Endo-Venous Laser Ablation (EVLA) is emerging as one of most important minimally invasive procedures for treating varicose veins, offering reduced patient discomfort compared to traditional methods. The procedure uses a laser beam to collapse and induce sclerosis in vein walls, effectively sealing the vein. Among the various medical wavelengths, recent advancements favor the use of 1900nm lasers, particularly those based on thulium-doped fiber technology, due to their highly localized heating effects. However, discrepancies in the literature regarding the optimal laser irradiation dose highlight the need for an applicator that integrates temperature sensors to provide the surgeon with real-time feedback. As a preliminary work the paper discusses the use of fiber Bragg gratings to measure the temperature distribution induced by two lasers emitting at the opposite edges of the commonly used therapeutic wavelength range. For easiness and better reproducibility the tests have been carried out on egg white phantoms, simulating vascular veins; the results demonstrate that heating at 1900nm outperforms that at 975nm by minimizing spurious temperature increases outside the target volume. Additionally, the experiments emphasize the importance of carefully tuning laser power to prevent carbonization. The outcomes of the ablation tests are in good agreement with those found in clinical trials, thus demonstrating promising capabilities of this novel applicator.

The optimization of laser ablation (LA) surgical procedures-specifically for the treatment of tumors-requires evaluating the temperature distribution across the entire area under treatment (e.g., the tumor volume). However, minimally invasive temperature sensors can only provide information in a limited number of points. Therefore, an effective prediction algorithm is required to reconstruct the temperature map for the entire heat affected tissue from as few temperature measurements as possible. This work presents an approach for predicting the temperature around the laser delivery fiber, based on the thermal Green's function, where patient-specific tissue thermal parameters are obtained through a fitting procedure using measurement of the temperature evolution at known locations. The proposed method is independent of the specific temperature sensor used; in the experiments reported, the temperature was measured both at the prediction points and at validation points using a quasi-distributed sensor composed of dense fiber Bragg grating (FBG) arrays, written with a femtosecond laser. A preliminary validation under ideal conditions, represented by ex vivo cases, has been performed through a series of experiments on bovine liver samples. The obtained results demonstrate that it is possible to predict the temperature distribution across the entire ablated area, with errors well below the commonly accepted uncertainty for treatments of this type.

This study investigates the accuracy of budget optical coherence tomography (OCT) for measuring the thickness of protective varnishes on ancient artifacts that have to undergo cleaning or restoration. Two sets of glass slides, deposited with layers that mimic the structure of ancient handcrafted objects (pigment and varnish), are analyzed. OCT measurements are compared with coating thickness gauge and destructive scanning electron microscope analysis. The results show that OCT provides reasonably accurate thickness measurements, with errors significantly lower than typical variability in cultural heritage applications. This suggests that even a low-cost OCT has the potential to become a valuable non-invasive tool for real-time monitoring of cleaning treatments of ancient artifacts.

Establishing permanent bases on the Moon will require to develop wireless power transmission systems using high-power fiber lasers to support lunar missions where solar or nuclear energy is insufficient. Key challenges include minimizing weight, managing extreme temperatures, and mitigating ionizing radiation's effects. This study investigates the sensitivity to X-rays of commercial rare-earth doped optical fibers for high-power lasers in accelerated tests. Different approaches are considered and compared, such as monitoring power degradation and fiber temperature changes, variation of the Rayleigh scattering signatures, and modifications of the spectral response of a fiber Bragg grating inscribed in a small section of the active fiber.

Monitoring pH is crucial across many fields due to its significant impact on chemical reactions, biological processes, and environmental conditions. While traditional pH measurement methods are limited to occasional use or require expensive and cumbersome equipment for continuous monitoring, the paper presents the preliminary study for a compact, cost-effective, and real-time photonic system for the early detection of pH variations in fluids. The detection is based on pH-induced changes in organic dyes fluorescence. The results on strongly alkaline pH are discussed under different environmental conditions

We report a reflection based multimode fiber surface plasmon resonance (SPR) sensor utilizing a high index silicon layer between silver metal and sensing medium layer. Theoretical studies have been carried out to optimize the suitable width of material layer to sense refractive index (RI) of the analyte surrounding the optical fiber sensing region using the transfer matrix method. The RI sensitivity of the proposed SPR sensor has been experimentally verified to reach 4774 nm/RIU with figure of merit of 36.07 and resolution of 6.28 × 10−5at 1.38 RI. Furthermore, the large thermo-optic coefficient and thermal expansion coefficient of the silicon layer has enhanced the experimental temperature sensitivity of the SPR sensor to 1.76 nm/°C.

