Marc Bohn

Next generation elastic optical networks: The vision of the European research project IDEALIST

In this work we detail the strategies adopted in the European research project IDEALIST to overcome the predicted data plane capacity crunch in optical networks. In order for core and metropolitan telecommunication systems to be able to catch up with Internet traffic, which keeps growing exponentially, we exploit the elastic optical networks paradigm for its astounding characteristics: flexible bandwidth allocation and reach tailoring through adaptive line rate, modulation formats, and spectral efficiency. We emphasize the novelties stemming from the flex-grid concept and report on the corresponding proposed target network scenarios. Fundamental building blocks, like the bandwidth-variable transponder and complementary node architectures ushering those systems, are detailed focusing on physical layer, monitoring aspects, and node architecture design.

107-Gb/s full-ETDM transmission over field installed fiber using vestigial sideband modulation

107-Gb/s full-ETDM transmission is shown over a 160-km field installed fiber link. A high tolerance towards narrowband optical filtering is demonstrated using vestigial sideband modulation to minimize the spectral width.

An adaptive optical equalizer concept for single channel distortion compensation

We present a new adaptive optical equalizer concept for single-channel distortion compensation and analyze the performance of an adaptive optical FIR-filter in lattice structure (cascaded MZI) with respect to equalization of residual dispersion, self-phase modulation and polarization-mode dispersion.

On the Mitigation of Optical Filtering Penalties Originating From ROADM Cascade

Wavelength selective switches (WSSs) that are integrated in reconfigurable optical add-drop multiplexers (ROADMs) induce penalties on the optical signal due to tight optical filtering, which increases as several ROADMs are cascaded in a meshed network. In this letter, we propose and analyze possible configurations for the mitigation of these penalties in optical domain using optical wave shaper (WS). Including one WS in every ROADM node allows transmission of 28 and 32 GBd signals, which are QPSK, 8-QAM, or 16-QAM modulated, through a cascade of 32 and 14 WSS filters, respectively. With an average bandwidth of 33 GHz per WSS, an optical signal to noise ratio penalty below 1 dB at BER=1×10-3 is observed.

Adaptive distortion compensation with integrated optical finite impulse response filters in high bitrate optical communication systems

In high-bit-rate optical transmission systems, distortions due to dynamic chromatic dispersion, polarization mode dispersion, and power changes are larger than the distortion tolerances of the system. To meet the tolerances and the desired quality of service, an adaptive equalizer is necessary. We demonstrate the capabilities of planar lightwave circuit integrated optical finite impulse response filters for mitigating distortions of the transmission channel, and we investigate two adaptive equalization approaches. The first approach uses an adaptive feedback generated from electrical spectrum monitoring; the second one uses intersymbol interference minimization with a least mean square error algorithm. We successfully demonstrated adaptive equalization of chromatic dispersion, self-phase modulation, and polarization mode dispersion, as well as combinations of these distortions.

Ultralong haul 1.28-Tb/s PM-16QAM WDM transmission employing hybrid amplification

In order to cope with the foreseeable capacity crunch next-generation optical transmission systems aim to utilize higher order quadrature amplitude modulation formats to achieve spectral efficiency (SE) higher than the current commercial systems. In particular, transmission rates as high as 1 Tb/s are envisioned, employing superchannel configuration achieved by closer than standard 50 GHz placement of Nyquist filtered wavelength-division multiplexed (WDM) channels. Moreover, increase in symbol rate of each subcarrier in a superchannel is desired to reduce the number of components per Tb/s and, consequently, overall cost. In this regard, we addressed a series of challenges namely intersymbolinterference (ISI) induced by low-pass filtering of digital-to-analog converter (DAC), intrasuperchannel crosstalk penalties, and selected suitable forward error correction (FEC) code considering limitations of electronic components. Digital preemphasis is employed to mitigate DAC induced ISI, a subcarrier spacing of 1.2 × symbol rate is chosen to limit crosstalk penalties below 0.5 dB in Q2 and a FEC overhead of 23% is established limiting transponder count to four, achieving 1 Tb/s net data rate. The superchannel is assigned a 200-GHz optical spectrum to achieve a SE of 5.0 b/s/Hz, and WDM transmission performance is evaluated over three different kinds of fibers: standard single-mode fiber (SSMF), large area pure silica core fiber (LAPSCF), and large effective area fiber (LEAF), having span lengths of 95/121, 82/164, and 81 km, respectively. The maximum reach of 1-Tb/s superchannel with 8 × 100-Gb/s WDM channels at pre-FEC threshold of 3.37 × 10-2 was found to be 1110, 1921, and 789 km for SSMF, LAPSCF, and LEAF, respectively. Further improvement in transmission performance is achieved by employing hybrid EDFA-Raman amplification, and achievable distance was extended to 2054, 2952, and 1341 km for SSMF, LAPSCF, and LEAF, respectively, at pre-FEC threshold. Mitigation of a nonlinear phase noise employing single-channel digital back propagation resulted in extension of maximum reach up to 2262, 3349, and 1530 km for SSMF, LAPSCF, and LEAF, respectively.

Long-haul terabit transmission (2272km) employing digitally pre-distorted quad-carrier PM-16QAM super-channel

We experimentally demonstrate long-haul WDM transmission of 36GBaud four-subcarrier Terabit PM-16QAM super-channel. Digital pre-distortion enables ~50% reach improvement for both LAPSCF and SSMF fiber-types, with maximum recorded reach of 2272km and 949km, respectively.

System impact of ripples in grating group delay

We present simple analytical expressions which relate fiber grating group-delay ripples to system performance and allow the estimation of expected penalties. Experiments show excellent agreement with our theory. A WDM transmission experiment shows that the system performance can be drastically improved if the channels are slightly detuned in wavelength.

Vendor-interoperable elastic optical interfaces: Standards, experiments, and challenges [Invited]

This paper aims to review the status of standardization activities on the black link (BL) and corresponding alien wavelength concepts. It discusses experimental work on filterless optical networks conducted within a dedicated Deutsche Telekom project. The general prospects and existing challenges concerning elastic extensions of the BL are also assessed. Furthermore, we present relevant work on control and management plane interoperability comprising generalized multi-protocol label switching and transport software defined networking aspects. In the second part of the article, we report on the latest dual-vendor experiments on data plane interoperability in terms of digital signal processing technology for next generation 1.28 Tb/s PM-16QAM super-channels. Finally, we present a network reachability analysis based on the widely used Gaussian noise model in the context of data plane interoperability. This analysis estimates the network-wide impact of the single-vendor versus the dual-vendor approach.

Next generation optical nodes: The vision of the European research project IDEALIST

As traffic demands become more uncertain and newer services continuously arise, novel network elements are needed to provide more flexibility, scalability, resilience and adaptability to todays optical networks. Considering these requirements, within the European project IDEALIST the investigation of elastic optical networks is undertaken with special focus on next generation optical node architectures. As an evolution of existent ROADMs and OXCs, these optical nodes will establish a new paradigm in which the network requirements will be efficiently addressed considering various emerging dimensions. In this article, we describe the drivers, architectures, and technologies that will enable these novel optical nodes. In addition, multivendor traffic interoperability, optical defragmentation, and node cascadability are also described as considerations in the node design.