184 research outputs found

    IEEE Access special section editorial: optical wireless technologies for 5G communications and beyond

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    Wide bandwidth and dense spatial reuse are of extreme importance for future wireless communication networks, including 5G and beyond. In particular, these properties are important to enable future wireless networks to cope with the explosive increase in the demand for high data-rate communications. Optical wireless communications (OWC) is a promising technology for achieving this goal due to the abundant reusable license-free optical spectrum. This potential of OWC attracted significant global attention both from communications and optoelectronics viewpoints, and continues to do so

    Spatial Light Modulation as a Flexible Platform for Optical Systems

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    Spatial light modulation is a technology with a demonstrated wide range of applications, especially in optical systems. Among the various spatial light modulator (SLM) technologies, e.g., liquid crystal (LC), magneto-optic, deformable mirror, multiple quantum well, and acoustic-optic Bragg cells, the ones based on liquid crystal on silicon (LCoS) have been gaining importance and relevance in a plethora of optical contexts, namely, in telecom, metrology, optical storage, and microdisplays. Their implementation in telecom has enabled the development of high-capacity optical components in system functionalities as multiplexing/demultiplexing, switching and optical signal processing. This technology combines the unique light-modulating properties of LC with the high-performance silicon complementary metal oxide semiconductor properties. Different types of modulation, i.e., phase, amplitude or combination of the two, can be achieved. In this book chapter, we address the most relevant applications of phase-only LCoS SLM for optical telecom purposes and the employment of SLM technology in photonic integrated circuits (PICs) (e.g., field-programmable silicon photonic (SiP) circuits and integrated SLM application to create versatile reconfigurable elements). Furthermore, a new SLM-based flexible coupling platform with applications in spatial division multiplexing (SDM) systems (e.g., to efficiently excite different cores in MCF) and characterization/testing of photonic integrated processors will be described

    VLC Systems with CGHs

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    The achievable data rate in indoor wireless systems that employ visible light communication (VLC) can be limited by multipath propagation. Here, we use computer generated holograms (CGHs) in VLC system design to improve the achievable system data rate. The CGHs are utilized to produce a fixed broad beam from the light source, selecting the light source that offers the best performance. The CGHs direct this beam to a specific zone on the room's communication floor where the receiver is located. This reduces the effect of diffuse reflections. Consequently, decreasing the intersymbol interference (ISI) and enabling the VLC indoor channel to support higher data rates. We consider two settings to examine our propose VLC system and consider lighting constraints. We evaluate the performance in idealistic and realistic room setting in a diffuse environment with up to second order reflections and also under mobility. The results show that using the CGHs enhances the 3 dB bandwidth of the VLC channel and improves the received optical power

    Holograms in Optical Wireless Communications

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    Adaptive beam steering in optical wireless communication (OWC) system has been shown to offer performance enhancements over traditional OWC systems. However, an increase in the computational cost is incurred. In this chapter, we introduce a fast hologram selection technique to speed up the adaptation process. We propose a fast delay, angle and power adaptive holograms (FDAPA-Holograms) approach based on a divide and conquer methodology and evaluate it with angle diversity receivers in a mobile optical wireless (OW) system. The fast and efficient fully adaptive FDAPA-Holograms system can improve the receiver signal to noise ratio (SNR) and reduce the required time to estimate the position of the receiver. The adaptation techniques (angle, power and delay) offer a degree of freedom in the system design. The proposed system FDAPA-Holograms is able to achieve high data rate of 5 Gb/s with full mobility. Simulation results show that the proposed 5 Gb/s FDAPA-Holograms achieves around 13 dB SNR under mobility and under eye safety regulations. Furthermore, a fast divide and conquer search algorithm is introduced to find the optimum hologram as well as to reduce the computation time. The proposed system (FDAPA-Holograms) reduces the computation time required to find the best hologram location from 64 ms using conventional adaptive system to around 14 ms

    High Speed Optical Wireless Communication Systems.

