Development Of Reflective Optical Fiber Level Sensor

As a kind of novel sensor,the mode interference based fiber optic sensors have been widely used in engineering,biochemical environment,and medical fields due to the advantages,such as small size,high precision,low cost,and easy to manufacture.Compared with the Mach-Zehnder interferometer,in-line Michelson interferometer(IMI)is more compact because its transmitter and receiver are located at the same side,which can realize probe measurement and facilitate the signal processing.Therein,in this paper,based on the principle of mode interference,two reflective fiber liquid-level sensors are designed and fabricated by using arc discharge technology.The main research contents are as follows:(1)Based on beam propagation method,the structures of core-mismatch and core-offset are simulated and analyzed.The key parameters of mode interferometer are optimized.Moreover,the characteristics of liquid level sensing of these two structures are studied,and the blue-shift feature of interference spectrum is verified with the increased liquid level.(2)Based on the core-mismatch structure,a Michelson-based mode interferometer is designed.The characteristics of mode coupling and interference spectrum are simulated,and the preparation parameters are optimized.Then the tests in terms of liquid level and temperature are performed.The experimental results show that,in the range of 0?40 mm,a good linear wavelength response is obtained with the changed liquid level and the sensitivity reaches-63.7 pm/mm.Furthermore,with the 99.5% temperature consistency of interference fringes,the differential method for self-compensation temperature is introduced to achieve high-precision and low crosstalk liquid level measurement.(3)Through off-core splicing,an on-off-type fiber liquid level sensor is developed based on a micro-sphere(MS)end-face.The core-offset value and micro-sphere diameter are optimized to get the fringe contrast as high as 14.43 d B in the MS-IMI.The experimental results show that,in the range of 0?70 mm,the linear wavelength response with the varied liquid level and the sensitivity is-31.7 pm/mm.But the linear response of intensity is presented significantly in the range of 70?100 mm and the corresponding sensitivity reaches-0.0885 d B/mm.Comparatively,the wavelength response shows the characteristic of "zero change ".Such "reverse" feature shows that the proposed MS-IMI can be used as an intensity demodulated "on-off" liquid level sensor with high practicality.