The recent interest in the upgrade and enhancements of metro transport networks and the availability of transponder cards with coherent receivers is opening the way to filterless solutions employing only passive splitters/couplers and optical amplifiers, potentially achieving significant capital expeditures and operating expenditures savings. However, the filterless option suffers from inefficiencies, mainly due to the broadcasting constraint and the reduced optical reach. To overcome such limitations, this paper proposes three complementary strategies to upgrade optical filterless metro networks (FMN). First, the number of supported channels is incremented by exploiting the full C + L -band. To this end, two design architectures (i.e., Single and Dual Region) are proposed and evaluated, targeting double capacity with respect to the standard C-band and an upgrade to cost reduction. Second, we investigate a dual-architecture solution, extending metro deployments with a low-cost filterless and unamplified L-band system. Its design trade-offs are evaluated to determine its suitability in providing direct low-latency connectivity between metro-access nodes with the aim of supporting edge-computing platforms. Finally, the flexibility of the FMN is extended by introducing disaggregated transponders with different bitrates (i.e., 100 Gbps and 400 Gbps) and configurable transmission parameters, such as the modulation format and the forward error correction). Such flexibility is exploited through the extension of the OpenConfig YANG model of the optical line system, thus enabling automatic spectrum and transmission parameter assignment by means of a centralized software-defined-network controller and achieving better resource utilization. Simulation and experimental results are provided, showing the effectiveness and the potential impact of filterless metro solutions in future deployments and low-cost network upgrades supporting edge/fog clusters and 5G.

We experimentally demonstrate a distance-wise, wavelength-dependent link tomography extraction scheme using receiver DSP. This approach permits the estimation of gain spectrum and tilt in C+L-band EDFAs with a maximum mean absolute error of 0.6 dB.

A successful migration from current C-band based optical networks to a multiband scenario primarily depends on the development of solutions that can reliably measure physical properties of optical links over broad spectral transmission windows. Additionally, these solutions must be capable of delivering wavelength-dependent and spatially-resolved indicators that can empower network operators to identify faults before they lead to severe service disruptions. Recently, the exploitation of receiver based digital signal processing as a tool for optical performance monitoring has gained tremendous popularity. One successful example is the so-called in-situ power profile estimator, which can reconstruct the per-channel longitudinal power profile along the optical fiber link solely processing the received signal samples. In this work, we propose a novel application for the in-situ power profile estimator by harnessing it on multiple wavelengths to accurately estimate the spectral gain profile of C+L-band in-line Erbium-doped fiber amplifiers deployed in a 280-km single mode fiber link. Furthermore, we show how this scheme can be efficiently used to detect amplification-related anomalies, such as gain tilt and narrowband gain compression. In our measurements, we achieved a sub-dB estimation accuracy by comparing the proposed gain extraction approach with the back-to-back characterization obtained from an optical spectrum analyzer.

One promising and competitive solution to keep up with the rapid growth in data traffic while at the same time addressing increasing network cost, is the efficient reuse of legacy optical fiber infrastructure. This is highly desirable as deployed single mode fibers represent a valuable asset in the network while new installations would require high additional investments. Multiband (MB) or ultra-wideband (UWB) systems, combined with high symbol rates and higher-order modulation formats, are promising solutions to capitalize the already existing fiber plants. In this contribution, we experimentally demonstrate S-C-L-band reception with 64 GBd dual-polarization (DP) 64-ary and 32-ary quadratureamplitude modulation (QAM) while using C-band components off-the-shelf (COTS) such as DP-IQ modulators and coherent receivers. To achieve such broadband operation with components that are not optimized for an out-of-band use, mitigation of the associated penalties is decisive. To this end, we apply an end-toend electro-optical Volterra-based coherent system identification followed by nonlinear digital predistortion of the transmitter. We achieve 150-nm operation bandwidth of the transmission system by performing only a single identification and predistortion at a reference wavelength of 1500 nm.

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We transmit a 28-GBd Nyquist PDM-16QAM channel with WDM-interferers (37.5-GHz grid) over 80-km SSMF spans. Interference noise analysis reveals substantial nonlinear phase noise for PDM-16QAM interferers compared to PDM-4QAM, while Q-penalty is kept small by appropriate CPE

There has been an ongoing quest for transceiver technologies to be employed in next-generation passive optical networks (PONs) beyond 25G due to the growing number of subscribers and connected devices per subscriber and the ever-increasing bandwidth demand per device/application. Given the cost and loss/power budget requirements, the candidates seem to be digital signal processing (DSP)-aided intensity-modulation/direct detection (IM-DD) and low-complexity coherent transceivers. Here, we experimentally demonstrate a 100G coherent-lite PON using a novel transceiver DSP chain that utilizes a frequency-diverse dual-polarization RF pilot tone pair. The proposed scheme enables the implementation of Alamouti coding for single-carrier signaling, which is used in conjunction with heterodyne detection, achieving a significant complexity reduction in a coherent optical network unit (ONU) receiver. It consists of a single balanced photodiode followed by an analog-to-digital converter, offering comparable optical complexity to its DD counterpart, at the expense of DSP complexity in the ONU. The performance of a transceiver architecture facilitated by the proposed DSP was assessed in both back-to-back operation and up to 80 km standard single-mode fiber transmission using an ∼ 1 MHz linewidth distributed feedback laser as an ONU laser. At the hard-decision forward error correction (7% overhead) threshold, assumed to be 4 × 10 − 3 , a receiver sensitivity of − 29.6 dBm and a loss budget of 36.6 dB at a launch power of 7 dBm are achieved.

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