Abstract
Diffraction gratings have been widely used in wavelength-controlled nonmechanical laser beam steering for high data-rate indoor optical wireless communications. Existing free-space diffraction gratings suffer from inherent difficulties of limited diffraction efficiency, bulky configuration, high cost, and significant coupling loss with optical fiber links. In this paper, a new optical approach for highly efficient, compact, and fiber compatible laser beam steering using an in-fiber diffraction grating is proposed and experimentally demonstrated for the first time to our best knowledge. In-fiber diffraction is made possible based on a 45° tilted fiber grating (TFG), where wavelength-dependent lateral scattering is obtained due to the strongly tilted grating structure. Improved diffraction efficiency of 93.5% has been achieved. In addition, the 45° TFG works perfectly for both light emission and reception, enabling full-duplex optical wireless transmission. Utility of the 45° TFG in all-fiber laser beam steering for multiuser full duplex optical wireless communications has been verified in experiments. About 1.4 m free-space full-duplex wireless transmission has been demonstrated with data rate up to 12 Gb/s per beam using 2.4 GHz bandwidth OFDM signals.
Highlights
W ITH significantly increased number of wireless personal devices and smart sensors connected in home area networks, there is ever increasing demand for higher data rate in indoor wireless communications in order to offer users better experience for fast internet access with unobstructed services
We demonstrate that the 45° tilted fiber grating (TFG) offers greatly improved diffraction efficiency (>93.5%) compared to normal ruled or holographic diffraction gratings that fall short in diffraction efficiency due to the inherent zeroth-order reflection and non-Littrow configuration
The proposed TFG-based beam steering solution offers inherent compatibility with existing fiber links, which is attractive in achieving seamless interface with fiber-to-the-home (FTTH) access networks
Summary
W ITH significantly increased number of wireless personal devices and smart sensors connected in home area networks, there is ever increasing demand for higher data rate in indoor wireless communications in order to offer users better experience for fast internet access with unobstructed services. Conventional radio wireless communication suffers from limited transmission speed and ever-worse spectrum congestion [1]. Despite that the approaching 5G wireless techniques offer much higher data rate up to gigabits per second, the available radio frequency bandwidth has nearly hit its limit and cannot fulfil the increasing demand of even higher data rate for indoor wireless transmission applications. Optical wireless communication (OWC) has recently attracted increasing interests as it provides a promising solution for speed and bandwidth challenges in conventional radio wireless communications [2]–[4]. Additional advantages of OWC include unlicensed spectrum, immunity to electromagnetic interference, spatial diversity and physically ensured security as light waves do not penetrate walls
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