Lower-order adaptive beam steering system in terrestrial free space point-to-point laser communication using fine tracking sensor

Abstract

The Terrestrial Free Space Point to Point Laser Communication (TFSPPLC) offers an attractive alternatives for transferring high -bandwidth data. The wave propagation takes place in optically inhomogeneous atmospheric channel. Various deleterious effects of the atmospheric channel leads the optical wave to serious signal fading, misalignments of fixed position and even complete loss of signal altogether. Therefore, understanding the atmospheric behavior to the optical wave propagation with the real time experimental data collected over long duration become significant. A TFSPPLC opto-electronic architecture is established for the range of 500m and 28.5m altitude above the surface of the earth. An Adaptive Optics (AO) based steering technique is incorporated in the experimental test-bed to mitigate the lower order temporal and spatial distortions measured at the receiver aperture. The technique of incorporating 2 Dimensional -4 Quadrant fine tracking sensor (2D-4QS) and Fast Steering Tip-Tilt Mirror (FSTTM) in the adaptive receiver in a closed loop control configuration is presented. An Adaptive Fuzzy Logic Controller (AFLC) is developed in the Field Programmable Gate Array (FPGA) and its performance is tested in real time with generating the control signal to drive the piezoelectric actuators of FSTTM. The method of compensating the atmospheric effects using FSTTM is described. The statistical analyses of the experimental data are also presented.

A Review–Unguided Optical Communications: Developments, Technology Evolution, and Challenges

“…The generation of double-sided or multiple-sided moderated signals can also be carried out using a single-arm-or a double-arm-driven MZM. For a dual-drive MZM, the output is defined as [83] E out (t) = 0.5E in (t) e j(π E 1 (t)…”

“…, and I 0 is the first sort of zero-order generalized Bessel function [83]. The beam centroid stability determines the precision and efficiency achieved using an efficient PAT system.…”

Historical perspective of free space optical communications: from the early dates to today's developments

“…In today's FSO long-range network, the RF communication system is also used as a backup network. Even though the FSO system has several advantages including the capability of handling heavy data traffic density, its availability ultimately depends on FSO channel conditions particularly fog in adverse weather resulting in attenuation (typically 50 dB/km at 375 m visibility [72][73][74] as well as rapid power fluctuation (signal fading) in clear channel condition due to the inhomogeneous temperature and wind changes. To ensure the link availability in all weather conditions and times, it is proposed to adapt RF systems with the FSO systems to operate it at a relatively low data rate whenever needed, i.e.…”