Tapered Fiber Bragg Grating Research Articles

Enhanced sensing performance of tapered profile in the apodized fiber Bragg grating for detection of cancerous cells utilizing their refractive index.

Tapered profiles are introduced in Bessel and Blackman apodized fiber Bragg grating, and their sensing performance is theoretically estimated. Reflectivity equation of proposed apodized tapered profiles is obtained using transfer matrix method and coupled mode theory. Since the effective refractive index (RI) of proposed waveguides varies with core radius therefore amplitude distribution and penetration depth of light in surroundings are modified. It is found that the exponential tapered profile with Bessel apodization shows a higher sensitivity of 682.5 nm/RIU, detection accuracy of 3858.45, and quality parameter 1718.02/RIU with minimum full width at half maxima (FWHM) 0.3972 nm of the reflection spectra. The spectral response of the tapered fiber Bragg grating is also analyzed through a group delay study. Again, exponential profile was found to be particularly effective, producing less group delay ripples 2.98 ps and is maximum slope of 42.43°. Hence, exponential tapered profile is demonstrated for detection of cancer cells lies between the refractive index of 1.3333-1.4412.

Modeling and calibration of micro/nano FBG temperature probe for scanning probe microscopy.

To accurately measure the local temperatures of the micro-nano area, we propose an optical method using a tapered fiber Bragg grating (FBG) probe with a nano tip for scanning probe microscopy (SPM). When the tapered FBG probe senses local temperature through near-field heat transfer, the intensity of the reflected spectrum decreases, along with a broadening bandwidth and a shift in the central peak position. Modeling the heat transfer between the probe and the sample shows that the tapered FBG probe is in a non-uniform temperature field when approaching the sample surface. Simulation of the probe's reflection spectrum reveals that the central peak position shifts nonlinearly with increasing local temperature. In addition, the near-field temperature calibration experiments show that the temperature sensitivity of the FBG probe increases nonlinearly from 6.2 pm/°C to 9.4 pm/°C as the sample surface temperature increases from 25.3°C to 160.4°C. The agreement of the experimental results with the theory and the reproducibility demonstrate that this method offers a promising approach for exploring micro-nano temperature.

A Temperature Independent Inclinometer Based on a Tapered Fiber Bragg Grating in a Fiber Ring Laser.

We demonstrate a new concept for an all-fiber inclinometer based on a tapered fiber Bragg grating (tFBG) in a fiber ring laser (FRL) with the capability of measuring the tilt angle and temperature simultaneously. The sensor performance is analyzed theoretically and investigated experimentally. The dependence of tilt angle on the spectral response in variable temperature conditions was measured. Two inclinometers with different lengths have been fabricated and characterized in FRL. The sensitivity is 0.583 dB/° and 0.849 dB/°, respectively, in the range of 0° to 90°. Thanks to the FRL system, narrow 3-dB bandwidth (<0.1 nm) and high optical signal-to-noise ratio (~60 dB) are achieved. The tFBG in the FRL system can be used for working as a temperature insensitive inclinometer. The results suggested that the proposed inclinometer has the advantages of compact size and convenient manufacture, enhancing its potential for application prospect.

An intensity-modulated and large bandwidth magnetic field sensor based on a tapered fiber Bragg grating

An intensity-modulated and large bandwidth magnetic field fiber sensor with tapered fiber Bragg grating (TFBG) had been proposed and demonstrated by experiments. Fiber Bragg grating (FBG) was created into a tapered fiber to form TFBG, which not only had powerful evanescent field but also possessed large bandwidth for the fiber refractive index decreased along the tapered region. The TFBG inserted into a 0.3 mm diameter glass tube which was filled with the magnetic-fluid (MF), and then this structure was packaged to form an integration magnetic-field fiber sensor. The refractive index of the MF will changed under varied magnetic-field, so the reflection spectral of the sensor should have a corresponding changed with the magnetic-field changed due to the tunable refractive index of MF. We designed the experiments and tested the sensor. The experimental results show that a nonlinear curve is between light intensity variation and changed MF intensity variation, the uniformity fitting degrees are 0.999 and 0.996 among the magnetic field increased and declined and the maximum sensitivity is −0.1933 dB/Oe and −0.1533 dB/Oe, respectively. Moreover, we find magnetic hysteresis has no obvious affection on the magnetic vectors (0 and 180 deg). This proposed magnetic-field sensor has the benefits of no direction disturbance, large bandwidth, high sensitivity, and integration.

