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We report on an extrinsic surface plasmon-enhancedrefractometer based on cladding mode resonance excitation in a photonic crystal fiber (PCF) equipped with a straight fiber Bragggrating (FBG). First, we show that the lattice pitch and the air hole diameter of the PCF microstructure define the spectral locationof the excited cladding mode resonances. Second, we demonstrate that if the PCF parameters are properly selected, those resonancesare sensitive to increases in steps of 1×10−4 refractive index units(RIU) of the refractive index value close to that of water. To thebest of our knowledge, this is the first time that the sensitivity of PCF cladding mode resonances to refractive index changesin water-based solutions is reported. We achieved experimental values of 40.3 nm/RIU in terms of wavelength sensitivity and −801dB/RIU in terms of amplitude sensitivity. The performance of our sensor is therefore comparable to that of tilted FBGs in step-indexfibers used for water refractometry, which indicates the potential ofour PCF sensor for biosensing. In addition, the sensor fabricationdoes not require any post-processing such as etching or polishing,which allows preserving the integrity of the fiber probe. Finally, thenarrowspectrum within which the PCF operates, allows envisagingmulti-target detection with a single fiber probe by using cascadedwavelength-multiplexed gratings.

Gold-coated tilted fiber Bragg gratings (TFBG) are refined plasmonic biosensors, highly sensitive to surrounding refractive index (RI) changes. Their interrogation usually relies on insertion loss measurements for single input polarized light, limiting the set of exploitable features. To overcome this limitation, we trigger the Jones formalism to retrieve the polarization enabling optimized plasmonic excitation for both phase and amplitude measurements. We present an experimental phase shift with a sensitivity as high as 45835°/RIU and further assess this approach to HER2 proteins sensing at 1µg/ml. We compare this angular modality with the one relying on the insertion loss using a quality factor that takes the shift as well as the dispersion into account. This strengthens its relevance in terms of precision for ultra-small RI variations.

We report on the thermal regeneration of tilted Bragg gratings (TFBGs) produced in hydrogen loaded SMF-28 optical fiber using two types of UV lasers: 266 nm femtosecond pulses and 193 nm nanosecond pulses. Different isochronal and isothermal annealing profiles are used to improve the regeneration of the cladding modes. Experimental results are in good agreement with simulation results. We show that TFBGs regenerate efficiently in the temperature range 850 °C – 900 °C when isothermal stepwise annealing profile is used. The regeneration efficiency of the cladding modes does not exceed 4.35%. The sensitivity to the surrounding refractive index is comparable to that of non-regenerated tilted Bragg gratings. These regenerated tilted Bragg gratings can be applied in several applications, like for example the follow up of high-temperature fabrication processes.

We report on highly reflective fiber Bragg gratings in photonic crystal fibers (PCF) that excite two types of cladding mode resonances. We consider two hexagonal lattice PCF structures with a similar air-filling fraction (0.4) but different lattice pitch values (2.5 and 3.6 μm). We demonstrate both experimentally and numerically that the lattice parameters of the microstructure influence the spectral location of the resonances and the spectral span that they occupy. For the PCF with the lattice pitch of 2.5 μm, we demonstrate its application for surface plasmon-enhanced refractometry of waterbased solutions with potential for biosensing applications.

To date, there is clear experimental evidence that gold-coated tilted fiber Bragg gratings (TFBGs) are highly sensitive plasmonicbiosensors that provide temperature-compensated detection of analytes at concentrations in the picomolar range. Asmost optical biosensors, they bring an evanescent wave in the surrounding medium, which makes them sensitive to both surface refractive index variations (= the useful biosensing signal) and to bulk refractive index changes (= the non-useful signal forbiosensing). This dual sensitivity makes them prone to drift. In this work, we study partially gold-coated TFBGs around theircross-section. These gratings present the ability to discriminate both volume and surface refractive index changes, which isinteresting in biosensing to enhance the signal-to-noise ratio. The effects induced in the TFBGs transmitted amplitude spectrawere analyzed for surrounding refractive index (SRI) changes in the range 1.3360–1.3370. Then, the gold film wasbiofunctionalized with human epidermal growth factor receptor (HER2) aptamers using thiol chemistry. The detection of HER2proteins (a relevant cancer biomarker) at 10−9g/mL, 10−8g/mL and 10−6g/mL demonstrated the advantage toidentifyenvironmental perturbations through the bare area of the TFBGs, which is left not functionalized. The non-specific driftsthatcould exist in samples are eliminated and a wavelength shift only related to the surface modification is obtained.&nbsp

We show the possibility of using a femtosecond IR point-by-point inscribed grating as a probe to monitor the regeneration process of a UV-inscribed grating.

