The Rise of Linear Drive Optics: A Promising Solution for Power-Efficient Optical Interconnects

Introduction

Linear Drive Optics (LPO), also known as non-retimed pluggable optics, has emerged as a hot topic in the optical networking industry. This technology promises to deliver significant power savings and improved thermal management for high-speed transceivers, making it an attractive solution for data centers and other applications demanding energy efficiency.

The Growing Need for Power-Efficient Optical Interconnects

As data centers continue to expand and demand for high-speed connectivity increases, the power consumption of transceivers has become a critical concern. Traditional retimed transceivers, which incorporate digital signal processing (DSP) chips, contribute substantially to overall power consumption and heat generation. This, in turn, necessitates robust cooling systems, further increasing energy demands and operational costs.

What are Linear Drive Optics?

Linear Drive Optics (LPO) is a novel approach that eliminates the need for DSP chips in transceivers. Instead of processing and retiming the electrical signals, LPO transceivers directly drive the optical components, such as lasers or modulators, with the incoming electrical signals. This simplified architecture results in lower power consumption and reduced heat generation, making LPO a promising solution for power-efficient optical interconnects.

Benefits of Linear Drive Optics

1. Power Savings:

• LPO transceivers can achieve power savings of 20% to 40% compared to traditional retimed transceivers, according to various vendor presentations.

• By eliminating DSP chips, LPO reduces the overall power consumption of transceivers.

• Lower power consumption translates into reduced cooling requirements, further contributing to energy savings.
  

2. Improved Thermal Management:

• The reduced heat generation of LPO transceivers can significantly impact the thermal management of networking equipment.

• As demonstrated by Arista Networks, a switch equipped with 64 LPO modules ran 14°C cooler than a switch with 64 standard 800G transceivers.

3. Potential Cost Savings:

• By simplifying the transceiver design and reducing the number of components, LPO could potentially offer cost savings in manufacturing and assembly.
  

Progress and Interoperability

The industry has made significant strides in the development and adoption of LPO technology. At the CIOE 2023 trade show, an interoperability demonstration showcased LPO modules from various vendors, including Cloudlight, Eoptolink, and Hisense, successfully operating with Broadcom's VCSELs and Macom's IC chips.

Standardization Efforts

Recognizing the potential of LPO, the Optical Internetworking Forum (OIF) has initiated two projects related to this technology:

1. Power Efficient Optical Interconnects – This project explores LPO as one of the solutions for improving power efficiency in optical interconnects.

2. CEI-112-Linear Test Point Methodology – Considered a critical step for bringing LPO to market, this project focuses on developing a standardized test methodology for LPO transceivers.

Challenges and Considerations

While LPO offers promising benefits, it also presents several challenges and considerations:

1. Performance Variations:

• The performance of LPO transceivers can vary depending on the optical components used, such as VCSELs, EMLs, or silicon photonics, as highlighted by HiSilicon's research.

• Switch ASICs may require additional functionality to compensate for these performance variations.

2. Design Complexities:

• As pointed out by Marvell, designing LPO transceivers requires higher bandwidth electronic and optical components, as well as increased voltage swing compared to retimed transceivers.

• Simply removing the DSP chip from a retimed transceiver is not sufficient to create an LPO module.

3. Coexistence with Retimed Transceivers:

• While LPO offers advantages in specific use cases, retimed transceivers are expected to continue dominating the market.

• Both technologies are likely to coexist, with LPO finding adoption in applications where power efficiency is a critical requirement.
  

Industry Adoption and Roadmap

Major players in the industry are actively evaluating and adopting LPO technology. NVIDIA has announced plans to deploy LPO in their internal AI clusters by the end of 2023, while several cloud companies are also evaluating this solution. As the technology matures and standardization efforts progress, broader adoption across the industry is anticipated.

LightCounting, a leading market research firm, expects to publish an updated forecast for LPO in December 2023, titled "AOCs, DACs and Linear Drive Optics," providing insights into the projected market growth and adoption trends.

Conclusion

Linear Drive Optics (LPO) represents a promising solution for power-efficient optical interconnects, offering significant power savings and improved thermal management. While challenges and design complexities exist, the industry is actively addressing these through standardization efforts and technological advancements. As data centers and high-speed connectivity demands continue to grow, LPO could play a pivotal role in enabling more energy-efficient and sustainable optical networking solutions.

Reference

[1] LightCounting Market Research (2023, September 20). “Progress in Linear Drive Pluggable Optics”. https://lightcounting.com/