Dual-Parameter Optical Fiber Sensor for Temperature and Pressure Discrimination Featuring Cascaded Tapered-FBG and Ball-EFPI

A dual parameter optical fiber sensor for temperature and pressure discrimination has been proposed and experimentally realized. A tapered fiber Bragg grating (tapered-FBG) and an extrinsic Fabry–Perot interferometer with a ball shape (ball-EFPI) are the two main sensing structures. The taper is fabricated by elongating it during an arc-discharge provided by the fusion splicer. Then, the femtosecond laser is used to inscribe a first-order Bragg grating in the taper region, adopting the point-by-point direct-writing technique. The ball-EFPI is fabricated using the chemical etching and arc-discharge enlargement method. The test temperature range is 40 °–400°, and the test pressure range is 0–2 MPa on the basis of ambient pressure. Experimental results show that the tapered-FBG has good temperature response while the ball-EFPI is sensitive to pressure. By analyzing the sensitivity matrix, the temperature and pressure discrimination can be achieved using the proposed hybrid sensor.

Development of a 1-DOF Force Sensor Prototype Incorporating Tapered Fiber Bragg Grating for Microsurgical Instruments

Decoupling between axial and transversal forces is an essential during tool-tissue interaction in many medicine surgeries; in particular where fine and precise manipulation is required to save the delicate tissues. One example of which is the vitreoretinal microsurgery (VRMS). When fiber Bragg grating based sensing technique is utilized, the cross-talk noise between the axial and transversal forces always show up severely due to its conventional wavelength shift method. To address the challenge, we have introduced theoretical method in which a combination of tapered FBG (TFBG) and bandwidth modulation method instead are used. Here in this paper, first phase of our ongoing progress to proof the concept and validate the simulation results is demonstrated experimentally. We have developed a prototype incorporated TFBG mimicking the structure of the ophthalmia's needle to measure temperature-insensitive 1-DOF axial forces. High speed plug and play (I-MON-256USB (Ibsen)) is used to monitor the reflection spectrum of the prototype sensor. An automated calibration system using LabVIEW with efficient algorithms have been developed to calculate and keep track the bandwidth variations as different values of axial forces applied. Calibration procedures are repeated three times to validate the consistency of the sensor response. Experimental results show that, the estimated force values of our prototype are consistent with their actual values with RMS error less than 0.356 N over the range (1N-10N), while temperature insensitivity is guaranteed.

A Temperature Fiber Sensor Based on Tapered Fiber Bragg Grating Fabricated by Femtosecond Laser

A temperature fiber sensor based on tapered fiber Bragg grating (tapered FBG) fabricated by femtosecond laser has been proposed and realized with good reproducibility. Firstly, the fiber taper with 25 μm diameter and 1000 μm length is fabricated by arc-discharge elongation using two standard single-mode fibers. Secondly, two first-order FBGs are fabricated in tapered and non-tapered fiber regions for comparison. Both FBGs are point-by-point direct-written by femtosecond laser, and the grating lengths are 1000 μm. Thirdly, a temperature experiment is performed using a heating chamber, and experimental results show that in the range of 30~350 °C, the temperature sensitivity of the tapered FBG has increased from 11.0 pm/°C to 12.3 pm/°C. The tapered FBG proposed here can be further configured for sensing other parameters in physical, chemical, and biomedical applications.

Enhanced Relative Humidity Sensing Based on a Tapered Fiber Bragg Grating with Zinc Oxide Nanostructure-Embedded Coatings

A novel concept for an intrinsic relative humidity (RH) sensor that uses a tapered fiber Bragg grating (FBG) with zinc oxide nanostructure-embedded coatings is presented. Tests in a controlled environment indicate that the sensor has a linear and stable response behavior at 55% to 80% RH. The tapered FBG is fabricated using a chemical etching method followed by the coating of zinc oxide (ZnO) nanostructures onto the surface of the taper. Experimental results show that the ZnO coated FBG produced a better sensitivity of 2.51 pm/% in comparison to only 1.36 pm/% for the uncoated FBG in terms of its Bragg wavelength shift. The performance of the humidity sensor in regards to the reflected output power is also presented, showing a significant improvement in sensitivity from 0.0012 dBm/% for bare tapered fiber to 0.089 dBm/% with the ZnO coating. These results indicate the potential of ZnO nanostructures coating in enhancing the performance of the sensor for relative humidity sensing.

