Optical Add-drop Multiplexer Research Articles

Multi-span optical power spectrum prediction using cascaded learning with one-shot end-to-end measurement

Scalable methods for optical transmission performance prediction using machine learning (ML) are studied in metro reconfigurable optical add-drop multiplexer (ROADM) networks. A cascaded learning framework is introduced to encompass the use of cascaded component models for end-to-end (E2E) optical path prediction augmented with different combinations of E2E performance data and models. Additional E2E optical path data and models are used to reduce the prediction error accumulation in the cascade. Off-line training (pre-trained prior to deployment) and transfer learning are used for component-level erbium-doped fiber amplifier (EDFA) gain models to ensure scalability. Considering channel power prediction, we show that the data collection process of the pre-trained EDFA model can be reduced to only 5% of the original training set using transfer learning. We evaluate the proposed method under three different topologies with field deployed fibers and achieve a mean absolute error of 0.16 dB with a single (one-shot) E2E measurement on the deployed 6-span system with 12 EDFAs.

Photonic WDM switches architecture for multi-band optical networks

Addressing the capacity, low cost, and low power challenges of 6G distribution networks, this paper proposes and demonstrates a multi-band optical metro-access network architecture employing semiconductor optical amplifier (SOA)-based wavelength division multiplexing (WDM) switches as low-cost and low-power multi-band optical add-drop multiplexers (MB-OADMs) to extend the capacity beyond C-band limits. We implemented and evaluated the performance of an SOA-based MB-OADM prototype in the C- and O-bands including the network reconfigurability, the node scalability, and the capability to support high-capacity transmission. Experimental results show that the MB-OADM-based network maintains high optical signal-to-noise ratio (OSNR) values up to 35.38 dB in the C-band and 33.56 dB in the O-band over 100 km across five nodes with a 20 km linkspan in between (a total of 100 km) without additional optical amplifiers at 25 Gbps. This work also assesses the MB-OADM-based network scalability in terms of nodes and data rate. Results indicated that the architecture supports cascading through nine C-band nodes over 45 km with a 3.6 dB power penalty at 25 Gbps for a bit error rate (BER) of 10−6 and through four O-band nodes with a 3 dB penalty at 25 Gbps for a BER of 10−6, maintaining nearly uniform power levels across channels at a BER under the FEC threshold. It successfully demonstrates PAM-4 at 50 Gbps and 100 Gbps data rate transmission operation crossing four nodes over a 4 km distance, with 2 dB and 2.4 dB power penalty at a BER of 10−3 in the C-band and 1.85 dB and 2.2 dB power penalty at a BER of 10−3 in the O-band, respectively.

Low-Power-Consumption and Broadband 16-Channel Variable Optical Attenuator Array Based on Polymer/Silica Hybrid Waveguide

A variable optical attenuator (VOA) is a crucial component for optical communication, especially for a variable multiplexer (VMUX) and reconfigurable optical add-drop multiplexer (ROADM). With the capacity increasing dramatically, a large-port-count and low-power-consumption VOA array is urgent for an on-chip system. In this paper, we experimentally demonstrate a 16-channel VOA array based on a polymer/silica hybrid waveguide. The proposed array is able to work over C and L bands. The VOA array shows an average attenuation larger than 14.38 dB with a low power consumption of 15.53 mW. The low power consumption makes it possible to integrate silica-based passive devices with a large port count on-chip.

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.

Optical Add-Drop Multiplexers: Enhancing High Transmission Bit Rates in Next-Generation Communication Networks

The development of optical networks in the telecommunications sector is becoming much closer by considering the help of an Optical Add Drop Multiplexer (OADM) based on a novel technology called Wavelength Division Multiplexing (DWDM). The objective of the current study to examine high transmission bit rates for next-generation optical communication networks using the technology of OADM Based on DWDM. Artificial neural networks (ANNs) were developed via MATLAB software to predict three main parameters in this filed such as transmitted signal power (PT), transmitted signal bandwidth (B.Wsig), and transmission bit rate capacity (Bsh) at different fiber cable lengths, such as L=200, 250, and 300 km. The ANNs results showed that, standard error (SE) for predicting PT as a function of the number of transmitted channels (Nch) was 0.115 mW, 0.095 mW and 0.077 mW, for 200, 250 and 300 km, respectively. Additionally, the SE for predicting B.Wsig was 0.067 GHz, 0.051 GHz and 0.040 GHz for 200, 250 and 300 km, respectively. Lastly, the SE for predicting Bsh was 1.665, 1.311 Gbit/sec and 1.076Gbit/sec for 200, 250 and 300 km, respectively. The SE for predicting PT as a function of the Signal Wavelength (λ) was 0.116, 0.096 and 0.079 mW for 200, 250 and 300 km, respectively. Additionally, the SE for predicting B.Wsig was 0.067, 0.052 and 0.052 GHz for 200, 250 and 300 km, respectively. Lastly, the SE for predicting Bsh was 1.688, 1.417 and 1.110 Gbit/sec for 200, 250 and 300 km, respectively. The low SE in ANNs demonstrated the efficiency, motivating further advancements in optimizing network performance for high-bit-rate transmission.

Architecture for low-cost and highly flexible metro-access networks using SOA-based OADM nodes and digital subcarrier multiplexing with power loading.

