The geometry mismatch between active and passive fibers and particularly the presence of a pedestal around the core of active fibers creates a light coupling from this pedestal to the cladding of the passive fiber when spliced together. This signal light propagating in the cladding can results in a beam degradation that reduces the laser performances. We proposed a new solution consisting in using a perfectly matched couple of fibers by adding a pedestal around the core of the passive fiber. This pedestal maintains the coupling light in a quasi-single-mode pedestal area that will not lead to any power losses and not degrade the output beam.

We have developed an innovative anti-resonant hollow-core fiber design with capillaries of alternating thicknesses. This unique arrangement, featuring six silica capillaries of two different thicknesses, effectively narrows the transmission bandwidth while maintaining low attenuation. Validated through simulations, our design marks a significant step in developing the first in-line hollow-core bandwidth filter fiber. We envision that our novel fiber design has a variety of applications, such as suppressing non-linear effects and developing wavelength-selective components for future conventional and quantum communication networks.

Unlike traditional silica-based fibers, ZBLAN fibers possess exceptionally low phonon energy, making them ideal for transmitting signals in the mid-infrared (mid-IR) range. This characteristic is particularly significant because the mid-IR range harbors a wealth of information about molecular structures, enabling applications in environmental monitoring, medical diagnostics, and chemical sensing. However, to fully unlock the midIR capabilities of those fibers, we need to demonstrate repeatable procedures for handling these fibers, such as efficient connections between silica and ZBLAN fibers and between ZBLAN and ZBLAN fibers doped and passive ones.

Working with soft-glass fibers such as ZBLAN fibers, it is required to have precise control of the thermal splicing conditions. This paper extensively investigates the splicing thermal conditions using the Vytran GPX-3400 system to achieve controllable and low-loss thermal splicing between ZBLAN to ZBLAN and ZBLAN to silica fibers. The temperature information in the filament was monitored using a silica FBG sensor by adjusting the Power, the splicing duration, and airflow of the Argon gas, and the calibration curves were extracted.

Distributed fiber optic sensing (DFOS) technique is a promising and robust non-destructive testing tool that can seamlessly acquire environmental conditions over large scales. Therefore, it has found extensive applications in structural health monitoring. Its appeal for monitoring underground facilities lies in the intrinsic properties of the optical fiber, such as immunity to magnetic interference, small size, chemical inertia, etc. This paper provides a concise overview of DFOS applications in underground facility monitoring. Following a brief introduction to the working principle of the DFOS technique, various examples are provided to demonstrate how distributed fiber sensors contribute to monitoring underground facilities. The paper presents unpublished field test results with an emphasis in the energy sector, including monitoring gas storage facilities, geothermal reservoir exploration, and ground movement detection. Furthermore, the paper identifies several directions for enhancing the DFOS system.

The glass of optical fibers can withstand very high temperatures. However, the protecting coating materials cannot. Usual temperature range is limited at around +85°C concerning standard acrylate materials used in the telecom industry. While this is enough for most data centers or data connections, some applications require higher temperature resistance. Those include data transmission or sensing in harsh environments, which can be oil and gas, structure monitoring, automotive or aviation. J-fiber is working on fibers with coating materials that can withstand elevated temperatures. This includes mainly high-temperature acrylate and polyimide materials, which can endure up to 150°C and 300°C respectively, depending on fiber requirements. We will explain drawing conditions of such fibers, fiber properties and fiber characterization tools as well as lifetime expectations based on defined acceptance criteria. The most important include fiber attenuation and microbending performance, strip force of the coating, i.e. the strength the coating sticks to the glass, and tensile strength of the fiber. We will review the way these parameters are tested in accordance with existing IEC standards and their meaning for the application.

Conventional analytical instruments for detecting biochemical and biological species are often expensive, complex and voluminous. Research efforts have to be made to develop simple and compact devices to provide complementary solutions to traditional analytical techniques. These biosensors must interface between the physical, chemical and biological environments by combining molecular recognition elements with a detection transducer.

This study relies on an innovative approach called Lab-Around-Fiber. This method consists in biofunctionalizing silica optical fibers by grafting antibodies onto their external surface, resulting in the specific capture of biological targets of interest. The optical fiber sensor, in our case a fiber Bragg grating, acts as a transducer converting the biochemical signal into an optical signal; the functional layer (gold nanoparticle and antibodies) grafted onto the fiber surface serves as a bioreceptor; collectively forming the integrated sensor. Its proper functioning and sensitivity enable the detection of target biomolecules binding, such as those associated with Antimicrobial resistance.

