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

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (30 June 2019).

Special Issue Editors

Guest Editor
Prof. Zhongqi Pan

Department of Electrical and Computer Engineering, Bell South Mobility/LEQSF Regents Endowed Professor in Telecommunications; Harold Callais/BORSF Endowed Professor in Electrical Engineering II, University of Louisiana at Lafayette, Lafayette, LA 70504-3890, USA
Website | E-Mail
Interests: photonic devices; fiber communications; wavelength-division-multiplexing (WDM) technologies; optical performance monitoring; space-division-multiplexing (SDM) technologies; fiber sensor technologies; digital signal processing (DSP)
Guest Editor
Dr. Yang Yue

Juniper Networks, Sunnyvale, CA 94089, USA
Website | E-Mail
Interests: optical communications and networking; optical interconnect; detection and display technology; integrated photonics; free-space and fiber optics

Special Issue Information

Dear Colleagues,

Network traffic has been increasing exponentially over decades. This enormous growth rate will continue, in the foreseeable future, due to many newly-emerging and unanticipated digital applications and services. To fulfill the ever-growing bandwidth demand, not only spectral efficiency of optical fiber communication system needs to be improved, but also power/wavelength needs to be reduced so that higher individual data rates per wavelength of up to multi-Tb/s can be achieved with total aggregate capacities beyond Pb/s. As one of the most prominent enable technologies, digital signal processing (DSP) has played a critical role in coherent system to accommodate channel impairments mitigation, to enable advanced modulation formats for spectral efficiency transmission, and to realize flexible bandwidth.

This Special Issue aims to explore the novel advanced DSP techniques to enable multi-Tb/s/channel optical transmission for addressing the pressing bandwidth and power-efficiency demands. It will focus on the state-of-the-art advances and future perspectives of DSP. Topics of interest include, but are not limited to, the following areas:

  • DSP for mitigation/compensation of fiber channel and optical transceiver impairments.
  • Digital fiber nonlinearity mitigation/compensation.
  • DSP for multi-dimensional modulation and constellation shaping.
  • MIMO signal processing for space-division multiplexing.
  • DSP for direct detection and short-reach fiber systems.
  • Power efficient DSP.

Prof. Zhongqi Pan
Dr. Yang Yue
Guest Editors

Manuscript Submission Information

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Keywords

  • Digital signal processing
  • Fiber communications
  • Coherent optical transport
  • MIMO signal processing
  • Spatial division multiplexing
  • Chromatic dispersion
  • Polarization mode dispersion
  • Fiber nonlinearities
  • High-order modulations
  • Constellation shaping
  • Data center

Published Papers (8 papers)

