Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications

The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well

Machine learning for performance improvement of periodic NFT-based communication system

We compare performance of several machine learning methods, including support vector machine, k-nearest neighbours, k-means clustering, and Gaussian mixture model, used for increasing transmission reach in the optical communication system based on the periodic nonlinear Fourier transform signal processin

Outage probability due to crosstalk from multiple interfering cores in PAM4 inter-datacenter connections

In this work, we propose to use four-level pulse amplitude modulation (PAM4) and multicore fibers (MCFs) to support very high capacity datacenter interconnect (DCI) links. The limitations imposed by inter-core crosstalk (ICXT) on the performance of 112 Gb/s up to 80 km-long optically amplified PAM4 inter-DCI links with intensity-modulation and direct-detection and full chromatic dispersion compensation in the optical domain are analyzed through numerical simulation for high and low skew-symbol rate product (SSRP). With only one interfering core, we show that those PAM4 inter-DCI links achieve an outage probability (OP) of 10−4 with a maximum ICXT level of −13.9 dB for high SSRP and require an ICXT level reduction of about 8.1 dB to achieve the same OP for low SSRP. Due to using full dispersion compensation, for an OP of 10−4, the maximum acceptable ICXT level shows only a 1.4 dB variation with the MCF length increase from 10 km to 80 km. When considering the ICXT induced by several interfering cores, the maximum ICXT level per interfering core for an OP of 10−4 decreases around 3 dB when doubling the number of interfering cores. This conclusion holds for high and low SSRP regimes. For two interfering cores, we show that a single interfering core with low SSRP is enough to induce a severe reduction of the maximum acceptable ICXT level.info:eu-repo/semantics/publishedVersio

A Programmable ROADM System for SDM/WDM Networks

This paper proposed and evaluated a programmable ROADM system for MCF-based SDM/WDM networks. The proposed ROADM system employing both bypass connection and Route-and-Select wavelength switching enables adaptable virtual topology in optical networks by dynamically configuring bypass connection cores. The simulation results confirmed this ROADM system could provide acceptable performance with an around 10–20% reduction in the total cost including the number of ports and WSSs by comparing with a fully flexible SDM/WDM ROADM system, which cannot be implemented due to the required extremely high-port-count WSSs

Efficient Visible Light Communication Transmitters Based on Switching-Mode dc-dc Converters

Visible light communication (VLC) based on solid-state lighting (SSL) is a promising option either to supplement or to substitute existing radio frequency (RF) wireless communication in indoor environments. VLC systems take advantage of the fast modulation of the visible light that light emitting diodes (LEDs) enable. The switching-mode dc-to-dc converter (SMCdc-dc) must be the cornerstone of the LED driver of VLC transmitters in order to incorporate the communication functionality into LED lighting, keeping high power efficiency. However, the new requirements related to the communication, especially the high bandwidth that the LED driver must achieve, converts the design of the SMCdc-dc into a very challenging task. In this work, three different methods for achieving such a high bandwidth with an SMCdc-dc are presented: increasing the order of the SMCdc-dc output filter, increasing the number of voltage inputs, and increasing the number of phases. These three strategies are combinable and the optimum design depends on the particular VLC application, which determines the requirements of the VLC transmitter. As an example, an experimental VLC transmitter based on a two-phase buck converter with a fourth-order output filter will demonstrate that a bandwidth of several hundred kilohertz (kHz) can be achieved with output power levels close to 10Wand power efficiencies between 85% and 90%. In conclusion, the design strategy presented allows us to incorporate VLC into SSL, achieving high bit rates without damaging the power efficiency of LED lightin

Low complexity DSP for high speed optical access networking

A novel low-cost and energy-efficient approach for reaching 40 Gb/s signals is proposed for cost-sensitive optical access networks. Our proposed design is constituted of an innovative low-complex high-performance digital signal processing (DSP) architecture for pulse amplitude modulation (PAM-4), reuses existing commercial cost-effective 10-G components and eliminates the need of a power-hungry radio frequency (RF) component in the transmitter. Using a multi-functional 17-tap reconfigurable adaptive Volterra-based nonlinear equalizer with noise suppression, significant improvement in receiver optical power sensitivity is achieved. Results show that over 30 km of single-mode fiber (SMF) a link power budget of 33 dB is feasible at a bit-error-rate (BER) threshold of 10−3.</jats:p

