Modulation of Depolarization for Optical Data Links

Controlled depolarization of a polychromatic carrier can be applied simultaneously with polarization-shift keying (PolSK) to achieve a three-dimensional symbol space using only a direct-detection Stokes-vector receiver. I present a scheme to implement such modulation of a two-tone carrier, analyzing the noise statistics of the received degree-of-polarization (DOP) variable to compute the bit-error rate (BER). I then quantify the impact to simultaneous PolSK signaling and determine the optimal DOP that minimizes the overall BER. Finally, I compare the new combined format to conventional multilevel intensity modulation.