Tilted Fiber Bragg Grating Research Articles

Polyaniline-coated tilted fiber Bragg gratings for pH sensing

In this paper, we report an optical fiber pH sensor based on a polyaniline coating deposited on the surface of a tilted fiber Bragg grating. The pH-sensitive film was synthesized by in situ chemical oxidative polymerization keeping track of the deposition time in order to optimize the sensor response. As a result, the sensor reacts to pH changes in the range of 2–12 with a fast response and its sensitivity is directly related to the film thickness. The main advantages of this PAni-TFBG pH sensor are its biochemical compatibility, temperature independence, long-term stability and remote real-time multipoint sensing features.

Principle and experiment of protein detection based on optical fiber sensing

A method for detecting protein molecules based on the tilted fiber Bragg grating (TFBG) surface plasma resonance (SPR) is proposed to achieve the quick online real-time detection of trace amount of proteins. The detection principles of the TFBG-SPR protein molecular probe are analyzed, and its feasibility is demonstrated. The intermediary material between the protein molecules and the golden layer outside of the fiber gratings is cysteamine hydrochloride. When the concentration of the cysteamine hydrochloride solution is 2 M, the shift of the TFBG resonance peak is 2.23 nm, illustrating that the cysteamine hydrochloride modifies the gold film successfully. IgG antigen solution is poured on the surface of the cysteamine hydrochloride modifying the gold-deposited TFBG. Finally, antigen-antibody hybridization experiment is carried out with a 10 mg/mL antibody solution, and after two hours of hybridization the resonance peak of the TFBG shifts 5.1 nm, which validates the feasibility and effectiveness of the TFBG-SPR protein molecular probe.

Biosensing with optical fiber gratings

AbstractOptical fiber gratings (OFGs), especially long-period gratings (LPGs) and etched or tilted fiber Bragg gratings (FBGs), are playing an increasing role in the chemical and biochemical sensing based on the measurement of a surface refractive index (RI) change through a label-free configuration. In these devices, the electric field evanescent wave at the fiber/surrounding medium interface changes its optical properties (i.e. intensity and wavelength) as a result of the RI variation due to the interaction between a biological recognition layer deposited over the fiber and the analyte under investigation. The use of OFG-based technology platforms takes the advantages of optical fiber peculiarities, which are hardly offered by the other sensing systems, such as compactness, lightness, high compatibility with optoelectronic devices (both sources and detectors), and multiplexing and remote measurement capability as the signal is spectrally modulated. During the last decade, the growing request in practical applications pushed the technology behind the OFG-based sensors over its limits by means of the deposition of thin film overlays, nanocoatings, and nanostructures, in general. Here, we review efforts toward utilizing these nanomaterials as coatings for high-performance and low-detection limit devices. Moreover, we review the recent development in OFG-based biosensing and identify some of the key challenges for practical applications. While high-performance metrics are starting to be achieved experimentally, there are still open questions pertaining to an effective and reliable detection of small molecules, possibly up to single molecule, sensing in vivo and multi-target detection using OFG-based technology platforms.

Narrowband interrogation of plasmonic optical fiber biosensors based on spectral combs

Gold-coated tilted fiber Bragg gratings can probe surface Plasmon polaritons with high resolution and sensitivity. In this work, we report two configurations to interrogate such plasmonic biosensors, with the aim of providing more efficient alternatives to the widespread spectrometer-based techniques. To this aim, the interrogation is based on measuring the optical power evolution of the cladding modes with respect to surrounding refractive index changes instead of computing their wavelength shift. Both setups are composed of a broadband source and a photodiode and enable a narrowband interrogation around the cladding mode that excites the surface Plasmon resonance. The first configuration makes use of a uniform fiber Bragg grating to filter the broadband response of the source in a way that the final interrogation is based on an intensity modulation measured in transmission. The second setup uses a uniform fiber grating too, but located beyond the sensor and acting as a selective optical mirror, so the interrogation is carried out in reflection. Both configurations are compared, showing interesting differential features. The first one exhibits a very high sensitivity while the second one has an almost temperature-insensitive behavior. Hence, the choice of the most appropriate method will be driven by the requirements of the target application.

