Reconfigurable Optical Add-drop Multiplexers Research Articles

Low-loss and polarization insensitive 32 × 4 optical switch for ROADM applications

Integrated switches play a crucial role in the development of reconfigurable optical add-drop multiplexers (ROADMs) that have greater flexibility and compactness, ultimately leading to robust single-chip solutions. Despite decades of research on switches with various structures and platforms, achieving a balance between dense integration, low insertion loss (IL), and polarization-dependent loss (PDL) remains a significant challenge. In this paper, we propose and demonstrate a 32 × 4 optical switch using high-index doped silica glass (HDSG) for ROADM applications. This switch is designed to route any of the 32 inputs to the express ports or drop any channels from 32 inputs to the target 4 drop ports or add any of the 4 ports to any of the 32 express channels. The switch comprises 188 Mach-Zehnder Interferometer (MZI) type switch elements, 88 optical vias for the 44 optical bridges, and 618 waveguide-waveguide crossings with three-dimensional (3D) structures. At 1550 nm, the fiber-to-fiber loss for each express channel is below 2 dB, and across the C and L bands, below 3 dB. For each input channel to all 4 drop/add channels at 1550 nm, the loss is less than 3.5 dB and less than 5 dB across the C and L bands. The PDLs for all express and input channels to the 4 drop/add channels are below 0.3 dB over the C band, and the crosstalk is under −50 dB for both the C and L bands.

Fiber–Chip–Fiber Mode/Polarization/Wavelength Transmission and Processing with Few‐Mode Fiber, (de)Multiplexing SiO2 Chip and ROADM Si Chip

AbstractThe emergence of optical communications has opened up new perspectives for high‐capacity data transmission and signal processing, to meet the demand of the increasing data traffic. Despite significant progress in multi‐dimensional multiplexing for capacity scaling in fiber–optic communications or photonic networks‐on‐chip, achieving high‐capacity data transmission and signal processing in an entire fiber–chip–fiber system remains a great challenge. This challenge is attributed to the lack of effective multi‐dimensional coupling between fiber and chip. Here, the 3D (de)multiplexing SiO2 chip inscribed by femtosecond laser direct writing is proposed to achieve the multi‐dimensional coupling between the few‐mode fiber (FMF) transmission link and the silicon processing network. Combined with the 2D silicon chip fabricated by a standard lithography process, a multi‐dimensional fiber–chip–fiber communication system designed to transmit and process the hybrid wavelength‐, mode‐ and polarization‐division multiplexing signals in FMF is constructed. The silicon chip integrates Mach–Zehnder interferometer (MZI) switches and arrayed‐waveguide gratings (AWGs) to serve as a reconfigurable optical add/drop multiplexer (ROADM). As a proof‐of‐concept demonstration, a 96‐channel FMF–chip–FMF communication system with a data transmission capacity of 4.032 Tbit s−1, achieving a bit‐error ratio (BER) of less than 3.8 × 10−3, is successfully implemented.

Digital-twin-assisted meta learning for soft-failure localization in ROADM-based optical networks

Reconfigurable optical add/drop multiplexer (ROADM) nodes are evolving towards high-degree architectures to support growing traffic and enable flexible network connectivity. Due to the complex composition of high-degree ROADMs, soft failures may occur between both inter- and intra-node components, like wavelength selective switches and fiber spans. The intricate ROADM structure significantly contributes to the challenge of localizing inter-/intra-node soft failures in ROADM-based optical networks. Machine learning (ML) has shown to be a promising solution to the problem of soft-failure localization, enabling network operators to take accurate and swift measures to overcome such challenges. However, data scarcity is a main hindrance when using ML for soft-failure localization, especially in the complex scenario of inter- and intra-node soft failures. In this work, we propose a digital-twin-assisted meta-learning framework to localize inter-/intra-node soft failures with limited samples. In our proposed framework, we construct several mirror models using a digital twin of the physical optical network and then generate multiple training tasks. These training tasks serve as pretraining data for the meta learner. Then, we use real data for fine-tuning and testing of the meta learner. The proposed framework is compared with the rule-based reasoning method, transfer-learning-based method, and artificial-neural-network-based method with no pretraining. Experimental results indicate that the proposed framework improves localization accuracy by over 15%, 33%, and 54%, on average, compared to benchmark approaches, respectively.