A Novel Technique Employing Tapered Fiber Bragg Grating to Solve the Axial/Transverse Forces Crosstalk in Microsurgical Instruments

This paper demonstrates the capability of retinal microsurgical instruments constructed with customized fiber Bragg gratings (FBGs) sensors to completely decouple the transverse and axial force components. In contrast to the constantly shifting Bragg wavelength, FBG bandwidth can only be tuned when a nonuniform strain/temperature distribution is applied. Using a tapered FBG (TFBG) at the neutral axis of the instrument makes the bandwidth tune-ability possible by applying forces both transversely and axially, while the bandwidth of the outer/lateral standard FBG (SFBG) due to the fiber symmetry remains insensitive to axial forces. Therefore, the crosstalk (transverse forces) in the TFBG can be easily filtered out when mixed forces are applied simultaneously. Tapered fiber mode analysis is carried out to calculate the local modes and is used in the analytic coupled-mode solution. Transfer-matrix method, then, is developed to analyze the reflected spectrum of the TFBG. We provide a developed mathematical model algorithm to show how force vectors can be measured. Tuning the reflected bandwidth is directly corresponding to the amount of the reflected optical power. Thus, the results show that the simulated needle sensors are able to measure transverse and axial forces with a sensitivity of 0.049 and 0.0026 dBm/mN, while the SFBG is insensitive to the axial forces. This novel method is applicable for microsurgical applications, i.e., vascular and cochlear implant surgeries and catheterization procedures.

Temperature Independent Tapered Fiber Bragg Grating-Based Inclinometer

A new concept for an optical fiber inclinometer based on tapered fiber Bragg grating (TFBG) is presented. The sensor was characterized by the experimental measurement of the dependence of inclination angle on the spectral response in fluctuating temperature conditions. The research showed that the TFBG made it possible to simultaneously measure both the inclination angle and temperature, and to operate as a temperature insensitive 0°–90° tilt sensor, in a different interrogation regime. Inscription of the FBG in the tapered optical fiber section offered not only sensor miniaturization, but also the possibility of temperature sensing by the fiber section adjacent to the inclination area. Moreover, due to the reflective mode of the TFBG, the sensor offers excellent sensitivity due to the double-loss operation.

Dual-Parameter Sensor Based on Tapered FBG Combined With Microfiber Cavity

A hybrid sensor based on tapered fiber Bragg grating (FBG) combined with microfiber cavity tapered FBG combined with a microfiber cavity is proposed and demonstrated in this letter. It is fabricated by taper-drawing from a normal FBG. The FBG taper and microfiber end form an interferometric cavity. Temperature and refractive index (RI) can be measured simultaneously using such a hybrid structure. The temperature and RI variation are determined by the wavelength shift and fringe contrast change, respectively, thus the temperature and RI measurement base on the proposed structure is free of cross-sensitivity intrinsically. The obtained temperature sensitivity is ${\sim}{\rm 13}~{\rm pm}/^{\circ}{\rm C}$ for temperature, whereas the RI sensitivity is ${\sim}{\rm 15}~{\rm dB}$ /RIU for the RI range from 1.33 to 1.43.

H2 Sensing Based on a Pd-Coated Tapered-FBG Fabricated by DUV Femtosecond Laser Technique

An optical fiber probe sensor based on a tapered-fiber Bragg grating (FBG) coated with 150-nm-thick Pd film is proposed for hydrogen detection. The FBG was written in a 50-μm-diameter tapered fiber by deep ultraviolet femtosecond laser technology. A second FBG was inscribed in the 125 μm-fiber section for temperature compensation. The sensing head was able to detect H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration in the range 0%-1% (v/v) H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> at room temperature; a maximum sensitivity of 81.8 pm/% (v/v) H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was attained with temperature compensation. The influence of the Pd coating over temperature sensitivity of standard and tapered-FBGs is also presented.

Photonic Microwave True-Time Delay Based on a Tapered Fiber Bragg Grating With Resistive Coating

A photonic microwave true-time delay based on a tapered fiber Bragg grating (FBG) with resistive coating has been proposed and demonstrated. It features voltage-controlled continuous operation, requiring no moving parts and no mechanical perturbation. The time delay of a microwave signal carried over an optical signal is obtained by electrically controlling the reflection positions of it from the tapered FBG via the thermooptic effect. The achieved time delay was about 105 ps with the electrical power consumption of 48 mW.

Analysis of linearly tapered fiber Bragg grating for dispersion slope compensation

We demonstrate that linearly tapered fiber Bragg gratings (FBGs) display nonlinear group delay under strain or stress. The nonlinear group delay of the tapered FBG is analyzed theoretically. Experimental results show a good agreement with the analysis. We are the first to find that linearly tapered FBGs can be used in dispersion slope compensation.

Tunable dispersion device based on a tapered fiber Bragg grating and nonuniform magnetic fields

We present a new variable dispersion device based on tuning the chirp of a tapered fiber Bragg grating by means of a magnetic transducer. By using a nonuniform magnetic field, we demonstrate a 188-472-ps/nm dispersion tuning range, suitable for tunable radio-frequency filters and dispersion compensation, among others.