The conception of excellent waveguide crossing by making the optical beam to pass over the intersecting silicon wire waveguide is numerically investigated in the paper. It is realized by means of vertical up and down coupling through the silica buffer of tapered Si wires with the upper polymer strip waveguide constructed by SU-8 (with refractive index 1.56). For the case of silicon wire with height 220 nm and width 450 nm the following parameters are used in the optimal structure: the silica buffer - 180 nm, the taper length and tip - 30 mkm and 160 nm, SU-8 polymer height and width - 1.7 mkm and 1.5 mkm, respectively. At the central optical wavelength of 1.55 mkm it provides the total loss about 0.1 dB for the through path: silicon wire – upper polymer – silicon wire. Thus, it provides the possibility for several silicon wire crossings at a moderate loss. For the cross pass direction the optical wave passes through the straight silicon waveguide and senses the present of the crossing waveguides only by the evanescent field. Thus, it provides negligible losses and the possibility for multi-hundreds waveguide crossings. In order to study the task of light propagation through the multiple crossings we use the modified method of lines and the effective index method approximation. Our results were tested by the numerical experiments by 3D finite difference time domain (FDTD) method. The simulations prove that the proposed structure provides almost a lossless silicon wire crossing (<0.002 dB) which can find multiple applications in photonics for the cases when effective multiple crossings are needed.

Date Published: 7 May 2013
PDF: 12 pages
Proc. SPIE 8781, Integrated Optics: Physics and Simulations, 878112 (7 May 2013); doi: 10.1117/12.2017082

Published in SPIE Proceedings Vol. 8781:
Integrated Optics: Physics and Simulations
Pavel Cheben; Jiří Čtyroký; Iñigo Molina-Fernandez, Editor(s)