Patent ID: 8224139

Claim:
An optical filter, comprising: a substrate; a first coupler provided on the substrate; a first heater provided on the substrate, the first heater configured to adjust a temperature of the first coupler to thereby vary a coupling ratio of a portion of the first coupler; a first interferometer provided on the substrate, the first interferometer having a first arm and a second arm, each of the first and second arms having first and second ends, the first coupler being coupled to the first ends of the first and second arms of the first interferometer; a second coupler provided on the substrate, the second coupler being coupled to the second ends of the first and second arms of the first interferometer; a second heater provided on the substrate, the second heater configured to adjust a temperature of a portion of the second coupler to thereby vary a coupling ratio of the second coupler; a second interferometer provided on the substrate, the second interferometer having a first arm and a second arm, each of the first and second arms of the second interferometer having first and second ends, the second coupler being coupled to the first ends of the first and second arms of the second interferometer; a third coupler provided on the substrate, the third coupler being coupled to the second ends of the first and second arms of the second interferometer; a third heater provided on the substrate and configured to adjust a temperature of a portion of the third coupler to thereby vary a coupling ratio of the third coupler; and a third interferometer provided on the substrate, the third interferometer having a first arm and a second arm, each of the first and second arms of the third interferometer having first and second ends, the first ends of the first and second arms of the third interferometer being coupled to the third coupler, wherein a difference in length between the first and second arms of the first interferometer is different than a difference in length between the first and second arms of the second interferometer, and the difference in length between the first and second arms of the first interferometer is L, the difference in length between the first and second arms of the second interferometer is 4L, and the difference in length between the first and second arms of the third interferometer is 9L.