DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Free-space indoor optical communication deploying pencil beams can offer ultra-high wireless capacity individually per user device. By means of 2D diffractive modules, such as a pair of crossed gratings, 2D steering of multiple beams by just tuning the wavelength of each beam can be achieved. The design aspects of an indoor system fed via an intelligent optical fiber backbone network are discussed. 2D angular beam steering over a 6°×12° area was achieved by wavelength tuning from 1505 to 1630nm. System experiments using PAM-4 modulation have shown a capacity of 32Gbit/s per infrared beam. With radioover-fiber techniques and optical carrier recovery from the downstream signal, 10Gbit/s upstream transmission of a 60GHz radio signal has been shown using adaptive DMT modulation.Index Terms-indoor wireless communication, diffractive optical beam steering, radio over fiber, optical signal routing, optical wireless communication

The optical spectrum offers great opportunities to resolve the congestion in radio-based communication, aggravated by the booming demand for wireless connectivity. High-speed infrared optical components in the 1500 nm window have reached high levels of sophistication and are extensively used already in fibre-optic networks. Moreover, infrared light beyond 1400 nm is eye-safe and is not noticeable by the users. Deploying steerable narrow infrared beams, wireless links with huge capacity can be established to users individually, at minimum power consumption levels and at very high levels of privacy. Fully passive diffractive optical modules can handle many beams individually and accurately steer narrow beams two-dimensionally by just remotely tuning the wavelength of each beam. The system design aspects are discussed, encompassing the beam-steering transmitter, wide field-of-view optical receiver and the localization of the user's wireless devices. Prototype system demonstrators are reported, capable of supporting up to 128 beams carrying up to 112 Gbit s −1 per beam. Hybrid bidirectional systems which use a high-speed downstream optical link and an upstream radio link at a lower speed can provide powerful asymmetric wireless connections. All-optical bidirectional beam-steered wireless communication will be able to offer the ultimate in wireless capacity to the user while minimizing power consumption. This article is part of the theme issue ‘Optical wireless communication’.

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DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: