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.

中文翻译：

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使用可变焦距镜头的无信标PAT和自适应光束控制，用于自由空间光通信系统

自由空间光通信（FSOC）最近已经成为各种通信场景的有前途的解决方案。但是，指向，获取和跟踪（PAT）是一个技术难题，特别是在机载FSOC系统中。在本文中，我们提出了一种使用可变焦距镜头结合无信标PAT的自适应光束控制技术。通过使用可电动调节焦距的镜头，我们可以通过增大光束大小来简化粗略的PAT，并通过根据链接条件自适应地调节光束发散角来减轻指向误差的不利影响。所提出的方案的主要优点在于，可以以简单而紧凑的方式实现光束控制，而无需依靠机械运动。我们对104 m上的10 Gb / s自由空间光链路进行了拟议方案的概念验证实验演示。演示表明，通过使用所提出的方案，PAT成功的可能性可以大大提高。它还表明，所提出的方案可以使系统损耗降低6.4 dB，并提高对指向错误的容忍度，最大可达500μ弧度为10的目标误码率^-3。镜头的响应时间测得小于211 ms。我们通过实验确认，接收器的大小和指向误差的大小决定了接收器的最佳波束大小。