Abstract: The theoretical analysis was proposed for the optical filter realized by combination of microring resonator and cross information channel. The transfer functions of drop port and output port were derived with the signal flow graph method，the influences of coupling coefficient on output spectrum were analysed with simulation. The simulation results showed that the drop port could obtain rectangular waves approximating flat top and steep edge through optimizing the coupling coefficient. The numerical calculation showed that the filter had good filtering performance，the quality factor could reach 10³ order，the fineness was up to 4. 75 and the extinction ratio was 68 dB. This device can be used as wavelength- selective filter in dense wavelength division multiplexing （DWDM） system ，also this structure can be cascaded to design wavelength division multiplexers. With thermal-optical property of SOI，and heating micro-ring resonator，we found that the output spectrum of drop port showed rightward shift and achieved the filter′s tunability.

Key words: integrated optics, optical filter, micro-ring resonator, signal flow graph method