Parameter Extraction of Silicon Photonic Devices Using Optical Coherence Tomography

In this work, a novel characterization technique taking advantage of the maturity and high sensitivity of Fourier domain optical coherence tomography ( FD-OCT). The method has been experimentally verified on a silicon photonic chip fabricated using imec-ePIXfab passive technology with a waveguide height and width of 220 nm and 500 nm, respectively. The silicon is surrounded by air from top and by silicon-oxide from bottom and sides. The design assumes quasi Transverse Magnetic (TM) mode with an effective refractive index n(eff) of 1.61 and group effective refractive index n(g) of about 3.471 at 1550 nm. The method is applied on a simple 1.46 mm length waveguide ended by grating couplers from both sides. Using that length and by inspecting the spatial response obtained after inverse Fast Fourier Transformation (FFT), the extracted mean group effective refractive index n(g) of the straight waveguide is 3.597. This value is attributed to the fabrication tolerance in the width of the structure leading to a width error of about 7.7 %.