Polarization compensation in silicon-on-insulator arrayed waveguide grating devices

As the AWG size is reduced our experimental and theoretical work demonstrates that it becomes increasingly difficult to suppress higher order modes and birefringence using ridge dimension alone. In part, it simply becomes difficult to meet the required fabrication tolerances when the ridge dimension approaches the order of a micron. We show that a novel polarization compensator scheme similar to that previously reported for a grating based demultiplexer in InP and consisting of simple shallow etched regions in the combiner sections of an SOI AWG, can eliminate the polarization sensitivity of the device by reducing the initial polarization dispersion of 2.22 nm to 0.04 nm. By combining the polarization compensator with mode filtering using appropriate array waveguide curvature, the shape of the array waveguides is no longer constrained. This allows the size of an AWG device to be scaled down to very small dimensions (e.g. less than a millimeter) and also permits the use of simple fabrication techniques such as wet etching. Our results were obtained on AWG devices based on 1.5 micrometers thick Si-on-insulator waveguides with a typical waveguide array area of a few square millimeters.