Single Mode Fiber Bragg Grating Research Articles

Investigation of Transmission and Reflection of Single Mode Fiber Bragg Grating

The use of Single Mode Fiber Bragg Grating (SMFBG) has been increasing in recent years due to its compact size, low cost, fast response and immunity to electromagnetic interference. It is commonly integrated into medical devices for long-distance light transmission and collection due to its high flexibility, low propagation loss, compatibility and tolerance to electromagnetic interference. SMFBG is a device made of thin glass material that is used as a medium for transmitting information in the form of light signals sourced from lasers or LEDs from one location to another. It consists of 3 main components, namely core with a certain grating, blanket (cladding) and jacket (coating). The advantage of optical fiber is that the data when transmitted is converted into light so as to reduce the risk of data damage. Other advantages include very small size, minimal interference with electromagnetic waves, resistance to temperature changes, attenuation when the transmission process is small enough, and large enough bandwidth. The orientation of this literature review is to understand the concept of optical fiber, the concept of reflection and refraction, and how light propagates in optical fiber.

Au coated etched FBG SPR sensor for the detection of ethanol in aqueous solution

Over the past few years, there has been a growing need for reliable ethanol sensors in the pharmaceutical and food industries. These industries require constant monitoring to ensure that the acceptable ethanol levels are maintained. This study reports a new fiber optic sensor that uses etched single mode fiber Bragg grating (FBG) coated with the thin layer of 45 nm gold to produce Surface Plasmon Resonance (SPR). A thin layer of 45 nm gold improves the sensitivity of sensor by improving the evanescent wave around the fiber, resulting in better interaction with the analyte. The sensing performance of developed structure was examined by analyzing the change in wavelength shift observed by varying ethanol concentration in aqueous solution from 0 to 100 %. The performance of developed sensor in terms of sensitivity is 20 pm/RIU. Which is expected to play an important role in food and pharmaceutical industries to protect human health from detrimental affects due to high concentration of ethanol.

Fiber Bragg grating-based linear-cavity fiber laser.

A fiber Bragg grating-based linear-cavity fiber laser is proposed and demonstrated experimentally. A single-mode fiber Bragg grating is used as a wavelength selector in the fundamental mode, and four few-mode fiber Bragg gratings are used to reflect LP01 mode, LP11 mode, LP21 mode and LP02 mode at the same wavelength. Different modes can be reflected at the same wavelength between a single-mode fiber Bragg grating and four few-mode fiber Bragg gratings to form four sub-linear-cavities. This fiber laser, which enables simultaneous lasing of LP01 mode, LP11 mode, LP21 mode and LP02 mode at the same wavelength, plays an important role in the field of mode-division multiplexing fiber-optic communications.

All-fiber switchable orbital angular momentum mode-locked laser based on TM-FBG

In this paper, a simple all-fiber switchable orbital angular momentum (OAM) mode-locked laser is demonstrated. The laser is mainly composed of a single-mode fiber Bragg grating (FBG), a two-mode fiber Bragg grating (TM-FBG), a two-mode circulator, and a nonlinear polarization rotation system. The coupling properties of the TM-FBG are verified, and an OAM mode-locked laser with switchable topological charges of −1, 0, and 1 is realized. When the pump power is 462 mW, the output powers of the fundamental mode and OAM±1 mode-locked lasers are 9.750 and 2.707 mW, respectively. Their repetition rates are both 10.16 MHz, and the signal-to-noise ratios are 60 and 59 dB. When the pump power is increased to 774 mW, the mode-locked laser can operate in the single-pulse, double-pulse, and triple-pulse states. Their output powers are 5.1, 7.4, and 10.1 mW, respectively. The OAM mode purity higher than 98.9% is experimentally realized.

Highly Sensitive Ultrasonic Sensor Based on Polymer Bragg Grating and its Application for 3D Imaging of Seismic Physical Model

A miniaturepolymer Bragg grating (PBG) sensor is fabricated and employed for ultrasonic imaging of seismic physical models (SPMs). The sensing Bragg grating is inscribed into an ultraviolet (UV) glue polymer waveguide with a femtosecond laser. The uniform polymer waveguide is fabricated by sealing the UV glue into a capillary fibre through capillary effect. By using line-by-line inscription technique, the laser beam is scanned transversely to periodically modulate the refractive index of the polymer waveguide, leading to the formation of the PBGs with various grating lengths. The sensor response to ultrasonic waves are investigated experimentally. When compared to single-mode fiber Bragg grating and phase-shifted fiber Bragg grating, the PBG with the same reflectivity presents a higher response amplitude due to its lower Young’s modulus. Besides, the sensor has a good spectral stability when transferred from air to water due to the waterproof coating on the sensor end. Finally, the sensor is used to scan a large-scale 3D SPM and the structural features, such as fault, fluctuation, and depositional termination, can be distinctly reconstructed. The proposed PBG sensor provides a new technique with easy fabrication, high sensitivity, and good stability for high-fidelity ultrasonic imaging of seismicphysical models.

