Colja Schubert

Bio: Colja Schubert is an academic researcher from Heinrich Hertz Institute. The author has contributed to research in topics: Wavelength-division multiplexing & Optical amplifier. The author has an hindex of 28, co-authored 214 publications receiving 3274 citations. Previous affiliations of Colja Schubert include Fraunhofer Society.

Terahertz Technologies to Deliver Optical Network Quality of Experience in Wireless Systems Beyond 5G

Abstract: This article discusses the basic system architecture for THz wireless links with bandwidths of more than 50 GHz into optical networks. New design principles and breakthrough technologies are required in order to demonstrate terabit- per-second data rates at near zero latency using the proposed system concept. Specifically, we present the concept of designing the baseband signal processing for both the optical and wireless links and using an E2E error correction approach for the combined link. We provide two possible electro-optical baseband interface architectures, namely transparent optical-link and digital- link architectures, which are currently under investigation. THz wireless link requirements are given as well as the main principles and research directions for the development of a new generation of transceiver front-ends that will be capable of operating at ultra-high spectral efficiency by employing higher-order modulation schemes. Moreover, we discuss the need for developing a novel THz network information theory framework, which will take into account the channel characteristics and the nature of interference in the THz band. Finally, we highlight the role of PBF, which is required in order to overcome the propagation losses, as well as the physical layer and medium access control challenges.

Single channel 1.28 Tbit/s and 2.56 Tbit/s DQPSK transmission

Abstract: By combining the techniques of optical TDM with polarisation multiplexing and DQPSK modulation format, 240 km transmission of 1.28 Tbit/s and 160 km transmission of 2.56 Tbit/s has been performed in a single wavelength channel.

Ultrahigh-Speed OTDM-Transmission Technology

Abstract: This paper reviews ultrahigh-speed data transmission in optical fibers based on optical time division multiplexing (OTDM) transmission technology. Optical signal processing in the transmitter and receiver as well as the requirements on ultrahigh-speed data transmission over a fiber link are discussed. Finally, results of several OTDM-transmission experiments, including 160-Gb/s transmission over 4320 km, 1.28-Tb/s transmission over 240 km, and 2.56-Tb/s transmission over 160-km fiber link, are described

Transmission of Single-Channel 16-QAM Data Signals at Terabaud Symbol Rates

Abstract: We present latest results for OTDM transmission systems in combination with digital coherent detection achieving record-high serial data rates in a single-wavelength channel. We show serial data transmission of 5.1 Tb/s (640 GBd) over 80-km and 10.2 Tb/s (1.28 TBd) over 29-km dispersion managed fiber (DMF). For 5.1-Tb/s transmission over 80-km DMF, the BER of all 128 OTDM-tributaries (both polarizations) is found to be below the hard-decision FEC-threshold, corresponding to an error-free net data rate of 4.8 Tb/s. In a 10.2-Tb/s experiment, the BER of all 256 TDM-tributaries (both polarizations) is found to be below the FEC-threshold in the back-to-back configuration. This translates to an error-free net data rate of 9.5 Tb/s. After transmission over a 29-km DMF negligible pulse broadening and a BER below the FEC limit is found.

Nonlinear Digital Pre-distortion of Transmitter Components

Abstract: We present a linear and nonlinear digital pre-distortion (DPD) tailored to the components of an optical transmitter. The DPD concept uses nonlinear models of the transmitter devices, which are obtained from direct component measurements. While the digital-to-analog converter and driver amplifier are modeled jointly by a Volterra series, the modulator is modeled independently as a Wiener system. This allows for a block-wise compensation of the modulator by a Hammerstein system and a pre-distortion of the electrical components by a second Volterra series. In simulations and extensive experiments, the performance of our approach for nonlinear DPD is compared to an equivalent linear solution as well as to a configuration without any DPD. The experiments were performed using M -ary quadrature-amplitude modulation ( M -QAM) formats ranging from 16- to 128-QAM at a symbol rate of 32 GBd. It is shown that the DPD improves the required optical signal-to-noise ratio at a bit error ratio of 2·10 −2 by at least 1.2 dB. Nonlinear DPD outperforms linear DPD by an additional 0.9 and 2.7 dB for higher-order modulation formats such as 64-QAM and 128-QAM, respectively.

Terabit free-space data transmission employing orbital angular momentum multiplexing

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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.

Multirate digital signal processing

Abstract: 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

Advanced Optical Modulation Formats

Abstract: 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