Photonic Gateway accommodating all types of wavelength paths for digital-coherent and IM-DD user terminals in all-photonic metro-access converged networks

In access and metro networks, there is increasing demand for guaranteed wide-bandwidth and stringent/deterministic end-to-end latency characteristics. Converging these networks by expanding dense wavelength-division-multiplexed metro networks to access areas is a promising approach to satisfy this demand. An All-Photonics Metro-Access Converged Network (APN) dynamically and flexibly provides a wavelength connection between any two points including user premises. This evolution in network architecture presents some technical challenges. First, from the access-node architecture viewpoint, conventional reconfigurable optical add/drop multiplexers (ROADMs) do not have functions for remote and in-channel user-terminal (UT) control or turn-back connection within the access area. Therefore, the APN cannot be achieved by simply adopting ROADMs as access nodes, which are defined as Photonic Gateways. Remote and in-channel UT controls are required to control the endpoints of a wavelength path beyond the carrier control-plane network. These types of control should be independent of the protocol and modulation/detection method for the main signal. In addition, the Photonic Gateway must flexibly and efficiently support a new type of wavelength path, specifically a turn-back connection within the access area, due to metro/access convergence. Second, from the viewpoint of the process for dynamic wavelength-path provisioning, the APN controller should autonomously discover physical connectivity between a UT and the Photonic Gateway connected via field access fibers. This paper proposes a novel Photonic Gateway architecture that flexibly and scalably provides various UTs with direct optical connections including turn-back configurations. This paper also proposes a method that autonomously recognizes physical connections between newly connected UTs and the Photonic Gateway. The proposed architecture and method are experimentally verified based on all types of wavelength-path provisioning that take at most 72 s using Photonic Gateway prototypes, 100-Gb/s digital-coherent UTs, and 10-Gb/s intensity-modulation direct-detection UTs. All types of wavelength paths that are provided over the APN architecture are considered including a turn-back connection between two UTs within the same access area and connections between two UTs that traverse the metro area with or without optical/electrical conversion.

Optimizing performance in elastic optical networks using advanced reconfigurable optical add-drop multiplexers: A novel design approach and comprehensive analysis

Network operators diversify service offerings and enhance network efficiency by leveraging bandwidth-variable transceivers and colorless flexible-grid reconfigurable optical add-drop multiplexers (ROADMs). Nonetheless, the paradigm shift from rigid to elastic optical networks (EONs) has affected several key parameters, including bit rate, center frequency spacing, modulation format, and optical reach. This study investigated the transformative impact of emerging technologies on the design and structure of optical network architectures, including spectrally efficient multicarrier systems and bandwidth-variable wavelength-selective switches. A cost-effective ROADM architecture applying an order-based connecting approach was introduced, which presented a high connectivity level and a blockage probability of less than 10-4. When this architecture was implemented in the EON, the data transportation rate was 1 Tb/s. This outcome successfully accommodated a 20 % surge in traffic demand, while the optimized network architecture significantly improved fiber utilization by 3.4 %. Consequently, this study contributed a practical and efficient solution for implementing flexible optical networks, effectively addressing current concerns and propelling the optical communication system sector forward.

Optical Networks Automation Overview: A Survey

The increasing demand for data has driven the advancement of optical networks from traditional architectures to more flexible, dynamic and efficient solutions. This includes technologies like flexgrid reconfigurable optical add-drop multiplexers (ROADMs), variable bandwidth transponders (VBTs) providing different modulation, coding schemes and baud rates. These advancements have brought about new challenges that concerns to the routing and spectrum allocation (RSA), fragmented spectrum, need for rapid and efficient channel restoration, and operation and maintenance management of optical networks. To address these challenges, a dynamic and flexible network requires a highly advanced network operational system (OS) capable of efficiently managing and allocating network resources. It relies on network abstraction, sensors, actuators, and software-defined networking (SDN) to enable algorithms, management, control, and decision-making. Improving the sensing capabilities of the network is crucial. Modern hardware and sensor technology can help forecast fiber breaks, equipment failures, and other potential issues in advance, allowing for proactive actions to be taken. Machine learning (ML) methods have been proposed in the literature to enhance the accuracy of quality of transmission (QoT) estimation, mitigate nonlinearities and provide decisions. This reduces the need for conservative design margins, maximizes the capacity of optical network systems and reduces the investment in infrastructure. Failure management is a critical aspect of optical networks. Providing early-warning and proactive protection is essential. This includes detecting failures, localizing them, identifying the root causes, and estimating their magnitude. Quick response to failures is vital to maintaining network reliability

