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4 pages, 179 KiB

Open AccessEditorial

Micro-/Nano-Fiber Sensors and Optical Integration Devices

by Jin Li

Sensors 2022, 22(19), 7673; https://doi.org/10.3390/s22197673 - 10 Oct 2022

Cited by 4 | Viewed by 1891

Abstract

Because of their strong surface evanescent field, micro-/nanofibers have been used to develop optical sensors and modulation devices with a high performance and integration [...] Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

Research

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11 pages, 5879 KiB

Open AccessArticle

Broadband Acoustic Sensing with Optical Nanofiber Couplers Working at the Dispersion Turning Point

by Xu Gao, Jiajie Wen, Jiajia Wang and Kaiwei Li

Sensors 2022, 22(13), 4940; https://doi.org/10.3390/s22134940 - 30 Jun 2022

Cited by 7 | Viewed by 2144

Abstract

Herein, a broadband ultrasensitive acoustic sensor based on an optical nanofiber coupler (ONC) attached to a diaphragm is designed and experimentally demonstrated. The ONC is sensitive to axial strain and works as the core transducing element to monitor the deformation of the diaphragm [...] Read more.

Herein, a broadband ultrasensitive acoustic sensor based on an optical nanofiber coupler (ONC) attached to a diaphragm is designed and experimentally demonstrated. The ONC is sensitive to axial strain and works as the core transducing element to monitor the deformation of the diaphragm driven by acoustic waves. We first theoretically studied the sensing property of the ONC to axial strain and the deformation of the diaphragm. The results reveal that ONC working at the dispersion turning point (DTP) shows improved ultra-sensitivity towards axial strain, and the largest deformation of the circular diaphragm occurs at the center. Guided by the theoretical results, we fabricated an ONC with a DPT at 1550 nm, and we fixed one end of the ONC to the center of the diaphragm and the other end to the edge to construct the acoustic sensor. Finally, the experimental results show that the sensor can achieve accurate measurement in the broadband acoustic wave range of 30~20,000 Hz with good linearity. Specifically, when the input acoustic wave frequency is 120 Hz, the sensitivity reaches 1923 mV/Pa, the signal-to-noise ratio is 42.45 dB, and the minimum detectable sound pressure is 330 μPa/Hz^1/2. The sensor has the merits of simple structure, low cost, and high performance, and it provides a new method for acoustic wave detection. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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8 pages, 1969 KiB

Open AccessCommunication

Theoretical and Experimental Studies of Micro-Surface Crack Detections Based on BOTDA

by Baolong Yuan, Yu Ying, Maurizio Morgese and Farhad Ansari

Sensors 2022, 22(9), 3529; https://doi.org/10.3390/s22093529 - 6 May 2022

Cited by 6 | Viewed by 2050

Abstract

Micro-surface crack detection is important for the health monitoring of civil structures. The present literature review shows that micro-surface cracks can be detected by the Brillouin scattering process in optical fibers. However, the existing reports focus on experiment research. The comparison between theory [...] Read more.

Micro-surface crack detection is important for the health monitoring of civil structures. The present literature review shows that micro-surface cracks can be detected by the Brillouin scattering process in optical fibers. However, the existing reports focus on experiment research. The comparison between theory and experiment for Brillouin-scattering-based optical sensors is rarely reported. In this paper, a distributed optical fiber sensor for monitoring micro-surface cracks is presented and demonstrated. In the simulation, by using finite element methods, an assemblage of a three-dimensional beam model for Brillouin optical time domain analysis (BOTDA) was built. The change in Brillouin frequency (distributed strain) as a function of different cracks was numerically investigated. Simulation results indicate that the amplitudes of the Brillouin peak increase from 27 με to 140 με when the crack opening displacement (COD) is enlarged from 0.002 mm to 0.009 mm. The experiment program was designed to evaluate the cracks in a beam with the length of 15 m. Experimental results indicate that it is possible to detect the COD in the length of 0.002~0.009 mm, which is consistent with the simulation data. The limitations of the proposed sensing method are discussed, and the future research direction is prospected. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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12 pages, 2534 KiB