A novel FBG inscription method in cyclic transparent fluoropolymer (CYTOP) polymer optical fiber through the over-clad using phase mask technique and a femtosecond (fs) pulsed laser at 400 nm is reported. It shows that 8 mm-long uniform grating is obtained in less than 20 s with 500 µW average beam power.

An electro-plasmonic optical fiber grating biosensor was designed to attract and specifically detect breast cancer biomarkers (HER2) using aptamers. The developed biosensor exhibits a high sensitivity with an enhanced limit of detection to HER2.

Plasmonic tilted fiber Bragg gratings (TFBGs) are very efficient for fast, accurate, and minimally invasive biosensing. Their transmitted amplitude spectrum is a dense comb of narrowband cladding mode resonances (full width at half maximum

An electro-plasmonic biosensor is used to attract proteins and cells on the surface of a fiber optic probe by controlled biomolecular migration. Concentrating targets on a high performance plasmon-assisted fiber grating sensor leads to a drastic enhancement of the limit of detection. This architecture relies on a biofunctionalized gold coated tilted fiber Bragg grating (TFBG) that operates as a working electrode to enable electrophoresis in the probed medium. The applied electric field triggers the attraction of proteins over a distance of almost 250 μm from the sensor surface, which is more than two orders of magnitude larger than the intrinsic penetration depth of the plasmon wave. Quantitative determination of target analytes was performed by cyclic voltammetry measurements using the gold coated fiber as an electrode, simultaneously with optical transmission measurements of the underlying fiber grating. In our work, these electro-plasmonic optrodes were used against a clinically-relevant biomarker in breast cancer diagnosis, namely HER2 (Human Epidermal Growth Factor Receptor-2). In vitro assays confirm that their limit of detection lies in the subpicomolar range for proteins, which is beyond reach of similar sensors without voltammetry. The improved detection limit is further facilitated by an improvement of the signal-to-noise ratio of the read-out process. Whole cell capture is finally demonstrated by the same micro-system.

Fiber Bragg gratings (FBGs) in cyclic transparent fluoropolymer (CYTOP) optical fiber are the subject of a lot of research as they can be of interest for many applications, such as temperature, humidity, strain, and radiation sensing. We report here a new technique to produce high quality FBGs in CYTOP fiber. It uses a femtosecond laser system operating at 400 nm and a phase mask. In contrast to previously reported results, the gratings are obtained in a few seconds with a writing power as low as 80 μW. With this setup, 2 mm-long gratings with reflectivity up to 92 % and full width at half maximum bandwidth around 0.5 nm were obtained in less than 10 s. The resonance wavelengths of the FBGs are confirmed by numerical computation in the graded-index multimode CYTOP fiber, and the mode selection characteristic of FBGs in CYTOP is investigated. Finally, the temperature sensitivity of CYTOP FBG is measured in different mode groups for heating up and cooling down, showing values independent of the mode group measured, but with a small hysteresis.

Bare and gold-coated tilted fiber Bragg gratings (TFBGs) can nowadays be considered as a mature technology for volume and surface refractometric sensing, respectively. As for other technologies, a continuous effort is made towards the production of even more sensitive sensors, thereby enabling a high-resolution screening of the surroundings and the possible detection of rare events. To this aim, we study in this work the development of TFBG refractometers in 4-core fibers. In particular, we show that the refractometric sensitivity of the cut-off mode can reach 100 nm/RIU for a bare grating. Using another demodulation method, a tenfold sensitivity increase is obtained when tracking the extremum of the SPR (surface plasmon resonance) envelope for a gold-coated TFBG configuration. Immobilization of DNA probes was performed as a proof-of-concept to assess the high surface sensitivity of the device.

A plasmonic optical fiber grating aptasensor was developed for real-time detection of the HER2 breast cancer biomarker. The designed biosensor shows an accurate and selective sensing of HER2 with respect to a biomarker negative control.

