Research On Micro Taper Long Period Fiber Grating Sensors

Optical fiber serves as a medium for signal transmission.Due to its unique advantages such as corrosion resistance and high sensitivity,it is widely used in fields such as national defense,military industry,and civil engineering.The development of optical fiber sensing technology is crucial for the construction of fiber optic communication networks.At present,most optical fiber sensors are designed based on special optical fibers to achieve functional diversity and high sensitivity performance improvement.Although special optical fibers have a relatively special structure and unique optical characteristics,they also have limitations such as high cost,difficult to control mode excitation,and complex device manufacturing processes.In contrast,single-mode fiber has a simple structure and low cost.The design and innovation of single-mode fiber optic sensor structures can be achieved through various structural processing technologies,enabling single-mode optical fiber sensors to meet the sensing needs of different usage environments.Therefore,single-mode fiber still holds a place in the field of fiber optic sensing today.Long period fiber grating is a typical passive device with advantages such as wide bandwidth and high sensitivity.If single-mode fiber is used as the carrier,fiber optic sensors with unique functions can be achieved through the improvement of grating engraving process.This paper designs multiple sensors with different functions based on single-mode optical fibers,and conducts in-depth research on the sensing characteristics of the devices from both theoretical analysis and experimental measurements.The main work of this thesis includes:1.A micro taper long period fiber grating sensor was designed based on single mode fiber.When fabricating long-period fiber gratings,axial tension is pre applied to a single-mode fiber to generate a micro taper structure,and the superposition of the micro cone structures constitutes the long-period fiber grating.The experimental results show that the sensing structure excites the LP₁₅ mode at the resonant peak wavelength,and can also identify the direction of torsion based on the changes in the resonant peak.The sensitivity is as high as-0.2087 nm/(rad·m^-1).2.The micro helix long period fiber grating is manufactured by introducing torsion during the micro cone manufacturing process.This sensing structure has a higher axial strain sensitivity compared to ordinary micro cone long period fiber gratings,and experimental results show that the sensitivity ranges from 0 to 3500μεThe sensitivity of axial strain within the range is-3.478 pm/με（0.001624 d B/με）。Compared with untwisted micro cone gratings,there is a significant improvement in sensitivity.3.On the basis of micro helix tapers,the chirp function layout was introduced to design a micro helix taper shaped chirped long period fiber grating physical deformation sensor.The introduction of chirped structures and the distribution of micro spiral cones are conducive to the excitation of cladding modes and the improvement of device integration.The experimental results indicate that the sensor not only has high torsional,axial strain,and bending sensitivity(-0.1575 nm/(rad·m^-1),-0.006846 nm/με,-10.62 nm/m^-1).In addition,it has a lower temperature sensitivity（0.04330 nm/°C）.