Ricardo M. Ferreira

Terabit+ (192 × 10 Gb/s) Nyquist shaped UDWDM coherent PON with upstream and downstream over a 12.8 nm band

In this paper, we numerically and experimentally demonstrate a bidirectional Terabit+ ultradense wavelength-division multiplexing (UDWDM) coherent passive optical network with Nyquist shaped 16-ary quadrature amplitude modulation, offering up to 10 Gb/s service capabilities per user/wavelength in a total spectrum of 12.8 nm over 40 km of standard single-mode fiber. This paper first demonstrates the capability of Nyquist pulse shaping to mitigate crosstalk arising from back-reflections and nonlinear effects in UDWDM networks with coherent transceivers. The latter part of the paper experimentally investigates the bidirectional transmission in terms of receiver sensitivity and nonlinear tolerance under different network transmission capacity conditions, e.g., number of users and bit rate per users.

Ultra High Capacity Self-Homodyne PON With Simplified ONU and Burst-Mode Upstream

In this letter, we demonstrate a proof of concept fully loaded bidirectional ultrahigh capacity coherent passive optical network (2 × 1008 × 8.3 Gb/s). This was achieved using partial spectrum overlap, Nyquist shaping, digital frequency shifting, self-homodyne detection, and pilot tone remodulation. Upstream burst mode operation is also demonstrated.

Ultra-High-Capacity Passive Optical Network Systems with Free-Space Optical Communications

Abstract This article experimentally demonstrates a hybrid fiber–free-space passive optical network that enables high spectral density, aggregated capacity, and total throughput through ultra-dense wavelength-division multiplexing baseband and radio-over-fiber channels. Ultra-dense wavelength-division multiplexing 10-Gb/s Nyquist-shaped 16-ary quadrature amplitude modulation, 10-Gb/s radio-over-fiber orthogonal frequency-division multiplexing, and 8.75-Gb/s baseband orthogonal frequency-division multiplexing signals per user were transmitted through a maximum 40-km passive optical network, which includes a 6-m free-space optics link with acceptable performance.

Coherent Access: A Review

In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Experimental Assessment of the Adaptive Stokes Space-Based Polarization Demultiplexing for Optical Metro and Access Networks

We experimentally analyze an adaptive polarization-demultiplexing (PolDemux) technique based on the representation of the state of polarization of the signal in the Stokes space. The performance and convergence speed of the Stokes PolDemux are compared with the constant modulus algorithm, for dual polarization QPSK and 16QAM modulation formats in a system with a maximum polarization rotation of 6 kHz. Moreover, the applicability of the adaptive Stokes algorithm is tested in an ultradense wavelength-division multiplexing scenario over 80 km of standard single-mode fiber. The BER results show a very small power penalty confirming the suitability of the adaptive Stokes method in systems where the accumulated chromatic and polarization-mode dispersion are small, such as high capacity optical metro and access networks scenarios.

Low Complexity Advanced DBP Algorithms for Ultra-Long-Haul 400 G Transmission Systems

We experimentally assess the performance versus complexity tradeoff of advanced split-step and Volterra-based digital backpropagation (DBP) techniques, applied to aWDM (75-GHz flexigrid) ultra-long-haul (ULH) transmission system composed of five dual-carrier PM-16 quadratic-amplitude modulation 400 G superchannels. Using the recently proposed weighted Volterra series nonlinear equalizer (W-VSNE), we demonstrate a maximum reach improvement of 600 km, obtained at the expense of only six DBP steps for an entire >5000-km optical link (1000 km/step), representing a ~90% reduction on the total number of DBP steps relatively to the widely used split-step Fourier method (SSFM) implementation. The W-VSNE technique is also shown to be more accurate than the correspondent weighted SSFM (W-SSFM) algorithm when applied in medium (10-50 DBP steps) and low complexity (<;5 DBP steps) regimes. The achieved reduction of computational effort (up to 88%), together with the associated latency savings (up to 90%), demonstrates the feasibility of low complexity and efficient DBP for high-speed ULH transmission systems.

Coherent UDWDM-PON With Dual-Polarization Transceivers in Real-Time

We report a real-time experimental demonstration of a long-reach coherent ultra-dense wavelength-division multiplexing (WDM)-passive optical network (PON) system with quadratic-amplitude modulation (QAM)-based dual-polarization optical transceivers. Using field-programmable gate array-based digital signal processing, the transmission of 20-WDM channels in 2.5-GHz grid, employing both 2.5-Gb/s dual-polarization quadrature phase-shift keying (DP-QPSK) and 3.75-Gb/s DP-8PSK signals, is successfully demonstrated with bit-error rate in real-time. The performance is evaluated over 100-km standard single mode fiber in terms of receiver sensitivity and ODN power budget for both modulation formats, showing the feasibility of coherent PON scenarios using flexible dual-polarization strategies supported by software-defined transceivers.

Performance optimization of nyquist signaling for spectrally efficient optical access networks [Invited]

In this work, Nyquist pulse-shaping technology is exploited for future implementations of optical access networks. The paper first presents technical issues regarding digital implementation of Nyquist spectral shaping for low-symbol-rate systems. Second, the potential benefits regarding mitigation of cross talk (linear and nonlinear) of Nyquist pulse shaping in symmetric and bidirectional wavelength-division multiplexing passive optical networks (WDM-PONs) are presented. Lastly, the paper proposes a WDM-PON solution employing self-coherent detection at the optical network unit and heterodyne coherent detection at the optical line terminal. In this proposed architecture, a multi-objective optimization strategy is developed to enhance the transmission performance of the Nyquist-shaped bands in full-duplex mode.

Real-Time Bidirectional Coherent Nyquist UDWDM-PON Coexisting With Multiple Deployed Systems in Field-Trial

We experimentally characterize a bidirectional 2.5 Gb/s UDWDM-PON system based on Nyquist shaped DQPSK with digital signal processing in real time. The optical distribution network power budget of this system is evaluated and in coexistence of UDWDM channels with upstream TWDM-PON and RF video overlay signals, a set of optimum parameters and their impact on the network operation is driven. Additionally, we report the first field-trial of bidirectional coherent Nyquist UDWDM-PON using commercial real-time FPGA-based transceivers, coexisting with the deployed GPON, RF video overlay, and NG-PON2 technologies. A -44.5 dBm receiver sensitivity is achieved for 64 × 2.5 Gb/s DQPSK downstream channels and a 17 dB tolerance in dynamic power range of upstream channels is performed.

Fully Coherent Self- Homodyne Bi-directional Enhanced Performance PON

We present a coherent-PON employing partial overlap of downstream/upstream Nyquist spectra, allowing bi-directional operation and enhanced spectral efficiency (2×120Gb/s@50GHz). Additionally, frequency shifting of Nyquist bands from the carrier allowed reduced RBS and dynamic SRS.