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Research

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Open AccessArticle
Post-FEC Performance of Pilot-Aided Carrier Phase Estimation over Cycle Slip
Appl. Sci. 2019, 9(13), 2749; https://doi.org/10.3390/app9132749
Received: 27 June 2019 / Revised: 2 July 2019 / Accepted: 3 July 2019 / Published: 8 July 2019
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Abstract
The POST-forward error correction (FEC) bit error rate (BER) performance and the cycle-slip (CS) probability of the carrier phase estimation (CPE) scheme based on Viterbi–Viterbi phase estimation (VVPE) algorithm and the VV cascaded by pilot-aided-phase-unwrap (PAPU) algorithm have been experimentally investigated in a [...] Read more.
The POST-forward error correction (FEC) bit error rate (BER) performance and the cycle-slip (CS) probability of the carrier phase estimation (CPE) scheme based on Viterbi–Viterbi phase estimation (VVPE) algorithm and the VV cascaded by pilot-aided-phase-unwrap (PAPU) algorithm have been experimentally investigated in a 56 Gbit/s quadrature phase-shift keying (QPSK) coherent communication system. Experimental results show that, with 0.78% pilot overhead, the VVPE + PAPU scheme greatly improves the POST-FEC performance degraded by continuous CS, maintaining a low CS probability with less influence of filter length. Comparing with the VVPE scheme, the VVPE + PAPU scheme can respectively obtain about 3.1 dB, 1.3 dB, 0.6 dB PRE-FEC optical signal noise ratio (OSNR) gains at PRE-BER of 1.8 × 10−2. Meanwhile, the VVPE + PAPU scheme respectively achieves about 3 dB, 1 dB, and 0.5 dB POST-FEC OSNR gain and improves the FEC limit from 2.5 × 10−3 to 1.4 × 10−2, from 8.9 × 10−3 to 1.8 × 10−2, and from 1.6 × 10−2 to 1.9 × 10−2 under the CPE filter length of 8, 16, and 20. Full article
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Open AccessArticle
Experimental Investigation of 400 Gb/s Data Center Interconnect Using Unamplified High-Baud-Rate and High-Order QAM Single-Carrier Signal
Appl. Sci. 2019, 9(12), 2455; https://doi.org/10.3390/app9122455
Received: 16 March 2019 / Revised: 26 May 2019 / Accepted: 13 June 2019 / Published: 15 June 2019
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Abstract
In this article, we review the latest progress on data center interconnect (DCI). We then discuss different perspectives on the 400G pluggable module, including form factor, architecture, digital signal processing (DSP), and module power consumption, following 400G pluggable optics in DCI applications. Next, [...] Read more.
In this article, we review the latest progress on data center interconnect (DCI). We then discuss different perspectives on the 400G pluggable module, including form factor, architecture, digital signal processing (DSP), and module power consumption, following 400G pluggable optics in DCI applications. Next, we experimentally investigate the capacity-reach matrix for high-baud-rate and high-order quadrature amplitude modulation (QAM) single-carrier signals in the unamplified single-mode optical fiber (SMF) link. We show that the 64 GBd 16-QAM, and 64-QAM signals can potentially enable 400 Gb/s and 600 Gb/s DCI application for 40 km and beyond of unamplified fiber link. Full article
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Open AccessArticle
IBP Based Caching Strategy in D2D
Appl. Sci. 2019, 9(12), 2416; https://doi.org/10.3390/app9122416
Received: 31 March 2019 / Revised: 15 May 2019 / Accepted: 27 May 2019 / Published: 13 June 2019
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Abstract
Device to Device (D2D) communication is a key technology in 5th generation wireless systems to increase communication capacity and spectral efficiency. Applying caching into D2D communication networks, the device can retrieve content from other devices by establishing D2D communication links. In this way, [...] Read more.
Device to Device (D2D) communication is a key technology in 5th generation wireless systems to increase communication capacity and spectral efficiency. Applying caching into D2D communication networks, the device can retrieve content from other devices by establishing D2D communication links. In this way, the backhaul traffic can be significantly reduced. However, most of the existing caching schemes in D2D are proactive caching, which cannot satisfy the requirement of real-time updating. In this paper, we propose an Indian Buffet Process based D2D caching strategy (IBPSC). Firstly, we construct a geographical D2D communication network to provide high quality D2D communications according to physical closeness between devices. Then devices are divided into several social communities. Devices are ranked by their node importance to community in each community. The base station makes caching decisions for devices according to contrition degree. Experimental results show that IBPSC achieves best network performance. Full article
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Open AccessArticle
Adaptive Compensation of Bandwidth Narrowing Effect for Coherent In-Phase Quadrature Transponder through Finite Impulse Response Filter
Appl. Sci. 2019, 9(9), 1950; https://doi.org/10.3390/app9091950
Received: 5 February 2019 / Revised: 3 May 2019 / Accepted: 8 May 2019 / Published: 13 May 2019
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Abstract