Wide Range Refractive Index Measurement Using a Multi-Angle Tilted Fiber Bragg Grating

The conventional single-angle tilted fiber Bragg grating (TFBG) can only excite a certain range of cladding modes, limiting it for refractive index (RI) measurement in a wide range. In this letter, we fabricate and demonstrate a multi-angle TFBG, in which five individual TFBGs with tilt angles ranging from 5° to 25° are sequentially inscribed along the core of a single mode fiber within a length of 20 mm. The multi-angle TFBG excites a continuous spectral comb of narrowband-cladding modes over a much wider wavelength range (>170 nm) than a single-angle TFBG, making it suitable for dynamic RI measurement over a wide range (1.15–1.45). We have experimentally measured aqueous solutions with RI ranging from 1.30 to 1.45 using the uncoated (by monitoring the cut-off mode) and gold-coated (by monitoring the surface Plasmon resonance) multi-angle TFBGs, and both methods show linear responses, with RI sensitivities about 500 nm/RIU.

Tilted fiber Bragg gratings in multicore optical fibers for optical sensing.

We have inscribed a tilted fiber Bragg grating (TFBG) in selected cores of a multicore optical fiber. The presence of the TFBG permits to couple light from the incident-guided mode to the cladding modes and to the neighbor cores, and this interaction can be used for optical sensing. We measured different magnitudes: strain, curvature magnitude and direction, and external refractive index. The curvature results show a linear dependence of the maximum crosstalk with the curvature magnitude with a sensitivity of 2.5 dB/m-1 as the curvature magnitude increases and at the same time a wavelength shift of 70 pm/m-1. Changes in the external refractive index gradually vanish the cladding modes resonances and the crosstalk between the different cores, obtaining a reduction of the 90% of the optical spectra integral area for refractive indexes between 1.398 and 1.474.

Simultaneously two‐parameter measurement using tilted fiber grating and long period fiber grating

ABSTRACTWe proposed and demonstrated a complex sensor, which combined a tilted fiber Bragg grating and a long period fiber grating. We used this sensor to measure the surrounding refractive index and temperature of an unknown liquid. The measured range of the temperature and environmental refractive index were 30–70°CC and 1.33–1.4, respectively. The measured results have linearly trend with high sensitivity. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1122–1125, 2017

Fabrication of chirped and tilted fiber Bragg gratings and suppression of stimulated Raman scattering in fiber amplifiers.

Stimulated Raman scattering (SRS) is one of the main limits for fiber lasers further power scaling. We report on the suppression of the stimulated Raman scattering in fiber laser amplifier using chirped and tilted fiber Bragg gratings (CTFBGs) for the first time. In this paper, we design and fabricate a CTFBG used to suppress the SRS in 1090 nm fiber laser output, and establish a system to test the effect of suppression. A maximum suppression ratio nearly 25 dB is achieved. Experimental results demonstrate that CTFBGs can increase the Raman threshold and promote the slope efficiency of the whole system, which is significant for further power scaling in high power oscillators and amplifiers.

啁啾倾斜Bragg光纤光栅制作及Raman滤除研究

啁啾倾斜Bragg光纤光栅制作及Raman滤除研究

Immunosensing with Near-Infrared Plasmonic Optical Fiber Gratings.

Surface Plasmon resonance (SPR) optical fiber biosensors constitute a miniaturized counterpart to the bulky prism configuration and offer remote operation in very small volumes of analyte. They are a cost-effective and relatively straightforward technique to yield in situ (or even possibly in vivo) molecular detection. They are usually obtained from a gold-coated fiber segment for which the core-guided light is brought into contact with the surrounding medium, either by etching (or side-polishing) or by using grating coupling. Recently, SPR generation was achieved in gold-coated tilted fiber Bragg gratings (TFBGs). These sensors probe the surrounding medium with near-infrared narrowband resonances, which enhances both the penetration depth of the evanescent field in the external medium and the wavelength resolution of the interrogation. They constitute the unique configuration able to probe all the fiber cladding modes individually, with high Q-factors. We use these unique spectral features in our work to sense proteins and extra-cellular membrane receptors that are both overexpressed in cancerous tissues. Impressive limit of detection (LOD) and sensitivity are reported, which paves the way for the further use of such immunosensors for cancer diagnosis.

