In this paper, we describe the impact of quadrature imbalance (QI) in the presence of frequency offset in an optical coherent offset quadrature phase shift keying (OQPSK) receiver. Arbitrary conjugate misalignment was realized in a 2？ 90？optical hybrid, and the ellipse correction (EC) method of quadrature imbalance was applied in our simulation. In the case of transmission, the EC method can significantly improve the system performance.
