Study of Fiber Optic Sensors and Highly Flexible Optical Waveguides

• Main Authors: Chih-Yuan Tsou, 鄒智元
• Other Authors: Shih-Hsiang Hsu
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/5rayy6

博士 === 國立臺灣科技大學 === 電子工程系 === 102 === Optical waveguide has been widely used in various applications because it is immunity to electromagnetic interference. The most common optical waveguide for long-distance transmission is optical fiber. Due to optical fibers offer the advantages of low propagation loss, light weight, and low costs, it has been widely applied to fiber-optics sensor as well. But optical fiber is difficult to achieve in-device integration. However, optical polymer waveguides and silicon waveguides can resolve this problem because of their ability to satisfy the high-density integration. In this thesis, we introduce these optical waveguides and their applications. We propose using a two-stage optical low-coherence Mach-Zehnder (MZ) interferometer containing a super-luminescent emitting diode (SLED) for fiber sensing sensitivity enhancement. This fiber-optic structure was used to several types of sensors such as strain, force, and birefringence sensors. An single mode fiber with a 3-m-long sensing arm exhibited strain and force sensitivities as high as 6.8 μm/με and 8.5 μm/mN, respectively. In addition, the beat-length value of a polarization-maintaining fiber (PMF) was measured using an optical MZ interferometer. The experimental results indicate that the birefringence values of 1-m and 3-m PM fibers were 3.85 × 10-4 and 3.92 × 10-4, respectively. Using an optical ruler derived from a 1310-nm wavelength distributed feedback (DFB) laser assisted by a stable stepper motor improved strain resolution. Theoretically, a 3-m-long fiber sensing arm in a MZ interferometer can be used to obtain a 2.7-nε high-strain resolution. The sensitivity values of 1-m and 30-m fiber strain sensing were 2.3 and 66.7 μm/με, respectively. The experimental results indicated that a long optical fiber provides high sensitivity. In addition, we propose using a flexible multimode waveguide for high-speed transmission. We demonstrated that a highly flexible multimode waveguide implemented on an electronic printed circuit board (PCB) can be used in folded-type applications. An optical interconnection using polymer waveguides on an optical and electronic printed circuit board (OEPCB) was designed and fabricated to achieve low optical propagation loss and a high-speed data rate. The optical flexible waveguides were fabricated using the roll-to-roll lamination method. To achieve a simple fabrication process and high position accuracy, the polymer waveguides were forming 45° reflective mirrors using dicing approach and followed by the e-beam deposition for 90° beam turning. To simplify the fabrication process, laser-to-waveguide and waveguide-to-detector coupling were implemented using the total internal reflection (TIR) method. A transmission rate of up to 12.5 Gb/s and an optical propagation loss of 0.1 dB/cm were produced using the board-embedded flexible polymer waveguide. The additional optical loss of 0.3 dB was experimentally shown on the 2-mm bending radius and 180° curvature angle. Because of the advantageous effects of silicon material on transparency in telecommunication wavelengths, complementary metal–oxide–semiconductor (CMOS)-compatible processing, and the high index contrast for a small footprint, the silicon-on-insulator (SOI) platform has attracted increasing attention for processing photonic integrated circuits in a massive electronics fabrication infrastructure. We developed the use of SOI photonic wire microring resonators, which use a multimode interference (MMI) coupler between the ring and waveguides. The MMI coupler exhibited a wide operating wavelength and high fabrication tolerance for maintaining insensitivity MMI-coupled ring resonator. The MMI-coupled ring resonator was designed and fabricated with a circumference of 110 μm and a stable quality factor of 1199 across a wide range of wavelengths. The use of a tunable microwave phase shifter (a tunable phase shift range of 350°) based on a wavelength-tuning SOI microring resonator, which can be tuned using a tunable laser source (TLS). Based on the rapid development of silicon and polymer waveguide transmissions, a concept of unidirectional interconnection between silicon and polymer waveguides is proposed in this study. The concept of combining flexible polymeric waveguide links with CMOS-compatible silicon waveguides is also proposed for next-generation applications.