Coupling Efficiency Study on Silicon Wire Interface

• Main Authors: Yi-Liang Lin, 林奕良
• Other Authors: Shih-Hsiang Hsu
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/25976571568241648747

碩士 === 國立臺灣科技大學 === 光電工程研究所 === 98 === A silicon-on-insulator platform is extensively utilized for both of low power consumption high-speed microelectronic and highly integrated photonic devices due to its fully compatible processing with the complementary metal-oxide-semiconductor (CMOS) standard process. Moreover, the large refractive-index difference between silicon and silicon dioxide layers can significantly reduce the device size to form the silicon wire waveguides for submicron silicon photonics applications. The current challenge for submicron silicon photonics mainly comes from the mode mismatch caused poor coupling efficiency between the silicon wire and traditional optical fiber. In this thesis, nanotaper and grating coupler were comprehensively studied and simulated to demonstrate the possibility for optical interconnection. Nanotaper simulation illustrated that both effective index and mode size of silicon wires are changing with the waveguide geometry using beam propagation method (BPM) and finite-difference time-domain (FDTD) methods. The polarization dependent loss of the silicon wire would be minimized and achieved 50.8% (-2.94dB) coupling efficiency at the width of 0.4 μm and height of 0.26 μm when the taper length and tip width were taken as 40 μm and 0.11 μm, respectively. The phase match conditions were theoretically and experimentally applied to demonstrate the grating coupling efficiency with the vertical and oblique incident angles. The oblique incident grating was utilized to avoid the second order diffraction and increase directionality in the silicon wire. The TE polarization from 2-D FDTD method was taken to simulate the coupling efficiency for vertical and oblique grating coupler as 46% (-3.37dB) and 29.25% (-5.34dB), respectively. The experimental data were showing a high coupling loss of 38.8 dB, which mainly came from the contaminated rough surface scattering and over-etched grating teeth.