基于石墨烯涂覆倾斜光纤光栅的折射率传感

基于石墨烯涂覆倾斜光纤光栅的折射率传感

Multimode interference-based fiber sensor in a cavity ring-down system for refractive index measurement

This work reports a multimode interference-based fiber sensor in a cavity ring-down system (CRD) for sensing temperature-induced refractive index (RI) changes of water. The sensing head is based in multimodal interference (MMI) and it is placed inside the fiber loop cavity of the CRD system. A modulated laser source was used to send pulses down into the fiber loop cavity and an erbium-doped fiber amplifier (EDFA) was placed in the fiber ring to provide an observable signal with a reasonable decay time. The behavior of the sensing head to temperature was studied due to its intrinsic sensitivity to said parameter – a sensitivity of −1.6×10−9μs/°C was attained. This allowed eliminating the temperature component from RI measurement of water and a linear sensitivity of 580μs/RIU in the RI range of 1.324–1.331 was obtained. The use of a MMI fiber sensor in the proposed CRD configuration allowed achieving a sensitivity ∼4-fold than that obtained with a tilted fiber Bragg grating and ∼2-fold than that when a micrometric channel inscribed in the fiber was used.

Liquid Crystal-Embedded Tilted Fiber Grating Electric Field Intensity Sensor

We propose and experimentally demonstrate a novel electric field intensity sensor by using a tilted fiber Bragg grating (TFBG) interacting with liquid crystal. The TFBG is surrounded by the liquid crystal whose effective refractive index changes over the range from 1.53 to 1.70 in response to the strength of external electric fields. The guiding properties of cladding modes excited in the TFBG are, therefore, sensitive to the external electric field. By monitoring the amplitude of a selected cladding mode resonance, we measured electric field strength over a range of 1.0–4.8 kV/cm. The sensor demonstrated better than 99% linearity with a sensitivity of 0.287 dB/kV/cm. Temperature cross-sensitivity can be effectively reduced by referenced to the core mode of the proposed TFBG sensor.

Temperature-insensitive simultaneous rotation and displacement (bending) sensor based on tilted fiber Bragg grating.

In this paper, we present a method for the simultaneous measurement of rotation and displacement or rotation and bending using single tilted fiber Bragg grating (TFBG). The insensitivity of the proposed system to temperature changes and the stretching direction of the fiber section in the sensing structure have been demonstrated. The experimentally determined sensitivities for rotation, displacement and bending are as follows: -0.0018 1/deg., 0.0054 nm/mm, and -0.055 1/mm over the measurement ranges of approximately 25-80 degrees, 34-74 mm, and 26.4-20 mm, respectively. The presented measurement system is versatile due to the ability to tune the measurement range by changing the fiber-loop radius.

Investigations on highly sensitive fiber Bragg gratings with different grating shapes for far field applications

The Fiber Brag Grating (FBG) optical sensor is investigated with uniform fiber grating (UFBG), superstructure fiber Bragg grating (SFBG) and tilted fiber Bragg grating (TFBG) using Finite Difference Time Domain (FDTD). The effect of variation in Refractive Index (RI) on the far field pattern of the guided light, reflection and the transmission power spectra of the gratings have been observed. TFBG reported the best performance exhibiting maximum peak amplitude of far field is 0.218 a. u., followed by UFBG is 0.0467 a. u. and SFBG is 0.0383 a. u. Further, the coupling efficiency of the gratings has been calculated from the mode overlap integral. The TFBG reported the highest value of 5.622%. SFBG followed it with 0.466% and UFBG with 0.012%. The SFBG reported the maximum value of reflected power i.e. 1.9456dB which is 3 times to that of UFBG (0.6317dB) and 5.67 times to that of TFBG (0.3433dB).

