| Summary: | 碩士 === 龍華科技大學 === 電機工程研究所 === 98 === This paper is about the design and analysis of optical delay lines in two-dimensional photonic crystals. Three types of optical delay lines are discussed, including coupled cavity waveguide (CCW), continuous dielectric column (CDC), and periodic continuous dielectric column (pCDC). The plane wave expansion method is employed to calculate photonic bandgap and dispersion relation. And the finite-difference time-domain (FDTD) method is used to simulate wave propagation such that time delay and frequency response of the proposed optical delay lines can be obtained. Although the traditional CCW delay line exhibits a larger time delay, its high-transmission bandwidth is smaller than 0.3% of the central frequency. On the other hand, although the CDC and pCDC delay lines exhibit smaller time delay, their bandwidths are as large as 9.12% and 9.38%, respectively, of the central frequency. Moreover, we propose 2pCDC delay lines employing high-transmission chamfered bends to dramatically increase time delay per unit chip area. From their transmission spectra, we confirmed that these delay line structures exhibit broad bandwidths.
We employ the principle of Fabry-Perot etalon to depict the frequency response of these delay lines. The spectra predicted by this model match well with those obtained by the FDTD simulation. We also calculate group velocities from the dispersion curves of these delay line waveguides. Time delays predicted by the group velocities also agree well with those by the FDTD simulation.
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