Performance Optimization of Apodized FBG Biomedical Sensor for Variation in Temperature and Presence of Noise

In this work, comprehensive analysis on single and dual mode, uniform and apodized Fiber Bragg Grating (FBG) based gas concentration measurement sensor performance in the presence of noise and temperature variations is presented. Different scenarios are formulated. Firstly, the indirect sensing method for gas concentration measurement is presented, followed by the discussion on single and dual mode uniform FBG sensor design. Thereafter single and dual mode Gaussian apodized FBG sensor design and its pros and cons are discussed. The effect of temperature variations and noise on FBG sensor is also discussed. Afterwards as per referred literature the simulation results for uniform and apodized FBG in the presence or absence of noise, temperature variations and strain applications are validated. The quantitative analysis shows that the single mode apodized FBG has highest side lobes suppression ratio which is 88.21%. In terms of FWHM single mode apodized FBG has narrowest bandwidth of amplitude 0.18. While dual mode apodized FBG has highest reflectivity, that is, −0.20571. It is observed that reflection spectrum of uniform FBG sensor contains large strength of side lobes at adjacent wavelength. Moreover, the dual mode FBG sensor performance is more affected by variation in temperature and noise but dual mode FBG sensor works better as compared to single mode FBG sensor in context of minimum side lobes, high absorption depth and enhanced reflectivity. The presented investigation will be helpful to prescribe the correct amount of dosage for biomedical application. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Study of Temporal Thermal Response of Microfiber Bragg Grating

Fiber Bragg grating has been successfully fabricated in the silica microfiber by the use of femtosecond laser point-by-point inscription. Temporal thermal response of the fabricated silica microfiber Bragg grating has been measured by the use of the CO2 laser thermal excitation method, and the result shows that the time constant of the microfiber Bragg grating is reduced by an order of magnitude compared with the traditional single-mode fiber Bragg grating and the measured time constant is ~ 21ms.

Comparison of Fiber Bragg Grating based on SMF and MMF over Temperature Sensitivity

We have successfully fabricated and demonstrated a simple, cost-effective and easy to use of fiber Bragg grating (FBG) based on single mode, and multimode fiber which have been employed for temperature monitoring. The study purposely compared the performance of two types of FBGs; single mode FBG (SM-FBG) and multimode FBG (MM-FBG). The FBGs sensor is fabricated by phase mask technique which being exposed to ArF excimer laser with 20 mm uniform grating length and 99% reflectivity. The proposed FBG is studied for temperature monitoring starting at room temperature until 120 °C, and the configurations with SM-FBG and MM-FBG achieved a sensitivity of 10.9 pm/°C and 13.23 pm/°C, respectively whereas linear response correlation coefficient of 0.98229 and 0.99929. These show the MM-FBG has better sensitivity to be used in sensor applications.

Spectral Narrowing and Stabilization of 10-W Broad-Area Laser With Fiber Pump Delivery System

The emission spectrum of a 10-W commercial broad-area laser operated at full power was narrowed and stabilized by coupling an off-axis portion of its far-field emission to a single-mode fiber Bragg grating. The feedback produced in this partial compound cavity configuration narrowed the FWHM linewidth of the laser by $7\times $ compared with the free-running case and stabilized its peak wavelength over a 7° temperature range. Furthermore, the feedback improved the spectral density of the emission by $2\times $ over a 1.5° temperature range and over most of the far-field emission angles, indicating a robust concept suitable for manufacturing. This proof-of-concept experiment can be translated into a fiber pump delivery system that can capture all the broad-area laser (BAL) output while providing feedback to improve the spectral and potentially spatial properties of BAL emission.

Damage and recovery of fiber Bragg grating under radiation environment**Project supported by the Project for the State Key Laboratory of Optoelectronic Materials and Technologies of China (Grant No. 09010-32031708) and the Project for Zhuhai Key Laboratory of Center for Space Technology of China (Grant No. 71000-42080001).

To develop the application of fiber Bragg gratings as temperature and strain sensors in space environments, it is necessary to understand the effect of high-energy radiation on the performance of the fiber Bragg grating. We performed an experiment involving Co60-γ ionizing irradiation with a total dose of 1.01 × 106 rad on two Ge-doped single-mode fiber Bragg gratings with central wavelengths of 825 and 835 nm, respectively. We found that, with the increase of radiation dose, the redshift of the peak wavelength of the reflection spectrum of the fiber Bragg gratings indicated the increase of the refractive index and the number of color centers. After irradiation, the refractive index decreased with the decreasing number of color centers. We analyzed the influence of ionizing irradiation on the transmission performance of the fiber Bragg gratings using a color-center model, which explained the experimental results. The proposed model was used to determine the creation rate and annihilation rates of the color center, which are foundational data for using the fiber Bragg gratings in space applications.

