Beaconless PAT and adaptive beam control using variable focus lens for free-space optical communication systems

Abstract

Free-space optical communications (FSOCs) have recently emerged as a promising solution for various communication scenarios. However, the pointing, acquisition, and tracking (PAT) is a technically challenging issue, especially in airborne FSOC systems. In this paper, we present an adaptive beam control technique combined with beaconless PAT using a variable focus lens. By using the lens whose focal length can be tuned electrically, we facilitate the coarse PAT by enlarging the beam size and also mitigate the adverse effects of pointing errors by adjusting the beam divergence angle adaptively to the link conditions. The major benefit of the proposed scheme is that the beam control can be implemented in a simple and compact manner, without relying on mechanical movements. We carry out a proof-of-concept experimental demonstration of the proposed scheme for a 10-Gb/s free-space optical link over 104 m. The demonstration shows that the probability of PAT success can be improved considerably by using the proposed scheme. It also shows that the proposed scheme could result in a system loss reduction of 6.4 dB and improve the tolerance to pointing errors up to 500 μrad for a target bit-error ratio of 10−3. The response time of the lens is measured to be <211 ms. We confirm experimentally that the receiver size and the amount of pointing error determine the optimum beam size at the receiver.

A Review of Variable-Beam Divergence Angle FSO Communication Systems

“…Therefore, liquid lenses with larger apertures are best used in vertical and downward positions and are not suitable for rotation with a turntable. A. J. Williams et al [48] and V. V. Mai et al [49] used liquid lenses to change beam divergence angles. M. ZOHRABI et al [50] used three mechanical hydraulic liquid lenses in combination with wide-angle fisheye lenses to achieve 2D beam scanning of ±75°, as shown in Figure 13.…”

Adaptive Beam Divergence for Expanding Range of Link Distance in FSO With Moving Nodes Toward 6G

“…In this paper, we address an adaptive beam divergence control on the basis of the FSO link distance to expand the link range. The beam divergence control has been studied for various purposes [8][9][10][11][12]. In [11], the beam divergence angle is controlled for the coarse and fine tracking eliminating the beacon.…”

“…The beam divergence control has been studied for various purposes [8][9][10][11][12]. In [11], the beam divergence angle is controlled for the coarse and fine tracking eliminating the beacon. In [8,10,12], the beam divergence angle is adjusted optimally for the system performance according to the amount of the pointing error caused by vibrations and beam wandering.…”

High-sensitivity multi-channel DPSK system with real-time phase lock controller for free-space optical communication

“…Because of its high-bandwidth, high-speed, and high-security features [1][2][3][4][5], freespace optical communication (FSOC) offers a feasible and valid solution for bottlenecks in microwave communication and for realizing massive real-time transmission of data. Concurrently, and because of the inherent benefits of its small size, lightweight, and low power consumption-capable of keeping up with the communication demands of booming space activities-the FSOC terminal can be considered an ideal satellite payload [6,7]. Thus far, the data rate of satellite laser communication links has been found to approach Gbps magnitude [8,9].…”