This paper presents a configurable optical filter based on a multi-stage cascaded delay interferometer

which can be refigured as two types of filters to achieve the tuning of the filter bandwidth:single delay interferometer and multiple delay interferometer The former tunes the filtering period and bandwidth by increasing the retardation and the other tunes the bandwidth of the constant filtering period by changing the number of the cascaded stages and the splitting ratio of the MZI switches.It builds a theoretical model of this delay interference filter by using the transfer matrix method and performs its simulation.The test results of the secondary and third delay interferometers show that the bandstop filter bandwidth can vary by over 1/3filter period.