Molybdenum disulfide (MoS2) has emerged as a versatile two-dimensional material platform for many optical and optoelectronic applications due to its layer-dependent band structure, which can be tuned from direct to indirect by increasing the number of layers. In this work, the integration of MoS2 layers onto a D-shaped side-polished optical fiber has been demonstrated using an inkjet printing technique. We show that MoS2 devices exhibit a strong wavelength dependent transmission spectrum, with a transmittance dip of ~ –50 dB, which can be tuned from near to the mid-infrared wavelength regions by varying the printing paths. Exposure of the MoS2 device to deionized water has revealed that the wavelength position of dip changes by more than 70 nm in response to the mode’s interaction with the liquid. These results indicate that inkjet-printed MoS2 devices could find applications for the development of environmental gas or humidity sensors.

We demonstrate two types of all-fiber speckle spectrometer. One of the spectrometers is composed by cascading a coreless fiber (CLF) and an all-solid photonic crystal fiber (PCF). Using a 10 cm-long fiber with 20-segment-PCF spliced elements, the spectrometer achieves a resolution of 0.03 nm over a bandwidth from 1540 to 1560 nm. The other spectrometer is realized by using the periodically tapered CLF. A remarkable spectral resolution of 0.03 nm in the near-infrared spectrum can be achieved with a 5-cm long fiber. Our compact spectrometers based on CLF promise picometer-resolution spectroscopy in portable applications, providing a new way for miniature spectrometer systems.

This invited talk includes the latest developments on opto-electronic sensor system using specialty optical fibers, mainly the well-known polymer optical fibers (POFs), in their many variants, and novel nanoparticles (NP) doped optical fibers. Both fibers have intrinsic advantages over the standard telecommunication fibers regarding their higher sensitivities, which are presented for both POF and NP-doped fibers in different aspects. For the POFs, there is a higher sensitivity and dynamic range for force and strain sensing, respectively, whereas the NPdoped fibers have higher Rayleigh backscattering signal, which lead to the development of low-cost distributed optical fiber sensors with higher spatial resolution. Thus, the applications of specialty optical fibers in human life are discussed and reviewed.

The biosensor is extremely important for the early diagnosis, drug discovery, healthcare, and clinical applications. Here we propose a unique LPG/FBG hybrid structure yielding ultra-narrow and high signal-to-noise ratio reflection resonances. It is the first time to report high order cladding-cladding mode coupling beyond core-core and core-cladding coupling. The proposed device has been exploited as optical biosensor for the detection of human haemoglobin achieving a high sensitivity. The proposed sensor can be further developed as a point-of-care device for portable and label-free biomedical diagnostic applications.

In this work, we present a novel corrugated long-period grating. The structure was made through the periodic distribution of a photopolymerizable resin onto the surface of an optical fiber, followed by an etching process. The device showed capabilities to be used in strain, displacement, and temperature applications. For the strain measurement, the resonance dip power was linearly increased at a rate of 1.3 dB/mε, showing negligible wavelength shift, making it ideal for lowcost intensity detection schemes. Regarding the displacement characterization, it was verified the capability to measure this parameter in both power and wavelength detection schemes, being the most attractive feature its wide measurement range, i.e. ≈ 25 mm, being above the ones reported in literature. For the temperature, it was verified that there is a direct correlation between the increase of the temperature and the dip wavelength shift.

We present the inscription and characterization of fiber Bragg gratings (FBGs) in polypropylene coreless cylindrical fibers. Polypropylene material offers several advantages, such as strong chemical resistance, biocompatibility, and high tensibility. Therefore, polypropylene FBGs can be useful for sensing in chemically aggressive environments and in biomedical applications. The coreless, cylindrical polypropylene waveguides used in these experiments had a diameter of 150 μm, typical length up to 20 cm, and a refractive index of 1.49. The inscription was performed in the 1550 nm transparency window by using a phase mask technique and 193 nm excimer laser radiation. Inscribed FBGs demonstrated complex multi-peak reflection spectra due to highly multi-mode nature of the polypropylene waveguides. Due to a high attenuation of the polypropylene, the maximum waveguide FBG interrogation length -in reflection- was 6 cm. Gratings characterization demonstrated a strain sensitivity of 0.9 pm/με, a temperature sensitivity of -60.4 pm/°C and humidity-insensitive behavior.