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    Visible light communication (VLC) systems have become promising candidates to complement conventional radio frequency (RF) systems due to the increasingly saturated RF spectrum and the potentially high data rates that can be achieved by VLC systems. Over the last decade, significant research efforts have been directed towards the development of VLC systems due to their numerous advantages over RF communication systems, such as the availability of simple transmitters (light emitting diodes, (LEDs)) and receivers (silicon photo detectors), better security at the physical layer, improved energy efficiency due to the dual functionally (i.e., illumination and communication) and hundreds of THz of license-free bandwidth. However, several challenges face VLC systems to achieve high data rates (multi gigabits per second). These challenges include the low modulation bandwidth of the LEDs, inter symbol interference (ISI) due to multipath propagation, co-channel interference (CCI) and the light unit (i.e., VLC transmitter) should be ‘‘ON’’ all the time to ensure continuous communication. This thesis investigates a number of techniques to design robust highspeed indoor VLC systems that support a single user and multi-users. Light engines composed of RYGB laser diodes (LDs) are used for communication and illumination. The main goal of using LDs is to enable the VLC system to achieve high data rates while using simple modulation techniques (such as on off keying (OOK)), which adds simplicity to VLC systems. Three VLC systems based on the computer generated holograms (CGHs) are proposed in this thesis, which are single beam static CGH-VLC system, static CGH-VLC system and adaptive CGH-VLC system. Whereas in the first and the second systems a single photodetector is used (added simplicity), an imaging receiver is used in the third one to obtain spatial multiplexing. We consider the lighting constraints where illumination should be at an acceptable level and should consider diffuse reflections (up to second order) to find the maximum data rate that can be offered by each system. In the first system, the CGH is used to produce one fixed broad beam from the best light unit and focus it to a specific area on the communication floor. In the second system, the CGH generates 100 beams (all these beams carry same data) from the best transmitter and directs these beams to an area of 2 m × 2 m on the communication floor. In the third system, the CGH is used to generate eight beams from the best transmitter and steer these beams to the receiver’s location. In addition, each one of these eight beams carries a different data stream. This thesis also presents an indoor VLC system in conjunction with an imaging receiver with parallel data transmission (spatial multiplexing) to reduce the effects of inter-symbol-interference (ISI). To distinguish between light units (transmitters) and to match the light units used (to convey the data) with the pixels of the imaging receiver, we proposed the use of subcarrier multiplexing (SCM) tones. Each light unit transmission is multiplexed with a unique tone. At the receiver, a SCM tone decision system is utilised to measure the power level of each SCM tone and consequently associate each pixel with a light unit. We proposed a high data rate single user VLC system based on wavelength division multiplexing (WDM) in this thesis. An imaging diversity receiver (IMDR) is used as an optical receiver. Based on the location of the IMDR, each colour of the RYGB LDs sends a different data stream at a different rate where the variable data rates are attributed mainly to the different power levels assigned to the colours to yield the desired white colour. Each pixel of the IMDR is covered by a specific colour optical filter. WDM in conjunction with the SCM tones are used to realise a high data rate multi-user VLC system in this thesis. The SCM tones are used to allocate an optimum transmitter to each user and to calculate the co-channel interference (CCI). Two novel optical receivers are used to evaluate the performance of the VLC systems: an array of non-imaging receivers (NI-R) and an array of non-imaging angle diversity receivers (NI-ADR). This thesis proposes a multi-branch transmitter (MBT) as a solution that can improve the VLC system performance over an indoor channel and support multi-user operation. The MBT has many transmitter branches (TBs) where each branch is directed to a specific area. By reducing the semi angle of each TB, the effect of multipath propagations is reduced and the received optical power is improved. The performance of the MBT is evaluated with a single user VLC system using a wide field of view (W-FOV) receiver and then with an angle diversity receiver (ADR). The results show that this system can provide a data rate of 4 Gb/s and 10 Gb/s when using wide FOV receiver and ADR, respectively. In addition, the performance of the MBT is evaluated in a multi-user scenario. We used the MBT with WDM and SCM tones to realise a high data rate multiuser indoor VLC system. Four colour laser diodes (RYGB LDs) are used as sources of illumination and data communication. One colour of these four colours is used to convey the SCM tones at the beginning of the connection to set up the connection. When the connection is set up, the data is transmitted in parallel through the RYGB LDs
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