Experimental demonstration of a “pin-like” low-divergence beam in a 1-Gbit/s OOK FSO link using a limited-size receiver aperture at various propagation distances
Nanzhe Hu, Huibin Zhou, Runzhou Zhang, Haoqian Song, Kai Pang, Kaiheng Zou, Hao Song, Xinzhou Su, Cong Liu, Brittany Lynn, Moshe Tur, Alan E. Willner
Abstract
In free-space optical (FSO) communications, there are scenarios (e.g., from a ground station to a drone/airplane) in which: (i) the transmitter (Tx) can have a relatively large aperture whereas the receiver (Rx) aperture should preferably be much smaller, and (ii) the distance between the Tx and Rx can vary such that beam divergence will cause a variation in the recovered signal power. In such cases, transmission using a fundamental Gaussian beam can be significantly degraded due to beam truncation caused by a limited-size Rx aperture. Here, we experimentally demonstrate a 1-Gbit/s on-off keying (OOK) FSO transmission link using a structured “pin-like” beam with a limited-size Rx aperture at various distances. The pin-like beam is generated by passing a Gaussian beam through an “Airy-type” phase pattern in the radial direction. When propagating, this structured beam first narrows and then tends to maintain its narrow beam size over a fairly wide range of distances. In comparison to its Gaussian counterpart, our experimental results show that the pin-like beam has ∼13 to 8 dB less power loss at distances ranging from 0.45 m to 0.8 m with an Rx aperture diameter of 1 mm. Moreover, we simulate the propagation of the pin-like beam and show its relatively lower power loss for a wide distance variation in a longer link (e.g., ∼1 km) with a limited-size Rx aperture. Furthermore, our results show that the pin-like beam can have a wider range of low-power-loss distances than a Gaussian beam that is focused to a given distance.