Investigation on Hollow Beam Propagation through Turbulence Conditions in Free Space Optical Communication

Abstract

In Free Space Optical Communication (FSO), the optical signal from the laser source severely affects while travelling through free space atmospheric channel due to scattering, absorption and other effects of atmospheric turbulence conditions. This degrades the performance of FSO communication. In this article, we have generated the hollow beam from the laser output by the inverse axicon lens called inverted axicon beam. An artificial controlled turbulence chamber is created and the test signal has been transmitted through the turbulence conditions by employing various modulation schemes such as PAM, PWM, PPM, ASK, BPSK and QPSK separately. In all cases, we measured parameters phase jitter and Time jitter experimentally and the results are compared. Two types of wavelength laser sources such as red and green lasers are used for the analysis. In which, ASK provides a better withstand ability to jitter than other modulation techniques with atmospheric turbulence.