A. M. Porter, J. M. Kahn, and U. Padan, "Heterodyne detection of 310-Mbit/s quadriphase-shift keying using a fourth-power optical phase-locked loop,"
in Conference on Optical Fiber Communication/International Conference on Integrated Optics and Optical Fiber Communication,
Vol. 4 of 1993 OSA Technical Digest Series
(Optical Society of America, 1993), paper ThH2.