Fiber optic relative humidity sensor based on the tilted fiber Bragg grating coated with graphene oxide

A fiber optic relative humidity (RH) sensor based on the tilted fiber Bragg grating (TFBG) coated with graphene oxide (GO) film was presented. Amplitudes of the cladding mode resonances of the TFGB varies with the water sorption and desorption processes of the GO film, because of the strong interactions between the excited backward propagating cladding modes and the GO film. By detecting the transmission intensity changes of the cladding mode resonant dips at the wavelength of 1557 nm, the maximum sensitivity of 0.129 dB/%RH with a linear correlation coefficient of 99% under the RH range of 10–80% was obtained. The Bragg mode of TFBG can be used as power or wavelength references, since it is inherently insensitive to RH changes. In addition, the proposed humidity sensor shows a good performance in repeatability and stability.

Electrochemical Surface Plasmon Resonance Fiber-Optic Sensor: In Situ Detection of Electroactive Biofilms.

Spectroelectrochemistry has been found to be an efficient technique for revealing extracellular electron transfer (EET) mechanism of electroactive biofilms (EABs). Herein, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor for monitoring EABs in situ. The sensor uses a tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber and coated with nanoscale gold film for high-efficiency SPR excitation. The wavelength shift of the surface plasmon resonance (SPR) over the fiber surface clearly identifies the electrochemical activity of the surface localized (adjacent to the electrode interface) bacterial cells in EABs, which differs from the "bulk" detections of the conventional electrochemical measurements. A close relationship between the variations of redox state of the EABs and the changes of the SPR under potentiostatic conditions has been achieved, pointing to a new way to study the EET mechanism of the EABs. Benefiting from its compact size, high sensitivity, and ease of use, together with remote operation ability, the proposed sensor opens up a multitude of opportunities for monitoring EABs in various hard-to-reach environments.

Fiber Grating-Assisted Surface Plasmon Resonance for Biochemical and Electrochemical Sensing

Surface plasmon resonance (SPR) optical fiber sensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for in situ high sensitivity biochemical and electrochemical measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo . Grating-assisted and polarization control are two key properties of fiber-optic SPR sensors to achieve unprecedented sensitivities and limits of detection. The biosensor configuration presented here utilizes a nanoscale metal-coated tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber core with no structural modifications. Such sensor provides an additional resonant mechanism of high-density narrow cladding mode spectral combs that overlap with the broader absorption of the surface plasmon for high accuracy interrogation. In this paper, we briefly review the principle, characterization and implementation of plasmonic TFBG sensors, followed by our recent developments of the “surface” and “localized” affinity studies of the biomolecules for real life problems and the electrochemical actives of electroactive biofilms for clean energy resources.

High resolution fiber optic surface plasmon resonance sensors with single-sided gold coatings.

The surface plasmon resonance (SPR) performance of gold coated tilted fiber Bragg gratings (TFBG) at near infrared wavelengths is evaluated as a function of the angle between the tilt plane orientation and the direction of single- and double-sided, nominally 50 nm-thick gold metal depositions. Scanning electron microscope images show that the coating are highly non-uniform around the fiber circumference, varying between near zero and 50 nm. In spite of these variations, the experimental results show that the spectral signature of the TFBG-SPR sensors is similar to that of simulations based on perfectly uniform coatings, provided that the depositions are suitably oriented along the tilt plane direction. Furthermore, it is shown that even a (properly oriented) single-sided coating (over only half of the fiber circumference) is sufficient to provide a theoretically perfect SPR response with a bandwidth under 5 nm, and 90% attenuation. Finally, using a pair of adjacent TFBG resonances within the SPR response envelope, a power detection scheme is used to demonstrate a limit of detection of 3 × 10-6 refractive index units.

Influence of the cladding diameter of optical fiber on the simultaneous measurement of the refractive index and temperature of liquids using tilted fiber Bragg grating

We considered the influence of the core and cladding diameters on the simultaneous measurement of the refractive index and temperature of liquids using a tilted fiber Bragg grating (TFBG). When the cladding diameter of a TFBG was only reduced from 125 to 123 µm, the calculated refractive index differed by 0.0068 from the expected value. When the core diameter was reduced from 9.6 to 7.8 µm, the change was less than 0.0005. We found that equalization of cladding diameter is required to improve the precision of the simultaneous measurement of the refractive index and temperature of liquids.