All Fiber Mach–Zehnder Interferometer Using First-order and Second-order Fiber Bragg Gratings

• Main Authors: Chia-Ming Hu, 胡家銘
• Other Authors: Nai-Hsiang Sun
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/yw3p6e

博士 === 義守大學 === 電機工程學系 === 102 === In the dissertation, we measure the transmission and reflection efficiencies of first-order and second-order fiber Bragg gratings. The tunable laser is an optical source in our experimental set up, and the power meter receives the transmitted and reflected powers. Besides, the radiated power of second-order fiber Bragg gratings is detected by a 10 mm diameter photo-detector combined with a power meter. We also observe an image of a near field intensity and 3D view of field pattern scans by using infrared camera and Beam profile, respectively. For the first-order fiber Bragg gratings, we derive the solutions of first-order fiber Bragg gratings with single optical signal and double optical signals by using coupled mode theory. We change the parameters of fiber gratings, which including the core index, core radius, grating length and nσ, to simulate and analyze the reflection spectrum. To realize the effect of the reflection spectrum by various parameters, we varied the parameters of fiber gratings to match the experimental results for transmission and reflection spectrum of first-order FBGs. We have successfully matched the experimental results of first-order FBGs by coupled mode theory. The experimental results of Mach-Zenher interferometer with first-order fiber Bragg gratings are also discussed. According to the parameters, the analytical results and experimental results for the MZI with FBGs are also compared and discussed. As a result, the phase difference of the MZI with FBGs can determine the direction and output power efficiency of transmission and reflection. For the second-order fiber Bragg gratings, the FBGs are made of a single-mode hydrogen-loaded fiber SMF-28 from Corning Inc. and a photosensitivity fiber PS-1500 from Fiber-Core Corp. exposed by a KrF 248 nm excimer laser. There are four batches of fiber gratings, which are various exposure time and fabricated in different time-frames. The transmission, reflection and radiation spectrum of second-order FBGs is measured and compared. We also measure the interference effect of the MZI with second-order fiber Bragg gratings. As a result, the extreme value of the radiation efficiency is varied with the phase difference of two waves. Because of the narrow beam divergence of second-order fiber Bragg gratings, the radiated power can be detected by multi-mode fiber. The fiber gratings for SMF-28 with exposure time of 9 minutes and PS-1500 with exposure time of 7 minutes have significant wavelength select effect. The experimental results for coupling light into the fiber by second-order fiber Bragg gratings are measured. Although the coupling efficiency of light into a fiber using these second order FBGs is very weak in this initial experiment, demonstrating the concept, matching the laser spot size to the spatial extent of the FBGs and the fiber core will provide substantial improvement in coupling efficiency.