Fabrication Of Optical Fiber Sensor Based On Fabry-perot Interferometer

Since optical fiber sensor has got many advantages comparing to those traditional sensors, such as its small size, anti-electromagnetic interference, high sensitivity, insulation and its ability to work in severe environment instead of human, it has become a hot research topic in field of sensors. In this thesis, fabrication of optical fiber sensor based on Fabry-Perot interferometer is introduced in detail. Furthermore, due to the excellent property of optical fibers, fabrication and test of optical fiber micro lens are studied as well. The major contributions and highlights in this thesis are summarized as follows.1) Development history of optical fiber sensor has been summarized. Four kinds of fiber sensors are introduced, and their features as well. Research status of optical fiber sensor at home and abroad has been summarized. What’s more, research significance of fiber sensor has been discussed and its important application in engineering and scientific research as well.2) Two different kinds of key technology used in the thesis are introduced, and they are femtosecond laser technology and CO2 laser technology. For femtosecond laser technology, machining characteristic and its processing methods are summarized, and experimental system of femtosecond laser is also introduced in detail. For CO2 laser technology, its processing methods and experimental system are introduced as well. Besides, a welding experiment using CO2 laser technology is described in detail and the result is proved to be satisfying.3) A new kind of optical fiber extrinsic Fabry-Perot interferometer(EFPI) is designed and fabricated for refractive index sensing. In this thesis, we propose a new kind of Fabry-Perot interferometer based refractive index sensor that is assembled by a silica glass capillary and composed of two fiber end faces coated with gold film, one of which is processed by femtosecond laser to form a semicircular gold film. Semicircular gold film here acts as a reflector which could stop the transmission of the light, so that we can enhance the reflected light on the fiber end face in order to enhance the optical interference. By the way, the semicircular fiber end face which has been processed by femtosecond laser could let the light pass through to the other fiber end face in order to generate two different light paths. After that, the two fiber ends are assembled by a silica glass capillary to form a typical Fabry-Perot interferometer.4) Two different methods are adopted in the Fabry-Perot interferometer to test the refractive index of liquid, the wavelength tracking method and the Fourier-transform white-light interferometry(FTWLI). The sensitivities of sensors with the cavity length of 288.1μm and 358.5μm are 702.312nm/RIU and 396.362μm/RIU respectively by the two methods. Further experiments show that the Fabry-Perot interferometer is insensitive to temperature.5) Two different kinds of optical fiber micro lens are fabricated by femtosecond laser technology and CO2 laser technology respectively, and they are optical fiber cylindrical lens and spherical lens. Optical fiber micro lens with different shapes and focal length have many applications in micro-optical system and it is of great significance to develop different methods for micro lens fabrication. A new experimental system for focal length measurement is designed and set up. Optical fiber micro lens fabricated by femtosecond laser technology and CO2 laser technology are tested by the system. The focal length measured by the system is in agreement with the theoretical one calculated according to the focal length formula within the margin of error.