Digital All-Optical Physical-Layer Network Coding

Network coding (NC) has recently attracted intense research focus for its potential to provide network throughput enhancements, security and reduced network congestions, improving in this way the overall network performance without requiring additional resources. In this chapter, the all-optical physical-layer network coding (AOPNC) technique is presented, focusing on digital encoding schemes that are based on optical XOR logical gates. It is also discussed how digital AOPNC can be implemented between sub-carrier-modulated (SCM) optical signals in radio-over-fiber (RoF) networks, circumventing the enhanced complexity arising by the use of SCM signals and the asynchrony that might exist between the data arriving at the encoding unit. AOPNC demonstrations are described for simple on/off keyed (OOK)-SCM data signals, as well as for more sophisticated higher-order phase modulation formats aiming to further improve spectrum efficiency and transmission capacity

Real-time 10Gbps polarization independent quasicoherent receiver for NG-PON2 access networks

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksIn this paper, we propose and test experimentally a real-time 10 Gbps polarization independent quasicoherent receiver for NG-PON2 access networks. The proposed 10 Gbps quasicoherent receiver exhibits a sensitivity of -35.2 dBm after 40 km SSMF transmission with a commercial generic EML as transmitter. This sensitivity means a 14.9 dB improvement over a direct detection scheme with a photodiode after 40 km SSMF transmission. Therefore, the use of the proposed 10 Gbps quasicoherent receiver with the tested EML will provide a power budget of 34.76 dB (class E1) and a splitting ratio of 128 after the 40 km SSMF transmission. Finally, the proposed 10 Gbps quasicoherent receiver allows a colorless and optical filterless operation because wavelength selection is done by tuning the local oscillator wavelength and using electrical intermediate frequency filtering.Peer ReviewedPostprint (author's final draft

Longer Wavelength GaAs-Based VCSELs for Extended-Reach Optical Interconnects

Data centers of today are increasing in size and are built to accommodate strong traffic demands while providing sustainably by having clients sharing resources under one roof. Their massive scale puts pressure on the server network topology and has incited a need for data transmission links that are energy efficient and capable of operation at high bit rates with reach up to a few kilometers. Optical interconnects (OIs) offer large bandwidth and low attenuation at long distances, and are therefore suitable for this task. The most commonly used OIs, with 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) and multi-mode fiber (MMF), have a 25 Gb/s reach that is limited to a few hundred meters. However, the fiber chromatic dispersion and attenuation that limit the OI reach can be reduced significantly by increasing the wavelength of this very same technology. The upper limit of the GaAs-based VCSEL technology, with strained InGaAs quantum wells (QWs), is about 1100 nm.With further improved OI performance, new hyperscale data center topologies can be realized and explored. This will lead to a larger number of possible solutions in traffic engineering as well as for power management. 1060 nm VCSELs could soon open up for lane rates of 100+ Gb/s over distances up to 2 km and help reach the Tb/s link speed aim of data center OI standards, in which capacity is built up mainly by employing multiple parallel lanes, increasing symbol rate by going from binary to four-level pulse amplitude modulation (PAM-4), and optimizing with electrical mitigation techniques such as digital signal processing.In this work we show that 1060 nm GaAs VCSELs are suitable light sources for long-reach OIs by first demonstrating their overall stable performance and capability of error-free data transmission up to 50 Gb/s back-to-back and 25 Gb/s over 1 km of MMF. With PAM-4, we show 100 Gb/s error-free capability over 100 m of MMF, suitable for wavelength division multiplexed OIs that can transmit data at several wavelengths from 850 to 1060 nm over the same fiber channel. We also assemble single-mode 1060 nm VCSEL and single-mode fiber links and demonstrate 50 Gb/s error-free transmission over 1 km using pre-emphasis and 40 Gb/s over 2 km without the use of any electrical mitigation techniques. These results stem from careful VCSEL design, including strained InGaAs QWs with GaAsP barriers, doped AlGaAs distributed Bragg reflectors, a short optical cavity and multiple oxide layers. In addition, we show that the fabrication of such a device poses no increase in complexity and can be realized using standard processing techniques