Low-loss flat-top passband arrayed waveguide gratings realised by first-order mode assistance method

A novel method of flattening the passband of an arrayed waveguide grating with a small excess loss is described, which employs a new concept that uses the assistance of the weak first-order mode. A 16-channel 100 GHz-spacing demultiplexer with a fibre-to-fibre loss of less than 3.6 dB and a flattened excess loss of 1.85 dB is demonstrated. The 1 dB down passband is widened 2.2 times.