Research On Femtosecond Laser Fabrication Of New Type Optical Fiber Sensor

Nowadays,the development of optical fiber sensors is more and more rapid,and novel optical fiber sensors emerge in endlessly.Today,China's sensor market has exceeded 200 billion,and the demand for sensors in the information age is still growing.Among them,optical fiber sensors have attracted much attention.Therefore,optical fiber sensors with simple structure,simple manufacture and large-scale production potential have become a research hotspot.In recent years,the outstanding performance of femtosecond laser in fiber micromachining provides a new possibility for the development of fiber sensors.Femtosecond laser processing has high precision,small damage,and can complete dozens or even several microns of structure,making the structure more compact.Femtosecond laser combined with processing platform can make the processing programmed and simplify the processing process.In order to obtain a more compact and easy to make fiber sensor,based on femtosecond laser ablation and refractive index modification of fiber,three kinds of fiber probe sensors are designed and manufactured.The sensors complete the measurement of temperature,pressure,refractive index and humidity.The main work of this thesis is as follows(1)A gas pressure sensor based on capillary quartz tube is designed and fabricated by femtosecond laser cutting.The selection of capillary length and inner diameter is analyzed.The length of the whole structure is less than 50?m.the response characteristics of gas pressure and temperature of the sensor are tested.The pressure sensitivity of 4.4571nm/MPa is obtained.When the temperature reaches 75?,the sensor is not sensitive to temperature change,which can avoid the crosstalk caused by temperature.(2)A Fabry Perot interferometer based on fiber micropores is designed and fabricated by femtosecond laser ablation.Cylindrical micropores are machined by femtosecond laser near the end face of the fiber to form three mirrors with the size of about 20?m.The temperature,humidity,refractive index and air pressure response characteristics of the sensor were tested.The low temperature sensitivity of -0.0669 dB/?,humidity sensitivity of 0.74nm/%RH,refractive index sensitivity of 6.5nm/RIU,high temperature sensitivity of 12.23pm/? and air pressure sensitivity of 1.743 dB/MPa were obtained.The sensor can be used to measure a variety of parameters.(3)A fiber Michelson interferometer based on femtosecond laser refractive index modification is designed and fabricated.Femtosecond laser is used to modify the refractive index of single-mode fiber core,so that part of the light is transmitted into the fiber cladding,and the refractive index modification area is 100?m.The temperature sensitivity of the sensor is 5.3pm/? before 280? and 16.9pm/? between 280 and 580?.