The optimization of tumor laser ablation requires the evaluation of the temperature distribution in the tumor volume, but minimally invasive sensors can only provide information in one dimension, and often with consistent errors. Therefore, a suitable prediction algorithm, combined with accurate measurements, are required to reconstruct the temperature map in the tumor mass. This work provides preliminary results on the temperature mapping in an agar-gel phantom, using a quasi-distributed temperature sensor made of a fiber Bragg grating array with improved accuracy, and an algorithm of estimation of the temperature spatial distribution based on the thermal Green's function. Details on the fabrication and packaging of the sensor are provided along with an experimental evaluation of the thermal diffusivity in the phantom. Furthermore, it is shown how the accuracy on the evaluation of diffusivity is influenced by the synchronization error, which is the delay between the firing of the laser and the temperature acquisition.

Optical Coherence Tomography (OCT) is an imaging technique commonly used in the biomedical field to obtain below the surface pictures of the tissues. Being a non-contact, fast, and non-invasive method, it can also support conservators during cleaning treatments of painted ancient artifacts. The paper analyzes the reliability of the estimation of the protective varnish thickness from OCT images. Several samples made of Paraloid (R) B72, a protective material commonly used in conservation, applied on Egyptian blue painting were realized and characterized in comparison with scanning electron microscope images, which is the ultimate tool of conservators to assess the composition and morphology of the surface of artifacts. The results proved to be very promising as the two techniques led to compatible results, demonstrating that OCT can become a routine tool for online monitoring of cleaning treatments.

Soft glass fibers are emerging as an attractive alternative to silicate fibers for visible and mid-infrared lasers. The paper reports on the inscription of Bragg gratings with characteristic suitable for the realization of monolithic laser cavities in some soft glass fibers, in particular in a custom developed fluoride fiber. The first results have been obtained at around 1550 nm for simplicity of characterization, but the approach can be extended to other wavelengths

In this work, we present the detection of proteins expressed by poxvirus with fiber-optic probes based on a semi- distributed interferometer (SDI) assisted by a fiber Bragg grating (FBG), performing the measurement directly into a wastewater sample. Modern biosafety applications benefit from real-time, dynamic-sensing technologies that can perform diagnostic tasks into a wide set of analytes, with a particular emphasis on wastewater, which appears to collect a significant number of viral titers in urban and indoor environments. The SDI/FBG probe can perform substantial progress in this field, as it embeds a dual sensitivity mechanism to refractive index changes (sensitivity up to 266.1 dB/RIU (refractive index units)) that can be exploited in biosensing, while simultaneously having the capability to measure the temperature (sensitivity 9.888 pm/degrees C), thus providing an intrinsic cross-sensitivity compensation. In addition, a standard FBG analyzer can be used as an interrogator, improving affordability and real-time detection over previous works. The probes have been functionalized with antibodies specific for L1, A27 and A33 vaccinia virus proteins, performing detection of a protein concentration in a scenario compatible with online viral threat detection. Direct detection of wastewater samples shows that the L1functionalized sensor has a higher response, 9.1-11.3 times higher than A33 and A27, respectively, with a maximum response of up to 1.99 dB and excellent specificity. Dynamic detection in wastewater shows that the sensors have a response over multiple detection cycles, with a sensitivity of 0.024-0.153 dB for each 10-fold increase of concentration.

The paper presents an all-optical system for the detection of bacterial contamination in flowing water that combines the readings from a multi-functional fiber Surface Plasmon Resonance (SPR) sensor with fluorescence measurements. The preliminary application to cases of water contaminated with Escherichia coli is discussed.

In this work, we present the development and biofunctionalization of a fiber-optic ball-resonator biosensor for the real-time detection of vaccinia poxvirus. We fabricated several ball-tip resonators, functionalized through a silanization process to immobilize two bioreceptors: the monoclonal anti-L1R antibody targeting the L1R protein, and the polyclonal rabbit serum antibodies targeting the whole vaccinia virus (VV) pathogen. Experimental measurements were carried out to detect VV in concentrations from 10 3 to 10 8 plaque-forming units (PFU), with a limit of detection of around 1.7–4.3 × 10 3 PFU and a log-quadratic pattern, with a response up to 5 × 10 −4 RIU (refractive index units). The specificity was assessed against herpes simplex virus, used as a non-specific control, with the best results obtained with anti-L1R monoclonal antibodies, and through the detection of vaccinia virus/herpes simplex-1 combination. The obtained results provide a real-time viral recognition with a label-free sensing platform, having rapid response and ease of manufacturing, and paving the road to the seamless detection of poxviruses affecting different human and animal species using optical fibers.

