Electric field distribution in a grating of a folded arrayed-waveguide multiplexer

We present direct measurements of the electric field distribution at the reflecting surface folding a grating of an arrayed-waveguide multiplexer. The field distribution obtained using different input channels of a device can be described by a single-Gaussian function. Grating and coupler-slab waveguide mode-field radii were determined directly. The field profile was used to model the transmission spectrum of the device. Excellent agreement was found between the measured and calculated spectra.