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Helical Long-Period Gratings Inscribed in Polarization-Maintaining Fibers by CO2-Laser
摘要： We demonstrate fabrication of helical long-period gratings (HLPGs) in a polarization-maintaining fiber using CO2-laser. The maximum polarization dependent loss (PDL) of the grating was measured to be more than 30 dB at the resonance wavelength. The HLPG was found to have a high index sensitivity of -7248.6 nm/RIU when the surrounding refractive index changes in the range of 1.4470-1.4600, temperature sensitivity of 158.8 pm/°C, and strain sensitivity of 3.17 pm/με. The twist sensitivities based on intensity variation were measured to be 5.98 dB/ (rad/m) (co-directional twist) and -5.97 dB/ (rad/m) (contra-directional twist), respectively. The demonstrated grating devices have promising applications as high-sensitivity fiber sensors, PDL compensator etc.
关键词： optical fiber sensors,Fiber gratings,polarization-maintaining fibers,helical long-period gratings
更新于2025-11-28 14:24:03
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High-Resolution Temperature Sensor Based on Single-Frequency Ring Fiber Laser via Optical Heterodyne Spectroscopy Technology
摘要： We demonstrate a high-resolution temperature sensor based on optical heterodyne spectroscopy technology by virtue of the narrow linewidth characteristic of a single-frequency fiber laser. When the single-frequency ring fiber laser has a Lorentzian-linewidth <1 kHz and the temperature sensor operates in the range of 3?85 ?C, an average sensitivity of 14.74 pm/?C is obtained by an optical spectrum analyzer. Furthermore, a resolution as high as ~5 × 10?3 ?C is demonstrated through optical heterodyne spectroscopy technology by an electrical spectrum analyzer in the range of 18.26–18.71 ?C with the figure of merit up to 3.1 × 105 in the experiment.
关键词： fiber optics sensors,high resolution,heterodyne spectroscopy,single-frequency laser
更新于2025-11-28 14:24:03
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Tailoring Properties of Microcavity In-line Mach-Zehnder Interferometer by the Microcavity Enlargement using Femtosecond Laser
摘要： This work presents a theoretical analysis and experimental verification of fine-tuning of the spectral response and refractive index (RI) sensitivity of microcavity in-line Mach-Zehnder interferometer (μIMZI). The μIMZIs were fabricated using femtosecond (fs) laser micromachining in standard single-mode fibers as circular cavities with a diameter of 60 μm. Next, the structures underwent fs laser post-processing, which included fabrication of an additional cavity with the same diameter but shifted by 15 μm or 30 μm against the center of the initial microcavity. Different depths of the additional structures were investigated. The enlargement of the microcavity allows for tailoring the spectral response, i.e., it shifts the interference pattern by more than 200 nm, with no introduction of any additional losses and distortions in the spectrum. As the additional effect, regardless of the size of the extension, the sensitivity of the enlarged μIMZI was improved by 32%.
关键词： Fiber optics sensors,Laser materials processing,Interferometry,Microcavities,Microstructure fabrication
更新于2025-11-28 14:23:57
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Stable injection locking with slotted Fabry–Perot lasers at 2 <i>μ</i> m
摘要： Injection locking has many applications in telecommunications systems, such as narrowing linewidths, increasing bandwidth and improving filtering. Beyond telecommunications, injection locking is widely used in remote sensing. This is of particular interest for applications in the 2 μm region, where gases such as carbon dioxide, water vapour and methane have identifiable absorption features. In this paper, we demonstrate stable injection locking with slotted Fabry–Perot lasers in the 2 μm wavelength region. Injection locking was observed in both the optical domain and power spectrum; with key features recorded such as injection ‘pulling’, side-mode suppression and the characteristic quiet region in the electrical domain denoting single-frequency emission and stable locking. The effect of varying the injection ratio was investigated, with a decreased injection ratio corresponding to a reduction in the locking bandwidth. Finally, the lasers were shown to remain injection locked, with no thermal drift, for over 24 h, indicating their suitability for implementation in a real-world telecommunications system.
关键词： injection-locked lasers,semiconductor lasers,optical communications,optical sensing and sensors
更新于2025-11-28 14:23:57
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[IEEE 2018 IEEE Sensors - New Delhi (2018.10.28-2018.10.31)] 2018 IEEE SENSORS - Highly Sensitive Refractometer Using a Fiber Bragg Grating Fabricated by Femtosecond Laser
摘要： A highly localized fiber Bragg grating is inscribed using point-by-point femtosecond laser direct writing technique. By monitoring the location of the cut off wavelength, we demonstrate that the FBG has a highly-linear sensitivity for refractive index (RI) measurement. By monitoring the “peak-to- dip” intensity change near the cut-off wavelength, an ultra-high refractive index sensitivity of 2924.3dB/RIU and a RI resolution of 3.4×10-7 are achieved. As different surrounding refractive index corresponds to different location of the cut off wavelength, this FBG based refractometer can measure RI with wide range measurement range together with high sensitivity.
