Mode conversion and birefringence adjustment by focused-ion-beam etching for slanted rib waveguide walls

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Abstract
We describe how focused-ion-beam (FIB) etching of slanted rib waveguide walls can be used to modify the differential group delay in a waveguide and introduce TE to TM mode conversion in a silicon-on-insulator rib waveguide. We achieved mode conversion by modifying the geometric cross section of a single-mode rib by FIB trimming. Waveguides with different lengths of 45° slant angle rib waveguide walls were fabricated and characterized. We measured the differential group delays and the mode conversion achieved for waveguides with different lengths of a FIB-trimmed slanted rib wall.