Metro-access networks exploiting wavelength division multiplexing (WDM) to cope with the ever-growing bandwidth demands are sensitive to cost and need to be fast-configurable to meet the requirements of many new network services. Optical add-drop multiplexers (OADMs) are a key component in enabling fast dynamic wavelength allocation and optimization. In this Letter, we propose and demonstrate, to our knowledge, a novel architecture for high-performance metro-access networks that utilizes semiconductor optical amplifier (SOA)-based OADM nodes, digital subcarrier multiplexing (DSCM), low-cost direct detection receivers, and power loading techniques, which makes the designed metro-access network cost-effective, fast reconfigurable, and flexible for bandwidth allocation on demand. Through a proof-of-concept experiment, we have successfully demonstrated a prototype horseshoe optical network consisting of up to four SOA-based OADM nodes at 40 Gb/s per wavelength channel by leveraging the proposed scheme. The flexible bandwidth allocation and dynamic add and drop operations have also been achieved in an emulated WDM optical network. All results indicate the great scalability and flexibility of the proposed architecture.

Transmission challenges in metropolitan area optical networks

Abstract For implementing wide/metropolitan area network in optical fiber communication system the key technology that can be utilized is wavelength division multiplexing (WDM). We discuss the use of WDM in metropolitan networks along with its special feature of using optical add drop multiplexers and also design issues in implementing these systems. The issue of nonlinear crosstalk induced in metropolitan networks is considered in terms of power penalty. Also, the effect of dispersion induced in optical fibers is considered by using two types of transmission systems. One is considering the non-zero dispersion shifted fiber (NZDSF) in dispersion effected environment and second is, implementing dispersion compensation after normal single mode fiber (SMF + DCF). The effect of nonlinear cross talk which can limit transmission performance is discussed in both cases in context with different parameters like power penalty, frequency difference between signal & crosstalk and transmission distance etc.

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.

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

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

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

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.

Cost-Aware Optimization of Optical Add-Drop Multiplexers Placement in Packet-Optical xHaul Access Networks

This work concentrates on the problem of optimizing the cost of a passive wavelength division multiplexing (WDM) optical network used as a transport network for carrying the xHaul packet traffic between a set of remote radio sites and a central hub in a 5G radio access network (RAN). In this scope, we investigate the flexible use of optical add-drop multiplexers (OADMs) for the aggregation of traffic from a number of remote sites, where the type/capacity of optical devices—OADMs and optical multiplexers (MUXs)—is selected in accordance with the traffic demand. The approach is referred to as Flex-O. To this end, we formulate the xHaul network planning problem consisting in the joint provisioning of transmission paths (TPs) between the remote sites and the hub with optimized selection and placement of OADMs on the paths and proper selection of MUXs at the ends of the TPs. The problem formulation takes into accounts the optical power budget that limits the maximum transmission distance in a function of the amount and type of optical devices installed on the TPs. The network planning problem is modeled and solved as a mixed-integer linear programming (MILP) optimization problem. Several network scenarios are analyzed to evaluate the cost savings from the flexible (optimized) use of OADMs. The scenarios differ in terms of the availability of OADMs and the capacity of the WDM devices applied on the TPs. The numerical experiments performed in three mesh networks of different size show that the cost savings of up to between 35 and 45% can be achieved if the selection of OADMs is optimized comparing to the networks in which either single-type OADMs are used or the OADMs are not applied.

The efficient employment of the space division multiplexing technique with OADMs for more flexibility and scalability in optical systems

Abstract The optical add drop multiplexers (OADMs) to be modeled and analyzed depends up on the simulation variables are demonstrated. Transmitted power per channel variations are studied against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. Received power from each channel variations are demonstrated against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. The bit error rate variations are clarified against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. The optical link map through fiber cable core is clarified. Total pulse broadening variations are illustrated against both fiber length and number of transmitted channels at receiver bandwidth of 40 GHz and temperature of 25 °C. The lighted signal/noise ratio variations are demonstrated against both receiver bandwidth and number of transmitted channels at transmission distance of 200 km and temperature of 25 °C. Channel capacity variations are also demonstrated against both receiver bandwidth and number of transmitted channels at transmission distance of 200 km and temperature of 25 °C.

Dedicated Path Protection With Wavelength Aggregation in 5G Packet-Optical Xhaul Access Networks

Packet-optical xHaul transport networks are a promising solution for assuring low-cost connectivity between a large number of antennas, located at remote sites, and a central site (hub), in which traffic is gathered and baseband processing is performed, in dense 5G radio access networks (RANs). The demand for fiber connections in such networks can be reduced by means of optical add-drop multiplexers (OADMs), which allow to aggregate traffic from a number of remote sites onto a single optical transmission path. An important issue here is the protection of transmission paths since the failure of a single link may result in the loss of connectivity of a number of antennas. In this work, we focus on the problem of planning a survivable 5G packet-optical xHaul access network, in which the remote sites are connected with the hub by means of disjoint primary-backup paths. The network scenario is based on a passive wavelength division multiplexing (WDM) system in which the maximum transmission distance depends on the number of OADMs installed on the transmission path. In the solution proposed, network survivability is achieved using a dedicated path protection with wavelength aggregation (DPPWA) mechanism. The network planning problem is modeled and solved as an integer linear programming (ILP) problem. Numerical results indicate, among others, that cost savings of between 20%–40% can be achieved in lower traffic load scenarios due to the traffic aggregation by means of OADMs, and that the savings increase with the cost of dark fiber lease.

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.