Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

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Terabit free-space data transmission employing orbital angular momentum multiplexing

A key enabler for the intelligent information society of 2030, 6G networks are expected to provide performance superior to 5G and satisfy emerging services and applications. In this article, we present our vision of what 6G will be and describe usage scenarios and requirements for multi-terabyte per second (Tb/s) and intelligent 6G networks. We present a large-dimensional and autonomous network architecture that integrates space, air, ground, and underwater networks to provide ubiquitous and unlimited wireless connectivity. We also discuss artificial intelligence (AI) and machine learning [1], [2] for autonomous networks and innovative air-interface design. Finally, we identify several promising technologies for the 6G ecosystem, including terahertz (THz) communications, very-large-scale antenna arrays [i.e., supermassive (SM) multiple-input, multiple-output (MIMO)], large intelligent surfaces (LISs) and holographic beamforming (HBF), orbital angular momentum (OAM) multiplexing, laser and visible-light communications (VLC), blockchain-based spectrum sharing, quantum communications and computing, molecular communications, and the Internet of Nano-Things.

6G Wireless Networks: Vision, Requirements, Architecture, and Key Technologies

One property of electromagnetic waves that has been recently explored is the ability to multiplex multiple beams, such that each beam has a unique helical phase front. The amount of phase front ‘twisting’ indicates the orbital angular momentum state number, and beams with different orbital angular momentum are orthogonal. Such orbital angular momentum based multiplexing can potentially increase the system capacity and spectral efficiency of millimetre-wave wireless communication links with a single aperture pair by transmitting multiple coaxial data streams. Here we demonstrate a 32-Gbit s−1 millimetre-wave link over 2.5 metres with a spectral efficiency of ~16 bit s−1 Hz−1 using four independent orbital–angular momentum beams on each of two polarizations. All eight orbital angular momentum channels are recovered with bit-error rates below 3.8 × 10−3. In addition, we demonstrate a millimetre-wave orbital angular momentum mode demultiplexer to demultiplex four orbital angular momentum channels with crosstalk less than −12.5 dB and show an 8-Gbit s−1 link containing two orbital angular momentum beams on each of two polarizations. High speed data transmission using orbital angular momentum beams has been recently demonstrated. Here, Yan et al. demonstrate a 32 Gbit/s millimetre-wave communication link using eight coaxially propagating independent orbital angular momentum beams with four orbital angular momentum states on two orthogonal polarizations.

/pdf/high-capacity-millimetre-wave-communications-with-orbital-7yf6ayr0p8.pdf

High-capacity millimetre-wave communications with orbital angular momentum multiplexing

There has been a great deal of material in the area of discrete-time transforms that has been published in recent years. This book does an excellent job of presenting important aspects of such material in a clear manner. The book has 11 chapters and a very useful appendix. Seven of these chapters are essentially devoted to the Fourier series/transform, discrete Fourier transform, fast Fourier transform (FFT), and applications of the FFT in the area of spectral estimation. Chapters 8 through 10 deal with many other discrete-time transforms and algorithms to compute them. Of these transforms, the KarhunenLoeve, the discrete cosine, and the Walsh-Hadamard transform are perhaps the most well-known. A lucid discussion of number theoretic transforms i5 presented in Chapter 11. This reviewer feels that the authors have done a fine job of compiling the pertinent material and presenting it in a concise and clear manner. There are a number of problems at the end of each chapter, an appreciable number of which are challenging. The authors have included a comprehensive set of references at the end of the book. In brief, this book is a valuable contribution to the general areas of signal processing and communications. It can be used for a graduate level course in perhaps two ways. One would be to cover the first seven chapters in great detail. The other would be to cover the whole book by focussing on different topics in a selective manner. This book  by  Elliott  and Rao  is extremely  useful to researchers/engineers who are working  in the areas of signal processing and communications. It i s also an excellent reference book, and hence a valuable addition to one’s library

http://ieeexplore.ieee.org/iel5/5/31347/01457444.pdf

Multirate digital signal processing

Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Optical Modulation Formats

We extend our concept for distributed ultra-dense frequency-division multiplex of single-polarization subcarriers to multiplex of polarization-division multiplexed (PDM) subcarriers. Precise frequency allocation of PDM subcarriers within a 400-Gb/s superchannel is experimentally validated with Nyquist-shaped PDM-QPSK subcarriers.

http://ieeexplore.ieee.org/iel7/7318283/7341603/07341856.pdf

Spatially distributed aggregation of a polarization-division multiplexed superchannel by frequency conversion in fiber

We demonstrate 64-GBd signal generation up to bipolar-8-ASK utilizing a single MZM, monolithically integrated with segmented drivers in SiGe. Using polarization multiplexing, 300-Gb/s net data rate transmission over 120 km SSMF is shown.

64-GBd DP-Bipolar-8ASK Transmission Over 120 km SSMF Employing a Monolithically Integrated Driver and MZM in 0.25-μm SiGe BiCMOS Technology

Summary form only given. The transmission capacity of the fiber is expanded by increasing both the number of wavelength channels (wavelength-division multiplexing, WDM) and the bit rate per WDM-channel (time-division multiplexing, TDM). A channel bit rate of 40 Gbit/s will soon be installed and the next generation TDM bit rate of 160 Gbit/s is under active study in several research laboratories. As electrical signal processing is not available at 160 Gbit/s today, the TDM bit rate of 160 Gbit/s requires the optical time division multiplexing (OTDM) technique. In this paper, we report on components and techniques enabling 160 Gbit/s OTDM transmission. We focus on semiconductor based devices.

High-speed all-optical signal processing in optical communication systems

We present continuously tuneable signal frequency shifting up to 4 THz using a dispersion and dispersion-slope reduced highly nonlinear fibre. A 1.6-Tb/s DP-16QAM WDM signal is arbitrarily translated to different wavelengths across the C-band during a 160-km error-free transmission.

Any-to-Any Signal Frequency Shifting Across Entire C-Band Using Continuously Tuneable Optical Frequency Shifter

Error-free wavelength conversion of a 40 Gb/s DPSK signal is presented in a wavelength range of 45 nm using a dual pump four-wave mixing scheme in a 1.3 μm quantum-dot semiconductor optical amplifier.

Colja Schubert

Papers

Spatially distributed aggregation of a polarization-division multiplexed superchannel by frequency conversion in fiber

64-GBd DP-Bipolar-8ASK Transmission Over 120 km SSMF Employing a Monolithically Integrated Driver and MZM in 0.25-μm SiGe BiCMOS Technology

High-speed all-optical signal processing in optical communication systems

Any-to-Any Signal Frequency Shifting Across Entire C-Band Using Continuously Tuneable Optical Frequency Shifter

Wavelength conversion of 40-Gb/s NRZ DPSK signals within a 45-nm range using a 1.3 μm quantum-dot semiconductor optical amplifier