OCP EMEA 2025: FiberMall Demonstrates 800G Pluggable Optical Modules with Immersion Cooling Systems

Traditional pluggable optical modules incorporate digital signal processors (DSPs) that perform full digital equalization for both electrical and optical signals. Because these DSPs are power-intensive, accounting for over 40% of total power consumption, efforts have been made in 800G and higher transceivers to reduce power usage by eliminating the DSP entirely. The Linear Pluggable Optical (LPO) approach achieves significant energy savings by removing the DSP, while the Linear Hybrid Pluggable Optical (LRO) design, which retains only a portion of the DSP functionality, also offers notable power reductions. Such improvements are expected to be critical enablers for AI and machine learning applications.

The elimination of the DSP in LPO modules not only reduces power consumption but also removes the re-timing function. One of the most apparent benefits is the reduction in latency—a feature that is particularly advantageous for artificial intelligence applications. In addition, the lower component count helps to reduce the overall module cost.

Another key benefit is enhanced reliability. DSPs tend to elevate the operating temperature of other components in the module, which can negatively affect both reliability and performance. In contrast, LPO modules, with fewer active circuits, operate at lower temperatures. From an MTBF (Mean Time Between Failures) perspective, the reliability and performance of LPO modules can be as much as three times greater than those of their DSP-equipped counterparts. For example, test data from 64 ports on a switch using the 800G DR8 configuration shows that even when employing linear LPO optical modules, the Bit Error Rate (BER) performance remains excellent.

For the 800G 2*FR4 LPO optical modules, despite the smaller data volume, the modules can achieve transmission distances of up to 2 km while still maintaining very favorable BER performance over short, medium, and long channels.

The use of LPO optical modules contributes to overall system power reduction. For instance, compared with current 800G DSP optical modules, testing of a 51.2T LPO switch demonstrated power savings of 700 W—or 40%—and a 102.4T LPO switch is expected to achieve a similar 40% reduction, equating to approximately 1000 W saved. These power consumption figures have been provided by Silicon Photonics.

FiberMall compared the power consumption of three module types—LPO, LRO, and DSP—for both 800G DR8 and 800G 2*FR4 configurations. The DSP modules consume 17.5 pj/bit and 17.1 pj/bit, respectively. In contrast, the energy consumption of the LPO modules is 9 pj/bit and 9.7 pj/bit, respectively, representing roughly a 50% improvement in energy efficiency. The LRO modules, which represent an intermediate design, consume 11.3 pj/bit and 11.9 pj/bit.

Additional evidence of reduced power consumption was obtained during tests wherein all 64 optical modules within a switch were operated simultaneously. Under identical conditions and at various fan speeds (50%, 75%, and 100%), measurements of temperature and power consumption were taken. A switch equipped with DSP components exhibited an approximate overall power consumption of 2000 W at an operating temperature near 56°C, whereas a switch using LPO components ran at about 1600 W with temperatures around 48°C. Moreover, the average temperature of the LPO modules was approximately 15°C lower than that of the DSP modules, indicating that LPO modules demand less cooling power.

FiberMall also compared different cooling methods. When contrasted with air cooling, two-phase immersion cooling provided a markedly improved Power Usage Effectiveness (PUE), thereby enhancing energy efficiency. As a result, tests were conducted using transceivers designed to be compatible with immersion cooling.

At OFC2025, experiments were performed using Celestica’s DS5000 switch configured with loopback links to establish various network scenarios. In one image, the upper portion of the water tank displays three modules—LPO, LRO, and DSP—from left to right.

A further comparison of immersion cooling effects among the modules reveals that the cooling liquid, which has a boiling point of 50°C, causes the temperature of the DSP module to approach 50°C. This rise results in visible bubbling on the surface of the DSP transceiver. Such observations underscore the high level of design quality in many optical connector products; integrators or customers need only to custom-design fiber optic jumpers for the specific cooling liquid. These jumpers ensure that the liquid does not enter the transceiver while maintaining sufficient spring force. Although the temperature differences between the three modules are minimal, there is a tendency for a higher error rate in the DSP modules. Notably, the demonstration of module-level performance was conducted by the transceiver manufacturer.

In conclusion, linear pluggable optical (LPO) modules that eliminate the DSP from the transceiver offer several advantages over traditional DSP-based modules. These advantages include reduced power consumption at both the module and system levels, lower latency, reduced costs, and enhanced reliability. FiberMall’s demonstration of the 800G pluggable optical module with immersion cooling showcases a significant improvement in energy efficiency. However, thus far there has been limited system-level interoperability, underscoring the need for further research and advancement in immersion-cooled optical modules.