Reconfigurable optical add-drop multiplexers for hybrid mode-/wavelength-division-multiplexing systems

Reconfigurable optical add-drop multiplexers for hybrid mode-/wavelength-division-multiplexing systems

Networking assessment of ROADM architecture based on a photonics integrated WSS for 800G multi-band optical transport

The capacity of the optical transport network must be expanded to support the increasing demand due to bandwidth-intensive applications. Multi-band transmission solutions can achieve this goal by exploiting the low-loss optical spectrum windows while maintaining the same existing fiber infrastructure, increasing the network’s capacity, and minimizing the operator capital expenditure (CAPEX) by limiting the need for a new fiber deployment. In the context of multi-band transmission, this work proposes a novel reconfigurable optical add–drop multiplexer (ROADM) architecture using a modular photonic integrated multi-band wavelength selective switch (WSS) that operates over multi-bands (S + C + L). This study focuses on conducting a comprehensive network performance analysis of different settings, enabling operation from 400G up to 800G using the proposed multi-band WSS on two real network topologies: German and Italian. The results provide the potential benefits of transitioning from traditional C-band transmission to multi-band transmission based on overall network performance.

Open EDFA gain spectrum dataset and its applications in data-driven EDFA gain modeling

Optical networks satisfy high bandwidth and low latency requirements for telecommunication networks and data center interconnection. To improve network resource utilization, machine learning (ML) is used to accurately model optical amplifiers such as erbium-doped fiber amplifiers (EDFAs), which impact end-to-end system performance such as quality of transmission. However, a comprehensive measurement dataset is required for ML to accurately predict an EDFA’s wavelength-dependent gain. We present an open dataset consisting of 202,752 gain spectrum measurements collected from 16 commercial-grade reconfigurable optical add–drop multiplexer (ROADM) booster and pre-amplifier EDFAs under varying gain settings and diverse channel-loading configurations over 2,785 hours in total, with a total dataset size of 3.1 GB. With this EDFA dataset, we implemented component-level deep-neural-network-based EDFA models and use transfer learning (TL) to transfer the EDFA model among 16 ROADM EDFAs, which achieve less than 0.18/0.24 dB mean absolute error for booster/pre-amplifier gain prediction using only 0.5% of the full target training set. We also showed that TL reduces the EDFA data collection requirements on a new gain setting or a different type of EDFA on the same ROADM.

Channel power equalization based on joint optimization of EDFA and ROADM configuration in open optical network.

Deterioration of the signal-to-noise ratio (SNR) is an important challenge in ultra-long multi optical line system (OLS) optical transmission systems. The non-uniform gain and cascading of the Erbium-doped fiber amplifier (EDFA) lead to SNR deterioration in transmission systems. In this paper, we propose two channel power equalization methods based on joint optimization of EDFA and Reconfigurable optical add-drop multiplexer (ROADM) configurations: 1) reinforcement learning (RL)-based channel power equalization (RL-PE) and 2) covariance matrix adaptive evolution strategy (CMA-ES) channel power equalization (CMA-PE). The simulation results indicate that the power equalization effect was improved by 1.9 dB through the CMA-PE method, while the RL-PE method led to a 1.5 dB improvement in an ultra-long 80-channel 7-OLS transmission system.

Dimensioning networks of ROADM cluster nodes

Next-generation optical networks require high-degree, high-capacity reconfigurable optical add-drop multiplexer (ROADM) nodes and intelligent network planning schemes. We propose a cluster ROADM node design and a network dimensioning method that optimizes the resource utilization of optical networks with cluster nodes. The proposed ROADM cluster node offers a flexible add-drop rate, scaling to 100s of degrees, and a cost per degree similar to today’s ROADM. It disaggregates the cluster’s line and add-drop functions into different chassis. The low-cost node architecture is complemented by an order-based connection management algorithm that achieves better than 10−4 blocking despite being equipped with less than 30% dilation in the cluster design. For an optical network with ROADM cluster nodes, we propose a network dimensioning scheme that proactively uses network knowledge to determine the optimum degree for ROADM nodes as demand increases. The results show a much-improved blocking rate, particularly at medium to high loading and an average of 3.1% increased utilization on each network’s fiber compared with reactive schemes.