Micro-structured optical fiber sensor for simultaneous measurement of temperature and refractive index

Abstract Through using micro-machining method for optical fiber sensor, a kind of miniature, compact and composite structural all-fiber sensor is presented. Based on manufacturing two micro-holes with certain distance in ordinary single-mode fiber Bragg grating (FBG) by excimer laser processing technique, we fabricate a dual Fabry–Perot-FBG (FP-FBG) composite fiber interferometric sensor, which can be used in simultaneous measurement for liquid’s refractive index (RI) and temperature change. Due to every micro-hole and the dual micro-holes in fiber acting as different Fabry–Perot (FP) cavities, this kind of sensor has not only different RI sensitivities but also different temperature sensitivities, which are corresponding to the wavelength shifts of the fine interference fringes and spectral envelope, respectively. The experimental results show that the spectral wavelength shift keep better linear response for temperature and RI change, so that we can select the higher temperature and RI sensitivities as well as the analyzed sensitivities of FBG to utilize them for constituting a sensitivity coefficients matrix. Finally, the variations of liquid’s temperature and RI are detected effectively, and the resolutions can reach to 0.1 °C and 1.0 × 10 - 5 RIU. These characteristics are what other single-type sensors don’t have, so that this kind of all-fiber dual FP-FBG composite fiber interferometric sensor can be used in extremely tiny liquid environment for measuring different physical quantities simultaneously.

Fabricating phase-shifted fiber Bragg grating by simple postprocessing using femtosecond laser

Fabricating of phase-shifted fiber Bragg grating (PSFBG) by a femtosecond (fs) laser postprocessing of standard single mode fiber Bragg grating (FBG) without phase mask is demonstrated. A central region of grating is irradiated by an fs laser assisted with a rotating jig, which produces a π phase shift at the central region of the grating and forms a π phase-shifted FBG. The procedure is simple, fast, and has good reproductivity. The bandwidth of transmission peak of PSFBG grows with an increasing amount of laser energy or length of irradiation and decreasing of translation speed; the transmission loss decreases with increasing irradiation length. Additionally, the repeatability of fs postprocessing and temperature stability of PSFBG were investigated.

Fiber Bragg grating assisted surface plasmon resonance sensor with graphene oxide sensing layer

A single mode fiber Bragg grating (FBG) is used to generate Surface Plasmon Resonance (SPR). The uniform gratings of the FBG are used to scatter light from the fiber optic core into the cladding thus enabling the interaction between the light and a thin gold film in order to generate SPR. Applying this technique, the cladding around the FBG is left intact, making this sensor very robust and easy to handle. A thin film of graphene oxide (GO) is deposited over a 45nm gold film to enhance the sensitivity of the SPR sensor. The gold coated sensor demonstrated high sensitivity of approximately 200nm/RIU when tested with different concentrations of ethanol in an aqueous medium. A 2.5 times improvement in sensitivity is observed with the GO enhancement compared to the gold coated sensor.

Method for independent strain and temperature measurement in polymeric tensile test specimen using embedded FBG sensors

A novel method to obtain independent strain and temperature measurements using embedded Fibre Bragg Grating (FBG) in polymeric tensile test specimens is presented in this paper. The FBG strain and temperature cross-sensitivity was decoupled using two single mode FBG sensors, which were embedded in the specimen material with a certain angle between them. It is demonstrated that, during temperature variation, both FBG sensors show the same signal response. However, for any applied load the signal response is different, which is caused by the different levels of strain acting in each sensor. Equations to calculate independently the strain and temperature are presented in the article, together with a measurement resolution study.This multi-parameter measurement method was applied to an epoxy tensile specimen, tested in a unidirectional tensile test machine with a temperature controlled cabinet. A full calibration procedure (temperature and strain) was performed to this material-sensor pair, where a calibration error < 1% was achieved. This was followed by a strain-temperature test case, where multiple two loading/strain stages of ε = 0.30% and ε = 0.50% were applied during a continuous variation of temperature, from 40 °C to –10 °C.The consistency of the expected theoretical results with the calibration procedure and the experimental validation shows that this proposed method is applicable to measure accurate strain and temperature in polymers during static or fatigue tensile testing. Two different calibration protocols are presented and analysed.

