Refractive Index and Temperature Sensing Using Inter-Core Crosstalk in Multicore Fibers

[EN] Multicore optical fibers are of great interest in the optical sensing field. Their core diversity and spatial distribution enable the development of sensing mechanisms that are not possible in single-core fibers. In this paper, we study the use of the inter-core crosstalk phenomena for the implementation of a surrounding refractive index (SRI) sensor. The selective inscription of a tilted fiber Bragg grating (TFBG) intentionally increases the inter-core crosstalk between the inscribed cores and makes it sensitive to the SRI. With this technique we simplify the measurement of the SRI and improve the identification and tracking of the excited cladding modes, as compared with the analysis of the transmission spectrum of a TFBG in single-core fibers. The proposed device is also sensitive to temperature. Temperature is obtained from the crosstalk wavelength shift with a measured sensitivity of 9.75 pm/degrees C. The SRI is obtained from the measurement of the crosstalk optical power. For increasing SRIs the cladding modes gradually fade, reducing the crosstalk optical power. We observed that the higher the tilt, the higher the sensor sensitivity. For a 7 degrees TFBG the SRI sensitivity obtained is -74.2 dB/RIU from 1.31 to 1.39 and -250.8 dB/RIU from 1.39 to 1.44.This work was supported in part by the Spanish Ministry of Economy and Competitiveness under the DIMENSION TEC2017 88029-R Project and in part by the Generalitat Valenciana by PROMETEO 2017/103 research excellency award and IDI/FEDER/2018 GVA Infraestructura. The work of J. Madrigal was supported by Universitat Politecnica de Valencia scholarship PAID-01-18. The work of D. Barrera was supported by Spanish MICINN fellowship IJCI-2017-32476.Madrigal-Madrigal, J.; Barrera Vilar, D.; Sales Maicas, S. (2019). Refractive Index and Temperature Sensing Using Inter-Core Crosstalk in Multicore Fibers. Journal of Lightwave Technology. 37(18):4703-4709. https://doi.org/10.1109/JLT.2019.2917629S47034709371

Optimization of multicore optical fibers with fiber Bragg gratings towards bend and shape sensing

A shape sensor based on fiber Bragg gratings (FBGs) in multicore fibers is a complex device with multiple factors which have to be accounted for a successful measure- ment system. In this dissertation, I considered several aspects of such shape and curvature sensors

Polarization dependent cladding modes coupling and spectral analyses of excessively tilted fiber grating

We report on the detailed analyses of mode coupling from fiber core to cladding in excessively tilted fiber gratings (ETFGs). Cladding modes responsible for the typical dual peak pairs in the transmission spectrum of ETFGs are identified with phase matching condition, which suggests two set of dual peak pairs generated from coupling to cladding modes with even and odd azimuthal order. The polarization dependence of those dual peak pairs are also investigated by calculating the coupling coefficients of cladding modes for two orthogonal polarizations. With the calculated coupling coefficients, the measured polarization dependent spectra can be reproduced numerically

Optical fiber sensors by direct laser processing: a review

The consolidation of laser micro/nano processing technologies has led to a continuous increase in the complexity of optical fiber sensors. This new avenue offers novel possibilities for advanced sensing in a wide set of application sectors and, especially in the industrial and medical fields. In this review, the most important transducing structures carried out by laser processing in optical fiber are shown. The work covers different types of fiber Bragg gratings with an emphasis in the direct-write technique and their most interesting inscription configurations. Along with gratings, cladding waveguide structures in optical fibers have reached notable importance in the development of new optical fiber transducers. That is why a detailed study is made of the different laser inscription configurations that can be adopted, as well as their current applications. Microcavities manufactured in optical fibers can be used as both optical transducer and hybrid structure to reach advanced soft-matter optical sensing approaches based on optofluidic concepts. These in-fiber cavities manufactured by femtosecond laser irradiation followed by chemical etching are promising tools for biophotonic devices. Finally, the enhanced Rayleigh backscattering fibers by femtosecond laser dots inscription are also discussed, as a consequence of the new sensing possibilities they enableThis research was funded by the Ministerio de Economía y Competitividad of Spain (TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (PID2019- 107270RB-C21), and the Ministerio de Educación, Cultura y Deporte of Spain (PhD grant FPU2018/02797)

