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2 pages, 164 KiB

Open AccessEditorial

Special Issue on “Advancements in Fiber Bragg Grating Research”

by Wei Zhang and Xuewen Shu

Photonics 2021, 8(9), 347; https://doi.org/10.3390/photonics8090347 - 25 Aug 2021

Cited by 1 | Viewed by 1715

Abstract

Since the discovery of photosensitivity in optical fibers, there has been great interest in fiber Bragg grating (FBG) research [...] Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

Research

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8 pages, 3147 KiB

Open AccessArticle

Sensitivity-Tunable Oscillator-Accelerometer Based on Optical Fiber Bragg Grating

by Xiangpeng Xiao, Jinpeng Tao, Qingguo Song, Yuezhen Sun, Jiang Yang and Zhijun Yan

Photonics 2021, 8(6), 223; https://doi.org/10.3390/photonics8060223 - 15 Jun 2021

Cited by 4 | Viewed by 2313

Abstract

We demonstrate a fiber Bragg grating (FBG)-based oscillator-accelerometer in which the acceleration sensitivity can be tuned by controlling the location of the mass oscillator. We theoretically and experimentally investigated the performance of the proposed accelerometer. Theoretical analysis showed that both the mass and [...] Read more.

We demonstrate a fiber Bragg grating (FBG)-based oscillator-accelerometer in which the acceleration sensitivity can be tuned by controlling the location of the mass oscillator. We theoretically and experimentally investigated the performance of the proposed accelerometer. Theoretical analysis showed that both the mass and location of the oscillator affect the sensitivity and resonant frequency of the accelerometer. To simplify the analysis, a nondimensional parameter, P, was introduced to tune the sensitivity of the FBG-based oscillator-accelerometer, which is related to the location of the mass oscillator. Numerical analysis showed that the accelerometer sensitivity is linearly proportional to the P parameter. In the experiment, six FBG-based oscillator-accelerometers with different P parameters (0.125, 0.25, 0.375, 0.5, 0.625, 0.75) were fabricated and tested. The experimental results agree very well with the numerical analysis, in which the sensitivity of the proposed accelerometer linearly increased with the increase in parameter P (7.6 pm/g, 15.8 pm/g, 19.3 pm/g, 25.4 pm/g, 30.6 pm/g, 35.7 pm/g). The resonance frequency is quadratically proportional to parameter P, and the resonance frequency reaches the minimum of 440 Hz when P is equal to 0.5. The proposed oscillator-accelerometer showed very good orthogonal vibration isolation. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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8 pages, 1704 KiB

Open AccessArticle

Performances of PMMA-Based Optical Fiber Bragg Grating Sensor in Extended Temperature Range

by Wei Zhang and David J. Webb

Photonics 2021, 8(6), 180; https://doi.org/10.3390/photonics8060180 - 23 May 2021

Cited by 3 | Viewed by 2156

Abstract

PMMA based optical fiber Bragg grating (POFBG) sensors are investigated in an environmental chamber with controlled temperature and relative humidity at temperature extended to 70 °C. At below a critical temperature of 50 °C the POFBG sensor exhibits good linearity and sensitivity for [...] Read more.

PMMA based optical fiber Bragg grating (POFBG) sensors are investigated in an environmental chamber with controlled temperature and relative humidity at temperature extended to 70 °C. At below a critical temperature of 50 °C the POFBG sensor exhibits good linearity and sensitivity for both temperature and humidity sensing. Nonlinear responses are observed at higher temperature, giving rise to varying, reduced magnitudes of sensitivities. An important feature of POFBG humidity sensing is observed at above critical temperature where the POFBG humidity sensitivity turns from positive to negative. A theoretical model based on Lorentz–Lorenz equation is presented to estimate the dependence of POFBG refractive index on temperature and relative humidity. The experimental results qualitatively agree with the theoretical analyses. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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9 pages, 3760 KiB

Open AccessCommunication

Femtosecond Laser Fabricated Apodized Fiber Bragg Gratings Based on Energy Regulation

by Qi Guo, Zhongming Zheng, Bo Wang, Xuepeng Pan, Shanren Liu, Zhennan Tian, Chao Chen and Yongsen Yu

Photonics 2021, 8(4), 110; https://doi.org/10.3390/photonics8040110 - 7 Apr 2021

Cited by 16 | Viewed by 2799

Abstract

In this paper, an energy regulation method based on the combination of a half-wave plate (HWP) and a polarization beam splitter (PBS) is proposed for the fabrication of apodized fiber gratings, which can effectively improve the side lobe suppression ratio of high-reflectivity fiber [...] Read more.

