible to near infrared range.

The results of an investigation of polymethylmetacrylate deformation due to applied high-load utilizing its birefringence are presented in the paper. The sample under the test was placed between two plane polarizers, illuminated by white light and gradually stressed using a machine for fatigue testing of materials. The spectra of transmitted light were measured as function of load and deformation using optical fiber spectral analyzers for visible (VIS) and near infrared (NIR) spectral ranges. The measured spectra were normalized and light intensities for selected wavelengths as function of load and deformation were compared with the dependences according to models describing the stress-induced birefringence of PMMA as function of load and deformation, respectively. A good match between the dependences resulting from the measured data and those calculated according to models implies the models can be used for calculating calibrations curves of PMMA-based sensors of load and/or deformation

We introduce a Raman scattering based detector of carbon isotopes in gaseous mixtures. A solid state 532 nm 5 W CW laser focused into a gaseoussample by a custom-built diffraction-limited objective was used for excitation of Raman signal. Raman signal was collected by an f-matcher with edge filter at excitation wavelength of 532 nm. A Czerny-Turner scheme based spectrometer and a cooled down to -40°C CMOS camera were used to register the signal.

Salinity profile is an indicator of quality of water and marine life. Existing electrical salinity sensors are not very selective and suffer interference from presence of different kinds of ions. Thus they are being readily supplanted with optical fiber sensors, with added remote sensing capabilities and selectivity. Furthermore, the refractive index (RI) of the solutions bear strong correlation with amount of salt contained, thus rendering salinity measurement based on refractrometric techniques appropriate. In this paper, an etched fiber Bragg grating (eFBG) based evanescent field sensor is proposed that is capable of detecting salinity with sensitivity of approximately 1.825 nm/RIU at a concentration of 25% (% w/w) of sodium chloride (NaCl) at a constant temperature of 25°C.

In this paper, sensitivity analysis of fuel adulteration has been carried out. Kerosene is used as an adulterant due to its easy miscibility and cheap cost. It is noticed that net refractive index (RI) of adulterated diesel decreases as the kerosene level increased but reverse in the case of adulterated petrol. In our proposed sensor, we utilizes the etched Fiber Bragg Grating (eFBG) which enhanced the interaction between evanescent field and sensing medium to a greater extent. Concentration mixing is chosen in the succession of 10% in each case to detect the adulteration level in kerosene-diesel and kerosene-petrol. The experimental results of Bragg wavelength shifting and sensitivity was investigated. Sensitivity of 26.97 nm/RIU in the case diesel and 49.98 nm/RIU in the case petrol were recorded respectively. This kind of sensor is suitable for real time on-road sensing.

We experimentally demonstrated a temperature sensor by selectively infiltrating refractive index liquid (RIL) in the central air hole of a twin-core photonic crystal fiber (PCF). The selective liquid infiltration was realized by putting the PCF in the bulk liquid with its central air hole open for liquid infiltration using capillary effect. The rest of the air holes were covered by UV glue. The three-dimensional stage was used to translate the PCF, and a tapered SMF was used to transfer the UV glue to cover the air holes under the microscope. After UV glue was solidified by exposing the fiber end under the UV light, the PCF end was dipped into the RIL to fill the central air hole by capillary effect. Due to the large thermos-optic coefficient of the RIL, the RIL filled air channel would act as a liquid core whose core modes would be highly dependent on the ambient temperature. The core modes of the RIL filled core would be phase matched to the fundamental mode of the two solid cores. Therefore, the phase matching wavelengths for the mode coupling among the two solid cores of PCF and the liquid core were highly temperature sensitive. The resonant dips in the transmission spectrum were measured to estimate the temperature sensitivity. The experiment used a commercially available twin core PCF, and blocked all but the central airhole at one of the ends facets by UV glue (NOA81, Norland), the remaining open holes are infiltrated over a length of 10 cm by capillary force with fluid (Cargille Laboratories Inc. index-matching fluid, series A) that possesses a refractive index of 1.46 at 589.3nm, 25°C, and the thermal coefficient is – 0.000389 RIU/°C, which is around 10 times of that coefficient of silica. Any temperature induced changes will have an influence on the propagation properties because of the highly temperature response of the refractive index of the fluid. With a fiber cleaver, a 1.8 cm long PCF was then cut from the longer length of the partially liquid filled twin core PCF and then fusion spliced with SMFs at both ends to observe its transmission spectrum when the sample is heated. When the temperature increase to around 54°C, the liquid RI drops quickly to match that of silica, and a three parallel waveguide structure is formed, in which the central liquid waveguide have the same index value with the two solid core. Because of the small separation between adjacent waveguides, a strong mode-field overlap occurs, which leads to a significant enhancement of the coupling coefficient, therefore, light energy can be easily transferred between two solid cores and the liquid rod in a short coupling length. Thus, the transmission spectrum of the device contain two sets of interference fringe pattern, the large spectrum envelope originated from the interference between the three eigenmodes generated by three-parallel waveguide structure based on the mode coupling theory, and fine interference fringes generated by the interference between the higher order modes in one core. By tracking the dip wavelength shift of the large spectrum envelope, the sensor exhibited a high temperature sensitivity of up to 37.011 nm/°C within the temperature range from 53.8°C to 55°C due to the satisfaction of phase match condition, and maintain a high sensitivity of 19.681 nm/°C from 55°C to 58.2°C, which is benefit from the high thermal optic coefficient of the selectively filled liquid in the twin core PCF.