We investigated post-irradiation variations of the radiation induced attenuation (RIA) of polymer perfluorinated (CYTOP) optical fiber exposed to gamma radiation. The RIA measured five months after the irradiation was qualitatively similar to that measured several hours after irradiation. However, quantitatively the RIA post-irradiation evolution significantly depends on the spectral range: in the visible range, the transmission partly recovers, while in the infrared, at wavelengths above 1300 nm the RIA grows and then saturates becoming permanent. The latter feature is prospective for gamma radiation dosimetry as a permanent long-term indicator of received radiation dose.

In the biomedical detection context, plasmonic tilted fiber Bragg gratings (TFBGs) have been demonstrated to be a very accurate and sensitive sensing tool, especially well-adapted for biochemical detection. In this work, we have developed an aptasensor following a triple strategy to improve the overall sensing performances and robustness. Single polarization fiber (SPF) is used as biosensor substrate while the demodulation is based on tracking a peculiar feature of the lower envelope of the cladding mode resonances spectrum. This method is highly sensitive and yields wavelength shifts several tens of times higher than the ones reported so far based on the tracking of individual modes of the spectrum. An amplification of the response is further performed through a sandwich assay by the use of specific antibodies. These improvements have been achieved on a biosensor developed for the detection of the HER2 (Human Epidermal Growth Factor Receptor-2) protein, a relevant breast cancer biomarker. These advanced developments can be very interesting for point-of-care biomedical measurements in a convenient practical way.

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.

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.

PubMed: 32168970, Instrumentation techniques, implementation and installation methods are major concerns in today's distributed and quasi-distributed monitoring applications using fiber optic sensors. Although many successful traffic monitoring experiments have been reported using Fiber Bragg Gratings (FBGs), there has been no standardized solution proposed so far to have FBG seamlessly implemented in roads. In this work, we investigate a mobile platform including FBG sensors that can be positioned on roads for the purpose of vehicle speed measurements. The experimental results prove the efficiency of the proposed platform, providing a perspective toward weigh-in-motion systems.

This study reports on high temperature behaviour and stability tests of type I and type IA FBGs. The gratings temperature is firstly increased monotonously up to 650 °C, then fixed at this temperature for several hours. By monitoring the reflection spectra of the gratings we show that standard type I grating disappears and then regenerates while type IA grating decreases monotonously and shifts to lower wavelength before it disappears without regenerating.

Type-I fiber Bragg gratings photo-inscribed in hydrogen-loaded B/Ge co-doped silica single-mode optical fibers have been regenerated efficiently at 450°C, which is the lowest temperature reported so far. The mechanical strength of the annealed fiber is preserved while ensuring temperature sensing of the regenerated gratings up to 900°C. Unlike low temperature cycles (≤600°C), an annealing process at higher temperatures revealed faster regeneration for strong gratings. Changes in grating strength were also measured before the regeneration cycle. These behaviors suggest the contribution of different mechanisms to the regeneration process with different relative dynamics.

Saccharide sensors represent a broad research area in the scope of sensing devices and their involvement in the medical diagnosis field is particularly relevant for cancer detection at early stage. In that context, we present a non-enzymatic optical fiber-based sensor that makes use of plasmon-assisted tilted fiber Bragg gratings (TFBGs) functionalized for D-glucose biosensing through polydopamine (PDA)-immobilized concanavalin A (Con A). Our probe allows a live and accurate monitoring of the PDA layer deposition leading improved surface biochemistry. The SPR shift observed was assessed to 3.83 ± 0.05 nm within 20 min for a 2 mg/mL dopamine solution. Tests performed in different D-Glucose solutions have revealed a limit of detection close to 10−7 M with the highest sensitivity in the 10−6 to 10−4 M range. This configuration has the capability to overcome the limitations of current enzyme-based solutions.

7th European Workshop on Optical Fibre Sensors (EWOFS); OCT 01-04, 2019; Limassol, Cyprus, This paper shows that fiber Bragg gratings written in standard single mode optical fiber with IR femtosecond pulses and point-by-point technique are high temperature resistant (< 1000 degrees C). Moreover, after calibration process, these gratings can be used as a reference to study and discriminate between different high temperature annealing mechanisms involved in other types of gratings and/or fibers. Here we have considered the regeneration process of gratings written by UV laser in boron/germanium co-doped single mode optical fiber. Hence, the monitoring of grating strength and differential wavelength shift between femtosecond and type-I gratings during annealing cycle yields the wavelength shift due to the annealing of doping (mainly boron) and UV-related defects and their relative contributions to the regeneration mechanism.