In this paper, an energy regulation method based on the combination of a half-wave plate (HWP) and a polarization beam splitter (PBS) is proposed for the fabrication of apodized fiber gratings, which can effectively improve the side lobe suppression ratio of high-reflectivity fiber Bragg gratings (FBGs) fabricated by femtosecond laser. The apodized FBGs prepared by this method has good repeatability and flexibility. By inputting different types of apodization functions through the program, the rotation speed of the stepping motor can be adjusted synchronously, and then the position of the HWP can be accurately controlled so that the laser energy can be distributed as an apodization function along the axial direction of the fiber. By using the energy apodization method, the gratings with a reflectivity of 75% and a side lobe suppression ratio of 25 and 32 dB are fabricated in the fiber with a core diameter of 9 and 4.4 μm, respectively. The temperature and strain sensitivities of the energy-apodized fiber gratings with a core diameter of 4.4 μm are 10.36 pm/°C and 0.9 pm/με, respectively. The high-reflectivity gratings fabricated by this energy apodization method are expected to be used in high-power narrow-linewidth lasers and wavelength division multiplexing (WDM) systems. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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16 pages, 7437 KiB

Open AccessArticle

Heating Device Based on Modified Microwave Oven: Improved to Measure Liquid Temperature by Using FBG Sensors

by Jesus Garavito, Carlos Galvis, Ana Milena López, Arlet Patricia Franco, Francisco Barreiro, Rosa Liliana Tarazona and Claudia Milena Serpa-Imbett

Photonics 2021, 8(4), 104; https://doi.org/10.3390/photonics8040104 - 6 Apr 2021

Cited by 6 | Viewed by 2572

Abstract

A prototype device based on a modified domestic microwave oven for liquid food products pasteurization is presented. This novel design has a coiling glass pipe adapted inside a microwave cavity to allow liquid continuous flow, in which several temperature optical sensors based on [...] Read more.

A prototype device based on a modified domestic microwave oven for liquid food products pasteurization is presented. This novel design has a coiling glass pipe adapted inside a microwave cavity to allow liquid continuous flow, in which several temperature optical sensors based on Fiber Bragg Grating were installed to measure, by means of contact, the circulating liquid temperature in the pipe, while the oven is on, to obtain the profile temperature as a function of time at different pipe points. The temperatures at liquid input and output were also measured with thermocouples. This device was tested to establish how well it may perform using different standardized liquids with well-known physicochemical and dielectric properties, such as water, water with dissolved sugars, water with dissolved salts, and water with dissolved sugars and salts. It could be observed that the maximum temperature reached was 90 °C for distilled water, 80 °C for water with dissolved salts, 60 °C for water with dissolved sugars and 80 °C for water with dissolved sugars and salts, showing that these data were in agreement with previous results in the literature. This type of device would be potentially useful to establish the device’s efficiency in terms of retention time, energy consumption, and volume of processed liquid, thus, broadening the use of this microwave heating technology with several types of liquid substances. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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8 pages, 2084 KiB

Open AccessCommunication

Transverse Asymmetry of the Index Modulation Profile in Few-Mode Fiber Bragg Grating

by Peihong Guan, Min Tang, Min Cao, Yuean Mi, Mei Liu, Wenhua Ren and Guobin Ren

Photonics 2021, 8(3), 87; https://doi.org/10.3390/photonics8030087 - 23 Mar 2021

Cited by 2 | Viewed by 2253

Abstract

The transverse asymmetry of the index modulation profile in the asymmetric few-mode fiber Bragg grating (FM-FBG) was investigated. The transverse asymmetry of the index modulation profile will lead to mode conversion between modes with the different azimuthal orders, and this asymmetry is characterized [...] Read more.