On the Mitigation of WSS Filtering Penalties: Single- vs Multi-Carrier Modulation

The tight channel filtering imposed by long cascades of reconfigurable optical add-drop multiplexers (ROADMs) represents, nowadays, one of the major performance-limiting aspects for optically-routed coherent optical fiber systems. This makes it vital to perform a ROADM-aware optimization of the network performance at the physical layer. In particular, the use of different modulation options is known to have a strong impact on the extent of the filtering-induced penalties. In that regard, a long debate between single- and multi-carrier modulation has been taking place during the last few years, sometimes leading to apparently contradictory results. Following the open scientific discussion on this topic, in this work, we investigate by simulation and experimentally the wavelength selective switch (WSS) filtering tolerance of single-carrier (SC) and digital subcarrier multiplexing (DSCM) signals. In order to promote a fair comparison, both modulation options are carefully designed to minimize the ROADM-filtering penalties, namely resorting to the use of entropy loading together with baud rate optimization. After some preliminary numerical assessment, a comprehensive set of experiments are carried out for the transmission of 21-WDM 95–105 Gbaud SC and DSCM signals over a 2040 km straight line of fiber with regularly spaced WSSs. In general, our results allow to conclude that the two modulation options yield similar performance if the overall baud rate is optimized for each filtering scenario, keeping the baud rate at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 5% of the optimized value.

Suspect fault screen assisted graph aggregation network for intra-/inter-node failure localization in ROADM-based optical networks

In optical networks, failure localization is essential to stable operation and service restoration. Several approaches have been presented to achieve accurate failure localization of nodes and inter-nodes. However, due to increasing traffic and demand for flexibility, the reconfigurable optical add/drop multiplexer (ROADM) is evolving towards a multi-degree architecture. Therefore, each ROADM is composed of multiple devices, which makes intra-node failures become more complex. In this context, intra-node failure localization can effectively reduce the pressure on network operators to further find specific devices. In this work, we redefine the intra-/inter-node failure model for multi-degree ROADM-based optical networks and propose a suspect fault screen assisted graph aggregation network (SFS-GRN) for intra-/inter-node failure localization. The SFS is responsible for screening out suspect fault devices from all devices and reducing the number of candidate devices. The GRN is used to analyze these monitoring data from an optical performance monitoring (OPM) node and network wide and to determine the most likely failure device. The proposed scheme is evaluated in a nine-node simulated network and three-node testbed network. Extensive results show that the SFS-GRN achieves higher accuracy compared with existing methods under different percentages of OPM deployment, numbers of service requests, and failure types. The SFS can remove more than 98% of devices, which is beneficial to further detection and repair for network operators. Moreover, the proposed strategy takes about 10 ms to detect a potential failure, and it has the potential to be applied to a real scenario.

End-to-End Real-Time Service Provisioning Over a SDN-Controllable Analog mmWave Fiber -Wireless 5G X-Haul Network

The current work presents the first experimental demonstration of real-time Ethernet (ETH) trial services and 4K-Ultra High Definition (UHD) video application transmission over a 2λ Wavelength Division Multiplexing (WDM) analog Fiber-Wireless (FiWi) mmWave X-haul network, supporting dynamic flexible capacity allocation through an integrated silicon photonic Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Reconfigurable Optical Add Drop Multiplexer (ROADM) and 60 GHz wireless transmission across a 7 m V-band link distance, while controlled by a Software Defined Network (SDN) controller based on Open Daylight. Analog X-haul transport of the radio signals is based on an Intermediate Frequency over Fiber (IFoF) scheme centered at 1.5 GHz using an Orthogonal Frequency Division Multiplexing (OFDM) radio-waveform with a bandwidth of 204 MHz, generated by a Field Programmable Gated Array (FPGA)-based RF System-on-Chip (SoC) processor that converts on-the-fly the real-time ETH downlink traffic to analog radio and vice-versa for the uplink. Dynamic allocation of the X-haul traffic capacity is handled through the use of the 802.1Q Virtual Local Area Network (VLAN) tag-mechanism, which controls the forwarding operation to the proper DAC and InP EML for optical modulation using Intensity Modulation/Direct Detection (IM/DD) schemes, while the wavelength routing operation is handled by the low-loss four-port Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ROADM featuring only 2.5 dB fiber-to-fiber losses based on a cascaded MZI-interleaver design on the TriPleX platform, routing the real-time traffic to a second mmWave antenna site. Detailed measurements and traffic statistics indicate end-to-end latency of less than 260 μs and a packet loss less than 0.0054% across a dynamic range of at least 6.5 dB in the optical domain, while the high user bandwidth and signal quality are validated by an uninterrupted 4K-UHD video transmission across the FiWi X-haul mmWave transport network. The current work aims to shape a complete technology roadmap for Point-to-Multipoint FiWi transport network architectures with high spectral efficiency X-haul transport for dense areas and 5G/6G hotspots of future mmWave Centralized Radio Access Networks (C-RANs).

