| Summary: | 博士 === 逢甲大學 === 電機與通訊工程博士學位學程 === 102 === The main content of this dissertation is to investigate a new multi-mode interference hetero-core fiber sensor for applying in bending or refractive index measurements. The multi-mode interference (MMI) fiber sensor is composed of a piece of no-core fiber (NCF) sandwiched between two single-mode fibers (SMFs). The section of NCF can be viewed as a multi-mode fiber (MMF) with an inner core of 125 μm which is surrounded by outer materials with a lower-refractive-index outer environment. Furthermore, this sensor is combined with a fiber Bragg grating to achieve a multi-function fiber sensor.
For the bending measurement, as the curvature is increased, the transmission-dip of the multi-mode interference hetero-core fiber sensor is blue shifted with the bending sensitivity of -183.788 nm/m-1. At the same time, the dip-depth of the other mode becomes shallower. Based on this phenomenon, a fiber Bragg grating (FBG) is connected to the MMI fiber sensor so that the reflectivity of the FBG is varied with the bending sensitivity of -26.79 dBm/m-1. Moreover, this MMI fiber sensor has a maximum sensitivity of 7792.85 nm/RIU as the testing refractive index becomes nearly equal to the index of no-core fiber. In addition, by connecting a FBG to the MMI fiber sensor, a dual-parameter optical sensor is achieved with the ability of simultaneously measuring temperature and the external refractive index. This is due to that the optical response between the transmission spectra of both FBG and MMI is different and then the variation both of refractive index and temperature will cause the variation of the transmission wavelength of the FBG and MMI simultaneously.
The application of the periodic damage tracks in optical fibers formed by using the fiber fuse technique. A refractive index sensor with a sensitivity of 350 nm/RIU is experimentally demonstrated. This technique can be utilized mass production by incorporating small sections of the damaged fiber into each device.
To coat different index materials on the surface of no-core fiber can be investigated for physical and biochemical detection systems. This configuration can provide a kind of simple-structure, low-cost, and high-sensitivity method for applying in bending and refractive index measurement systems. In the future, we expect that the fabrication process can be optimized for improving the sensitivity of cheap and disposable biochemical sensors.
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