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Special Dual-core Fiber Sensors With Embedded Long Period Fiber Grating

Posted on:2022-07-31Degree:MasterType:Thesis
Country:ChinaCandidate:Z X WeiFull Text:PDF
GTID:2518306350982649Subject:Optical Engineering
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With the intorduction of the concept of the Internet of things,the requirements for the construction of optical fiber communication network are constantly improved.As a pivotal link,optical fiber sensing has important applications in production,life,national defense,science and technology and other fields.Sensors based on traditional single-mode fiber are increasingly difficult to satisfy the needs of high precision,high integration and multi-function.Therefore,the special optical fiber can be used to achieve highly integrated fiber sensing with diversified functions and higher stability and sensitivity due to its special physical structure and rich optical properties.As a typical fiber passive device,long-period fiber grating has advantages of wide band width and high sensitivity,etc.If special fiber is used as carrier,more advantageous fiber sensors can be designed.This paper designs sensors with different functions based on two kinds of special dual-core optical fibers,and studies their sensing characteristics from theoretical analysis and experimental test.The main work of this thesis includes:A long period fiber grating torsion sensor with preloaded torsion force is designed based on symmetric dual-core fiber.Before the preparation of long period fiber gratings,pre-torsion force is applied to the dual-core fiber to make it has frozen shear strain.Two long period fiber gratings with different cycles and opposite pre-torsion directions are written at different positions of the dual-core fiber.After the fiber is untwisted,the shapes of the gratings will be left helix or right helix.Because the pre-torsion direction of the two parts of the gratings is different,they have opposite torsion response and the torsion sensitivity is doubled.The experimental results show that the torsion sensitivity of the sensor structure reaches 0.171 nm/radm-1 in the range of-60?60 rad/m.The temperature sensitivity is about 76 pm/?in the range of 20?180?.The maximum axial strain sensitivity is-0.27 pm/??in the range of 0?2000??.A temperature and humidity dual-parameter sensor based on air hole assisted dual-core fiber with a directional coupler and a long period fiber grating is designed.The resonant peak generated by the directional coupler formed by the air hole assisted dual-core fiber responds only to temperature variation but not to humidity variation.Long period fiber grating is written on the central core to realize the coupling between the core mode and the higher-order cladding mode,grating resonant peak responds to boss temperature and humidity change.Therefore,the resonant peak formed by the directional coupler can be used for temperature sensing,and the temperature crosstalk during the long period fiber grating resonance peak humidity sensing can be compensated to realize the humidity sensor without temperature crosstalk.The experimental results show that the humidity sensitivity of grating resonance peak is about 73.88 pm/%RH in the range of 45?90%RH,and the directional coupler resonance peak is not sensitive to humidity change.The temperature sensitivity of grating resonance peak in the temperature range of 20?90?is about 22.32 pm/?,and that of directional coupler resonance peak is about 18.75 pm/?.
Keywords/Search Tags:optical fiber sensing, long period fiber grating, coupled-mode theory, dual-core fiber
PDF Full Text Request
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