Due to circumstances beyond the presenter's control, and audio recording was not possible for this presentation.

Tilted fiber Bragg gratings (TFBGs) coupled to the surface plasmon resonance (SPR) phenomenon represent a powerful sensing solution especially for biodetection purposes. Indeed, the excitation of plasmonic waves at the metal-coated surface of the sensor brings a significant improvement in terms of surface sensitivity. Until now, most of experimental results involving SPR have been obtained by using TFBGs inscribed in standard single-mode optical fibers (SMF), which requires the use of a polarizer to select the right state of polarization for plasmonic excitation. Investigations for the development of even more sensitive or robust sensing tools remain a topic of current interest. In this study, the bulk and surface refractometric sensitivities of plasmonic TFBGs photo-inscribed in multimode fiber (MMF) are compared to the one of standard SMF. Gold-coated TFBG in SMF exhibits a sensitivity value of ~102 nm/RIU. Plasmonic MMF TFBGs are more sensitive with a value of ~124 nm/RIU (enhancement of ~22 %) and open the way to multiplexing thanks to the narrowness of their spectral response. Surface refractometry was also assessed through HER2 bioassays (Human Epidermal Growth Factor Receptor-2), a breast cancer biomarker. For that purpose, aptasensors based on antiHER2 aptamers were developed and tested by using these two fiber types. Similar surface sensitivities were obtained for both fiber types.

We report results on the development of an optical fiber long period grating sensor for organic vapor monitoring. A silk fibroin ovelayer with a thickness of the order of 400 nm is drop casted on the fiber cladding surface to enable sensing of volatile organic compound vapors. For increasing methanol vapor pressure up to 100 mbar the wavelength of the long period grating attenuation band exhibits a negative shift up to a maximum value of 4 nm. The strength of the grating attenuation band is also altered reaching a 0.27 dB strength decrease under the same maximum methanol vapor pressure. Furthermore, the recovery behavior of the sensor is presented and preliminary results of the response of the sensor to isopropanol and ethanol vapors are briefly discussed.

The possibility of transferring the idea of radio-frequency sequential heterodyne spectrum analysis to the optical range is considered. The similarity of signal processing of the radio and optical ranges by the method of sequential heterodyne analysis is noted. We consider the issue of a panoramic optical local oscillator in the form of a tunable laser, where stochastic phenomena are taken into account in the form of the sum of oscillations with a linear change in the instantaneous frequency and the stochastic component as interference, i.e. the spectrum is considered against the background of the generated interference. In this regard, it is proposed to use the technique of compression of radar signals to reduce the influence of the stochastic component of the oscillations of the laser panoramic local oscillator. It is noted that the main task on the path to realizing the idea put forward is to create a laser panoramic local oscillator with a low level of the stochastic radiation component of a tunable laser.

The role of spectral measurements in science and technology is noted. The measurement of optical spectra by an idealized spectral device based on an acousto-optic tunable filter is considered. It is shown that the acousto-optical methods of spectral measurements can be considered as a manifestation of the bilinear property of acousto-optical interaction. In this context, the transition to linear integral operators describing the measurement of the spectra of radio and optical signals is made. An analysis is given of the procedure for measuring the optical spectrum with a spectral device based on an acousto-optic tunable filter with an abrupt change in the frequency of the control signal. The comprehensive characteristic of such a device, its complex spread function, as well as the result of measuring the optical spectrum in the form of an energy spectrum, has been established.

Optical vortices are promising for increasing the bandwidth of optical communications by encoding information in the topological charge. For this purpose, it is essential to develop efficient and compact systems for generating and detecting vortex beams of different topological charges. We present the design and the theoretical and experimental analysis of a 2D liquid-crystal geometric-phase diffraction grating based on the optimal triplicator profile. The grating generates an array of 3x3 equi-energetic optical vortices of different integer topological charges and with the maximum theoretical diffraction efficiency. The performance of this grating as a vortex detector is demonstrated by illuminating it with vortex beams of different topological charges. In a recent work we mathematically proved a π/2 phase shift between the zero and the two lateral first diffraction orders generated by the optimal triplicator design. Here, we show the implications that this factor has in the polarization of the diffraction orders when the optimal triplicator is encoded as a geometric-phase element.