Waveguide birefringence almost always exists, except for cases where the two orthogonally polarized modes are incidentally degenerate. Birefringence is in general undesirable as it causes an unwanted polarization dependent phase shift and wavelength shift in all interferometric devices such as spectrometers, Mach-Zehnder interferometers, and ring resonators. The birefringence due to the waveguide core geometry in high-index-contrast material systems such as silicon-on-insulator can significantly increase with decreasing core dimensions. One solution is to separate the two orthogonally polarized TE and TM components of the optical signal and process them individually. Waveguide polarization splitters/filters are the key elements in this polarization diversity approach. In this work, novel passive polarization splitters/filters in the SOI platform using a geometrically balanced MachZehnder interferometer configuration are demonstrated experimentally. Polarization splitting/filtering functions are achieved by modifying the birefringence in one arm of the interferometer using a stressed cladding film. Only one additional fabrication step is required for patterning a stressed cladding film on top of the silicon ridge waveguides. A broadband polarization splitting performance was observed with an average extinction ratio of 10 dB in each of the output ports over the entire C-Band from 1530 to 1565nm. The device size is 2.5 mm × 16 μm. This work represents the first reported use of stress engineering for making SOI polarization splitters/filters.

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Keywords Mach-Zehnder interferometers, Passive polarization splitters, Silicon-on-insulator, Stress engineering
Persistent URL dx.doi.org/10.1117/12.701279
Conference Silicon Photonics II
Ye, W.N, Xu, D.-X. (Dan-Xia), Janz, S. (Siegfried), Waldron, P. (Philip), & Tarr, N.G. (2007). Broadband silicon-on-insulator passive polarization splitters. Presented at the Silicon Photonics II. doi:10.1117/12.701279