A direct and neural controller performance study with beam wandering mitigation control in free space optical link

Performance analysis of free space optical communication in open‐atmospheric turbulence conditions with beam wandering compensation control

“…The telescope, fast steering mirror (FSM), narrow band interference optical filter (NBIOF), variable beam splitter (VBS), optoelectronic position detector (OPD), mono‐pulse arithmetic circuit (MPAC), data acquisition card (DAC), neuro‐controller, piezo‐amplifier, photodiode (PD), transimpedance amplifier (TIA), real‐time scope, optical power meter and data logging computer are the optoelectronic devices at the receiver. FSM consists of three terminal piezoelectric actuators based moving platform on which the beam steering mirror is mounted [21, 36]. The schematic diagram of the experimental setup is shown in Fig.…”

“…The MPAC is constructed using operational amplifiers for computing the addition and subtraction of signal as given in (7). The reference signal V Ref is measured by the algebraic sum of signals from all the quadrants of OPD as in (8) [21] The analog output signals V Ex , V Ey and V Ref vary from −10 to +10 V and 0 to +10 V. Therefore, the beam wandering is measured purely based on the beam centroid information since the V Ex and V Ey are normalised with respect to the V Ref [13, 21, 36]. The MPAC output signals { V Ex , V Ey , V Ref } are applied to a 12 bit parallel data‐fetching A/D (AD1674 converter core) through an eight‐channel analog multiplexer (ADG509A) circuit.…”

“…The control commands, i.e. values of the neuro‐controller used to drive the FSM are the direct non‐linear mapping according to the displacement error values [21, 36]. These command signals drive the FSM in the counter (opposite) positions, i.e.…”

“…Therefore, the data rate must be greater than the sampling rate as well as beam wandering frequency. In this paper, the data rate is 155 Mbps, sampling rate is 4 kHz, maximum beam wandering frequency is 2 kHz and link range is 0.5 km, the neuro‐controller is implemented inside the FPGA, and hence the beam wandering measurement and subsequent mitigation is accomplished without the beacon beam [1, 4, 11, 21, 36]. The beacon beam is required in case the data rate is relatively low, low‐speed DAC/data processor is used and/or the control algorithm is implemented in the software (PC) environment.…”

“…Though there are many parameters that affect beam steering process in beam stabilisation, azimuth and elevation displacement errors contribute the greatest effect on the success of its operation [21, 36]. Advantageously, these parameters can easily be measured during the closed‐loop feedback control for beam steering operation with no additional cost and time [36]. These parameters are considered as the principal components in this paper since they directly affect beam stability and link quality.…”