Impact of Quadrature Imbalance in Optical Coherent QPSK Receiver

• Published in: IEEE photonics technology letters Vol. 21; no. 11; pp. 709 - 711
• Main Authors: Sun Hyok Chang, Sun Hyok Chang, Hwan Seok Chung, Hwan Seok Chung, Kwangjoon Kim, Kwangjoon Kim
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2009; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Coherence; Conjugates; Misalignment; Noise levels; Optical attenuators; Optical communication; Optical control; Optical coupling; Optical fiber communication; optical fiber devices; Optical noise; Optical polarization; Optical receivers; Optical signal processing; Quadrature phase shift keying; Quadratures; Receivers; Signal processing algorithms; Signal to noise ratio
• ISSN: 1041-1135; 1941-0174
• DOI: 10.1109/LPT.2009.2016759

In this letter, we present the impact of quadrature imbalance in an optical coherent quadrature phase-shift-keying (QPSK) receiver. Arbitrary conjugate misalignment was realized in all-fiber optical hybrid and two correction algorithms of quadrature imbalance, the ellipse correction method, and the Gram-Schmidt orthogonalization method, were independently applied. Bit-error-rate curves versus optical signal-to-noise ratio (OSNR) were measured for the 20-Gb/s optical QPSK signal. We show that OSNR penalty is reduced from ~6 to 1 dB at ~20deg conjugate misalignment with the help of correction algorithms.