A coherent array detection system, which uses multiple independent apertures/receivers whose IFs are electro- optically co-phased in real time and then added together, can mitigate the laser signal fluctuations and fading due to atmospheric turbulence for laser communications and radar. Thus the system performance greatly depends on the electo- optic phase-locked loops (EOPLL) used for the real time co- phase of signals from the independent aperture/receivers. But if the fast phase fluctuations due to atmospheric turbulence or a high Doppler frequency shift due to the target (satellite) movement are induced to the laser signal which is beyond the response speed of the EOPLL, the system can not mitigate the signal fluctuations and fading anymore. This paper presents a new scheme which can make the coherent array detection system get rid of the EOPLL. This scheme uses a reference laser beam as well as laser signal with different polarization as the transmitted beam. By separating the received laser reference beam and signal due to their polarization and through two stage mixing, the IF signals from the multiple independent aperture/receivers will be co-phased automatically.

Date Published: 26 April 1999
PDF: 6 pages
Proc. SPIE 3615, Free-Space Laser Communication Technologies XI, (26 April 1999); doi: 10.1117/12.346195

Published in SPIE Proceedings Vol. 3615:
Free-Space Laser Communication Technologies XI
G. Stephen Mecherle, Editor(s)