Research On Sensing Of D Type Optical Fiber Interference Device

Compared to general optical fiber, D-type optical fiber has two advantages. Firstly, the core of D-type optical fiber is closer to environment, so the D-type optical fiber is more sensitive to the change of external environment. Secondly, it is convenient to focus and etching for the laser micromachining system, because the side surface of the D-type optical fiber is a plane. Based on these advantages, D-type optical fiber interference devices have attracted much attention, an open Fabry-Perot(F-P) pressure sensor and a series distributed refractive index sensor are studied. The main contents of this work are as follows:(1) A D-type optical fiber F-P pressure sensor is designed and manufactured. The pressure sensor consists of an open F-P cavity, the sensing principle is mainly based on the refractive index changing with the change of pressure. It has high sensitivity to pressure and low cross sensitivity of temperature and pressure, and can realize the rapid response to the dynamic pressure. The grinding process and 157 nm laser micromachining technology are used to make the D-type optical fiber open F-P pressure sensor. The performance of static pressure and dynamic pressure of the pressure sensor is tested, and compared with the traditional optical fiber closed F-P pressure sensor. The experimental results show that the pressure sensitivity is about 1.6749rad/MPa, which is much higher than the closed type pressure sensor, the linearity is about 99.83%, and the pressure sensor has good stability and insensitivity to temperature. The pressure sensor has good dynamic response characteristics, the response time to pulse pressure is about 0.88 ms.(2) A D-type fiber F-P refractive index sensor is fabricated, the basic structure is a F-P cavity, and the length of the F-P cavity achieved the order of centimeters. Build a microwave test system based on a vector network analyzer to test the D-type fiber F-P refractive index sensor. The sensitivity, stability, repeatability and other properties of the refractive index sensor are tested by experiments. The refractive index sensitivity is about 5.08MHz/RIU. A cascaded of the D-type fiber F-P refractive index sensor are connected in series. In the microwave test system, it is able to distinguish different sensors, and realize to measure the performance of any one of the refractive index sensor. Then the distributed measurement of refractive index sensor is realized.(3) A D-type fiber periodic structure is proposed. The periodic structure is formed by the periodic arrangement of the air and the fiber core. Due to the high refractive index difference between the fiber core and the air chamber, it has high reflection at the interface. A high reflection peak of the periodic structure can be achieved even if the number of periods is reduced. Using finite element analysis software COMSOL Multiphysics to simulate the D-type fiber periodic structure. The change of the spectrum is analyzed by changing the refractive index of the air chamber and the structure parameters of the periodic structure.