Tilted fiber Bragg gratings (TFBGs) are now a well-established technology in the scientific literature, bringing numerous advantages, especially for biodetection. Significant sensitivity improvements are achieved by exciting plasmon waves on their metal-coated surface. Nowadays, a large part of advances in this topic relies on new strategies aimed at providing sensitivity enhancements. In this work, TFBGs are produced in both single-mode and multimode telecommunication-grade optical fibers, and their relative performances are evaluated for refractometry and biosensing purposes. TFBGs are biofunctionalized with aptamers oriented against HER2 (Human Epidermal Growth Factor Receptor-2), a relevant protein biomarker for breast cancer diagnosis. In vitro assays confirm that the sensing performances of TFBGs in multimode fiber are higher or identical to those of their counterparts in single-mode fiber, respectively, when bulk refractometry or surface biosensing is considered. These observations are confirmed by numerical simulations. TFBGs in multimode fiber bring valuable practical assets, featuring a reduced spectral bandwidth for improved multiplexing possibilities enabling the detection of several biomarkers.

It is common belief that photonic crystals behave similarly to isotropic and transparent media onlywhen their feature sizes are much smaller than the wavelength of light. Here, we counter that belief andwe report on photonic crystals that are transparent for anomalously high normalized frequencies up to0.9, where the crystal’s feature sizes are comparable with the free space wavelength. Using traditionalphotonic band theory, we demonstrate that the isofrequency curves can be circular in the region abovethe first stop band for triangular lattice photonic crystals. In addition, by simulating how efficiently atightly focused Gaussian beam propagates through the photonic crystal slab, we judge on the photoniccrystal’s transparency rather than on isotropy only. Using this approach, we identified a wide range ofphotonic crystal parameters that provide anomalous transparency. Our findings indicate the possibilityto scale up the features of photonic crystals and to extend their operational wavelength range forapplications including optical cloaking and graded index guiding. We applied our result in the domainof femtosecond laser micromachining, by demonstrating what we believe to be the first point-by-pointgrating inscribed in a multi-ring photonic crystal fiber.

In this Letter, we report the fast growth of high quality uniform Bragg gratings in trans-4-stilbenemethanol (TS)-doped poly(methyl methacrylate) (PMMA) step-index optical fibers. Grating manufacturing was obtained using a 400 nm femtosecond pulsed laser and a 1060-nm-period uniform phase mask. For 20 mW mean laser beam power, the grating reflectivity reaches 98% in ∼60 s.

Fiber Bragg gratings (FBGs) are well-known to be essential elements in optical communications, optical fiber based sensors and fiber lasers [1]. One of the most recent methods for fabricating FBGs is referred to as point-by-point inscription and uses femtosecond duration pulses of an infrared laser tightly focused to the fiber core region, such that every pulse forms a single grating period [2]. The periodicity of the grating is controlled by moving the fiber along its axis using translation stages at a pre-defined speed for a known repetition rate of the laser. A multi-photon absorption process is responsible for the local refractive index modification induced by a single pulse. Gratings obtained using point-by-point inscription can for example be used at much higher temperatures than those fabricated using conventional UV laser based inscription.

This work presents a novel technique known as polarization dependent loss (PDL) towards the accurate detection of small transverse strains using optical fiber Bragg gratings. The fundamentals of PDL are explained and the benefits discussed. A cure cycle of a cross-ply composite with embedded fibers was monitored using this PDL technique and the data from the experiments are discussed. As shown, differences in transverse strain of up to 500 μe will go unnoticed with normal read-out equipment (1 pm resolution), while PDL is capable of accurately detecting much smaller values. Using PDL, it was possible to detect transverse strain build-up due to matrix polymerization, which was found to cause 60 μe of difference in transverse strains. A method was proposed combining the benefits of both PDL and amplitude techniques to achieve superior resolution in FBG read-out.

