Design And Preparation Of Chalcogenide Fiber Optic Sensors Based On Femtosecond Laser Direct Writing

Compared with traditional electrical sensors,optical fiber sensors have many advantages such as miniaturization,high sensitivity,resistance to electromagnetic interference,corrosion resistance,and compact structure.At present,near-infrared optical fiber sensors based on communication fibers have been widely used in aerospace,petrochemical and structural health monitoring.The development of mid-infrared optical fiber sensors lags behind the development of near-infrared optical fiber sensors,which is mainly limited to the development of mid-infrared laser sources.In recent years,with the commercialization of quantum cascade lasers,mid-infrared fiber optic sensors have attracted widespread attention in the detection of biochemical molecules.As the only optical fiber medium that can cover mid-and far-infrared signal transmission,chalcogenide fiber is widely used in the construction of mid-infrared optical fiber sensing system.The chalcogenide fiber is drawn from the chalcogenide glass.It has advantages such as wide transmission range,high non-linearity,low phonon energy,adjustable composition,and easy drawing into silk,etc.Therefore,chalcogenide fibers have been widely concerned in infrared sensing systems.With the development of laser technology,femtosecond lasers have become increasingly prominent in the fields of photonic device preparation and material surface modification due to their ultrashort pulse width and super energy density.Based on the collation and summary of the research status of chalcogenide fiber sensors at home and abroad,this paper carried out the following aspects of work.(1)A high-sensitivity long-period fiber grating temperature sensor based on chalcogenide tapered fiber was designed.By optimizing the structural parameters of the optical fiber,the LPFG temperature sensor had a sensitivity of 1.89 nm/°C at a resonance wavelength of 1.55?m,which is an order of magnitude higher than the temperature sensitivity of the tapered silica LPFG.In addition,the sensor was insensitive to changes in the external refractive index.(2)A femtosecond laser direct writing platform was built.Based on this platform,a silica LPFG was prepared using a linear processing method,and the loss peak decreased to-16 d B,and the refractive index modulation degree of the fiber grating was 5×10^-4 through simulation calculation.Through the study of laser power,platform moving speed and defocusing processing parameters,the direct writing of LPFG on As₂S₃ single-mode fiber was realized.(3)A mid-infrared gas sensor based on four-hole chalcogenide suspension core optical fiber was designed and prepared.The prepared four-hole chalcogenide suspension core optical fiber had transmission range of 2-6?m and a minimum loss of 1 d B/m.The optical fiber can greatly increase the contact area between the light and the gas to be measured,and improve the sensitivity.In order to realize the real-time detection,a periodic channel was introduced by the femtosecond laser direct writing on the side of the suspended core optical fiber.Experiments showed that the minimum detection threshold of this sensor for methane was 100 ppm,and the response time was less than 20s.