Research On Inter-mode Interference Concentration Sensor Based On No-core Fiber

Optical fiber sensors are used to monitor various parameters,such as concentration,temperature,humidity,micro displacement,stress,and play an important role in aerospace,military science and technology,medical biology and other fields.Machzender interferometer(MZI)is used in various fields because of its own advantages,such as high sensitivity and simple fabrication.Based on the principle of intermode interference,three kinds of interferometric fiber concentration sensors are made by using no-core fiber(NCF),and the glycerol concentration characteristics of the three interferometric fiber concentration sensors are studied respectively.The main research is as follows.1.An in-line Mach-Zendel interferometer concentration sensor based on a lateral offset structure of NCF is designed and fabricated,and the concentration and temperature are measured.The structure consists of two segments of single-mode fiber(SMF)and NCF fused through a laterally offset microstructure The experimental results show that the sensitivities of the sensor with an NCF of 4 cm and a lateral offset of ～62.5μm are 0.166 nm/% in the 0-37% range,0.378 nm/% in the 37%-66%range and 1.440 nm/% in the 66%-82% range for glycerol concentration.The sensing structure has a temperature sensitivity of 0.083 nm/°C in the temperature range of25°C-80°C.The simple and low-cost construction of the sensor allows it to be used to control the concentration of various industrial solutions.2.An in-line Mach-Zendel interferometer concentration sensor based on NCF with a side-throw structure has been designed and fabricated,and the concentration and temperature are measured.The structure consists of a two-stage SMF and an NCF with a side-cast microstructure.The experimental results show that the sensitivity of the sensor with an NCF of 4 cm and a side throw depth ～58.6 μm is 0.168 nm/% in the 0-37% range,0.388 nm/% in the 37%-66% range and 2.090 nm/% in the66%-82% range for glycerol concentration.The temperature sensitivity of the sensing structure is 0.085 nm/°C in the temperature range of 25°C-80°C.The sensing structure is easy to manufacture and has a high sensitivity to glycerol concentration,which can be widely used for concentration detection in industrial sectors such as sugar,food and beverage.3.An in-line Mach-Zendel interferometer concentration sensor based on the NCF and U-shaped structure is designed for measuring concentration and temperature,and the sensing structure and its fabrication are described.The mode simulation and analysis of the curved structure are carried out using Rsoft.Experimental results show that the sensitivity of the sensor with an NCF of 4 cm and a bend diameter of ～2 mm is 1.338 nm/% of glycerol concentration in the range of 0-20%.The temperature sensitivity of the sensing structure is insensitive in the temperature range of25 °C-80 °C.The sensed structures have a very promising future in chemical and food processing.