Showing papers on "Fiber Bragg grating published in 2013"

Tilted fiber Bragg grating sensors

Abstract: Optical fiber gratings have developed into a mature technology with a wide range of applications in various areas, including physical sensing for temperature, strain, acoustic waves and pressure. All of these applications rely on the perturbation of the period or refractive index of a grating inscribed in the fiber core as a transducing mechanism between a quantity to be measured and the optical spectral response of the fiber grating. This paper presents a relatively recent variant of the fiber grating concept, whereby a small tilt of the grating fringes causes coupling of the optical power from the core mode into a multitude of cladding modes, each with its own wavevector and mode field shape. The main consequence of doing so is that the differential response of the modes can then be used to multiply the sensing modalities available for a single fiber grating and also to increase the sensor resolution by taking advantage of the large amount of data available. In particular, the temperature cross-sensitivity and power source fluctuation noise inherent in all fiber grating designs can be completely eliminated by referencing all the spectral measurements to the wavelength and power level of the core mode back-reflection. The mode resonances have a quality factor of 105, and they can be observed in reflection or transmission. A thorough review of experimental and theoretical results will show that tilted fiber Bragg gratings can be used for high resolution refractometry, surface plasmon resonance applications, and multiparameter physical sensing (strain, vibration, curvature, and temperature).

Modeling and evaluating the performance of Brillouin distributed optical fiber sensors

Abstract: A thorough analysis of the key factors impacting on the performance of Brillouin distributed optical fiber sensors is presented. An analytical expression is derived to estimate the error on the determination of the Brillouin peak gain frequency, based for the first time on real experimental conditions. This expression is experimentally validated, and describes how this frequency uncertainty depends on measurement parameters, such as Brillouin gain linewidth, frequency scanning step and signal-to-noise ratio. Based on the model leading to this expression and considering the limitations imposed by nonlinear effects and pump depletion, a figure-of-merit is proposed to fairly compare the performance of Brillouin distributed sensing systems. This figure-of-merit offers to the research community and to potential users the possibility to evaluate with an objective metric the real performance gain resulting from any proposed configuration.

1.06 μm Q-switched ytterbium-doped fiber laser using few-layer topological insulator Bi₂Se₃ as a saturable absorber.

Abstract: Passive Q-switching of an ytterbium-doped fiber (YDF) laser with few-layer topological insulator (TI) is, to the best of our knowledge, experimentally demonstrated for the first time. The few-layer TI: Bi2Se3 (2–4 layer thickness) is firstly fabricated by the liquid-phase exfoliation method, and has a low saturable optical intensity of 53 MW/cm2 measured by the Z-scan technique. The optical deposition technique is used to induce the few-layer TI in the solution onto a fiber ferrule for successfully constructing the fiber-integrated TI-based saturable absorber (SA). By inserting this SA into the YDF laser cavity, stable Q-switching operation at 1.06 μm is achieved. The Q-switched pulses have the shortest pulse duration of 1.95 μs, the maximum pulse energy of 17.9 nJ and a tunable pulse-repetition-rate from 8.3 to 29.1 kHz. Our results indicate that the TI as a SA is also available at 1 μm waveband, revealing its potential as another broadband SA (like graphene).

Versatile multi-wavelength ultrafast fiber laser mode-locked by carbon nanotubes.

Abstract: Multi-wavelength lasers have widespread applications (e.g. fiber telecommunications, pump-probe measurements, terahertz generation). Here, we report a nanotube-mode-locked all-fiber ultrafast oscillator emitting three wavelengths at the central wavelengths of about 1540, 1550 and 1560 nm, which are tunable by stretching fiber Bragg gratings. The output pulse duration is around 6 ps with a spectral width of ~0.5 nm, agreeing well with the numerical simulations. The triple-laser system is controlled precisely and insensitive to environmental perturbations with <0.04% amplitude fluctuation. Our method provides a simple, stable, low-cost, multi-wavelength ultrafast-pulsed source for spectroscopy, biomedical research and telecommunications.

