1. Solution Overview

As the demand for high-speed, high-bandwidth transmission continues to grow in scenarios such as 5G fronthaul, metropolitan area network (MAN) interconnection, and data center interconnect (DCI), 40G DWDM (Dense Wavelength Division Multiplexing) transmission solutions have become a crucial choice for network operators and enterprise users aiming to aggregate multiple services over limited fiber resources.

C-LIGHT  established in 2011, is a professional supplier of high-end optical transceivers with over 15 years of industry experience. The company specializes in the R&D and production of active optical modules, passive optical components, and data switching equipment. Its independently developed 40G DWDM optical transceiver series supports transmission distances of 10km and 40km, with wavelength options covering 96 channels on 50GHz or 100GHz spacing, addressing diverse network requirements.

This solution utilizes C-LIGHT 40G DWDM QSFP+ optical transceivers in a dual-fiber bidirectional transmission architecture to achieve 40Gbps high-speed data transmission over a distance of 40km between sites. It provides a cost-effective DWDM transmission solution for MAN capacity expansion, data center interconnection, and 5G fronthaul aggregation.

2. Product Specifications

2.1 Brand Overview

C-LIGHT is a high-tech enterprise focused on the R&D and production of optical communication transceiver products. Its portfolio includes a full range of high-speed optical modules such as 800G, 400G, 200G, 100G, 50G, 40G, 25G, and 10G, along with DWDM/CWDM active and passive products, fiber patch cords, connectors, and more. The company employs over 50 professional R&D engineers, serves customers in more than 100 countries and regions across five continents, and maintains a daily production capacity exceeding 8,000 units. C-LIGHT products are widely deployed in AI computing networks, data center networks, telecom FTTx broadband access, DWDM/CWDM wavelength division networks, industrial-grade fiber optic application networks, and 5G/6G mobile networks.

2.2 40G DWDM Optical Transceiver Specifications

The C-LIGHT 40G DWDM QSFP+ optical transceiver utilizes DWDM technology to multiplex four 10G optical signals into a single 40G signal transmitted over a pair of single-mode fibers, enabling 40Gbps interconnectivity between sites over a distance of 40km. The product supports CDR (Clock and Data Recovery) and offers an optional industrial-grade version capable of operating at temperatures up to 85°C for harsh deployment environments. The transceivers are compatible with switches from over 100 brands and come with a 3-year warranty along with original manufacturer technical support.

2.3 Supporting DWDM Multiplexer/Demultiplexer Equipment

To facilitate multi-wavelength multiplexed transmission with the 40G DWDM transceivers, an 8-channel or higher DWDM multiplexer/demultiplexer (MUX/DEMUX) can be deployed. Key parameters are as follows:

The DWDM multiplexer/demultiplexer is a fully passive device requiring no power supply or cooling, supporting deployment in metro, regional, and long-haul DWDM networks. The equipment is fully compatible with ITU-T standard 1G/10G/25G/40G/100G DWDM optical modules.

3. Solution Design

3.1 Transmission Architecture

This solution adopts a Dual-Fiber Bidirectional transmission architecture: two single-mode fibers are used, with one fiber carrying downstream data from Site A to Site B and the other carrying upstream data from Site B to Site A, achieving full-duplex communication.

Each site is equipped with the following devices:

• DWDM Multiplexer/Demultiplexer (MUX/DEMUX): Performs multiplexing and demultiplexing of multiple wavelength signals.

• 40G DWDM QSFP+ Optical Transceivers: Installed in switches/routers to provide 40G interfaces.

• Single-Mode Fiber Patch Cords (LC Connector): Connect transceivers to the MUX/DEMUX equipment.

System Composition Diagram:

3.2 Working Principle

At the transmit end of Site A, the C-LIGHT 40G DWDM QSFP+ optical transceiver outputs a 40G optical signal at a specific wavelength (internally multiplexed from four 10G DWDM wavelengths). This signal is connected via an LC patch cord to a channel port on the DWDM multiplexer. The MUX/DEMUX device combines optical signals from multiple channels (λ1, λ2, ..., λ8) at different wavelengths using wavelength division multiplexing technology onto a single trunk fiber for transmission. At the receive end of Site B, the DWDM demultiplexer separates the composite optical signal by wavelength and directs each to the corresponding 40G DWDM transceiver for reception.

