Optical design of an optical system for free space optical communication

An optical system for free space optical communication is designed, which are composed of three parts: Optical sender are designed as Schmidt-Cassegrain antenna to collimate the laser beam. lambda/2 plate and polarization beam splitter are used to decrease the interference of astigmatism and reflection. The dense-lines Fresnel lens as an optical receiver, and further an automatic tracking system is employed to eliminate the pointing error between communication terminals. Experiment shows that the laser divergence of 2 mrad is obtained for the communication system at the wavelength of 850nm, with pointing error less than 5 mu rad, and laser power of 10dB. The detector can receive -17.5dB even in middle fog condition 2 kin ranged. The system can be used for free space optical communication in 2km distance except under especial atrocious weather.