LED holographic beam-steering for visible-light communications Tuan-$QK 7UDQ DQG 'RPLQLF & 2ｶ%ULHQ Department of Engineering Science University of Oxford Oxford, United Kingdom OX1 3PJ {tuan-anh.tran; dominic.obrien}@eng.ox.ac.uk Abst ra ctｲHolographi c be am-st ee ring i s an attrac tive way to st ee r opti c al be ams and pot e ntially to e nginee r the c hanne l matrix in opti c al multi-input multi-output syst e ms. In vi sibl e- light communi c ations, a partially cohe r e nt LED i s typi c ally use d as the opti c al sour ce. Thi s pape r pr ese nt s a nove l algorithm to design be am-st ee ring holograms for suc h partially cohe r e nt sour ces. D e tail s of the algorithm and e xpe rime ntal r esults ar e shown. K eywordsｲvi sibl e light ; incoher e nt ; be am-st ee ring; hologram; algori t hm; autocorr e la t ion I. INTRODUCTION There has been substantial research in beam-steering for laser-based systems [1-5]. These techniques can be used to create optical switches [1] or for one-to-many communications [5]. Liquid-crystal spatial light modulators (SLMs) are used as the steering device due to their versatility and simplicity in displaying beam-steering patterns [6] and there have been schemes to employ SLMs efficiently and independently of the polarization of the illumination, e.g. [7]. Laser-based beam- steering relies on coherent diffraction with a digital hologram to send the light to the desired positions [8]. For visible-light communications, LEDs are typically used as optical sources for both illumination and communication purposes. Beam-steering would allow visible light from LEDs to be steered to alter optical wireless links (see Fig. 1) and to engineer the LED-based MIMO channel matrix [9]. However, only recently have holograms started to be used with incoherent illumination [10] and thus incoherent beam-steering is much less mature than with coherent light. Although coherent-hologram design techniques can be used to a certain extent in partially coherent systems, there has been little work so far in hologram design optimized for partially coherent illumination [11]. Section II of this paper proposes an algorithm that offers hologram optimization for partially coherent illumination. Section III describes the experimental results to verify the performance of this algorithm. Discussions and conclusions are presented in Section IV. II. PROPOSED ALGORITHM Most hologram design algorithms require light transmitted through the hologram to be propagated in full to the imaging plane [12-14]. With partially coherent illumination, this can be a computationally costly task. The basic theories of incoherent propagation [15] allow much more efficient ways to generate beam-steering holograms, by removing further propagation after the hologram plane. This is computationally efficient, whilst the holograms themselves are optimized for working with incoherent light. A. I mage int ensi ty in a 2-l ens syst em Fig. 2 shows a typical configuration for the beam-steering Fig. 1. Beam-steering in optical wireless communications Fig. 2. Schematic of the beam-steering system Globecom 2013 Workshop - Optical Wireless Communications 978-1-4799-2851-4/13/$31.00 ©2013IEEE 1099