The transverse asymmetry of the index modulation profile in the asymmetric few-mode fiber Bragg grating (FM-FBG) was investigated. The transverse asymmetry of the index modulation profile will lead to mode conversion between modes with the different azimuthal orders, and this asymmetry is characterized by the attenuation coefficient α. We evaluated that the value of attenuation coefficient α was 0.2 μm⁻¹, and grating amplitude χ was 2.8 × 10⁻⁴ for FM-FBG inscribed by UV single-side illumination. We found that the optimized value of α was 0.16 μm⁻¹, at which the maximum mode conversion efficiency of LP₀₁–LP₁₁ can be achieved. The results of this paper provide great potential application in few-mode fiber (FMF) devices and mode division multiplexing (MDM) optical communication. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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10 pages, 3784 KiB

Open AccessArticle

Arbitrary-Order Photonic Hilbert Transformers Based on Phase-Modulated Fiber Bragg Gratings in Transmission

by Yanxin Li, Xin Liu, Xuewen Shu and Lin Zhang

Photonics 2021, 8(2), 27; https://doi.org/10.3390/photonics8020027 - 21 Jan 2021

Cited by 4 | Viewed by 2380

Abstract

Photonic Hilbert transformers are fundamental components for optical computing and signal processing. Here, for the first time we propose all-optical arbitrary-order Hilbert transformers using phase-modulated fiber Bragg gratings (PM-FBGs) in transmission to our best knowledge. The PM-FBG is a kind of fiber grating, [...] Read more.

Photonic Hilbert transformers are fundamental components for optical computing and signal processing. Here, for the first time we propose all-optical arbitrary-order Hilbert transformers using phase-modulated fiber Bragg gratings (PM-FBGs) in transmission to our best knowledge. The PM-FBG is a kind of fiber grating, whose coupling strength remains almost uniform and period varies along the fiber length. For demonstration, we have designed and numerically simulated 0.5th-order, first-order, and 1.5th-order photonic Hilbert transformers, respectively. The profiles of those PM-FBGs are obtained employing quasi-Newton optimization algorithm. Simulation results show that the designed three Hilbert transformers are all in good agreement with the ideal results in bandwidths up to 500 GHz and can tolerate a large range of input pulse width. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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9 pages, 4782 KiB

Open AccessArticle

Transverse Load and Temperature Sensing Using Multiplexed Long-Period Fiber Gratings

by Ismael Torres-Gómez, Alejandro Martínez-Rios, Gilberto Anzueto-Sánchez, Daniel. E. Ceballos-Herrera and Guillermo Salceda-Delgado

Photonics 2021, 8(1), 1; https://doi.org/10.3390/photonics8010001 - 22 Dec 2020

Cited by 4 | Viewed by 2379

Abstract

The simultaneous measurement of transverse load and temperature using two long-period fiber gratings multiplexed in the wavelength domain is presented experimentally. For this, a mechanically induced long-period fiber grating (MI-LPFG) and a long-period fiber grating inscribed by a continuous-wave CO₂ laser (CO [...] Read more.

The simultaneous measurement of transverse load and temperature using two long-period fiber gratings multiplexed in the wavelength domain is presented experimentally. For this, a mechanically induced long-period fiber grating (MI-LPFG) and a long-period fiber grating inscribed by a continuous-wave CO₂ laser (CO₂ LPFG) are connected in cascade. First, the transverse load and the temperature measurements were individually performed by the multiplexed long-period fiber gratings configuration. The MI-LPFG is subject to a transverse load variation from 0–2000 g with steps of 500 g, whereas the CO₂ LPFG is unloaded and they are kept at room temperature. Similarly, the CO₂ LPFG is subject to a temperature variation from 30 to 110 °C by increments of 20 °C, while the MI-LPFG with a constant transverse load of 2000 g is kept at room temperature. Subsequently, the simultaneous measurement of the transverse load and the temperature is performed by the multiplexed long-period fiber grating following the steps outlined above. According to the experimental results, the transverse load and temperature measurement present high repeatability for the individual and simultaneous process. Moreover, the multiplexed LPFGs exhibit low cladding-mode crosstalk of transverse load and temperature. The coarse wavelength-division multiplexing (CWDM) of long-period fiber gratings is an attractive alternative technique in optical fiber distributed sensing applications. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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Review