Open AccessArticle

An Ultra-High-Resolution Bending Temperature Decoupled Measurement Sensor Based on a Novel Core Refractive Index-like Linear Distribution Doped Fiber

by Yunshan Zhang, Yulin Zhang, Xiafen Hu, Dan Wu, Li Fan, Zhaokui Wang and Linxing Kong

Sensors 2022, 22(8), 3007; https://doi.org/10.3390/s22083007 - 14 Apr 2022

Cited by 3 | Viewed by 1934

Abstract

A high-resolution and high-sensitivity fiber optic sensor based on the quasi-linear distribution of the core refractive index is designed and fabricated, which enables decouple measurement of bending and of temperature. First, single-mode fiber doped with Al₂O₃, Y₂O [...] Read more.

A high-resolution and high-sensitivity fiber optic sensor based on the quasi-linear distribution of the core refractive index is designed and fabricated, which enables decouple measurement of bending and of temperature. First, single-mode fiber doped with Al₂O₃, Y₂O₃, and P₂O₅ was drawn through a fiber drawing tower. The fiber grating was engraved on the fiber by a femtosecond laser. Modeling analysis was conducted from quantum theory. Experimental results show that the bending sensitivity of the grating can reach 21.85 dB/m⁻¹, which is larger than the reported sensitivity of similar sensors. In the high temperature range from room temperature to 1000 °C, the temperature sensitivity was 14.1 pm/°C. The doped grating sensor can achieve high temperature measurement without annealing, and it has a distinguished linear response from low temperature to high temperature. The bending resolution can reach 0.0004 m⁻¹, and the temperature resolution can reach 0.007 °C. Two-parameter decoupling measurement can be realized according to the distinctive characteristic trends of the spectrum. What’s more, the sensor exhibits excellent stability and a fast response time. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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13 pages, 3035 KiB

Open AccessArticle

A Novel Airborne Molecular Contaminants Sensor Based on Sagnac Microfiber Structure

by Guorui Zhou, Siheng Xiang, Hui You, Chunling Li, Longfei Niu, Yilan Jiang, Xinxiang Miao and Xiufang Xie

Sensors 2022, 22(4), 1520; https://doi.org/10.3390/s22041520 - 16 Feb 2022

Cited by 4 | Viewed by 1617

Abstract

The impact of airborne molecular contaminants (AMCs) on the lifetime of fused silica UV optics in high power lasers (HPLs) is a critical issue. In this work, we demonstrated the on-line monitoring method of AMCs concentration based on the Sagnac microfiber structure. In [...] Read more.

The impact of airborne molecular contaminants (AMCs) on the lifetime of fused silica UV optics in high power lasers (HPLs) is a critical issue. In this work, we demonstrated the on-line monitoring method of AMCs concentration based on the Sagnac microfiber structure. In the experiment, a Sagnac microfiber loop with mesoporous silica coating was fabricated by the microheater brushing technique and dip coating. The physical absorption of AMCs in the mesoporous coating results in modification of the surrounding refractive index (RI). By monitoring the spectral shift in the wavelength domain, the proposed structure can operate as an AMCs concentration sensor. The sensitivity of the AMCs sensor can achieve 0.11 nm (mg/m³). By evaluating the gas discharge characteristic of four different low volatilization greases in a coarse vacuum environment, we demonstrated the feasibility of the proposed sensors. The use of these sensors was shown to be very promising for meeting the requirements of detecting trace amounts of contaminants. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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16 pages, 7116 KiB

Open AccessArticle

Study of the Off-Axis Fresnel Zone Plate of a Microscopic Tomographic Aberration

by Lin Yang, Zhenyu Ma, Siqi Liu, Qingbin Jiao, Jiahang Zhang, Wei Zhang, Jian Pei, Hui Li, Yuhang Li, Yubo Zou, Yuxing Xu and Xin Tan

Sensors 2022, 22(3), 1113; https://doi.org/10.3390/s22031113 - 1 Feb 2022

Cited by 4 | Viewed by 2407

Abstract

A tomographic microscopy system can achieve instantaneous three-dimensional imaging, and this type of microscopy system has been widely used in the study of biological samples; however, existing chromatographic microscopes based on off-axis Fresnel zone plates have degraded image quality due to geometric aberrations [...] Read more.

A tomographic microscopy system can achieve instantaneous three-dimensional imaging, and this type of microscopy system has been widely used in the study of biological samples; however, existing chromatographic microscopes based on off-axis Fresnel zone plates have degraded image quality due to geometric aberrations such as spherical aberration, coma aberration, and image scattering. This issue hinders the further development of chromatographic microscopy systems. In this paper, we propose a method for the design of an off-axis Fresnel zone plate with the elimination of aberrations based on double exposure point holographic surface interference. The aberration coefficient model of the optical path function was used to solve the optimal recording parameters, and the principle of the aberration elimination tomography microscopic optical path was verified. The simulation and experimental verification were carried out utilizing a Seidel coefficient, average gradient, and signal-to-noise ratio. First, the aberration coefficient model of the optical path function was used to solve the optimal recording parameters. Then, the laminar mi-coroscopy optical system was constructed for the verification of the principle. Finally, the simulation calculation results and the experimental results were verified by comparing the Seidel coefficient, average gradient, and signal-to-noise ratio of the microscopic optical system before and after the aberration elimination. The results show that for the diffractive light at the orders 0 and ±1, the spherical aberration W040 decreases by 62–70%, the coma aberration W131 decreases by 96–98%, the image dispersion W222 decreases by 71–82%, and the field curvature W220 decreases by 96–96%, the average gradient increases by 2.8%, and the signal-to-noise ratio increases by 18%. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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9 pages, 2037 KiB

Open AccessCommunication

Characterization of a Mass-Produced SiPM at Liquid Nitrogen Temperature for CsI Neutrino Coherent Detectors

by Fang Liu, Xiaoxue Fan, Xilei Sun, Bin Liu, Junjie Li, Yong Deng, Huan Jiang, Tianze Jiang and Peiguang Yan

Sensors 2022, 22(3), 1099; https://doi.org/10.3390/s22031099 - 31 Jan 2022

Cited by 7 | Viewed by 2715

Abstract

Silicon Photomultiplier (SiPM) is a sensor that can detect low-light signals lower than the single-photon level. In order to study the properties of neutrinos at a low detection threshold and low radioactivity experimental background, a low-temperature CsI neutrino coherent scattering detector is designed [...] Read more.

Silicon Photomultiplier (SiPM) is a sensor that can detect low-light signals lower than the single-photon level. In order to study the properties of neutrinos at a low detection threshold and low radioactivity experimental background, a low-temperature CsI neutrino coherent scattering detector is designed to be read by the SiPM sensor. Less thermal noise of SiPM and more light yield of CsI crystals can be obtained at the working temperature of liquid nitrogen. The breakdown voltage (V_bd) and dark count rate (DCR) of SiPM at liquid nitrogen temperature are two key parameters for coherent scattering detection. In this paper, a low-temperature test is conducted on the mass-produced ON Semiconductor J-Series SiPM. We design a cryogenic system for cooling SiPM at liquid nitrogen temperature and the changes of operating voltage and dark noise from room to liquid nitrogen temperature are measured in detail. The results show that SiPM works at the liquid nitrogen temperature, and the dark count rate drops by six orders of magnitude from room temperature (120 kHz/mm²) to liquid nitrogen temperature (0.1 Hz/mm²). Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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13 pages, 4325 KiB

Open AccessArticle

Diagnosis of Bone Mineral Density Based on Backscattering Resonance Phenomenon Using Coregistered Functional Laser Photoacoustic and Ultrasonic Probes

by Lifeng Yang, Chulin Chen, Zhaojiang Zhang and Xin Wei

Sensors 2021, 21(24), 8243; https://doi.org/10.3390/s21248243 - 9 Dec 2021

Cited by 4 | Viewed by 2546

Abstract

Dual-energy X-ray absorptiometry (DXA) machines based on bone mineral density (BMD) represent the gold standard for osteoporosis diagnosis and assessment of fracture risk, but bone strength and toughness are strongly correlated with bone collagen content (CC). Early detection of osteoporosis combined with BMD [...] Read more.

Dual-energy X-ray absorptiometry (DXA) machines based on bone mineral density (BMD) represent the gold standard for osteoporosis diagnosis and assessment of fracture risk, but bone strength and toughness are strongly correlated with bone collagen content (CC). Early detection of osteoporosis combined with BMD and CC will provide improved predictability for avoiding fracture risk. The backscattering resonance (BR) phenomenon is present in both ultrasound (US) and photoacoustic (PA) signal transmissions through bone, and the peak frequencies of BR can be changed with BM and CC. This phenomenon can be explained by the formation of standing waves within the pores. Simulations were then conducted for the same bone µCT images and the resulting resonance frequencies were found to match those predicted using the standing wave hypothesis. Experiments were performed on the same bone sample using an 808 nm wavelength laser as the PA source and 3.5 MHz ultrasonic transducer as the US source. The backscattering resonance effect was observed in the transmitted waves. These results verify our hypothesis that the backscattering resonance phenomenon is present in both US and PA signal transmissions and can be explained using the standing waves model, which will provide a suitable method for the early detection of osteoporosis. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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12 pages, 2211 KiB

Open AccessArticle

An Ultra-Sensitive Multi-Functional Optical Micro/Nanofiber Based on Stretchable Encapsulation

by Siheng Xiang, Hui You, Xinxiang Miao, Longfei Niu, Caizhen Yao, Yilan Jiang and Guorui Zhou

Sensors 2021, 21(22), 7437; https://doi.org/10.3390/s21227437 - 9 Nov 2021

Cited by 12 | Viewed by 2472

Abstract

Stretchable optical fiber sensors (SOFSs), which are promising and ultra-sensitive next-generation sensors, have achieved prominent success in applications including health monitoring, robotics, and biological–electronic interfaces. Here, we report an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible polydimethylsiloxane (PDMS) membrane, which is compatible [...] Read more.

Stretchable optical fiber sensors (SOFSs), which are promising and ultra-sensitive next-generation sensors, have achieved prominent success in applications including health monitoring, robotics, and biological–electronic interfaces. Here, we report an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible polydimethylsiloxane (PDMS) membrane, which is compatible with wearable optical sensors. Based on the effect of a strong evanescent field, the as-fabricated SOFS is highly sensitive to strain, achieving high sensitivity with a peak gauge factor of 450. In addition, considering the large negative thermo-optic coefficient of PDMS, temperature measurements in the range of 30 to 60 °C were realized, resulting in a 0.02 dBm/°C response. In addition, wide-range detection of humidity was demonstrated by a peak sensitivity of 0.5 dB/% RH, with less than 10% variation at each humidity stage. The robust sensing performance, together with the flexibility, enables the real-time monitoring of pulse, body temperature, and respiration. This as-fabricated SOFS provides significant potential for the practical application of wearable healthcare sensors. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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10 pages, 2831 KiB

Open AccessCommunication

Multiplexed Weak Waist-Enlarged Fiber Taper Curvature Sensor and Its Rapid Inline Fabrication

by Duo Yi, Lina Wang, Youfu Geng, Yu Du, Xuejin Li and Xueming Hong

Sensors 2021, 21(20), 6782; https://doi.org/10.3390/s21206782 - 13 Oct 2021

Cited by 1 | Viewed by 1716

Abstract

This study proposes a multiplexed weak waist-enlarged fiber taper (WWFT) curvature sensor and its rapid fabrication method. Compared with other types of fiber taper, the proposed WWFT has no difference in appearance with the single mode fiber and has ultralow insertion loss. The [...] Read more.

