Digital-filter-aided crosstalk-mitigation for a high spatial resolution AWGR-based 2D IR beam-steered indoor optical wireless communication system.

The growing demand for wireless connectivity is attracting interest in optical wireless communication (OWC) technique. In this paper, a filter-aided crosstalk mitigation scheme, employing digital Nyquist filters, is proposed to eliminate the trade-off between the spatial resolution and the channel capacity for the AWGR-based 2D infrared beam-steered indoor OWC system. By shaping the transmitted signal for narrow spectral occupancy, the inter-channel crosstalk resulting from the imperfect AWGR filtering can be avoided, which enables a denser AWGR grid. In addition, the spectral-efficient signal reduces the bandwidth requirement of the AWGR, which allows a low-complexity AWGR design. Thirdly, the proposed method is not sensitive to the wavelength misalignment between AWGRs and lasers, which relaxes the design of high wavelength stability lasers. Moreover, the proposed method is cost-efficient as we can make use of the mature DSP technique without additional optical components. The 20-Gbit/s data rate OWC capacity using PAM4 format has been experimentally demonstrated over a 6-GHz bandwidth-limited AWGR-based 1.1-m free-space link. The experimental results show the feasibility and effectiveness of the proposed method. By combining our proposed method with the polarization orthogonality technique, a promising capacity per beam of 40 Gbit/s is potentially attainable.

Free-space transmission with passive 2D beam steering for multi-gigabit-per-second per-beam indoor optical wireless networks.

In order to circumvent radio spectrum congestion, we propose an innovative system which can provide multiple infrared optical wireless beams simultaneously where each beam supports multi-gigabit-per-second communication. Scalable two-dimensional beam steering by means of wavelength tuning is proposed. A passive beam-steering module constructed with cascaded reflection gratings is designed for simultaneous multi-user coverage. We experimentally characterized the beam-steered system and thoroughly evaluated the performance of steered channels using the spectrally efficient and robust discrete multitone modulation in a bandwidth-limited system deploying 10 GHz telecom transceivers. This study reports the achievement of at least 37 Gbps free-space transmission per beam over a distance of up to 2 m over 5.61° × 12.66° scanning angles.