关键词： Femtosecond laser,Fiber Bragg grating,Refractive index sensors
更新于2025-11-28 14:23:57
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Temperature fiber sensor based on single longitudinal mode fiber laser in 2?μm band with Sagnac interferometer
摘要： A single longitudinal mode (SLM) ?ber laser with a ring cavity based on Sagnac interferometer (SI) for temperature sensing in the 2-μm band is proposed and demonstrated. The simulation and experimental results show that the transmission spectrum of the SI ?lter is sensitive to temperature change. Based on this distinguishing feature, the correlation between the laser wavelength drift and temperature variation can be established. Experimental results show that the proposed laser operates stably at the resonant wavelength of 1988.21 nm and the optical signal-to-noise ratio is approximately 55 dB at ambient temperature. Through continuous measurement for 100 min, the ?uctuation of the output laser power is lower than 0.74 dB, and the resonant wavelength shift is less than the minimum resolution of the spectrometer of 0.05 nm. This indicates that it has good stability for a certain period of time. At the same time, the laser operates stably in SLM state. A temperature sensitivity of 2.09 nm/°C is obtained in experiment. Notably, the proposed ?ber laser sensor possesses the merits including high sensitivity, low cost and simple structure, which are bene?cial to its practical application.
关键词： Fiber optics sensors,Temperature measurement,Sagnac interferometer,Fiber laser,2-μm band
更新于2025-11-28 14:23:57
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Fiber laser based on a fiber Bragg grating and its application in high-temperature sensing
摘要： A fiber laser based on an FBG fabricated by femtosecond laser and a Sagnac loop as cavity mirrors is demonstrated. The fiber laser can work stably as a temperature sensor at 1000 ℃ after the FBG was annealed at 1100 ℃. The wavelength of the fiber laser had a quadratic dependence on temperature from room temperature to 1000 ℃. The temperature–wavelength had a good linear relationship from 300 ℃ to 1000 ℃. Its sensing sensitivity was about 15.9 pm/℃.
关键词： Optical fiber lasers,Fiber Bragg gratings,High temperature sensors
更新于2025-11-28 14:23:57
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Fast and simple interrogation of extrinsic Fabry–Perot interferometer sensor based on dual-wavelength intensity ratio
摘要： A fast and simple demodulation method for the variation of Fabry-Perot (FP) cavity length is proposed and demonstrated. Taking advantages of differentially detecting optical power intensities of dual-wavelength, a reliable linear correlation between the variation of FP cavity length and differential intensity ratio of dual-wavelength can be obtained. Besides, an extrinsic Fabry-Perot interferometer (EFPI) sensor with a length of 196.8 um was used to demonstrate performance of the method, and the time for each experimental operation is within 100 ms by the demodulation method and an integrable tunable laser assembly (ITLA). The demodulation resolution of 0.726 nm was achieved for the change of cavity length in a strain sensing experiment. By selecting two wavelengths at different positions in the system, the linear ranges of FP cavity length variation are 180 nm, 150 nm, and 130 nm responding to the sensitivities of -0.01099 nm-1, -0.01485 nm-1, and -0.02253 nm-1, respectively. It shows a high flexibility between the linear range and the sensitivity. Consequently, the different requirements of the EFPI sensor system can be easily fulfilled through appropriate selections of two different wavelengths. Moreover, the advantages of simplicity, fast speed, low cost can be fully revealed in the demodulation of large-scale production EFPI sensors.
关键词： Fabry-Perot cavity,Fiber sensors,Dual-wavelength.
更新于2025-11-28 14:23:57
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Long tapered fiber with array of FBG
摘要： A tapered optical fiber with an adiabatic transition from single-mode to a few-mode part has been fabricated with an array of fiber Bragg gratings being inscribed during the drawing process. We demonstrate that the propagating optical signal remains single-mode along the tapered fiber FBG array even in a multimode part of it. The spectral width of the reflected signal from the tapered optical fiber is 4 nm. The level of the reflected signal is up to 5% at some wavelengths.
关键词： Tapered optical fibers,Fiber optics sensors,Fiber Bragg gratings
更新于2025-11-28 14:23:57
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Refractive Index Measurement of Lithium Ion Battery Electrolyte with Etched Surface Cladding Waveguide Bragg Gratings and Cell Electrode State Monitoring by Optical Strain Sensors
摘要： In this scientific publication, a new sensor approach for status monitoring, such as state of charge and state of health, of lithium ion batteries by using special Bragg gratings inscribed into standard optical glass fibers is presented. In addition to well-known core gratings, embedded into the anode of 5 Ah lithium ion pouch cells as a strain monitoring unit, the manufacturing of a surface cladding waveguide Bragg grating sensor incorporated into the cell’s separator, that is sensitive to changes of the refractive index of the surrounding medium, is demonstrated. On the basis of the experiments carried out, characteristics of the cell behavior during standard cyclization and recognizable marks in subsequent post-mortem analyses of the cell components are shown. No negative influence on the cell performance due to the integrated sensors have been observed; however, the results show a clear correlation between fading cell capacity and changes of the interior optical signals. Additionally, with the novel photonic sensor, variations in the electrolyte characteristics are determinable as the refractive index of the solution changes at different molar compositions. Furthermore, with the manufactured battery cells, abuse tests by overcharging were conducted, and it was thereby demonstrated how internal battery sensors can derive additional information beyond conventional battery management systems to feasibly prevent catastrophic cell failures. The result of the research work is an early stage photonic sensor that combines chemical, mechanical and thermal information from inside the cell for an enhanced battery status analysis.
关键词： lithium ion,battery aging,cladding waveguide,battery electrolyte,optical sensors,battery safety,fiber Bragg grating,electrode active material,status monitoring
更新于2025-11-28 14:23:57