Advanced fibre gratings in near- and mid-infrared region and their applications for structure monitoring and biosensing

This thesis emphasises an elaborate research finding on the fabrication, analysis of resonance spectral response and sensing applications in various fields using different type of optical fibre grating devices over an entire wavelength range from near- to mid-infrared (IR). Firstly, the major contribution described in the thesis is a thorough investigation of sensor structures, detailed in respect to writing techniques for optical fibre gratings irradiated by a frequency-doubled Argon ion laser. Thereafter spectral modulation for these UV-inscribed fibre Bragg gratings (FBGs), long period gratings (LPGs) and tilted fibre gratings (TFGs) of small and large angled structures are analysed. Special LPG devices with both dual peaks and 1st&2nd orders, and excessively tilted TFGs (Ex-TFGs) are also achieved with the resonances in the mid-IR range for enhanced sensitivity. Investigations of different sensing measurements, such as temperature, strain, bending and surrounding refractive index (SRI) for these fibre grating devices are performed. Another important contribution is the study on experimental investigation for the fabrication of FBGs into multicore fibre such as four core fibre (4CF) with two different core spacings and seven core fibre (7CF) are explained. A selective inscription method is utilised for inscribing FBGs into different cores of multicore fibre (MCF). The measurement performance with vector bend/twist sensing results in an enhanced sensitivity for FBGs in the distributed cores around the circumference of 4CF and 7CF is analysed in detail, showing the effective detection of both amplitude and direction. Whereas, in 7CF the central core FBG acts as the temperature reference having low bending sensitivity of -8.83 pm/m-1, presenting extra function for eliminating temperature cross-talk effect. The application for these grating devices is largely associated to structural monitoring in astronomy, biomedical sciences, and robotics. Finally, I have investigated different enzyme functionalised and nano-deposited LPG devices for bio and environmental sensing applications. The experimental findings for these sensors are discussed in glucose sensing measurements by observing resonance wavelength shift. Whereas LPGs fabricated with mono or multi-layered deposition of 2D nanomaterials, such as graphene oxide (GO) solution and single walled carbon nanotubes (SWCNT) are demonstrated with SRI measurement. Here, the fabricated devices show a significant intensity change into the transmission spectrum. The resonance response is observed in the near- to mid-IR ranges. This enhanced sensitivity is utilised for haemoglobin sensing in the detection of anaemia in human body and relative humidity sensing for monitoring environmental condition respectively. All demonstrated optical fibre grating based sensors have potential for a wide range of future applications in industry, medical and environmental sectors

Symmetry selective cladding modes coupling in ultrafast-written fiber Bragg gratings in two-mode fiber

The lower order cladding mode resonances of a fiber Bragg grating (FBG) are sensitive to fiber bending but their spectral density makes their response to bending very complex. In this work we present a simple method to reduce and control the number of low order cladding mode resonances via FBGs written in a two-mode fiber (TMF) with an ultrafast laser. Owing to the larger core size of the TMF, a slight break of the cylindrical asymmetry of the grating patterns can be induced when using femtosecond side-irradiation with a small change in the writing condition. This allows us to control the mode families coupled by the grating, and in particular to those modes that have positive or negative bending responses along certain bend directions. Experimental results demonstrate that several lower-order neighboring-cladding mode pairs coupled by the asymmetric TMFBG have antagonistic loss responses (by several dB) for different bending directions, thus allowing full 2D bending measurements with many applications in shape sensing. Finally, this device has similar advantages as tilted FBGs, i.e. temperature de-correlation and the possibility of increasing the signal to noise ratio by averaging simultaneous measurements on several pairs of resonances

Recent advances in biomedical photonic sensors: a focus on optical-fibre-based sensing

In this invited review, we provide an overview of the recent advances in biomedical pho tonic sensors within the last five years. This review is focused on works using optical-fibre technology, employing diverse optical fibres, sensing techniques, and configurations applied in several medical fields. We identified technical innovations and advancements with increased implementations of optical-fibre sensors, multiparameter sensors, and control systems in real applications. Examples of outstanding optical-fibre sensor performances for physical and biochemical parameters are covered, including diverse sensing strategies and fibre-optical probes for integration into medical instruments such as catheters, needles, or endoscopes.This work was supported by Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-107270RB-C21/AEI/10.13039/501100011033), and TeDFeS Project (RTC-2017- 6321-1) co-funded by European FEDER funds. M.O. and J.F.A. received funding from Ministerio de Ciencia, Innovación y Universidades of Spain under Juan de la Cierva-Formación and Juan de la Cierva-Incorporación grants, respectively. P.R-V. received funding from Ministerio de Educación, Cultura y Deporte of Spain under PhD grant FPU2018/02797