Multi-MHz retinal OCT

Abstract: We analyze the benefits and problems of in vivo optical coherence tomography (OCT) imaging of the human retina at A-scan rates in excess of 1 MHz, using a 1050 nm Fourier-domain mode-locked (FDML) laser. Different scanning strategies enabled by MHz OCT line rates are investigated, and a simple multi-volume data processing approach is presented. In-vivo OCT of the human ocular fundus is performed at different axial scan rates of up to 6.7 MHz. High quality non-mydriatic retinal imaging over an ultra-wide field is achieved by a combination of several key improvements compared to previous setups. For the FDML laser, long coherence lengths and 72 nm wavelength tuning range are achieved using a chirped fiber Bragg grating in a laser cavity at 419.1 kHz fundamental tuning rate. Very large data sets can be acquired with sustained data transfer from the data acquisition card to host computer memory, enabling high-quality averaging of many frames and of multiple aligned data sets. Three imaging modes are investigated: Alignment and averaging of 24 data sets at 1.68 MHz axial line rate, ultra-dense transverse sampling at 3.35 MHz line rate, and dual-beam imaging with two laser spots on the retina at an effective line rate of 6.7 MHz.

High-Tg TOPAS microstructured polymer optical fiber for fiber Bragg grating strain sensing at 110 degrees

Abstract: We present the fabrication and characterization of fiber Bragg gratings (FBGs) in an endlessly single-mode microstructured polymer optical fiber (mPOF) made of humidity-insensitive high-Tg TOPAS cyclic olefin copolymer. The mPOF is the first made from grade 5013 TOPAS with a glass transition temperature of Tg = 135°C and we experimentally demonstrate high strain operation (2.5%) of the FBG at 98°C and stable operation up to a record high temperature of 110°C. The Bragg wavelengths of the FBGs are around 860 nm, where the propagation loss is 5.1 dB/m, close to the fiber loss minimum of 3.67 dB/m at 787 nm.

Demonstration of a heterogeneously integrated III-V/SOI single wavelength tunable laser

Abstract: A heterogeneously integrated III-V-on-silicon laser is reported, integrating a III-V gain section, a silicon ring resonator for wavelength selection and two silicon Bragg grating reflectors as back and front mirrors. Single wavelength operation with a side mode suppression ratio higher than 45 dB is obtained. An output power up to 10 mW at 20 °C and a thermo-optic wavelength tuning range of 8 nm are achieved. The laser linewidth is found to be 1.7 MHz.

Fast brillouin optical time domain analysis for dynamic sensing

Abstract: A method for conducting fast Brillouin optical time domain analysis for dynamic sensing of optical fibers is provided herein The method includes the following stages: injecting a pump pulse signal into a first end of an optical fiber and a probe signal into a second end of the optical fiber, wherein the probe and the pump pulse signals exhibit a frequency difference between them that is appropriate for an occurrence of a Brillouin effect; alternating the frequency of either the probe or the pulse signals, so as the alternated signal exhibits a series of signal sections, each signal section having a predefined common duration and a different frequency; measuring the Brillouin probe gain for each one of the alternating frequencies; and extracting physical properties of the optical fiber throughout its length at sample points associated with the sampled time and the frequencies, based on the measured Brillouin probe gain

Fiber humidity sensors with high sensitivity and selectivity based on interior nanofilm-coated photonic crystal fiber long-period gratings

Abstract: A photonic crystal fiber (PCF) long-period grating (LPG) humidity sensor has been developed with high sensitivity and selectivity for nondestructive detection of moisture ingression into structures that can potentially lead to corrosion. We have proposed two types of nanofilms to be coated on the surface of air channels in the grating region by electrostatic self-assembly deposition processing. The primary nanofilm does not affect LPG properties such as resonance wavelength or transmission intensity which can impact sensing characteristics; however it increases the sensitivity by changing the refractive index of the surrounding material. The secondary nanofilm is used for selectively adsorbing analyte molecules of interest. The experimental results reveal that, compared to the conventional fiber LPGs and exterior nanofilm-coated PCF-LPG, the interior nanofilm-coated PCF-LPG humidity sensors have both the most sensitive resonance intensity change of 0.00022%/10 −3 dBm from relative humidity (RH) of 38% to 39% and average wavelength shift of 0.0007%/pm for a relative humidity variation from 22% to 29%. The proposed sensor shows excellent thermal stability as well.

Narrow-band generation in random distributed feedback fiber laser.

