Tomoaki Ohtsuki, Iwao Sasase and Shinsaku Mori, "Coherent subcarrier multiplexing system using an orthogonal polarization state as a pilot signal in the presence of second and third intermodulation distortions" 1993 International Symposium on Nonlinear Theory and Its Applications, pp.883-886, Hawaii, U.S.A., Dec. 1993.