Preparation Of Fusion Type All-fiber MZI And LPFG And Their Sensing Characteristics

Fiber optic sensors have been widely used in many fields,such as oil and gas industry,electrical industry,civil construction,aerospace,high-speed railway,because of their advantages of low preparation cost,high sensitivity,anti-electromagnetic interference,and adoption to harsh environment.Especially in the past two decades,with the gradual deepening of research on grating type fiber sensor and the growing maturity of processing technology,the types of optical fiber sensors are constantly enriched,their functions get more complete,and the performances are more excellent.The optical fiber sensors based on the Maher-Zehnder Interferometer?MZI?and the long period fiber grating?LPFG?have reached more than 40%in the field of optical fiber sensing applications.In addition,the full fiber MZI,which integrates the reference arm and the sensing arm in one single fiber,shows the advantages of the flexible,high integration,and high cost performance of optical fiber sensors.In this thesis,a highly effective and reliable fiber fused taper system was designed based on the graphite electric heating.Based on our taper system,we fabricated the taper type,bulging,and torsional all fiber MZI and LPFG.With the taper,bulging,and torsional coupling units,a variety of composite full fiber MZI and LPFG were prepared by paralleling with the CO₂-LPFG?the ordinary long period fiber gratings prepared by high frequency CO₂ laser?to simultaneously measure the more parameters.The main contents of this thesis are summarized as follows:?1?An efficient and reliable optical fiber fused taper system has been developed.The system uses graphite heater for heating,which has higher reliability and stability than the traditional flame heating method.We used the system to prepare the all-optical fiber MZI and LPFG,and experimentally analyzed their temperature and strain sensing characteristics.?2?A method of molten expansion for preparing optical fiber devices has been proposed.We have used this method to prepare bulged MZI and LPFG on a single optical fiber.The advantage of this method is to avoid cutting the fiber and collimating the core.This preparation process is very simple,and the optical properties of the related optical fiber devices can be improved.?3?A method of making twisted coupling units by melting and releasing torque has been proposed.Based on this method,torsional all-optical fiber MZI and LPFG have been fabricated.The temperature and torque sensing characteristics of these two structures showed that the structures were highly sensitive for torsion directions.?4?A type of composite fiber optical sensors with the basic coupling unit of the taper,bulging,and torsional types have been designed and prepared.The temperature,strain,and torsion characteristics of these composite fiber sensors have been characterized in the experiments.The results showed that the transmission spectrum has a double resonant peak structure,and the sensitivities to temperature and strain or torsion were different,indicating that the proposed composite sensors can be used to simultaneously measure the temperature,strain/torsion,and many other parameters.