Ionizing radiation are widely employed in the medical field both for diagnosis and for radiotherapy treatments, where it is often required to measure the precise dose delivered along with radiation distribution in the target volume. This is even more important in emerging techniques such as the FLASH radiotherapy [1], in which very high dose rates (e.g. >40 Gy/s) are delivered over short times (<1 s). Quality Assurance in the FLASH radiotherapy planning process is essential to ensure the accurate dose delivery to the patient and to minimize the possibility of accidental exposure. In this framework, commissioning procedures involve the characterization of radiation beam using a water phantom during the simulated treatment. Furthermore, periodical tests are carried out in a similar way to ensure that there are no drifts in the machine performance, ensuring that measured and calculated doses lie within the agreement criteria. The characterization of the beam in the water phantom is performed by probes such as ionization chambers or scintillators that map the dose distribution in the target volume. A possible more convenient alternative for in-situ, real-time dose profiling is represented by optical fibres used as radiation sensors. However, standard silicate optical fibres for telecom applications exhibit little sensitivity to ionizing radiations. This issue can be addressed by developing ad-hoc silicate fibres, like those doped with aluminium or magnesium nanoparticles, which for their higher Rayleigh scattering behaviour have been named Enhanced Backscattering Fibres (EBFs). In a previous work [2], it was demonstrated the possibility to recover the radiation profile of an X-ray beam through the Radiation Induced Refractive Index Change (RRIC) in EBFs, by means of Optical Frequency Domain Reflectometry (OFDR). OFDR is a powerful tool, but the measurement is performed within seconds and may not be compatible with measurement of FLASH pulses. Fibre Bragg gratings (FBGs) may be used as pinpoint sensors, since they can be interrogated with fast FBG interrogators and spectrometers, but their radiation sensitivity is usually low. To overcome this problem, a novel pinpoint radiation sensor is being developed, based on an interferometric structure made by offset splicing an EBF, working as a multimode fibre, between two single mode pigtails [3]. This single mode-multimode-single mode (SMS) structure produces a periodic spectral response that is sensitive to temperature, strain and radiation. The SMS is also equipped with a FBG, inscribed in the EBF section by a femtosecond laser, for differential compensation of the strain (the SMS and the FBG exhibit opposite wavelength shift in response to strain). The sensor was characterized in a radiation chamber by exposure to X-rays at a dose rate of 11.6 Gy/s for up to 10 minutes. Although these testing conditions are not resembling FLASH treatments, they were chosen to provide a magnified effect while providing a reliable indication of the sensing capability. Fig. 1(a) shows the characterization setup that also includes a commercial FBG interrogator to track the shift of the spectrum under x-ray exposure. Fig. 1(b) depicts the shift of the SMS spectral pattern when exposed at a dose rate of 11.6 Gy/s for a total cumulated dose of 4900 Gy. Fig. 1(c) highlights the higher sensitivity of the SMS with respect to the FBG. This feature, combined with the easy fabrication of the SMS (which only requires a standard fusion splicer), makes it an attractive platform for radiation sensing.

A new system that exploits optical fiber distributed sensing for the detection of hydrocarbons is presented. The system relies on a custom-designed silica core/thin silicone cladding optical fiber to provide a quick and selective absorption of oil products through the cladding; moreover, it exhibits insensitivity to water. Optical fiber sensor interrogation is performed by detecting Rayleigh backscattering using an optical time domain reflectometer or, in a high-resolution version, an optical frequency domain reflectometer. The Rayleigh backscattering signal is influenced by a change in the refractive index of the cladding, which locally modifies the guiding properties of the fiber; and by the swelling of the cladding, resulting from hydrocarbon diffusion, that produces local stress and results in an associated increased reflection. The system has been tested with different solvents and has exhibited selectivity and a rapid response to exposure to high refractive index hydrocarbons, with the sensing fiber yielding a response time of the order of 1 s. The system, in its high-resolution version, is able to accurately locate leakages with an accuracy of 14 cm.