Coherent in-phase quadrature (IQ) transponders are ubiquitous in the long-haul and the metro optical networks. During the transmission, the coherent signal experiences a bandwidth narrowing effect after passing through multiple reconfigurable optical add-drop multiplexers (ROADMs). The coherent signal also experiences a bandwidth narrowing [...] Read more.
Coherent in-phase quadrature (IQ) transponders are ubiquitous in the long-haul and the metro optical networks. During the transmission, the coherent signal experiences a bandwidth narrowing effect after passing through multiple reconfigurable optical add-drop multiplexers (ROADMs). The coherent signal also experiences a bandwidth narrowing effect when electrical or optical components of the coherent IQ transponder experience aging. A dynamic method to compensate the bandwidth narrowing effect is thus required. In the coherent optical receiver, signal bandwidth is estimated from the raw analog-to-digital converter (ADC) outputs. By adaptively adjusting the tap coefficients of the finite impulse response (FIR) filter, simple post-ADC FIR filters can increase the resiliency of the coherent signal to the bandwidth narrowing effect. The influence of chromatic dispersion, polarization mode dispersion, and polarization dependent loss are studied comprehensively. Furthermore, the bandwidth information of the transmitted analog signal is fed back to the coherent optical transmitter for signal optimization, and the transmitter-side FIR filter thus changes accordingly. Full article
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Open AccessArticle
Compensation of Limited Bandwidth and Nonlinearity for Coherent Transponder
Appl. Sci. 2019, 9(9), 1758; https://doi.org/10.3390/app9091758
Received: 27 March 2019 / Revised: 17 April 2019 / Accepted: 23 April 2019 / Published: 28 April 2019
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Abstract
Coherent optical transponders are widely deployed in today’s long haul and metro optical networks using dense wavelength division multiplexing. To increase the data carrying capacity, the coherent transponder utilizes the high order modulation format and operates at a high baud rate. The limited [...] Read more.
Coherent optical transponders are widely deployed in today’s long haul and metro optical networks using dense wavelength division multiplexing. To increase the data carrying capacity, the coherent transponder utilizes the high order modulation format and operates at a high baud rate. The limited bandwidth and the nonlinearity are two critical impairments for the coherent in-phase quadrature transmitter. These impairments can be mitigated by digital filters. However, to accurately determine the coefficients of these filters is difficult because the impairment from the limited bandwidth and the impairment from nonlinearity are coupled together. In this paper, we present a novel method to solve this problem. During the initial power-up, we apply a sinusoidal stimulus to the coherent IQ transmitter. We then scan the frequency and amplitude of the stimulus and monitor the output power. By curve-fitting with an accurate mathematical model, we determine the limited bandwidth, the nonlinearity, the power imbalance, and the bias point of the transponder simultaneously. Optimized coefficients of the digital filters are determined accordingly. Furthermore, we utilize a coherent IQ transponder and demonstrate that the limited bandwidth is improved by the finite impulse response filter, while nonlinearity is mitigated by the memoryless Volterra filter. Full article
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Open AccessArticle
Optical Transmitters without Driver Amplifiers—Optimal Operation Conditions
Appl. Sci. 2018, 8(9), 1652; https://doi.org/10.3390/app8091652
Received: 22 August 2018 / Revised: 7 September 2018 / Accepted: 10 September 2018 / Published: 14 September 2018
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Abstract
An important challenge in optical communications is the generation of highest-quality waveforms with a Mach–Zehnder modulator with a limited electrical swing (Vpp). For this, we discuss, under limited Vpp, the influence of the waveform design on the root-mean-square amplitude, [...] Read more.
An important challenge in optical communications is the generation of highest-quality waveforms with a Mach–Zehnder modulator with a limited electrical swing (Vpp). For this, we discuss, under limited Vpp, the influence of the waveform design on the root-mean-square amplitude, and thus, the optical signal quality. We discuss the influence of the pulse shape, clipping, and digital pre-distortion on the signal quality after the electrical-to-optical conversion. Our simulations and experiments, e.g., suggest that pre-distortion comes at the expense of electrical swing of the eye-opening and results in a lower optical signal-to-noise ratio (OSNR). Conversely, digital post-distortion provides operation with larger eye-openings, and therefore, provides an SNR increase of at least 0.5 dB. Furthermore, we find that increasing the roll-off factor increases the electrical swing of the eye-opening. However, there is negligible benefit of increasing the roll-off factor of square-root-raised-cosine pulse shaped signals beyond 0.4. The findings are of interest for single-channel intensity modulation and direct detection (IM/DD) links, as well as optical coherent communication links. Full article
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Review

