| With the rapid development of optical communication technology,fiber optic sensing technology has gradually come into view.This paper focuses on the topic of fabricating fiber optic micro-cavities on single-mode optical fibers via femtosecond laser ablation,and introduces three high-sensitivity fiber optic micro-cavity sensors based on femtosecond laser ablation,which are respectively the fiber optic refractive index and temperature sensor,the temperature and humidity measurement sensor,and the gas pressure sensor.(1)In order to explore the sensitivity characteristics of the sensor to a single environmental parameter(refractive index or temperature),a fiber optic micro-cavity fabricated by femtosecond laser was used.Due to the depth of the cavity’s ablation being 62.5 μm,the fiber optic core was in direct contact with the external environment.Its sensing characteristics for the environmental refractive index were investigated,and it was found that this sensor has a good refractive index linear fitting curves in the range of 1.363-1.378 for saltwater,with a high sensitivity of-16660nm/RIU.In order to study the temperature characteristic,the temperature characteristic of the sensor before and after coating with ultraviolet glue was tested,and it was found that after the micro-cavity was coated with ultraviolet glue,the sensor’s temperature sensitivity could be improved by two orders of magnitude to7.934 nm/°C.(2)In order to explore the characteristics of simultaneous measurement of temperature and humidity,a fiber optic micro-cavity filling material technology was proposed.The micro-cavity was filled with polyimide material to increase the structure’s sensitivity to temperature and humidity in the environment.Simultaneous measurement of temperature and humidity in the environment can be achieved by wavelength demodulation and mathematical matrix methods,eliminating crosssensitivity problems.Through experiments,it was found that the temperature sensitivity is-819.7 pm/°C,and the humidity sensitivity is 503.1 pm/%RH.The temperature and humidity response time of the sensor was also tested and compared with other types of sensors that simultaneously measure temperature and humidity.(3)In order to explore the sensing characteristics of the micro-cavities to gas pressure,a novel open-chamber fiber optic micro-cavity pressure sensor was introduced.By conducting gas pressure experiments on a single fiber optic microcavity,it was found that the pressure sensitivity of a single micro-cavity can reach-5.4 nm/MPa.By designing two micro-cavities with similar free spectral ranges and forming a vernier effect with femtosecond laser micromachining,the sensor sensitivity was further improved.Experimental results showed that the sensitivity of the sensor achieved through the vernier effect is-15.6 nm/MPa,which is 2.89 times higher than that of the single micro-cavity sensor.The experimental results were not much different from the theoretical simulation amplification factor of 3. |
