High-Bandwidth Low-Cost High-Speed Optical Fiber Links using Organic Light Emitting Diodes

Record-high 200 Mbps transmission using an OLED with a 31 MHz 3 dB bandwidth using a 3-tap feedforward equaliser is achieved, demonstrating the potential of such devices for use in low-cost polymer optical fiber links.EPSRC Ultra Parallel Visible Light Communication Project (EP/K00042X/1) EPSRC Studentship 146672

Visible Light Communications towards 5G

5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of co-operating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks

A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined

Ultra-Low Cost High-Density Two-Dimensional Visible-Light Optical Interconnects

© 2019 IEEE. Visible light communications have attracted considerable interest in recent years owing to the ability of low-cost light emitting diodes (LEDs) to act both as illumination sources and data transmitters with moderate data transmission rates. In this paper, we propose the formation of ultra-low cost visible-light integrated optical links by interfacing dense micro-pixelated LED arrays with matching multi-layered multimode polymer waveguide arrays. The combination of these two optical technologies can offer relatively high aggregate data densities ≥ 0.5 Tb/s/mm2 using very low cost components that can be directly interfaced with CMOS electronics and integrated onto standard printed circuit boards. Here, we present the basic system design and report the first proof-of-principle demonstration of such a visible light system employing 4×4 μLED arrays on a pitch matching four-layered waveguide array samples. Different interconnection topologies and light coupling schemes are investigated and their performance in terms of loss and crosstalk is compared. Data transmission of 2.5 Gb/s with a bit error rate within the forward-error correction threshold of 3.8×10-3 is achieved over a single μLED-waveguide channel using PAM-4 modulation and equalization. The results presented here demonstrate the potential of such ultra-low cost visible-light optical interconnects.UK EPSRC via the Ultra Parallel Visible Light Communications Project (EP/K00042X/1

Free-Space Quantum Key Distribution

Based on the firm laws of physics rather than unproven foundations of mathematical complexity, quantum cryptography provides a radically different solution for encryption and promises unconditional security. Quantum cryptography systems are typically built between two nodes connected to each other through fiber optic. This chapter focuses on quantum cryptography systems operating over free-space optical channels as a cost-effective and license-free alternative to fiber optic counterparts. It provides an overview of the different parts of an experimental free-space quantum communication link developed in the Spanish National Research Council (Madrid, Spain).Comment: 22 pages, 15 figure

Analysis and Optimisation of an Organic Optical Link

Organic light-emitting diodes (OLEDs) have been historically used extensively for displays, and more recently for lighting applications. However, the low-cost of materials and direct-deposition manufacturing processes involved in organic semiconductor fabrication means that OLEDs are uniquely placed for low-cost integrated optical interconnects. This thesis presents novel high-speed analysis and optimisation of OLEDs for communications purposes. DC and small-signal measurement results for small-molecule OLEDs fabricated by Dr. Kou Yoshida at the University of St. Andrews are presented and are used to inform a detailed 5-layer OLED simulation model. Correlation is drawn between the experimental small signal impedance measurements and the experimental luminescent output, from which a novel electrical model is built to predict bandwidth. Extension of the OLED physical simulation shows for the first time that by using a constant fraction of the overall simulated device resistance (a ‘luminescent resistance’), this RC-based model can be used to predict device small signal bandwidths, which suggests validity of both the simulation and the electrical modelling approach, provided that the exciton lifetime is less than the RC time-constant. This simulation is then used to forecast trends in device performance, allowing traditional inorganic semiconductor engineering tools to be brought into the field of organic device optimisation. Finally, these OLEDs are used in an optical link to provide a world-record equalisation-free OLED communications data rate of 130 Mbps.EPSRC Studentship 1466721 EPSRC via the Ultra Parallel Visible Light Communication Project (EP/K00042X/1

Novel optical transmitters for high speed optical networks

The objective of this thesis is to investigate the performance of novel optical transmitter lasers for use in high speed optical networks. The laser technology considered is the discrete mode laser diode (DMLD) which is designed to achieve single wavelength operation by etching features on the surface of the ridge waveguide. This leads to a simplified manufacturing process by eliminating the regrowth step used in conventional approaches, presenting an economic approach to high volume manufacture of semiconductor lasers. Two application areas are investigated in this work. The bit rate in next generation access networks is moving to 10 Gbit/s. This work characterises the performance of DMLDs designed for high speed operation with the objective of identifying the limitations and improving performance to meet the specifications for uncooled operation at 10 Gbit/s. With the deployment of advanced modulation formats the phase noise of the laser source has become an important parameter, particularly for higher order formats. DMLDs were developed for narrow linewidth operation. The linewidth of these devices was characterised and a value as low as 70 kHz was demonstrated. Transmission experiments were also carried out using a coherent transmission test bed and the performance achieve is compared with that of an external cavity laser