Compact and low-loss integrated flat-top passband demux

We present a compact design for flattening the passband of a waveguide grating router theoretically without excess loss or chromatic dispersion. We demonstrate a 56-channel 100-GHz-spacing demultiplexer with with a 1-dB bandwidth greater than 70 GHz and less than 4-dB fiber-to-fiber loss (unpackaged, one polarization).