The dual-fiber bidirectional architecture uses separate fibers for transmission and reception, ensuring upstream and downstream signals do not interfere with each other, providing high signal isolation and transmission stability. This architecture is particularly suitable for DWDM multi-wavelength systems, effectively reducing inter-channel crosstalk and maintaining signal quality.

3.3 Wavelength Plan

C-LIGHT 40G DWDM optical transceivers support 96 channels in the C-band with 50GHz or 100GHz spacing, compliant with ITU-T G.694.1 standards. For this solution, a 100GHz spacing wavelength plan is recommended. An example 8-channel configuration using channels C21 through C28 is shown below:

3.4 Link Budget

For a 40km DWDM transmission link, the estimated link budget is as follows:

The link budget for a 40km single-mode fiber link falls within the receive sensitivity range of the C-LIGHT 40G DWDM optical transceiver, ensuring stable transmission. For extended distances (e.g., 60km to 80km), EDFA optical amplifiers and DCM dispersion compensation modules can be added.

3.5 Bill of Materials (Example for an 8-Channel Dual-Fiber DWDM System)

4. Application Scenarios

4.1 Metropolitan Area Network (MAN) Capacity Expansion

As service traffic in MANs continues to grow, existing 10G links may no longer meet bandwidth demands. This solution utilizes DWDM technology over existing fiber infrastructure to multiplex multiple 40G services onto a single fiber pair, multiplying bandwidth without deploying new fiber. It is ideal for high-speed interconnection between metro aggregation and core layers.

4.2 Data Center Interconnect (DCI)

With the rapid development of cloud computing and big data, interconnection between data centers is increasingly critical. The C-LIGHT 40G DWDM solution enables 40Gbps high-speed data synchronization and backup between two data centers located up to 40km apart, supporting intra-city disaster recovery, data migration, and load balancing scenarios. The 40km distance covers the vast majority of DCI requirements within a single city.

4.3 5G Fronthaul Bearer

5G network fronthaul requires high-speed, low-latency fiber transmission. C-LIGHT 40G DWDM optical transceivers are well-suited for 5G fronthaul and access network uplink applications requiring high bandwidth. The solution supports aggregation of traffic from multiple 5G base stations via DWDM wavelengths for uplink to the metro core network, efficiently conserving trunk fiber resources.

4.4 Enterprise and Government Dedicated Line Interconnection

Large organizations in government, finance, and education often require high-speed connectivity between multiple offices or campuses. This solution provides a stable and reliable 40G private transmission channel for campus and office interconnections. Additionally, C-LIGHT transceivers are compatible with mainstream switches from over 100 brands, enabling seamless integration with existing network equipment and reducing deployment costs.

5. Solution Advantages

5.1 High Performance and Reliability

C-LIGHT 40G DWDM optical transceivers support CDR functionality, effectively ensuring signal integrity. Both commercial and industrial operating temperature grades are available to suit various deployment environments. Products undergo a rigorous three-stage quality control process: initial testing, final testing, and factory inspection, guaranteeing high quality.

5.2 Rich Wavelength Resources

Support for 96 channels in the C-band with flexible 50GHz or 100GHz spacing enables high-capacity transmission over a single fiber pair, meeting future expansion needs.

5.3 Broad Compatibility

DWDM transceivers are compatible with mainstream switches from over 100 brands and come with a 3-year warranty and long-term repair support. Installing third-party modules does not affect the warranty service of network equipment.

5.4 Cost-Effectiveness

The passive DWDM multiplexing technology requires no power or maintenance, effectively reducing CAPEX and OPEX. Bandwidth can be multiplied over existing fiber infrastructure, avoiding the high cost of new fiber deployment. C-LIGHT maintains inventory for immediate shipment, with 90% of products ready for delivery within 2 to 3 days.

5.5 Flexibility and Scalability

The solution supports seamless expansion. New 40G or 100G services can be added to unused DWDM channels without disrupting existing links. Transmission distance can be extended beyond 80km by adding EDFA optical amplifiers and DCM dispersion compensation modules. The EXP expansion port allows connection to another DWDM device to increase wavelength count.

6. Service and Support

C-LIGHT provides comprehensive pre-sales and after-sales services, including free technical consultation, solution recommendations, test reports, and professional technical support. With over 15 years of experience in the optical communication industry and a team of more than 50 R&D engineers, C-LIGHT supports customer customization needs, offering full customization services from chip selection to circuit design and firmware development.