Zhang Xuebing, Liu Yu, Cao Zizheng, Li Fan, Li Zhaohui, Ismaeel R, Brambilla G, Chen Y, Koonen A M J
Opt Lett. 2018 Feb 15;43(4):723-726. doi: 10.1364/OL.43.000723.
Indoor optical wireless communication with optical beamsteering capability is currently attracting a lot of attention. One major two-dimensional (2D) optical beamsteering scheme is realized by 2D grating or its active counterpart, which is usually based on a spatial light modulator (SLM). However, there is a fundamental trade-off between the field of view (FoV) and power efficiency due to the inherent feature of gratings. In this Letter, we propose a new class of 2D beamsteering, named cyclically arranged optical beamsteering (CAO-BS), which can break that trade-off. Traditional 2D gratings extend the optical beam in the Cartesian coordinates (1D grating in horizontal + 1D grating in vertical), while CAO-BS extends the optical beam in the polar coordinates (1D grating + angular rotation). Since only 1D grating is engaged, the power efficiency increases with the number of grating lobes reduced. In the polar coordinates, the angle rotation tuning in a SLM is quasi-continuous in a full 2π range. The CAO-BS is demonstrated at the receiving end in an indoor experimental system. The FoV is 18° by 360° in polar coordinates without any additional mechanical parts. Based on the CAO-BS, 40 Gbit/s on-off keying data is also successfully transmitted over 1 km single-mode fiber and 0.5 m free space.
具有光束转向能力的室内光无线通信目前正吸引着大量关注。一种主要的二维（2D）光束转向方案是通过二维光栅或其有源对应物实现的，这通常基于空间光调制器（SLM）。然而，由于光栅的固有特性，在视场（FoV）和功率效率之间存在基本的权衡。在本信函中，我们提出了一种新型的二维光束转向，称为循环排列光束转向（CAO-BS），它可以打破这种权衡。传统的二维光栅在笛卡尔坐标系中扩展光束（水平方向的一维光栅 + 垂直方向的一维光栅），而CAO-BS在极坐标系中扩展光束（一维光栅 + 角度旋转）。由于仅使用一维光栅，随着光栅瓣数的减少，功率效率会提高。在极坐标系中，SLM中的角度旋转调谐在整个2π范围内是准连续的。在室内实验系统的接收端对CAO-BS进行了演示。在极坐标系中视场为18°×360°，无需任何额外的机械部件。基于CAO-BS，40 Gbit/s的开关键控数据也成功地通过1 km单模光纤和0.5 m自由空间进行了传输。