Optical fibre sensors have successfully entered several application fields and markets because they can overcome limitations of their conventional counterparts with an electrical readout. In particular, optical fibre sensors feature remote interrogation, electromagnetic interference-proof functionality and no direct electrical power supply. Concerning the latter, harsh environments as well as biomedical applications may greatly benefit from the replacement of an electric readout sensor with an optical fibre-based version. In this framework, a novel fibre optic flowmeter has been developed, relying on a single mode-multimode-single mode (SMS) interferometric structure [1]. The sensor is based on the hot-wire principle and the novelty lies in the SMS as a sensing element, which is easy to fabricate and more sensitive than other technologies, such as fibre Bragg gratings (FBGs). The schematic of the sensor is depicted in Fig. 1(a). The SMS structure is made by offset-splicing a 10 cm-long G.657A2 bend-insensitive fibre between two single mode pigtails at 1550 nm, to produce the excitation of high order modes in the bend-insensitive section. The input pigtail is actually a double cladding fibre that couples, by means of a feed-through signal/pump combiner, the radiation from a 9xx nm laser that acts as the heating source. Given the short length, the bend-insensitive section supports the propagation of two modes, which propagate at two different phase velocities and then interfere as in a Mach-Zender interferometer. The resulting spectral response is a periodic pattern in the frequency domain whose free spectral range (here selected to be about 20 nm) is inversely proportional to the length of the two-mode section. The multimode section, which is sensitive to strain and temperature, is coated with a graphite film that converts the 9xx nm radiation into heat, to increase the temperature and hence produce a red shift of the spectral response. On the other hand, a blue shift occurs when air or a fluid flows across the sensing surface, removing the optically induced heat. The SMS structure is terminated to provide sufficient reflectivity for the sensor to be monitored in reflection with a commercial FBG interrogator and be used as a probe. The SMS sensor was embedded in a 3D-printed fixture and characterized in comparison with a reference commercial sensor [2], demonstrating its sensing capability. Fig. 1(b) shows the shift of the spectral response of the SMS flowmeter when 1.5 W optical heating is applied. The wavelength shift of 6 nm corresponds to an increment of temperature up to 40 °C, which was also verified with a thermal camera. Fig. 1(c) depicts the measurement of an air flow (generated by an air pump) that simulates a respiratory activity. The SMS sensor readout was compared with that of the reference sensor, whose outcome is expressed in standard litres per minute (slm). The calibration factor was found to be 0.33 nm/slm, and the response at different flows exhibited good linearity. While the reference sensor has a quick response time (the datasheet reports a value $< 3$ ms), the SMS sensor exhibited a transitory with response time of seconds. However, the transitory is expected to be greatly reduced by optimizing the packaging (e.g., by replacing the 3D-printed plastic fixture with a metallic enclosure for a fast dissipation of the heat). These preliminary results demonstrate the feasibility of the design and suggests remarkable advantages in biomedical applications where remote and powerless operation are required.

The paper presents the development and investigation of distributed and a quasi-distributed fiber optic sensors for the real-time monitoring of radiations during cancer treatments. Both sensors rely on ad-hoc developed nanoparticle-doped optical fibers with enhanced sensitivity to radiation. The distributed sensor is interrogated with an OFDR-based instrument and allows the reconstruction of the spatial dose distribution along the fiber. The quasi-distributed sensor is implemented through fiber Bragg gratings inscribed with a femtosecond laser in the few-mode section of a single mode-multi mode-single mode interferometer.

Single mode-Multimode-Single mode (SMS) sensors have been attracted a relevant attention because of their simple manufacturing, their capability of sensing different quantities, and their enhanced sensitivity compared to the most common fiber optic sensor represented by Fiber Bragg Gratings (FBGs). Moreover, SMS sensors exhibit blue-shift sensitivity to strain, opposite to FBGs, making them suitable in applications where strain-temperature cross-sensitivity may be an issue. SMS sensors are made by splicing a short multimode, preferably a two mode or quasi two-mode, optical fiber jumper between single mode pigtails. The interference of the modes propagating at different phase velocities produces a spectral pattern that shifts with temperature, strain or any perturbation of the phase difference among the modes. In this paper we review the main features of SMSs as temperature sensors and we present a potential biomedical application in an all-fiber flowmeter based on the hot-wire principle: a fiber-coupled laser source at 980 nm is used as a controllable heating source of the SMS sensor that, when immersed in fluid flow, converts the temperature variation, caused by the heat removal, into a wavelength shift of the transmitted spectrum. Thermal characterization and proof-of-concept experiments show the feasibility and functionality of the sensor and provide an outlook on possible developments and potential applications.

Enhanced Rayleigh backscattering optical fibers, interrogated by an optical frequency domain reflectometer, are used to perform remote real-time measurements of X-ray irradiation profiles, with possible application as dosimeters in radiotherapy treatments. The enhanced Rayleigh backscattering is obtained by proper engineering of the composition of fiber core, either by introduction of Aluminum or Magnesium silicate nanoparticles as radiation-sensitive dopants. A detectable radiation-induced refractive index change can be spatially resolved through the measurement of the frequency shift of the Rayleigh backscattering along the fiber. It is experimentally demonstrated that two mechanisms of radiation-induced refractive index change take place. At doses nearly compatible with those delivered in radiotherapy, a negative refractive index is induced, whereas at high doses the change is positive. This behavior is also confirmed by the shift of Bragg wavelength of a fiber Bragg grating inscribed in the nanoparticles-doped fiber and used as a reference.