Abstract: Narrow-band emission of spectral width down to ~0.05 nm line-width is achieved in the random distributed feedback fiber laser employing narrow-band fiber Bragg grating or fiber Fabry-Perot interferometer filters. The observed line-width is ~10 times less than line-width of other demonstrated up to date random distributed feedback fiber lasers. The random DFB laser with Fabry-Perot interferometer filter provides simultaneously multi-wavelength and narrow-band (within each line) generation with possibility of further wavelength tuning.

Mid-infrared chalcogenide glass Raman fiber laser.

Abstract: We report the first demonstration of a Raman fiber laser (RFL) emitting in the mid-infrared, above 3 μm. The operation of a single-mode As2S3 chalcogenide glass based RFL at 3.34 μm is demonstrated by using a low-loss Fabry–Perot cavity formed by a pair of fiber Bragg gratings. A specially designed quasi-cw erbium-doped fluoride fiber laser emitting at 3.005 μm is used to pump the RFL. A laser output peak power of 0.6 W is obtained with a lasing efficiency of 39% with respect to the launched pump power.

All-optical switching in Sagnac loop mirror containing an ytterbium-doped fiber and fiber Bragg grating

Abstract: A configuration of all-optical switching based on a Signac loop mirror that incorporates an ytterbium-doped fiber and uniform fiber Bragg grating (FBG) is proposed in this paper. It is found that the transmission spectrum of this structure is the narrow splitting of the reflection spectrum of the FBG. The shift of this ultranarrow transmission spectrum is very sensitive to the intensity of the pump power. Thus, the threshold switching power can be greatly reduced by shifting such narrow transmission spectrum. Compared with the single FBG, the threshold switching power of this configuration is reduced by 4 orders of magnitude. In addition, the results indicate that this optical switching has a high extinction ratio of 20 dB and a ultrafast response time of 3 ns. The operation regime and switching performance under the cross-phase modulation cases are also investigated.

3D flexible needle steering in soft-tissue phantoms using Fiber Bragg Grating sensors

Abstract: Needle insertion procedures are commonly used for surgical interventions. In this paper, we develop a three-dimensional (3D) closed-loop control algorithm to robotically steer flexible needles with an asymmetric tip towards a target in a soft-tissue phantom. Twelve Fiber Bragg Grating (FBG) sensors are embedded on the needle shaft. FBG sensors measure the strain applied on the needle during insertion. A method is developed to reconstruct the needle shape using the strain data obtained from the FBG sensors. Four experimental cases are conducted to validate the reconstruction method (single-bend, double-bend, 3D double-bend and drilling insertions). In the experiments, the needle is inserted 120 mm into a soft-tissue phantom. Camera images are used as a reference for the reconstruction experiments. The results show that the mean needle tip accuracy of the reconstruction method is 1.8 mm. The reconstructed needle shape is used as feedback for the steering algorithm. The steering algorithm estimates the region that the needle can reach during insertion, and controls the needle to keep the target in this region. Steering experiments are performed for 110 mm insertion, and the mean targeting accuracy is 1.3 mm. The results demonstrate the capability of using FBG sensors to robotically steer needles.

Radiation Effects on Fiber Gratings

Abstract: Fiber Bragg and long period gratings are photonic components that find numerous applications in telecommunication and sensing. In some cases, such as space, high-energy physics, and nuclear industry, those applications include the presence of ionizing radiation. It is therefore essential to evaluate their radiation response. In this paper, we review radiation effects on various types of fiber gratings.

Fiber Bragg grating-based sensor for monitoring respiration and heart activity during magnetic resonance imaging examinations

Abstract: We present a fiber-optic sensor for monitoring respiration and heart activity designed to operate in the magnetic resonance imaging (MRI) environment. The sensor employs a Plexiglas springboard, which converts movements of the patient's body lying on the board (i.e., lung- and heart-induced vibrations) to strain, where a fiber Bragg grating attached to the board is used to measure this strain. Experimental studies are carried out during thoracic spine MRI examinations. The presence of the metal-free sensor construction in the MRI environment does not pose a threat to the patient and has no influence over the quality of imaging, and the signal is identical to that obtained without any electromagnetic interference. The results show that the sensor is able to accurately reflect the ballistocardiographic signal, enabling determinations of the respiration rate (RR) and heart rate (HR). The data delivered by the sensor are normally distributed on the Bland-Altman plot for the characteristic point determination and exhibit clear dependence on the RR and HR values for the RR and HR determinations, respectively. Measurement accuracies are better than 7% of the average values, and thus, with further development, the sensor will be implemented in routine MRI examinations.