Optical trapping has proven to be an efficient method to control particles, including biological cells, single biological macromolecules, colloidal microparticles, and nanoparticles. Multiple types of particles have been successfully trapped, leading to various applications of optical tweezers ranging from biomedical through physics to material sciences. However, precise manipulation of particles with complex composition or of sizes down to nanometer-scales can be difficult with conventional optical tweezers, and an alternative manipulation tool is desired. Incorporating optical nanofibers into an optical tweezers setup allows us to overcome some of these limitations. Optical nanofibers have the added advantages of being easily connected to a fibered experimental setup, being simple to fabricate, and providing strong electric field confinement and intense magnitude of evanescent fields at the nanofiber's surface. Many different particles have been trapped, rotated, transported, and assembled with such a system. Here, we discuss some recent observations of microparticle manipulation, such as Janus particle manipulation, negative torque, and transverse spin effects.

Several developed low-cost, highly sensitive, and simple to realize and to use plasmonic sensor configurations will be here recalled. In particular, the proposed sensor configurations are based on unconventional platforms that efficiently excite the plasmonic phenomena in gold nanofilms, continuous or nanostructured, such as polymer optical fibers and light-diffusing fibers (LDFs). The proposed platforms can be combined with chemical and biological receptors in several application fields. In these cases, we can obtain the selectivity for the substances of interest via the use of specific Molecular Recognition Elements (MREs) in contact with the plasmonic sensing surfaces, such as those based on molecularly imprinted polymers (MIPs), antibodies, aptamers, and nanoMIPs. The substances measured with the proposed approach are pollutants, viruses, bacteria, toxic metals, pesticides, or other molecules of interest to detect in aqueous solutions. So, the advantages and disadvantages of each biochemical sensor system are presented in detail.

Cochlear implantation surgery is the only available treatment to restore hearing for individuals afflicted with severe to profound sensorineural hearing impairment. This procedure involves the precise insertion of a cochlear electrode array (EA), within constrained anatomical spaces with bending radii as minimal as 2 mm. During the insertion of EAs, surgeons primarily face two challenges: the potential for cochlear damage and the ideal positioning of the EA within the cochlear pathway. Although the use of EAs fitted with fiber Bragg grating sensors has shown successful real-time force monitoring, its effectiveness for precise placement is hindered by its low spatial resolution, making accurate EA positioning acquisition difficult. This study investigates the use of an optical frequency domain reflectometry (OFDR) sensing system, which has a spatial resolution of 0.65 mm to aid in the precise positioning of EAs during insertion. We demonstrate that by using OFDR sensing technology, a bare single-mode silica optical fiber with cladding and coating diameters of 50 μm and 105 μm, respectively, could be used to pinpoint the exact location of an EA. The frequency shift response along the fiber length correlates with the bending radius of the CI model, underscoring the potential of OFDR sensing technology to assist in EA positioning during cochlear implantation surgery.

Plasmonic structures offer exciting possibilities for biosensors applications, such as neuro-endoscopy. However, the interaction of plasmonic structures with brain cells in an endoscopic fashion requires precise control of the excitation light achievable only through a microscopy-based sensing scheme, where it is possible to finely tune the distribution of intensity and phase of the excitation field. Here we describe the available technological strategies to incorporate plasmonic structures at the tip of multimode optical fibers, tackling both the fabrication and photonic coupling challenges.

The main goal of planetary exploration missions is the search for life and the study of the habitability. For this purpose, the development of instrumentation that can analyze parameters as pH, which is an indicator that provides astrobiological information, is of great interest.

The study is carried out with two kind of fiber optic sensors to demonstrate the feasibility for planetary exploration since they are sensitive to the surrounding refractive index: Long Period Fiber Gratings (LPFG) fabricated with two different methods and Tilted Fiber Bragg Gratings (TFBG).

In order to develop a fiber optic pH sensor, a polyvinyl alcohol (PVA)/polyacrylic Acid (PAA) hydrogel film (~ 2 μm thickness) has been deposited on the gratings and the first measurements have been performed. The refractive index of the polymer changes depending on the pH value, and this change is measured by monitoring the Dip Wavelength Shift (DWS) and the transmission power.

The experimental results obtained with the coated fiber optic sensors in a range from pH2 to pH8 show that the LPFGs have a higher sensitivity in terms of nm/pH than the TFBG as expected. It was observed that the longer the grating length of the sensors, the greater the hysteresis.