End-to-End Interoperable 400-GbE Optical Communications Through 2-km 400GBASE-FR4, 8 × 100-km 400G-OpenROADM and 125-km 400-ZR Fiber Lines

During many years, the WDM domain was dominated by vendors/system suppliers that logically proposed their proprietary solutions and technologies. This proprietary environment offered the space to innovate and allowed an unbelievable progress of optical transport networks that were able to cope with traffic increase for 25 years. Thereby, coherent technology enabled an incredible growth of data rate carried by wavelengths from 10G in the middle of 2000’s decade up to 400G today and soon 800G. However, for data center interconnect (DCI) and metro/regional applications, the lack of openness and interoperability of WDM systems appeared as a real weakness for service providers for both the control (i.e., management) and data (i.e., transceiver) plane. While in the Ethernet area (managed by IEEE) interworking and openness is a reality since a long time, it was not still the case in the WDM domain few years ago. Fortunately, Multi-Source Agreement (MSA) organizations like the Optical Internetworking Forum (OIF), OpenROADM, OpenZR+ and others but also standardization bodies like ITU-T started to break the vendors’ lock-in and fostered the emergence of interoperable WDM transceivers at 100G, 200G, 400G and soon at 800G. In parallel, the great progress of microelectronics and photonic integration also paved the way of a miniaturization of WDM interfaces allowing to have ever more powerful digital signal processing (DSP) engines at higher data rates with drastic power consumption reduction authorizing new fundamental applications like IP over WDM. In this paper, we present for the first time an end-to-end interoperable 400-GbEthernet (GbE) optical transmission on 927-km that integrates the most advanced 400G interoperable pluggable optics covering the needs of Ethernet client (IEEE 802.3 400GBASE), data-center interconnect (OIF 400-ZR), and metro/regional (400G-OpenROADM) networks. The generated 400-GbE data flows seamlessly cross three interoperable sections, i.e., 2-km 400GBASE-FR4, 8 × 100-km 400G-OpenROADM and 125-km 400-ZR standard single-mode fiber lines. The 400G optics used here come from various vendors and embed interoperable DSP chips provided by various suppliers, ensuring the full interoperability of the experimental set-up presented here. The sensitivity to a reconfigurable optical add-drop multiplexer (ROADM) cascade insertion in the OpenROADM section is also investigated.

(INVITED)Reconfigurable topology testbeds: A new approach to optical system experiments

Optical transmission systems provide high capacity, low latency and jitter, and high reliability for city-scale networks. Recirculating loop experiments have facilitated the study of signal propagation in long-haul optical transmission systems. However, they are unsuited for developing control and management software for city-scale optical networks with dozens or hundreds of reconfigurable optical add drop multiplexer (ROADM) units, diverse interconnection topologies, and dynamic traffic patterns. Large-scale testbeds can help, but may be inflexible and time- or cost-prohibitive. Reconfigurable testbeds such as COSMOS enable piece-wise emulation of a city-scale network by applying space and wavelength switching, dual-use software-defined networking (SDN) controllers, and comb sources, while digital twin models enable software emulation. Results from the development of a digital twin for COSMOS are presented for optical amplifiers and stimulated Raman scattering (SRS) including both analytical and machine learning (ML) models.

Scaling Optical Interconnects for Hyperscale Data Center Networks

Due to widespread applications and rapid development of cloud computing and Internet services, hyperscale data centers have experienced an unprecedented demand for networking. Data center networks are required not only to handle fast-growing traffic, which doubles almost every one to two years, but also to provide high flexibility and availability to support rapidly changing businesses as well. Therefore, hyperscale data center networks have become one of the main drivers for optical interconnect technologies in recent years. In this article, technologies for scaling optical interconnects for inter-data center interconnects (DCIs) are presented. We first describe hyperscale data center network architectures and requirements, as well as the differences between carrier’s optical transport networks and DCI optical networks, with the main focus on metro-DCI and campus-DCI networks. The scale and fast growth rates of DCI networks require innovations not only in data plane technologies but also in control and management planes as well. In data planes, high-capacity flexible coherent technology, pluggable wavelength-division-multiplexing (WDM) optical transponders, including 100G direct-detection four-level pulse-amplitude modulation (PAM4) and coherent 400ZR/800ZR, and flex-grid and disaggregated reconfigurable optical add-drop multiplexer (ROADM) optical networks are described. Control and management planes are an integral part of optical transport networks and crucial for effectively operating DCI networks. We show that standard protocols, data models, and modular design of a software platform are essential to building a scalable open and disaggregated optical network, which is fundamental to enabling high automation and intelligence in an optical network. An example control and management platform is discussed in detail. With current fiber capacity approaching the nonlinear Shannon limit, challenges to further scale DCI networks and some potential technologies to support ever-increasing traffic growth are discussed at the end.

