OEM Coherent Optical Module DML

DML-based coherent optical modules are high-performance, cost-effective solutions for 100G–400G data center interconnects, offering compact form factors, low power consumption, and flexible deployment options.

Overview of DML-Based Coherent Modules

Directly Modulated Lasers (DMLs) are semiconductor lasers where the optical output is modulated directly by the driving current, eliminating the need for external modulators. In coherent optical modules, DMLs are used to generate high-speed optical signals with formats such as PAM4 for short- to medium-reach applications. Lumentum, for example, offers 100G PAM4 DMLs capable of 2 km reach, suitable for 400G+ applications in data center interconnects (DCI) and metro networks, providing a smaller footprint and lower power consumption compared to traditional external modulator solutions .

Key Features

• High Data Rates: DML-based coherent modules support bit rates from 100G to 400G, enabling next-generation DCI and metro/regional networks .
• Compact Form Factor: Modules are available in CFP2-DCO and other pluggable formats, facilitating easy integration into existing network equipment .
• Cost and Power Efficiency: DMLs reduce the number of components and power requirements, making them suitable for large-scale deployment in data centers .
• Wavelength Control: DMLs often use distributed feedback (DFB) diode lasers with Bragg reflectors to lock the wavelength accurately, ensuring stable coherent transmission .
• Flexibility and Interoperability: Many modules support industry standards like OpenROADM, OpenZR+, and OIF 400G ZR, while also offering proprietary modes for optimized performance .

Applications

• Data Center Interconnects (DCI): DML-based coherent modules are ideal for short- to medium-reach links (up to 2 km for 100G FR and 400G FR4 CWDM applications), providing high-speed connectivity between data centers .
• Metro and Regional Networks: These modules can be deployed in metro/regional coherent networks, supporting flexible modulation formats and encryption features for secure transmission .
• Cost-Sensitive Deployments: OEMs and network operators benefit from the lower cost and simplified design of DML-based modules, which reduce operational complexity and maintenance requirements .

Comparison with EML-Based Coherent Modules

While DMLs are suitable for short- to medium-reach applications, Electro-absorption Modulated Lasers (EMLs), including differential EMLs (D-EMLs), are preferred for longer-reach coherent links due to higher output amplitude and better signal integrity. Coherent Corp. has demonstrated 400G D-EML modules for high-speed data center applications, offering superior optical modulation amplitude (OMA) and extinction ratio (ER) performance with integrated on-chip termination networks .

Summary

OEM coherent optical modules using DMLs provide a highly efficient, compact, and cost-effective solution for modern high-speed optical networks. They are particularly suited for data center interconnects and metro networks, supporting 100G–400G transmission with PAM4 modulation, flexible pluggable form factors, and industry-standard interoperability. For longer-reach or ultra-high-performance applications, EML-based coherent modules may be preferred, but DMLs remain a key technology for scalable, low-power, and economical optical networking deployments.