The aim of the future work is to submit the pH sensors to an ionizing radiation test to verify that the polymer does not suffer degradation in a harsh environment similar to the one encountered in future in-situ explorations for astrobiology studies.

This paper reports a methodology for the design of a segment transmitter for indoor spaces based on optical fibers with different geometric parameters. The segment transmitter made this way aims to simulate the characteristics of a typical VLC transmitter. The article deals with the possibilities of using optical fibers with the possibilities of lighting and communication using the visible spectrum. Design options are studied using a 3D software model, which is then verified using real measurements. A POF (Plastic Optical Fiber) with a large numerical aperture and a core diameter of 550 μm is used to construct the segment transmitter.

Traffic monitoring is the subject of scientific publications and technical solutions, primarily due to the need to optimize and increase traffic safety. There are many systems that can determine direction, velocity, or make vehicle classifications. These can be, for example, traditional camera systems, laser gates, LIDAR scanning, pneumatic sensors, or induction loops. A non-traditional approach is the use of optical fibers as a traffic sensor. Optical fiber sensors use different technologies, one of them being sensors that evaluate the phase change of light (interferometers). The enormous sensitivity of these sensors combined with electromagnetic inertia are promising parameters for deploying system in areas that may be disturbed by magnetic fields or require special security requirements. The focus of this research is an optical fiber sensor based on the Michelson interferometer. The paper deals with the sensitivity of the measuring arm when changing its arrangement. Different configurations of the measuring fiber arrangement in relation to the objects to be monitored lead to the construction of a monitoring system with properties useful for direction monitoring and velocity measurement. This paper deals with the asymmetric configuration of the measuring arm of an optical fiber interferometer. Experiments in outdoor vehicular traffic conditions together with frequency spectrum analysis investigate the usability of the measurement system. The system itself can be extended to classify the measured objects by analyzing the amplitude frequency spectrum and using machine learning.

In this study, we present a fiber-tip Fabry-Perot interferometer operating in reflective mode, fabricated on the end faces of standard single-mode optical fibers using the Two-Photon Polymerization 3D nanoprinting method. Theoretical analysis highlights the primary challenge in accurately fitting the geometric dimensions of the cavity due to light beam divergence at the end of a single-mode fiber. Therefore, significant emphasis was placed on creating a compact structure with a high-reflection mirror formed on the printed tip. Various shapes of reflective surfaces were tested, including flat and concave. Additionally, to improve reflection we used the cathode sputtering method to get thin metal films on the printed surfaces. During conducted research, it has been demonstrated that the optimal solution is to cover only one surface of the resonator. This necessitated the development of a structure with a unique shape, enabling the deposition of a thin metallic layer solely on the top surface while simultaneously preventing deposition on the core.

In this study, experimental investigation of fiber-based Fabry-Perot is compared against the theoretical predictions of Fabry-Perot resonators. The special emphasis in this study was placed on testing the perspectives for resonance enhancement by coating the fiber facets by highly reflective surfaces and by replacing the flat surfaces by concave mirrors fabricated by the Two-Photon Polymerization (2PP) 3D nano-printing method. Golden layers of varying thickness were deposited on both flat and concave mirrors of optical fiber Fabry-Perot resonators, which were constructed from simply two optical fiber tips carefully aligned parallel to each other. An improvement of extinction ratio by even 12.5 dB and higher finesse of the resonance signal was registered. The resonance spectra resulting from such modifications were measured and discussed in relation to the assumptions of the theory for free-space Fabry-Perot resonators. It was demonstrated that the most optimal reflectance (R) values of both mirrors for the standard Fabry-Perot cavities (R1 = R2) are not the most optimal in case of fiber Fabry-Perot cavities.

An output dielectric mirror is deposited on the central part (~15 μm diameter) at the end face of a 1-km graded-index fiber and tested as output mirror of multimode Raman laser with highly-multimode (M²~34) 940-nm LD pumping. In the cavity with highly-reflective input FBG, Raman lasing of Stokes wave at 976 nm starts at the threshold pump power of ~80 W. The output beam quality factor measured near the threshold (~1W at 976 nm) M²~2 confirms mode selective properties of such output mirror. The power scaling capabilities at increased pump power together with a more detailed characterization of the output beam (spatial profile, spectrum and its stability) are performed and the obtained characteristics are compared with those for output coupling based on Fresnel reflection from the mirror-free fiber end face.