Numerical analysis of a modified rooftop mirror using mode interference.

In this paper, an improved rooftop mirror is proposed and its characteristics are evaluated by numerical analysis. First, it is shown by FDTD analysis that it is not easy to obtain a high reflection characteristic with fundamental mode incidence in the conventional structure. Next, the reflection characteristics are analyzed for an improved structure in which the incident single-mode waveguide is connected to a multimode interference waveguide inside the rooftop. In such a process, comparison with the results obtained by FDTD analysis demonstrates that the simple guided mode propagation method neglecting the radiation mode is effective for design of a mode interference section. A reflectivity of 96% is attained by introduction of the mode interference section for both fundamental TE and TM mode incidence. Further, the wavelength characteristics of the reflection coefficient are studied. The effects of misalignment of the waveguide axis and shift of the apex angle of the rooftop on the reflection characteristics are discussed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(1): 1–8, 2004; Published online in Wiley InterScience (<URL>www.interscience.wiley.com</URL>). DOI 10.1002/ecjb.10172 [ABSTRACT FROM AUTHOR]