The demand for wireless bandwidth is increasing rapidly; however, the throughput of short-range radio frequency (RF) solutions, such as WiFi, are quickly reaching limits due to limited bandwidth in the RF spectrum. This problem can be overcome by utilizing unregulated infrared wavelengths in the optical spectrum. On the other hand, free-space optical (FSO) communication presents a challenge for mobility due to the line-of-sight nature of optics. We present a dual-channel optical link for short-range FSO communication, which consists of a 100 Mb / s, large diameter (60 cm at 3 m distance) optical femtocell with a 1.5 Gb / s, small diameter (1 cm at 3 m distance) optical attocell embedded within the femtocell. This hybrid femtocell–attocell optical link addresses the needs of various users by providing a high mobility femtocell link combined with an enhanced bandwidth attocell hotspot. A prototype hybrid system was assembled and evaluated in terms of bandwidth, range, and bit error rate (BER). In addition, the relationship between the incident angle of the transmitted beam relative to the receiver and the BER of the received data was evaluated. At a communication distance of 3 m, the BER is <10 − 4 when the incident angle is smaller than 30 deg for the optical femtocell, while the incident angle must be smaller than 10 deg for the optical attocell to achieve the same level of BER. In addition, we experimentally demonstrated simultaneous, error-free recovery of the data from both the femtocell and the attocell when these two cells are overlapped, which proves the feasibility of the dual-channel optical link for FSO communication.
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