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In-Fiber Grating Optic Sensors
Published in Shizhuo Yin, Paul B. Ruffin, Francis T. S. Yu, Fiber Optic Sensors, 2017
Lin Zhang, W. Zhang, I. Bennion
Recently, R&D efforts have been directed to a new class of grating devices—long-period fiber gratings (LPFGs). In contrast to the short-period (~1 m) FBGs, LPFGs have modulated refractive index periods typically in a range of 50–500 m and are capable of coupling light between the forward-propagating core and cladding modes, generating a series of attenuation resonance peaks in transmission. These types of devices, therefore, possess an intrinsically low level of back reflection and are inexpensive to batch-produce. The popularity of LPFGs has increased dramatically over the last few years as notable numbers of LPFG-based devices and systems have been demonstrated for a multitude of applications in optical fiber communications and sensing.
Monitoring relative humidity using a Mach-Zehnder interferometer (MZI) senor based upon a photonic crystal fiber (PCF) coated with polyvinyl alcohol (PVA)
Published in Instrumentation Science & Technology, 2023
Peng Gao, Xiaolin Zheng, Ying Liu, Zimu Wang
The photonic crystal fiber (PCF) is a new type of optical fiber that has a quartz-air composite structure with unique properties not present in ordinary optical fibers, including extremely high non-linearity, controlled dispersion, and birefringence properties. Commonly used moisture-sensitive materials include polyimide, agarose, chitosan, and polyvinyl alcohol.[9–12] So far, fiber optic relative humidity sensors based on different principles have been described that have included the Mach-Zehnder interferometer (MZI),[13] the Fabry-Perot interferometer,[14] the long period fiber grating,[15] the Sagnac ring,[16] and the fiber Bragg grating (FBG).[17]
Simultaneous measurement of humidity and temperature using a polyvinyl alcohol tapered fiber bragg grating
Published in Instrumentation Science & Technology, 2018
Sheng-xi Jiao, Yong Zhao, Jiang-jin Gu
In recent years, various humidity sensors based on optical fiber structures have been proposed, such as tapered fiber,[234] plastic optical fiber,[3] fiber Bragg grating,[56789] long-period fiber grating,[10111213] and Fabry–Perot interferometers.[14151617] However, conventional optical fiber is insensitive to humidity because the light is strictly bound in fiber core. Tapered fiber is efficient to reduce cladding region and leak out the light of core mode into the fiber cladding, and the humidity sensing can be achieved easily by coating humidity sensitive materials on the optical fiber sensing structures. The refractive index or thickness of hygroscopic materials changes with varied environmental humidity due to the swelling and deswelling effects.
Sensitivity-optimized long-period fiber gratings for refractive index and temperature sensing
Published in Instrumentation Science & Technology, 2018
Chao Du, Yong Zhao, Qi Wang, Feng Xia
The long-period fiber grating is sensitive to ambient refractive index, which is different from that of Fiber Bragg Grating due to that the coupling only occurs between core modes for Fiber Bragg Grating. Furthermore, the relatively narrower bandwidth of long-period fiber grating makes easy to realize high-accuracy signal demodulation. Based on this, there have been many articles on using long-period fiber grating for the measurement of refractive index,[567] especially in the fields of biological and chemical science.[8910] However, the refractive index sensitivity of bare long-period fiber grating cannot meet the higher measurement requirement, so the methods for enhancing the refractive index sensitivity have been deplored and developed by more and more researchers.