An optical multi/demultiplexing circuit includes at least one phase generating optical coupler and an optical delay line coupled to the phase generating optical coupler. The phase generating optical coupler consists of at least one input and at least two outputs. At least one of the phase generating optical coupler has a wavelength dependent or frequency dependent output phase difference in the passband of the circuit so that it can change the transmittance characteristics of the optical multi/demultiplexing circuit.