Label-free glucose biosensor based on enzymatic graphene oxide-functionalized tilted fiber grating

A label-free biosensor based on graphene oxide (GO) and glucose oxidase (GOD) functionalized tilted fiber grating (TFG) with large tilted angle is proposed for low concentration glucose detection. Taking advantages of sufficient binding sites of the GO with oxygen-containing groups, the enzymes (GOD) are covalently immobilized onto GO-deposited TFG via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxyl succinimide cross-liner. Surface characterizations with optical microscopy, scanning electron microscopy, Raman and infrared spectroscopy provide detailed assessments and evidences about the homogeneity of GO deposition and the effectiveness of enzyme modification. Through the specific catalysis reaction of GOD on the glucose, a considerable refractive index change in local microenvironment around the TFG results in the resonant wavelength shifts of cladding modes. The detection results of the low-concentration glucose demonstrate that the resonant wavelength has a linear response to the glucose concentration in the range of 0–8 mM with a response coefficient of ∼0.24 nm/mM, showing an enhanced sensitivity and bio-selectivity compared with the pristine TFG. The miniaturized size and remote label-free sensing capacity of the proposed device permit a multitude of opportunities for single-point measurement in harsh conditions and hard-to-reach spaces, presenting a promising candidate for label-free glucose detection for disease diagnosis, pharmaceutical research and bioengineering applications

Development of a fiber-based shape sensor for navigating flexible medical tools

Robot-assisted minimally invasive surgical procedure (RAMIS) is a subfield of minimally invasive surgeries with enhanced manual dexterity, manipulability, and intraoperative image guidance. In typical robotic surgeries, it is common to use rigid instruments with functional articulating tips. However, in some operations where no adequate and direct access to target anatomies is available, continuum robots can be more practical, as they provide curvilinear and flexible access. However, their inherent deformable design makes it difficult to accurately estimate their 3D shape during the operation in real-time. Despite extensive model-based research that relies on kinematics and mechanics, accurate shape sensing of continuum robots remains challenging. The state-of-the-art tracking technologies, including optical trackers, EM tracking systems, and intraoperative imaging modalities, are also unsuitable for this task, as they all have shortcomings. Optical fiber shape sensing solutions offer various advantages compared to other tracking modalities and can provide high-resolution shape measurements in real-time. However, commercially available fiber shape sensors are expensive and have limited accuracy. In this thesis, we propose two cost-effective fiber shape sensing solutions based on multiple single-mode fibers with FBG (fiber Bragg grating) arrays and eccentric FBGs. First, we present the fabrication and calibration process of two shape sensing prototypes based on multiple single-mode fibers with semi-rigid and super-elastic substrates. Then, we investigate the sensing mechanism of edge-FBGs, which are eccentric Bragg gratings inscribed off-axis in the fiber's core. Finally, we present a deep learning algorithm to model edge-FBG sensors that can directly predict the sensor's shape from its signal and does not require any calibration or shape reconstruction steps. In general, depending on the target application, each of the presented fiber shape sensing solutions can be used as a suitable tracking device. The developed fiber sensor with the semi-rigid substrate has a working channel in the middle and can accurately measure small deflections with an average tip error of 2.7 mm. The super-elastic sensor is suitable for measuring medium to large deflections, where a centimeter range tip error is still acceptable. The tip error in such super-elastic sensors is higher compared to semi-rigid sensors (9.9-16.2 mm in medium and large deflections, respectively), as there is a trade-off between accuracy and flexibility in substrate-based fiber sensors. Edge-FBG sensor, as the best performing sensing mechanism among the investigated fiber shape sensors, can achieve a tip accuracy of around 2 mm in complex shapes, where the fiber is heavily deflected. The developed edge-FBG shape sensing solution can compete with the state-of-the-art distributed fiber shape sensors that cost 30 times more

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications