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12 pages, 9653 KiB

Open AccessCommunication

1.1-µm Band Extended Wide-Bandwidth Wavelength-Swept Laser Based on Polygonal Scanning Wavelength Filter

by Gi Hyen Lee, Soyeon Ahn, Jinhwa Gene and Min Yong Jeon

Sensors 2021, 21(9), 3053; https://doi.org/10.3390/s21093053 - 27 Apr 2021

Cited by 7 | Viewed by 2815

Abstract

We demonstrated a 1.1-µm band extended wideband wavelength-swept laser (WSL) that combined two semiconductor optical amplifiers (SOAs) based on a polygonal scanning wavelength filter. The center wavelengths of the two SOAs were 1020 nm and 1140 nm, respectively. Two SOAs were connected in [...] Read more.

We demonstrated a 1.1-µm band extended wideband wavelength-swept laser (WSL) that combined two semiconductor optical amplifiers (SOAs) based on a polygonal scanning wavelength filter. The center wavelengths of the two SOAs were 1020 nm and 1140 nm, respectively. Two SOAs were connected in parallel in the form of a Mach-Zehnder interferometer. At a scanning speed of 1.8 kHz, the 10-dB bandwidth of the spectral output and the average power were approximately 228 nm and 16.88 mW, respectively. Owing to the nonlinear effect of the SOA, a decrease was observed in the bandwidth according to the scanning speed. Moreover, the intensity of the WSL decreased because the oscillation time was smaller than the buildup time. In addition, a cholesteric liquid crystal (CLC) cell was fabricated as an application of WSL, and the dynamic change of the first-order reflection of the CLC cell in the 1-µm band was observed using the WSL. The pitch jumps of the reflection band occurred according to the electric field applied to the CLC cell, and instantaneous changes were observed. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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14 pages, 29082 KiB

Open AccessArticle

Towards Detecting Red Palm Weevil Using Machine Learning and Fiber Optic Distributed Acoustic Sensing

by Biwei Wang, Yuan Mao, Islam Ashry, Yousef Al-Fehaid, Abdulmoneim Al-Shawaf, Tien Khee Ng, Changyuan Yu and Boon S. Ooi

Sensors 2021, 21(5), 1592; https://doi.org/10.3390/s21051592 - 25 Feb 2021

Cited by 32 | Viewed by 6593

Abstract

Red palm weevil (RPW) is a detrimental pest, which has wiped out many palm tree farms worldwide. Early detection of RPW is challenging, especially in large-scale farms. Here, we introduce the combination of machine learning and fiber optic distributed acoustic sensing (DAS) techniques [...] Read more.

Red palm weevil (RPW) is a detrimental pest, which has wiped out many palm tree farms worldwide. Early detection of RPW is challenging, especially in large-scale farms. Here, we introduce the combination of machine learning and fiber optic distributed acoustic sensing (DAS) techniques as a solution for the early detection of RPW in vast farms. Within the laboratory environment, we reconstructed the conditions of a farm that includes an infested tree with ∼12 day old weevil larvae and another healthy tree. Meanwhile, some noise sources are introduced, including wind and bird sounds around the trees. After training with the experimental time- and frequency-domain data provided by the fiber optic DAS system, a fully-connected artificial neural network (ANN) and a convolutional neural network (CNN) can efficiently recognize the healthy and infested trees with high classification accuracy values (99.9% by ANN with temporal data and 99.7% by CNN with spectral data, in reasonable noise conditions). This work paves the way for deploying the high efficiency and cost-effective fiber optic DAS to monitor RPW in open-air and large-scale farms containing thousands of trees. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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11 pages, 1750 KiB

Open AccessArticle

A Fibre-Optic Platform for Sensing Nitrate Using Conducting Polymers

by Soroush Shahnia, Heike Ebendorff-Heidepriem, Drew Evans and Shahraam Afshar

Sensors 2021, 21(1), 138; https://doi.org/10.3390/s21010138 - 28 Dec 2020

Cited by 7 | Viewed by 3632

Abstract

Monitoring nitrate ions is essential in agriculture, food industry, health sector and aquatic ecosystem. We show that a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), can be used for nitrate sensing through a process in which nitrate ion uptake leads to oxidation of PEDOT and change [...] Read more.

Monitoring nitrate ions is essential in agriculture, food industry, health sector and aquatic ecosystem. We show that a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), can be used for nitrate sensing through a process in which nitrate ion uptake leads to oxidation of PEDOT and change of its optical properties. In this study, a new platform is developed in which a single-mode fibre coated at the tip with PEDOT is used for nitrate sensing. A crucial step towards this goal is introduction of carbonate exposure to chemically reduced PEDOT to a baseline value. The proposed platform exhibits the change in optical behaviour of the PEDOT layer at the tip of the fibre as it undergoes chemical oxidation and reduction (redox). The change in optical properties due to redox switching varies with the intensity of light back reflected by the fibre coated with PEDOT. The proposed platform during oxidation demonstrates linear response for the uptake of nitrate ions in concentrations ranging between 0.2 and 40 parts per million (ppm), with a regression coefficient

R^{2} = 0.97

and a detection limit of 6.7 ppm. The procedure for redox switching is repeatable as the back reflection light intensity reaches

\pm 1.5 %

of the initial value after reduction. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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18 pages, 7508 KiB

Open AccessArticle

The Sensitivity Improvement Characterization of Distributed Strain Sensors Due to Weak Fiber Bragg Gratings

by Konstantin V. Stepanov, Andrey A. Zhirnov, Anton O. Chernutsky, Kirill I. Koshelev, Alexey B. Pnev, Alexey I. Lopunov and Oleg V. Butov

Sensors 2020, 20(22), 6431; https://doi.org/10.3390/s20226431 - 11 Nov 2020

Cited by 24 | Viewed by 2714

Abstract

Weak fiber Bragg gratings (WFBGs) in a phase-sensitive optical time-domain reflectometer (phi-OTDR) sensor offer opportunities to significantly improve the signal-to-noise ratio (SNR) and sensitivity of the device. Here, we demonstrate the process of the signal and noise components’ formation in the device reflectograms [...] Read more.

Weak fiber Bragg gratings (WFBGs) in a phase-sensitive optical time-domain reflectometer (phi-OTDR) sensor offer opportunities to significantly improve the signal-to-noise ratio (SNR) and sensitivity of the device. Here, we demonstrate the process of the signal and noise components’ formation in the device reflectograms for a Rayleigh scattering phi-OTDR and a WFBG-based OTDR. We theoretically calculated the increase in SNR when using the same optical and electrical components under the same external impacts for both setups. The obtained values are confirmed on experimental installations, demonstrating an improvement in the SNR by about 19 dB at frequencies of 20, 100, and 400 Hz. In this way, the minimum recorded impact (at the threshold SNR = 10) can be reduced from 100 nm per 20 m of fiber to less than 5 nm per 20 m of fiber sensor. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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12 pages, 4568 KiB

Open AccessArticle

Characteristic Test Analysis of Graphene Plus Optical Microfiber Coupler Combined Device and Its Application in Fiber Lasers

by Yang Yu, Hao Chen, Zhenfu Zhang, Dingbo Chen, Jianfei Wang, Zhengtong Wei, Junbo Yang and Peiguang Yan

Sensors 2020, 20(6), 1645; https://doi.org/10.3390/s20061645 - 16 Mar 2020

Cited by 4 | Viewed by 2344

Abstract

In this study, a graphene and optical microfiber coupler (OMC) integrated device (GOMC) was proposed and fabricated. After its characteristic analysis and testing, it was applied to the development of adjustable multi-wavelength fiber lasers. By integrating the OMC with graphene, the polarization dependence [...] Read more.

In this study, a graphene and optical microfiber coupler (OMC) integrated device (GOMC) was proposed and fabricated. After its characteristic analysis and testing, it was applied to the development of adjustable multi-wavelength fiber lasers. By integrating the OMC with graphene, the polarization dependence of OMC was enhanced. Meanwhile, the novel GOMC was given the capabilities of filtering, coupling, beam splitting, and polarization correlation. When the GOMC was integrated as a filter and beam splitter into the ring cavity of the fiber laser, the proposed GOMC-based fiber laser could achieve single-wavelength and multi-wavelength regulated output. The laser had a 3 dB linewidth of less than 30 pm, a signal-to-noise ratio of approximately 40 dB, and an output power fluctuation of less than 1 dB. The GOMC could also be used for the development of functional devices, such as adjustable mode lockers and mode coupling selectors, which provide an excellent experimental platform for new fiber lasers and the research of multi-dimensional light-field manipulation. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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Review

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32 pages, 5215 KiB

Open AccessReview

Ultrafast Fiber Lasers with Low-Dimensional Saturable Absorbers: Status and Prospects

by Pulak Chandra Debnath and Dong-Il Yeom

Sensors 2021, 21(11), 3676; https://doi.org/10.3390/s21113676 - 25 May 2021

Cited by 28 | Viewed by 5837

Abstract

Wide-spectral saturable absorption (SA) in low-dimensional (LD) nanomaterials such as zero-, one-, and two-dimensional materials has been proven experimentally with outstanding results, including low saturation intensity, deep modulation depth, and fast carrier recovery time. LD nanomaterials can therefore be used as SAs for [...] Read more.

Wide-spectral saturable absorption (SA) in low-dimensional (LD) nanomaterials such as zero-, one-, and two-dimensional materials has been proven experimentally with outstanding results, including low saturation intensity, deep modulation depth, and fast carrier recovery time. LD nanomaterials can therefore be used as SAs for mode-locking or Q-switching to generate ultrafast fiber laser pulses with a high repetition rate and short duration in the visible, near-infrared, and mid-infrared wavelength regions. Here, we review the recent development of emerging LD nanomaterials as SAs for ultrafast mode-locked fiber laser applications in different dispersion regimes such as anomalous and normal dispersion regimes of the laser cavity operating in the near-infrared region, especially at ~1550 nm. The preparation methods, nonlinear optical properties of LD SAs, and various integration schemes for incorporating LD SAs into fiber laser systems are introduced. In addition to these, externally (electrically or optically) controlled pulsed fiber laser behavior and other characteristics of various LD SAs are summarized. Finally, the perspectives and challenges facing LD SA-based mode-locked ultrafast fiber lasers are highlighted. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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23 pages, 5831 KiB

Open AccessReview

Recent Progress in Distributed Brillouin Sensors Based on Few-Mode Optical Fibers

by Yong Hyun Kim and Kwang Yong Song

Sensors 2021, 21(6), 2168; https://doi.org/10.3390/s21062168 - 19 Mar 2021

Cited by 9 | Viewed by 2914

Abstract

Brillouin scattering is a dominant inelastic scattering observed in optical fibers, where the energy and momentum transfer between photons and acoustic phonons takes place. Narrowband reflection (or gain and loss) spectra appear in the spontaneous (or stimulated) Brillouin scattering, and their linear dependence [...] Read more.

Brillouin scattering is a dominant inelastic scattering observed in optical fibers, where the energy and momentum transfer between photons and acoustic phonons takes place. Narrowband reflection (or gain and loss) spectra appear in the spontaneous (or stimulated) Brillouin scattering, and their linear dependence of the spectral shift on ambient temperature and strain variations is the operation principle of distributed Brillouin sensors, which have been developed for several decades. In few-mode optical fibers (FMF’s) where higher-order spatial modes are guided in addition to the fundamental mode, two different optical modes can be coupled by the process of stimulated Brillouin scattering (SBS), as observed in the phenomena called intermodal SBS (two photons + one acoustic phonon) and intermodal Brillouin dynamic grating (four photons + one acoustic phonon; BDG). These intermodal scattering processes show unique reflection (or gain and loss) spectra depending on the spatial mode structure of FMF, which are useful not only for the direct measurement of polarization and modal birefringence in the fiber, but also for the measurement of environmental variables like strain, temperature, and pressure affecting the birefringence. In this paper, we present a technical review on recent development of distributed Brillouin sensors on the platform of FMF’s. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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Other

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9 pages, 4323 KiB

Open AccessLetter

Metallic 2H-Tantalum Selenide Nanomaterials as Saturable Absorber for Dual-Wavelength Q-Switched Fiber Laser

by Lingling Yang, Ruwei Zhao, Duanduan Wu, Tianxiang Xu, Xiaobiao Liu, Qiuhua Nie and Shixun Dai

Sensors 2021, 21(1), 239; https://doi.org/10.3390/s21010239 - 1 Jan 2021

Cited by 4 | Viewed by 2627

Abstract

A novel 2H-phase transition metal dichalcogenide (TMD)–tantalum selenide (TaSe₂) with metallic bandgap structure is a potential photoelectric material. A band structure simulation of TaSe₂ via ab initio method indicated its metallic property. An effective multilayered TaSe₂ saturable absorber (SA) [...] Read more.

A novel 2H-phase transition metal dichalcogenide (TMD)–tantalum selenide (TaSe₂) with metallic bandgap structure is a potential photoelectric material. A band structure simulation of TaSe₂ via ab initio method indicated its metallic property. An effective multilayered TaSe₂ saturable absorber (SA) was fabricated using liquid-phase exfoliation and optically driven deposition. The prepared 2H–TaSe₂ SA was successfully used for a dual-wavelength Q-switched fiber laser with the minimum pulse width of 2.95 μs and the maximum peak power of 64 W. The repetition rate of the maximum pulse energy of 89.9 kHz was at the level of 188.9 nJ. The metallic 2H–TaSe₂ with satisfactory saturable absorbing capability is a promising candidate for pulsed laser applications. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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10 pages, 2792 KiB

Open AccessLetter

Spectral Reflectance Can Differentiate Tracheal and Esophageal Tissue in the Presence of Bodily Fluids and Soot

by David Berard, Chirantan Sen, Corinne D. Nawn, August N. Blackburn, Kathy L. Ryan and Megan B. Blackburn

Sensors 2020, 20(21), 6138; https://doi.org/10.3390/s20216138 - 28 Oct 2020

Cited by 2 | Viewed by 2086

Abstract

Endotracheal intubation is a common life-saving procedure implemented in emergency care to ensure patient oxygenation, but it is difficult and often performed in suboptimal conditions leading to high rates of patient complications. Undetected misplacement in the esophagus is a preventable complication that can [...] Read more.

Endotracheal intubation is a common life-saving procedure implemented in emergency care to ensure patient oxygenation, but it is difficult and often performed in suboptimal conditions leading to high rates of patient complications. Undetected misplacement in the esophagus is a preventable complication that can lead to fatalities in 5–10% of patients who undergo emergency intubation. End-tidal carbon dioxide monitoring and other proper placement detection methods are useful, yet the problem of misplacement persists. Our previous work demonstrated the utility of spectral reflectance sensors for differentiating esophageal and tracheal tissues, which can be used to confirm proper endotracheal tube placement. In this study, we examine the effectiveness of spectral characterization in the presence of saline, blood, “vomit”, and soot in the trachea. Our results show that spectral properties of the trachea that differentiate it from the esophagus persist in the presence of these substances. This work further confirms the potential usefulness of this novel detection technology in field applications. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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13 pages, 4875 KiB

Open AccessLetter

Characterization of Second-Order Reflection Bands from a Cholesteric Liquid Crystal Cell Based on a Wavelength-Swept Laser

by Soyeon Ahn, Myeong Ock Ko, Jong-Hyun Kim, Zhongping Chen and Min Yong Jeon

Sensors 2020, 20(16), 4643; https://doi.org/10.3390/s20164643 - 18 Aug 2020

Cited by 9 | Viewed by 2851

Abstract

We report the results of an experimental study of the characterization of second-order reflection bands from a cholesteric liquid crystal (CLC) cell that depends on the applied electric field, using a wide bandwidth wavelength-swept laser. The second-order reflection bands around 1300 nm and [...] Read more.

We report the results of an experimental study of the characterization of second-order reflection bands from a cholesteric liquid crystal (CLC) cell that depends on the applied electric field, using a wide bandwidth wavelength-swept laser. The second-order reflection bands around 1300 nm and 1500 nm were observed using an optical spectrum analyzer when an electric field was applied to a horizontally oriented electrode cell with a pitch of 1.77 μm. A second-order reflection spectrum began to appear when the intensity of the electric field was 1.03 V_rms/μm with the angle of incidence to the CLC cell fixed at 36°. The reflectance increased as the intensity of the electric field increased at an angle of incidence of 20°, whereas at an incident angle of 36°, when an electric field of a predetermined value or more was applied to the CLC cell, it was confirmed that deformation was completely formed in the liquid crystal and the reflectance was saturated to a constant level. As the intensity of the electric field increased further, the reflection band shifted to a longer wavelength and discontinuous wavelength shift due to the pitch jump was observed rather than a continuous wavelength increase. In addition, the reflection band changed when the angle of incidence on the CLC cell was changed. As the angle of incidence gradually increased, the center wavelength of the reflection band moved towards shorter wavelengths. In the future, we intend to develop a device for optical wavelength filters based on side-polished optical fibers. This is expected to have a potential application as a wavelength notch filter or a bandpass filter. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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