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Open AccessReview
Recent Advances in Equalization Technologies for Short-Reach Optical Links Based on PAM4 Modulation: A Review
Appl. Sci. 2019, 9(11), 2342; https://doi.org/10.3390/app9112342
Received: 2 May 2019 / Revised: 31 May 2019 / Accepted: 3 June 2019 / Published: 7 June 2019
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Abstract
In recent years, short-reach optical links have attracted much more attention and have come to constitute a key market segment due to the rapid development of data-center applications and cloud services. Four-level pulse amplitude modulation (PAM4) is a promising modulation format to provide [...] Read more.
In recent years, short-reach optical links have attracted much more attention and have come to constitute a key market segment due to the rapid development of data-center applications and cloud services. Four-level pulse amplitude modulation (PAM4) is a promising modulation format to provide both a high data rate and relatively low cost for short-reach optical links. However, the direct detector and low-cost components also pose immense challenges, which are unforeseen in coherent transmission. To compensate for the impairments and to truly meet data rate requirements in a cost-effective manner, various digital signal processing (DSP) technologies have been proposed and investigated for short-reach PAM4 optical links. In this paper, an overview of the latest progress on DSP equalization technologies is provided for short-reach optical links based on PAM4 modulation. We not only introduce the configuration and challenges of the transmission system, but also cover the principles and performance of different equalizers and some improved methods. Moreover, machine learning algorithms are discussed as well to mitigate the nonlinear distortion for next-generation short-reach PAM4 links. Finally, a summary of various equalization technologies is illustrated and our perspective for the future trend is given. Full article
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Open AccessReview
Recent Advances in DSP Techniques for Mode Division Multiplexing Optical Networks with MIMO Equalization: A Review
Appl. Sci. 2019, 9(6), 1178; https://doi.org/10.3390/app9061178
Received: 12 February 2019 / Revised: 3 March 2019 / Accepted: 7 March 2019 / Published: 20 March 2019
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Abstract
This paper provides a technical review regarding the latest progress on multi-input multi-output (MIMO) digital signal processing (DSP) equalization techniques for high-capacity fiber-optic communication networks. Space division multiplexing (SDM) technology was initially developed to improve the demanding capacity of optic-interconnect links through mode-division [...] Read more.
This paper provides a technical review regarding the latest progress on multi-input multi-output (MIMO) digital signal processing (DSP) equalization techniques for high-capacity fiber-optic communication networks. Space division multiplexing (SDM) technology was initially developed to improve the demanding capacity of optic-interconnect links through mode-division multiplexing (MDM) using few-mode fibers (FMF), or core-multiplexing exploiting multicore fibers (MCF). Primarily, adaptive MIMO filtering techniques were proposed to de-multiplex the signals upon different modes or cores, and to dynamically compensate for the differential mode group delays (DMGD) plus mode-dependent loss (MDL) via DSP. Particularly, the frequency-domain equalization (FDE) techniques suggestively lessen the algorithmic complexity, compared with time-domain equalization (TDE), while holding comparable performance, amongst which the least mean squares (LMS) and recursive least squares (RLS) algorithms are most ubiquitous and, hence, extensively premeditated. In this paper, we not only enclose the state of the art of MIMO equalizers, predominantly focusing on the advantage of implementing the space–time block-coding (STBC)-assisted MIMO technique, but we also cover the performance evaluation for different MIMO-FDE schemes of DMGD and MDL for adaptive coherent receivers. Moreover, the hardware complexity optimization for MIMO-DSP is discussed, and a joint-compensation scheme is deliberated for chromatic dispersion (CD) and DMGD, along with a number of recent experimental demonstrations using MIMO-DSP. Full article
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