Sagnac Interferometric Sensing Characteristics Based On Optical Fiber Over-Coupling Structure

In this paper,based on principle of coupled mode,the optical fiber over-coupling structure was carried out by the fusion taper technology.At the same time,the sensing characteristics of the Sagnac interferometer were explored,and the Sagnac interferometer based on the optical fiber over-coupling structure was developed.The main research contents are as follows:Based on the coupled mode principle,the optical fiber coupling structure and the light transmission principle in the coupling structure were studied,and the interference principle of the over-coupling structure is analyzed.Using beam propagation method,the interferometer structures with different coupling degrees are simulated and studied.The influence of taper parameters on coupling effect is explored.The preparation of overcoupling structure was studied by using the preparation method of melting taper.The influence of preparation parameters of the over-coupling structure on the output spectrum was analyzed in detail through the experimental tests of the height of the burner,the cone pulling speed,the hydrogen flow rate and the swing speed of the burner.By controlling the parameters,the transmission spectrum can achieve the purpose of sensing test.The sensing characteristics of the optical fiber over-coupling interferometer were studied.The experimental results show that the optical fiber over-coupling interferometer had good strain sensitivity,the sensitivity can reach 15.4 pm/με in the range of 0-750 μεand it has good linearity.Sensitivity of RI reached 2094.2 nm/RIU,temperature sensitivity is 111.0 pm/°C.Simultaneous measurement of strain and refractive index and strain and temperature was carried out.Sagnac interferometer based on fiber overcoupling structure was constructed,and the strain sensitivity was affected by the difference of Sagnac loop’s fiber length and waveband.Experiments show that with the increase of strain,the sensitivity difference of different bands is more obvious.And with the increase of fiber length in the loop,the sensitivity tends to decrease.Its high sensitivity is in the range of 600-750 με and the length of the fiber in the ring is 50 cm,the C-band strain sensitivity is 23.2 pm/με and the L-band sensitivity is 31.2 pm/με.