Data centers, the backbone of our digital infrastructure, face increasing pressure to reduce energy consumption. Linear Pluggable Optics (LPO) has emerged as a promising solution to address this challenge, offering a more efficient way to move data within server racks. Unlike its predecessor, Co-Packaged Optics (CPO), which integrates optical components directly into the electrical package, LPO focuses on removing the power-hungry Digital Signal Processor (DSP) from the pluggable optical module itself.
This approach shifts the DSP functionality to the Top-of-Rack (ToR) switch, enabling direct electrical signal transmission to the optical module. This eliminates the need for redundant DSP processing within the module, leading to significant power savings. While LPO may not achieve the same level of energy reduction as CPO, it offers a crucial advantage: improved thermal management. The ability to control the temperature of optical devices within the rack is critical for maintaining signal integrity, and LPO provides better protection against thermal drift compared to CPO.
However, the widespread adoption of LPO hinges on ensuring interoperability between modules from different vendors. Currently, the lack of standardized electrical interfaces poses a significant hurdle. To address this, the Optical Internetworking Forum (OIF) is developing electrical standards aimed at promoting interoperability. These standards will define the electrical parameters required for seamless integration of LPO modules, paving the way for broader deployment.
The increasing demand for faster data transfer within data centers has driven the adoption of fiber optic technology. While fiber has long been used for long-haul communications, its application is expanding to shorter links within data centers. The leaf-and-spine network architecture, prevalent in modern data centers, relies on fiber optic connections between ToR switches and spine switches. LPO further extends the use of fiber by optimizing the interface between the switch and the optical module.
Traditional optical modules, such as Octal Small Form-factor Pluggable (OSFP) modules, incorporate a DSP to clean up and retime the optical signal. This DSP consumes a substantial portion of the module’s power. Linear pluggable optics eliminates this DSP, leveraging the powerful DSP capabilities of the switch ASIC to handle signal processing. This direct drive approach reduces power consumption and simplifies the optical module design.
To further refine LPO technology, the OIF is also developing the Retimed TX Linear RX (RTLR) project. This approach incorporates a retimer in the transmit path of the optical module, improving signal quality and extending transmission distances. While RTLR introduces a slight increase in power consumption, it enhances interoperability and signal reach, making LPO more versatile for various data center applications.
LPO is expected to precede CPO in commercial availability, offering immediate power savings and improved thermal management. Although CPO holds the promise of even greater energy efficiency by eliminating the SerDes link, its development faces ongoing challenges. LPO provides a practical and efficient solution for current data center needs, paving the way for future advancements in optical interconnect technology.
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