Laser Safety Evaluation for ELSFP and Co-Packaged Optics in Data Centers

As data centers continue to scale for AI, cloud computing and high-performance networking, new optical architectures such as External Laser Small Form Factor Pluggable (ELSFP) and Co-packaged Optics (CPO) architectures are being introduced to support next-generation system designs. ELSFP-based CPO architectures fundamentally restructure how optical signals are generated and delivered within data center equipment, introducing new considerations for laser safety compliance. 

While this article focuses on ELSFP-based CPO architectures as a representative and increasingly standardized example of external laser integration, it is important to recognize that multiple approaches are being explored for CPO system architectures. Current implementations most commonly utilize external laser source approaches, such as ELSFP, in which the laser radiation is provided from a separate pluggable module. In addition to these external laser source implementations, alternative designs are being developed in which the laser is more closely integrated with the optical engine. While these approaches differ in system design, maturity and implementation, the laser safety principles discussed in this article are broadly applicable, particularly the distinction between component-level emission characteristics and system-level accessible radiation. 

As a representative example of an external laser-source implementation, an ELSFP module provides continuous-wave (CW) laser radiation to optical engines located within the host system rather than transmitting modulated optical signals directly to the external network. 

With traditional optical transceivers, the laser, modulation and fiber interface are integrated into a single pluggable module, and the modulated optical signal is directly accessible at the front panel of the equipment. In contrast, ELSFP-based CPO architectures separate these functions. 

In an ELSFP-based CPO architecture, the ELSFP laser source transmits laser radiation into the host system through a blind-mate optical interface. This optical power is routed internally, typically via fiber, to optical engines located near the switch’s application-specific integrated circuit (ASIC). These optical engines modulate the radiation, and the resulting data-bearing optical signals are then routed to front-panel connectors, where they are emitted externally to the network. The external emissions at this point are very similar to those emitted by traditional optical transceivers. 

ELSFP-based CPO architectures offer several advantages over traditional optical transceivers. For example, because the laser source is implemented as a pluggable element separate from the optical engines, it can be more easily replaced in the event of a failure without impacting other system components. In addition, separating the laser from the switch ASIC and optical engines provides greater flexibility in system design, including the ability to optimize thermal management by placing the laser source in a more favorable environment. 

While laser safety evaluations may be optional for components based on existing laser product safety standards (as is the case with traditional optical transceivers), ELSFP modules are often evaluated to IEC 60825-1 and FDA 21 CFR 1040 as laser-containing components. Component-level evaluations are often needed to determine the laser power levels and the classification of radiation emitted by the component. During these assessments, the module is powered and operated on the laboratory bench in a manner consistent with its operation within the final host system, and the emitted laser radiation is measured and classified per IEC 60825-1 and FDA 21 CFR 1040. Because this evaluation is performed without the protective features of the host enclosure, fiber cables or system-level controls, the resulting classification at the component level may be as high as Class 3B or Class 4, depending on the optical output power and other parameters. 

This classification reflects the emission characteristics of the ELSFP component itself. In the intended final application within the host system, however, this radiation is generally not expected to be accessible to the user. The ELSFP output is coupled into the host through blind-mate optical interfaces and routed internally. Enclosure design, fiber cables and system integration all work to prevent user exposure to the laser source during normal operation.

When the ELSFP is installed, the host system (such as a switch, server or other data center equipment) must be evaluated as the complete laser product. The system design is critical for laser safety because it provides the means of preventing access to internal laser radiation while also routing the modulated optical signal to user-accessible interfaces. Without this system-level assessment, the host system’s ability to safely mitigate potential higher-level radiation into a Class 1 scenario would remain unverified. (Class 1 laser products are considered safe during use, per IEC 60825-1:2014 Annex C.) 

An evaluation to IEC 60825-1 includes the measurement of accessible laser emission at external-facing locations such as the front panel connectors, as well as internally at locations that may become accessible during maintenance or service (e.g., when disconnecting a fiber cable). These measurements consider both normal operation and reasonably foreseeable single-fault conditions that may occur. 

An evaluation to IEC 60825-2 is also needed at the system level (which may include multiple pieces of data center equipment connected via fiber optic cables) to address the unique scenario of a closed-loop optical fiber communication system (OFCS). This evaluation determines the hazard levels throughout the system, quantifying the laser radiation that can become accessible during optical fiber disconnects or breaks. Where systems incorporate automatic power reduction (APR), this functionality is also evaluated to determine whether it effectively reduces or terminates laser emissions when required, based on the standard and installation location. 

The combination of IEC 60825-1 and IEC 60825-2 evaluations determines the requirements for construction, labeling and user/installation information to help mitigate potential laser hazards. 

For laser systems deployed in the United States, compliance with FDA 21 CFR 1040 (with or without the use of FDA Laser Notice 56) is required, which shares a similar intent, and some overlap, with IEC 60825-1. For Europe, EN 60825-1+A11 is applicable. This standard aligns closely with IEC 60825-1 but can vary depending on product specifics.

ELSFP-based CPO architectures are typically designed so that, under normal operating conditions, hazardous radiation is contained within the system, allowing equipment deployed in data centers to achieve a Class 1 classification. This design supports operational safety during routine use. 

However, data centers are environments where fiber connections may be installed, removed, maintained or serviced. During these activities, such as fiber disconnects, damage or misalignment, higher levels of radiation may become accessible if not properly controlled. For this reason, evaluating realistic use conditions and fault scenarios for both compliance and operational safety is essential.

UL Solutions offers comprehensive laser safety evaluation services for both component-level and system-level applications, including ELSFP components, ELSFP-based CPO host systems and other laser-source architectures used in data center optical systems. At the component level, we can perform controlled testing to classify laser emissions under representative operating conditions. At the system level, we evaluate accessible emissions, fiber-related hazards and fault conditions. All of this is performed in accordance with the established laser product safety standards, such as IEC 60825-1, IEC 60825-2, EN 60825-1+A11 and FDA 21 CFR 1040. 

By addressing both the emission characteristics of external laser sources such as ELSFP and the protective features of the final system, we help customers demonstrate compliance with applicable global laser safety requirements while supporting the performance and scalability demands of modern data centers.