400G ZR vs. Open ROADM vs. ZR+

As AI, video streaming, and cloud computing drive explosive traffic growth, global networks must scale efficiently—without compromising performance or cost. Coherent optical transmission has become essential for delivering high-speed, long-distance connectivity across dense fiber infrastructures.

A major milestone was the OIF’s introduction of the 400ZR standard, enabled by advances in photonic and electronic integration. This innovation brought compact 400G coherent modules optimized for data center interconnects (DCI). To meet broader needs such as metro and regional networks, the industry later introduced Open ROADM and OpenZR+ — standards offering extended reach, enhanced flexibility, and multi-vendor interoperability.

This article compares 400ZR, Open ROADM, and OpenZR+, outlining their capabilities and deployment scenarios to help you choose the best fit for your evolving network.

Technical Overview: What Are 400G ZR, ZR+, and Open ROADM?

400G ZR – Short-Range DCI with High Bandwidth

400G ZR is a standardized solution designed to deliver 400 Gbps over a single DWDM wavelength using 16QAM modulation. It’s purpose-built for metro DCI (data center interconnect) scenarios, supporting point-to-point links up to approximately 120 km in compact, low-power form factors such as QSFP-DD and OSFP. This reach limitation is mainly due to fiber chromatic dispersion and the constraints of continuous forward error correction (C-FEC).

By focusing on fixed reach and a single modulation format, 400G ZR simplifies deployment while ensuring power efficiency (~15W), interoperability, and ease of integration—making it ideal for cloud-scale and edge data center environments.

FS QSFPDD-ZR-400G Transceiver

ZR+ – Extended Reach with Flexible Line Rates

Building on 400G ZR, 400G ZR+ extends reach up to about 600 km and supports flexible line rates from 100G to 400G. It uses OpenFEC with QPSK and 16QAM modulation to balance distance and performance. Unlike 400G ZR’s fixed 120 km reach, ZR+ dynamically adapts capacity and reach, offering channel options of 4×100G, 3×100G, 2×100G, and 1×100G.

Key advantages over 400G ZR:

4×100G multiplexing for mixed-speed coexistence:

Since full 400G equipment upgrades are gradual, 400G and 100G interfaces often coexist. ZR+ supports multiplexing 4×100G to enable flexible long-distance links from 400G sources to 100G endpoints, easing network evolution without major hardware changes.

Longer reach and flexible rates:

While 400G ZR targets ~120 km, ZR+ supports up to 600 km using tunable C-band DWDM channels spaced at 75 or 100 GHz, in both amplified and unamplified modes. Advanced modulation and OpenFEC optimize performance on flexible-grid ROADMs with hybrid amplification (EDFA + Raman).

ZR+ also supports OTN and is available in QSFP-DD and OSFP form factors, ideal for metro, regional, and edge networks needing longer reach, flexible speeds, and strong interoperability.

FS QDD-ZRP-400G-HT Transceiver

Open ROADM – An Open, Disaggregated Network Model

Unlike ZR or ZR+, 400 G Open ROADM is more than a 400G pluggable module spec—it is a complete, open transport architecture purpose-built for multi-vendor interoperability. Born from carrier requirements, it disaggregates the network into three independently controllable functions—pluggable optics, transponder, and ROADM —all managed through open, standards-based APIs that an SDN controller can reach via NETCONF/YANG.

To meet surging traffic demands, Open ROADM simultaneously supports both Ethernet and OTN services across metro and long-haul distances. It offers high performance through a choice of uplink modulations—100G and 200G QPSK, plus 300G 8QAM—while leveraging the stronger Open FEC (oFEC) algorithm, defined for links up to 500 km, to deliver error-free transmission over multi-hop ROADM networks. Its emphasis on functional disaggregation and centralized orchestration makes it the architecture of choice for scalable, agile optical transport.

FS DWDM-400CFP2-DCO Transceiver

Technical Differences: 400ZR vs. ZR+ vs. Open ROADM

To better understand how 400G ZR, ZR+, and Open ROADM differ in practice, we’ve outlined their key technical attributes side by side. This comparison highlights critical factors such as interface type, power consumption, reach, and modulation — helping network architects and planners make informed decisions based on specific deployment needs.

Parameter	400G ZR	ZR+	Open ROADM
Host Interface	Ethernet only	Ethernet + OTN	Ethernet + OTN
Power Consumption	≤15W	≤20W	≤25W
Maximum Reach	≤120 km (Amplified) ≤80 km (Unamplified)	≤600+ km (some high-end models support longer distances)	≤500 km
Form Factor	QSFP-DD	QSFP-DD / OSFP	CFP2-DCO
Modulation Format	16QAM	QPSK / 16QAM	Tunable (QPSK/16QAM, etc.)
Network Architecture	Closed / Point-to-Point	Open / Flexible Mesh	SDN / Disaggregated
Typical Use Case	Data Center Interconnect (DCI)	Network Operators	DCI and Long-Haul Transmission
Power/Characteristics	Low power consumption, cost-effective	Dynamic optical path setup	Flexible, supports diverse requirements
FS Module Example	QSFPDD-ZR-400G	QDD-ZRP-400G	DWDM-400CFP2-DCO

Application Scenarios: Choosing the Right Coherent Module

When selecting a coherent pluggable solution, understanding your network environment and operational needs is essential. Below is a breakdown of how 400G ZR, ZR+, and Open ROADM fit various use cases and user profiles:

400G ZR

Optimized for short-distance data center interconnects (DCI) up to 120 km.

Favored by cloud providers and hyperscale data centers for its compact size, low power consumption, and Ethernet-only interface.

Ideal for high-density switch port deployments and simplified network architectures.

ZR+

Designed for regional and metro networks requiring extended reach beyond 120 km, often up to 600+ km.

Supports flexible modulation formats and both Ethernet and OTN interfaces.

Suitable for edge data centers, regional aggregation points, and operators evolving toward open and programmable networks.

Open ROADM

Targeted at large telecom operators and service providers needing multi-vendor interoperability.

Enables software-defined networking (SDN) control and functional disaggregation.

Fits complex metro and backbone network topologies with centralized management of ROADMs, transponders, and controllers.

Quick Selection Guide

Choose 400G ZR if

your network needs a cost-effective, low-power solution for short-range DCI within metro areas.

Choose ZR+ if

you require longer reach with flexible modulation and support for both Ethernet and OTN traffic.

Choose Open ROADM if

you manage large-scale, multi-vendor networks requiring SDN control and full network disaggregation.

A Look into the Future

As digital transformation accelerates across industries, the demand for scalable, flexible, and high-performance optical networking solutions continues to grow. Real-world deployments of 400G networks are expanding rapidly, with 400G ZR, ZR+, and Open ROADM coherent pluggable solutions playing a central role in meeting diverse network needs.

At FS, we are dedicated to supporting this evolution by offering a comprehensive portfolio of high-quality coherent modules tailored to various applications—whether you require the simplicity and efficiency of 400G ZR, the extended reach and flexibility of ZR+, or the openness and scalability of Open ROADM architectures.

No matter which solution you choose, FS delivers industry-leading performance and reliability, empowering your network to scale confidently and reach new heights.