This study proposes a multiplexed weak waist-enlarged fiber taper (WWFT) curvature sensor and its rapid fabrication method. Compared with other types of fiber taper, the proposed WWFT has no difference in appearance with the single mode fiber and has ultralow insertion loss. The fabrication of WWFT also does not need the repeated cleaving and splicing process, and thereby could be rapidly embedded into the inline sensing fiber without splicing point, which greatly enhances the sensor solidity. Owing to the ultralow insertion loss (as low as 0.15 dB), the WWFT-based interferometer is further used for multiplexed curvature sensing. The results show that the different curvatures can be individually detected by the multiplexed interferometers. Furthermore, it also shows that diverse responses for the curvature changes exist in two orthogonal directions, and the corresponding sensitivities are determined to be 79.1°/m⁻¹ and –48.0°/m⁻¹ respectively. This feature can be potentially applied for vector curvature sensing. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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12 pages, 4756 KiB

Open AccessCommunication

A Fiber-Integrated CRDS Sensor for In-Situ Measurement of Dissolved Carbon Dioxide in Seawater

by Mai Hu, Bing Chen, Lu Yao, Chenguang Yang, Xiang Chen and Ruifeng Kan

Sensors 2021, 21(19), 6436; https://doi.org/10.3390/s21196436 - 27 Sep 2021

Cited by 14 | Viewed by 2823

Abstract

Research on carbon dioxide (CO₂) geological and biogeochemical cycles in the ocean is important to support the geoscience study. Continuous in-situ measurement of dissolved CO₂ is critically needed. However, the time and spatial resolution are being restricted due to the [...] Read more.

Research on carbon dioxide (CO₂) geological and biogeochemical cycles in the ocean is important to support the geoscience study. Continuous in-situ measurement of dissolved CO₂ is critically needed. However, the time and spatial resolution are being restricted due to the challenges of very high submarine pressure and quite low efficiency in water-gas separation, which, therefore, are emerging the main barriers to deep sea investigation. We develop a fiber-integrated sensor based on cavity ring-down spectroscopy for in-situ CO₂ measurement. Furthermore, a fast concentration retrieval model using exponential fit is proposed at non-equilibrium condition. The in-situ dissolved CO₂ measurement achieves 10 times faster than conventional methods, where an equilibrium condition is needed. As a proof of principle, near-coast in-situ CO₂ measurement was implemented in Sanya City, Haina, China, obtaining an effective dissolved CO₂ concentration of ~950 ppm. The experimental results prove the feasibly for fast dissolved gas measurement, which would benefit the ocean investigation with more detailed scientific data. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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9 pages, 3690 KiB

Open AccessCommunication

Optical Fiber Based Mach-Zehnder Interferometer for APES Detection

by Huitong Deng, Xiaoman Chen, Zhenlin Huang, Shiqi Kang, Weijia Zhang, Hongliang Li, Fangzhou Shu, Tingting Lang, Chunliu Zhao and Changyu Shen

Sensors 2021, 21(17), 5870; https://doi.org/10.3390/s21175870 - 31 Aug 2021

Cited by 6 | Viewed by 2767

Abstract

A 3-aminopropyl-triethoxysilane (APES) fiber-optic sensor based on a Mach–Zehnder interferometer (MZI) was demonstrated. The MZI was constructed with a core-offset fusion single mode fiber (SMF) structure with a length of 3.0 cm. As APES gradually attaches to the MZI, the external environment of [...] Read more.

A 3-aminopropyl-triethoxysilane (APES) fiber-optic sensor based on a Mach–Zehnder interferometer (MZI) was demonstrated. The MZI was constructed with a core-offset fusion single mode fiber (SMF) structure with a length of 3.0 cm. As APES gradually attaches to the MZI, the external environment of the MZI changes, which in turn causes change in the MZI’s interference. That is the reason why we can obtain the relationships between the APES amount and resonance dip wavelength by measuring the transmission variations of the resonant dip wavelength of the MZI. The optimized amount of 1% APES for 3.0 cm MZI biosensors was 3 mL, whereas the optimized amount of 2% APES was 1.5 mL. Full article

(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)

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