Fiber Bragg Grating Strain Sensor Incorporated to Monitor Patient Vital Signs During MRI

Abstract: This paper reports on results obtained from monitoring the respiration and cardiac activity of a patient during a magnetic resonance imaging (MRI) survey using an optical strain sensor based on a fiber Bragg grating. The sensor is proposed specifically to acquire ballistocardiographic signals from a patient exposed to high intensity electromagnetic radiation. A Bland-Altman analysis shows the measurements that have a satisfactory accuracy for monitoring purposes, and the relative error is . The method is both noninvasive and safe for the patient. In addition, the sensor does not affect the MRI imaging quality.

A time- and wavelength-division multiplexing sensor network with ultra-weak fiber Bragg gratings

Abstract: A time- and wavelength-division multiplexing sensor network based on ultra-weak fiber Bragg gratings (FBGs) was proposed. The low insertion loss and the high multiplexing capability of the proposed sensor network were investigated through both theoretical analysis and experimental study. The demodulation system, which consists of two semiconductor optical amplifiers and one high-speed charge-coupled device module, was constructed to interrogate 2000 serial ultra-weak FBGs with peak reflectivity ranging from −47 dB to −51 dB and a spatial resolution of 2 m along an optical fiber. The distinct advantages of the proposed sensor network make it an excellent candidate for the large-scale sensing network.

On-line writing identical and weak fiber Bragg grating arrays

Abstract: We investigate the on-line writing identical fiber Bragg grating (FBG) arrays using the phase mask technique. Given the limitation of laser power, the energy density uniformity and the horizontal width of the writing spot cannot be further optimized. The results show that the FBG arrays obtained in the optimal process (drawing speed of 12 ± 0.15 m/min and average tension of 38.2 g) have a central wavelength bandwidth of less than 0.1 nm and an average reflectivity of 0.26%. Thus, the phase mask method is a promising alternative for on-line writing identical FBG arrays.

Radiation hard humidity sensors for high energy physics applications using polyimide-coated fiber Bragg gratings sensors

Abstract: This work is devoted to a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics (HEP) applications and in particular in experiments actually running at the European Organization for Nuclear Research (CERN). Due to the stringent sensors requirements concerning radiation hardness capability and low temperature operation, we focus our attention on the investigation of fiber optic humidity sensors based on polyimide-coated fiber Bragg gratings (FBG). Data here reported, obtained during a wide experimental campaign carried out in the laboratories of CERN, demonstrate that the selected technological platform is able to perform relative humidity (RH) measurements with percent resolution in the temperature range −15 to 20 °C as well as in presence of ionizing radiations up to 10 kGy, largely outperforming conventional humidity sensors, currently employed within CERN environment.

Long-Period Fiber Grating Cascaded to an S Fiber Taper for Simultaneous Measurement of Temperature and Refractive Index

Abstract: A novel, low-cost, and simple dual-parameter measurement scheme based on a cascaded optical fiber device composed of a long-period fiber grating (LPFG) and an S fiber taper Mach-Zehnder interferometer (SFT-MZI) is proposed and demonstrated. The crosstalk problem is solved as different resonance peaks of the LPFG and the MZI possess different refractive index (RI) and temperature sensitivities. Experimental results show distinctive spectral sensitivities of -52.57 nm/refractive index unit (RIU) and 45.87 pm/°C by the LPFG, and 311.48 nm/RIU (in the RI range of 1.33-1.37) and 12.87 pm/°C by the SFT-MZI. The simultaneous measurement of external RI and the temperature is experimentally demonstrated by the sensor. The RI and temperature calculated by the sensor matrix agree well with the actual RI and temperature in the experiment.

