Four-channel flat-top and low-loss filter for wide passband WDM access network

A broadband and flat-top wavelength response, which is required in wide passband WDM systems, has been realised for the first time by using planar-lightwave-circuit (PLC) technology and lattice-form circuit composition theory. The filter divides the signal every 20 nm with an insertion loss of 1.5 dB and a 1 dB passband width of 16 nm.