A high-power narrow-linewidth 1018 nm fiber laser based on a single-mode–few-mode–single-mode structure

We demonstrate an all-fiber high-power Yb-doped 1018 nm fiber laser with a Gaussian-shaped output beam profile based on a mismatched structure, which consists of a pair of single-mode fiber Bragg gratings and a section of few-mode double-cladding gain fiber. The output power is up to 107.5 W with an optical-to-optical efficiency of 63%, and the 3 dB band is 0.26 nm at this power level. Such a structure of single-mode–few-mode–single-mode fiber oscillator can be used to generate high-power narrow-linewidth lasing with excellent beam quality in other spectral ranges.

Absorbance properties of gold coated fiber Bragg grating sensor for aqueous ethanol

Optical Fiber Bragg Grating (FBG) is commonly deployed as a wavelength selective filter in telecommunication as well as to detect physical changes such as pressure, temperature and strain in sensing applications. This paper presents an investigation of FBG as a chemical sensor towards ethanol in aqueous solution. Telecommunication standard single mode FBGs were coated with different thicknesses of thin gold films via sputtering deposition method. The combination of Bragg gratings and gold film enhances the evanescent wave on the surface of the optical fiber. It was found that the FBG coated with 50 nm gold layer exhibits the strongest response towards water with varying concentrations of ethanol. The sensor shows 55% change in absorbance levels when the concentration of ethanol is increased from 0 to 99.7% in water.

Simultaneous Measurement of Temperature and Refractive Index Using a Fiber Bragg Grating and a Multimode Fiber

We introduce an all-fiber sensor capable of simultaneous measurement of temperature and refractive index (RI). The sensor system consists of a single mode fiber Bragg grating (FBG) and a single-mode-multimode-single-mode (SMS) structure which serves as a Mach-Zehnder interferometer (MZI), and the multimode fiber (MMF) is etched by hydrofluoric acid solution. The experimental results demonstrate that the temperature sensitivities of FBG and MZI are 0.016nm/°C and 0.093nm/°C, respectively, and the RI sensitivity of MZI achieves 226.25nm/RIU. The interesting properties of the sensor include compact size, high sensitivity and good operation linearity.

Free-space input and output coupling to an embedded fiber optic strain sensor: dual-ended interrogation via transmission

In this paper, we report a novel method of free-space passive optical coupling to completely embedded, transmission-based fiber Bragg grating (FBG) sensors. Fiber optic sensors (FOS's) have attracted intense research and commercial interest. A major challenge in implementing embedded FOS's, however, is improving upon the cumbersome and fragile ingress/egress techniques commonly used for bringing the sensing light into and out of the structures. In this paper, we successfully couple free-space light into and out of an embedded FBG sensor, without the use of physical connectorization. This coupling is enabled by splicing a multimode fiber (MMF) to a single mode fiber Bragg grating (SMFBG), and using hand polishing to integrate 45° mirrors onto the ingress and egress points of the MMF and SMFBG, respectively. We determine the total loss of the system to be 23 dB, which is considerably better than previous studies that did not use this hand polishing technique. We also demonstrate the application of this free-space coupling technique to strain measurement with a maximum strain of about 2000 µV. With this approach, no pigtailing of optical fibers is needed, and the FBG sensors can be completely embedded inside the structures, greatly increasing system simplicity and robustness.

Nonpigtail optical coupling to embedded fiber Bragg grating sensors

In recent decades, optical fiber has proven useful for many sensor applications. Specifically, fiber Bragg grating (FBG) sensors have shown great utility for integrity management and environmental sensing of composite structures. One major drawback of FBG sensors, however, is the lack of a robust, nonpigtail technique for coupling to the embedded FBG sensor. In this paper, a novel method of free-space passive coupling of light into FBG sensors is described. An angled 45-deg mirror integrated directly into the fiber was used as an input coupling technique. We investigated the application of this approach to both single- and multimode glass fibers containing FBGs. For multimode FBGs, we studied the grating's uniformity across the fiber diameter and its effect on normal free-space coupling. In single-mode investigations, a novel method of coupling to the sensor via splicing a multimode fiber to a single-mode FBG (SMFBG) was developed. Finally, free-space coupling to an embedded SMFBG was employed to measure the tensile strain. Excellent agreement was found between the FBG and conventional electrical resistance strain gauges. We conclude that this coupling method might eliminate the need for pigtailing by providing a more robust coupling method for FBG sensors.

Variable optical reflector for simultaneous strain and temperature measurement

We present a fibre optic sensing system for simultaneous strain and temperature measurement based on a narrow band variable optical reflector. The variable optical reflector comprises a single mode fibre Bragg grating and a fibre mode converter. A 2 µm m−1 strain resolution is achievable over a range of 2000 µm m−1 with a temperature accuracy of 0.3 °C. A strain sensor with a range of 12 000 µm m−1 is also demonstrated. The sensing system shows high strain and temperature sensitivities with very good stability.