Packet switching in quantum networks: A path to the quantum Internet

Large-scale quantum networks with thousands of nodes require scalable network protocols and physical hardware to realize. In this paper, we introduce packet switching as a paradigm for quantum data transmission in both future and near-term quantum networks. We propose a classical-quantum data frame structure and explore methods of frame generation and processing. Further, we present conceptual designs for a quantum reconfigurable optical add-drop multiplexer to realize the proposed transmission scheme. Packet switching allows for a universal design for a next-generation Internet where classical and quantum data share the same network protocols and infrastructure. In this quantum networking paradigm, entanglement distribution, as with quantum key distribution, is an application built on top of the quantum network rather than as a network designed especially for those purposes. For analysis of the network model, we simulate the feasibility of quantum packet switching for some preliminary models of quantum key and entanglement distribution. Finally, we discuss how our model can be integrated with other network models toward a realization of the quantum Internet.

96-Channel on-chip reconfigurable optical add-drop multiplexer for multidimensional multiplexing systems

Abstract The multi-dimensional multiplexing technology is very promising for further increasing the link capacity of optical interconnects. A 96-channel silicon-based on-chip reconfigurable optical add-drop multiplexer (ROADM) is proposed and demonstrated for the first time to satisfy the demands in hybrid mode/polarization/wavelengthdivision-multiplexing systems. The present ROADM consists of a six-channel mode/polarization de-multiplexer, a 6 × 16 array of microring-resonator (MRR)-based wavelength-selective switches, and a six-channel mode/polarization multiplexer. With such a ROADM, one can add/drop optical signals to/from any channels of the multimode bus waveguide arbitrarily. For the designed and fabricated ROADM chip, there are more than 1000 elements integrated monolithically, including 96 MRRs, 576 waveguide crossings, 192 grating couplers, 96 micro-heaters, 112 pads, six polarization-splitter-rotators (PSRs), four asymmetric adiabatic couplers and four asymmetric directional couplers. For any channel added/dropped with the fabricated ROADM, the on-chip excess loss is about 5–20 dB, the inter-mode crosstalk is &lt;−12 dB, and the inter-wavelength crosstalk is &lt;−24 dB. The system experiments are demonstrated by using 10-GBaud quadrature phase shift keying (QPSK) signals, showing that the observed optical signal noise ratio (OSNR) power penalties induced by the ROADM are less than 2 dB at a BER of 3.8 × 10−3.

Reconfigurable Fiber Wireless Fronthaul With A-RoF and D-RoF Co-Existence Through a Si3N4 ROADM for Heterogeneous Mmwave 5G C-RANs

Towards enabling bandwidth-hungry 5G applications, a Fiber-Wireless (FiWi) mobile fronthaul architecture is experimentally presented supporting the co-existence of spectrally efficient analog transport formats with Digital Radio over Fiber transport schemes, combined with millimeter wave (mmWave) high-capacity wireless channels. Flexible transport network reconfiguration is proposed by means of a low-loss 1 × 4 Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Reconfigurable Optical Add/Drop Multiplexer (ROADM) on TriPleX platform, selectively dropping four FiWi mmWave fronthaul links to four different antenna location. Detailed investigations of the proposed system are reported, including frequency characterization, multi-stage EVM penalty study and analog/digital traffic coexistence PHY layer feasibility. Following, four 10 Gb/s multi-band 16-QAM WDM FiWi analog IFoF links are transmitted through 10km fiber and 1-m directional V-band antennas and flexibly reconfigured by a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ROADM, achieving a record 40 Gb/s wavelength-routed fronthaul capacity for mmWave 5G, while simultaneously meeting multiple 5G Use Cases within 3GPP requirements.