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23 pages, 3631 KiB

Open AccessReview

In-Fiber Interferometric-Based Sensors: Overview and Recent Advances

by Amalia Miliou

Photonics 2021, 8(7), 265; https://doi.org/10.3390/photonics8070265 - 7 Jul 2021

Cited by 60 | Viewed by 5950

Abstract

In-fiber interferometric-based sensors are a rapidly growing field, as these sensors exhibit many desirable characteristics compared to their regular fiber-optic counterparts and are being implemented in many promising devices. These sensors have the capability to make extremely accurate measurements on a variety of [...] Read more.

In-fiber interferometric-based sensors are a rapidly growing field, as these sensors exhibit many desirable characteristics compared to their regular fiber-optic counterparts and are being implemented in many promising devices. These sensors have the capability to make extremely accurate measurements on a variety of physical or chemical quantities such as refractive index, temperature, pressure, curvature, concentration, etc. This article is a comprehensive overview of the different types of in-fiber interferometric sensors that presents and discusses recent developments in the field. Basic configurations, a brief approach of the operating principle and recent applications are introduced for each interferometric architecture, making it easy to compare them and select the most appropriate one for the application at hand. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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22 pages, 5459 KiB

Open AccessReview

Review of Helical Long-Period Fiber Gratings

by Chao Ma, Jian Wang and Libo Yuan

Photonics 2021, 8(6), 193; https://doi.org/10.3390/photonics8060193 - 30 May 2021

Cited by 9 | Viewed by 4142

Abstract

In this paper, comprehensive remarks are given that focus on the main fabrications and wide applications of helical long-period fiber gratings (HLPGs). Firstly, the techniques of fabricating HLPGs by CO₂ laser, hydrogen–oxygen flame heating, and arc discharge are summarized. Furthermore, the applications [...] Read more.

In this paper, comprehensive remarks are given that focus on the main fabrications and wide applications of helical long-period fiber gratings (HLPGs). Firstly, the techniques of fabricating HLPGs by CO₂ laser, hydrogen–oxygen flame heating, and arc discharge are summarized. Furthermore, the applications of HLPGs are investigated, i.e., orbital angular momentum (OAM) mode converters, all-fiber band-rejection filters, and sensors for measuring physical perturbation of torsion, strain, temperature, curvature, and surrounding refractive index (SRI). Furthermore, several long-period fiber gratings (LPFGs) of near-HLPG structures with periodic refractive index change along the azimuthal direction are introduced. Lastly, the prospects and key challenges for HLPGs are discussed. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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29 pages, 7503 KiB

Open AccessReview

Advances on Mode-Coupling Theories, Fabrication Techniques, and Applications of the Helical Long-Period Fiber Gratings: A Review

by Hua Zhao and Hongpu Li

Photonics 2021, 8(4), 106; https://doi.org/10.3390/photonics8040106 - 6 Apr 2021

Cited by 28 | Viewed by 4825

Abstract

In this paper, we have briefly review the developing history and recent advances made with regard to helical long-period fiber gratings (HLPGs) in three aspects, i.e., the mode-coupling theories, the fabrication techniques, and the applications. It is shown that, due to the intrinsic [...] Read more.

In this paper, we have briefly review the developing history and recent advances made with regard to helical long-period fiber gratings (HLPGs) in three aspects, i.e., the mode-coupling theories, the fabrication techniques, and the applications. It is shown that, due to the intrinsic helicity characteristics, which are especially suitable to control the loss, polarization, and orbit-angular-momentum (OAM) states of the light in optical fiber, HLPGs have recently attracted great research interest and have found various applications, such as the mode-converters, the torsion sensors, the band-rejection filters, wave plates, linear- and circular-light polarizers, and OAM mode generators, etc. It is believed that HLPGs and the HLPGs-based devices would find further applications to not only the fields of optical sensors and optical communication, but also other fields such as ultrahigh precision measurement, quantum optics, and biochemistry, etc. Full article

(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research)

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