Condition for gaussian schell-model beam to maintain the state of polarization on the propagation in free space

In the free space optical communication system with circlepolarization shift keying (CPolSK) modulation, the changes of polarization state of light beam have significant influence on the system performance. Keeping the state of polarization (SOP) unchanged on propagation can reduce the bit error rate. Based on the unified theory of coherence andpolarization, we derive the sufficient condition for Gaussian Schell-model (GSM) beam to keep the SOP unchanged. We found that when the three spectral correlation widths (δxx, δyyand δxy) equal to each other and a&sigmax: = aσy, the GSM beam maintains the SOP on propagation. This conclusion can be helpful for the design of the transmitter in the CPolSK system. © 2009 Optical Society of America.