Patent ID: 8422118
Filing Date: 2013-04-16
Classification: G02B,G02F,H04B

Abstract:
1. A Planar Lightwave Circuit (PLC)-type delay demodulation circuit comprising: a planar lightwave circuit that is formed on one PLC chip and demodulates a Differential Quadrature Phase Shift Keying (DQPSK)-modulated optical signal, wherein the planar lightwave circuit includes: an optical splitter that branches the DQPSK-modulated optical signal into two optical signals; and first and second Mach-Zehnder Interferometers (MZIs) that delay the branched optical signals by one bit so as to interfere with each other, wherein the length of a short delay line of the first MZI is different from the length of a short delay line of the second MZI, and the length of an optical path from the optical splitter to an output end of the first MZI through the short delay line of the first MZI is equal to that of an optical path from the optical splitter to an output end of the second MZI through the short delay line of the second MZI, wherein a first half-wave plate is inserted in a central portion of the short delay line of the first MZI and a central portion of the short delay line of the second MZI, and wherein a second half-wave plate is inserted at a position that deviates from the central portion of the short delay line of the first MZI and a position that deviates from the central portion of the short delay line of the second MZI.