Uniform-loss cyclic arrayed waveguide grating router using a mode-field converter based on a slab coupler and auxiliary waveguides

We designed and fabricated a silica-based 16×16 cyclic arrayed waveguide grating router (AWGR) with improved channel loss uniformity using a simple mode-field converter composed of a slab coupling region and auxiliary waveguides placed at the interface between the arrayed waveguides and the output star coupler of the AWGR. The mode-field converter transforms the fundamental Gaussian-shaped mode in the arrayed waveguides to a complex mode field which produces a flat-top far field at the image plane of the output star coupler. It does not change the overall construction of the AWGR and does not increase the device size. The experimental results show that loss non-uniformity for a 16×16 AWGR with 1.6 nm wavelength channel spacing is reduced from 3 to 0.5 dB after adapting the mode-field converter, and the crosstalk is improved by about 2 dB.