A Guide to Fiber Bragg Grating Sensors

Abstract: Optical fiber sensors (OFS) appeared just after the invention of the practical optical fiber by Corning Glass Works in 1970, now Corning Incorporated, that produced the first fiber with losses below 20 dB/km. At the beginning of this era, optical devices such as laser, photodetectors and the optical fibers were very expensive, afforded only by telecom companies to circumvent the old saturated copper telephone network. With the great diffusion of the optical fiber technology during the 1980’s and on, optoelectronic devices became less expensive, what favored their use in OFS.

Review of Femtosecond Laser Fabricated Fiber Bragg Gratings for High Temperature Sensing

Abstract: This paper reviews high temperature sensing applications based on fiber Bragg gratings fabricated by use of femtosecond laser. Type II fiber Bragg gratings fabricated in the silica fiber can sustain up to 1200 °C while that fabricated in the sapphire fiber have the good thermal stability up to 1745 °C.

Generation of 8 nJ pulses from a dissipative-soliton fiber laser with a nonlinear optical loop mirror

Abstract: Theoretical and experimental investigations of the behavior of normal-dispersion fiber lasers with nonlinear optical loop mirrors are presented. The use of a loop mirror causes the laser to generate relatively long, flat-topped pulses. The pulse energy can be high, but the pulse duration is limited to greater than 300 fs. Experimentally, 8 nJ pulses that can be dechirped to 340 fs duration are obtained. The laser is a step toward an all-fiber, environmentally stable design.

Femtosecond direct-writing of low-loss fiber Bragg gratings using a continuous core-scanning technique.

Abstract: We report the inscription of low-loss fiber Bragg gratings using focused femtosecond (fs) pulses and a continuous core-scanning technique. This direct-write technique produces high-fidelity Type I-IR gratings that share the inherent advantages of other direct-write methods, such as the point-by-point (PbP) method, for which the grating period is a free parameter. However, here we demonstrate an order of magnitude improvement in scattering loss compared to PbP gratings, to a level comparable with that of phase-mask-based fs inscription. A first-order grating was inscribed in standard telecommunications fiber with −49 dB transmission at the Bragg wavelength and 0.1 dB broadband scattering loss. Potential application of these gratings to large-mode-area fibers and chirped grating fabrication are highlighted.

Magnetic field sensor using tilted fiber grating interacting with magnetic fluid

Abstract: A novel magnetic field sensor using tilted fiber Bragg grating (TFBG) interacting with magnetic fluid is proposed and experimentally demonstrated. The TFBG is surrounded by magnetic fluid whose complex refractive index changes with external magnetic field. The guiding properties of cladding modes excited by the TFBG are therefore modulated by the external magnetic field. As a result, the magnetic field strength measurement is successfully achieved within a range up to 196 Gauss by monitoring extinction ratio of cladding mode resonance. Furthermore, temperature variation can be obtained simultaneously from the wavelength shift of the TFBG transmission spectrum.

A fast response intrinsic humidity sensor based on an etched singlemode polymer fiber Bragg grating

Abstract: A simple, low cost and fast response time intrinsic relative humidity sensor system based on an etched singlemode polymer fiber Bragg (POFBG) is presented in this paper. A macro-bend linear edge filter which converts the humidity induced wavelength shift into an intensity change is used as the interrogation technique. The singlemode POFBG is etched to micro-meters in diameter to improve the response time of the humidity sensor. A response time of 4.5 s is observed for a polymer FBG with a cladding diameter of 25 μm. The overall sensor system sensitivity was 0.23 mV/%RH. The etched POFBG humidity sensor shows anexponential decrease in response time with a decrease in fiber diameter. The developed sensor might have potential applications in a wide range of applications where fast and accurate real time humidity control is required.

Transverse mode switchable fiber laser through wavelength tuning

Abstract: We report a fiber laser design that is capable of producing switchable transverse modes through wavelength tuning. The transverse mode switching is realized by exploiting the particular transverse mode-wavelength association characteristics of the few-mode fiber Bragg grating. Different transverse mode outputs with high spatial mode quality can be obtained by adjusting the oscillating wavelength with a tunable filter within the fiber laser cavity. For each of the spatial mode outputs, the laser operates at the corresponding single wavelength with narrow linewidth. Through adding polarization controllers in the laser cavity, output modes with cylindrical vector polarization are also realized.