New dual temperature and strain sensor has been designed using eccentric second-order fiber Bragg gratings produced in standard single-mode optical fiber by point-by-point direct writing technique with tight focusing of 800 nm femtosecond laser pulses. With thin gold coating at the grating location, we experimentally show that such gratings exhibit a transmitted amplitude spectrum composed by the Bragg and cladding modes resonances that extend in a wide spectral range exceeding one octave. An overlapping of the first order and second order spectrum is then observed. High-order cladding modes belonging to the first order Bragg resonance coupling are close to the second order Bragg resonance, they show a negative axial strain sensitivity (−0.55 pm/με) compared to the Bragg resonance (1.20 pm/με) and the same temperature sensitivity (10.6 pm/°C). With this well conditioned system, temperature and strain can be determined independently with high sensitivity, in a wavelength range limited to a few nanometers.

In this work, eccentric Bragg gratings are photoinscribed in telecommunication-grade optical fibers. They are localized close to the core-cladding interface, yielding strong cladding mode resonance couplings and high photoinduced birefringence. Their transmitted amplitude spectrum is measured with polarized light while they are exposed to temperature changes up to 900°C. Despite the gratings' overall good thermal stability that confirms their robustness for high-temperature refractometry, we report an interesting polarization effect depending on both the cladding mode resonance family and mode order. While the core mode birefringence decreases with growing temperatures, certain cladding mode resonances show an increase in wavelength splitting between their orthogonally polarized components. This differential behavior is of high interest in developing high-resolution, multiparametric sensing platforms.

In this paper, we describe a theoretical study on the interference created by a phase mask when a femtosecond laser is used. The limitations of the phase mask-to-fiber distance are discussed and the optimal inscription range is established. Femtosecond lasers have the unique feature of short coherence length and thus the diffraction orders do not interfere after a certain distance travelled from the phase mask even if the phase mask has a poor zero order suppression. The equation describing this behaviour is presented and simulations are included for validation. The intensity profile of the overlapping ±1 diffraction orders after the phase mask is also studied for 1st order (1070 nm pitch) and for 2nd order (2140 nm pitch) phase masks.

We report highly localized second-order fibre Bragg gratings at 1585 nm inscribed by point-by-point focused infrared femtosecond pulses. A thin gold coating deposited on the fibre outer surface at the grating location allows shielding the cladding mode resonances from the outer medium, so that they remain present in the transmitted amplitude spectrum. The Bragg resonance of the second-order grating is surrounded by high-order cladding mode resonances of the first-order grating. These cladding modes exhibit the same temperature sensitivity as the Bragg resonance (10.6 pm/°C) but high differential strain sensitivity (-0.55 pm/μepsilon versus 1.20 pm/μepsilon for the Bragg mode). Therefore, the conditioning of the matrix inversion as demodulation method is fully satisfied, yielding a new design of fibre sensor able to discriminate between temperature and strain, with an unprecedented sensitivity.

In this paper, we report photo-inscription of uniform Bragg gratings in trans-4-stilbenemethanol-doped photosensitive step-index polymer optical fiber. Gratings were produced at ~1575 nm by the phase mask technique with a femtosecond laser emitting at 400 nm with different average optical powers (8 mW, 13 mW and 20 mW). The grating growth dynamics in transmission were monitored during the manufacturing process, showing that the grating grows faster with higher power. Using 20 mW laser beam power, the reflectivity reaches 94 % (8 dB transmission loss) in 70 seconds. Finally, the gratings were characterized in temperature in the range 20 - 45 °C. The thermal sensitivity has been computed equal to – 86.6 pm/°C.

An infrared femtosecond pulses laser is used to manufacture point-by-point gratings in telecommunication-grade optical fibres. The refractive index modulations are localized close to the core-cladding interface, yielding a strong coupling to cladding mode resonances together with an important photo-induced birefringence. Such gratings have been recently used for refractrometric measurements. In this work, their transmitted amplitude spectrum is measured with polarized light while they are exposed to temperature changes up to 900 °C. Despite an overall good thermal stability of the gratings that confirms their robustness for high-temperature refractometry, we report an interesting polarization effect depending on both the cladding mode resonance family (radially- and azimuthally-polarized modes) and mode order. While the birefringence of the core mode resonance decreases with the temperature, certain cladding mode resonances show an increase of the wavelength splitting between their orthogonally-polarized components. This differential behaviour can be of high interest to develop high-resolution multiparametric sensing platforms.

We have numerically identified hexagonal lattice parameters for PCF cladding that allow point-by-point grating writing. We designed and fabricated a PCF with suitable parameters and successfully inscribed a femtosecond point-by-point Bragg grating.