The application of coherent light Technology in data centers

With the continuous expansion of data center scale and the explosive growth of data traffic, traditional optical communication technologies are gradually unable to meet the modern data center's demands for high-speed, long-distance and highly reliable transmission. Coherent light technology, with its outstanding performance and flexibility, is becoming an important solution for data center interconnection (DCI) and internal connectivity.

The application of coherent light Technology in data centers

Introduction to Coherent Light Technology

Coherent optical communication technology originated in the 1980s. Compared with the traditional intensity modulation - Direct Detection (IM-DD) system, coherent optical communication has the advantages of high sensitivity, long relay distance, large communication capacity and flexible modulation mode. The core of coherent light technology lies in modulation and demodulation by utilizing the phase and amplitude of light, and achieving high signal-to-noise ratio and high data rate transmission through coherent detection technology.

The key characteristics of coherent light technology

Advanced Modulation Format

Coherent optical transmission relies on advanced modulation formats to further enhance spectral efficiency and data rate. Orthogonal Amplitude Modulation (QAM) is a common modulation method that can encode multiple data bits of each symbol. By adopting high-order QAM schemes (such as 16-QAM or 64-QAM), coherent optical systems can achieve higher data rates within the same bandwidth.

Digital Signal Processing (DSP

Digital signal processing algorithms are an important component of coherent optical transmission systems. At the receiver end, DSP algorithms are used to reduce damage and optimize signal quality, such as compensating for optical distortions like dispersion and polarization mode dispersion. By applying complex DSP technology, coherent optical systems can maintain a high signal-to-noise ratio and achieve reliable data transmission over long distances.

Optimize the signal-to-noise ratio

Coherent optical modules mainly optimize the signal-to-noise ratio and solve the problem of limited bandwidth development rate when data center optical modules are accelerated from 100G to 200G and 400G. Compared with PAM4 modulation, coherent technology, although more expensive, performs better in optimizing the signal-to-noise ratio, especially suitable for long-distance transmission.

The application scenarios of coherent light technology in data centers

Data Center Interconnection (DCI

Data center interconnection is one of the main application scenarios of coherent optical technology. As the scale of data centers expands, the distances between them are also getting farther and farther, usually ranging from tens of kilometers to hundreds of kilometers. Coherent light technology can provide high-speed, long-distance and large-capacity data transmission, meeting the demand for large-scale data exchange between data centers.

Metropolitan Data Center Interconnection (Metro DCI) : Within a distance of 100 kilometers, currently developing from 400G ZR to 800G ZR, coherent technology is replacing COLORZ and PAM-4 implementation solutions in this field.

Ultra-long-distance interconnection: Coherent optical technology performs well in long-distance transmission and can support backbone network transmission over 1,000 kilometers.

Internal connection of the data center

Coherent light technology is gradually entering the interior of data centers for rack-to-rack or rack-to-optical cross-connections. The high signal-to-noise ratio and fault tolerance of coherent technology give it an advantage in high-density and low-power consumption scenarios.

Park application: The distance is between 2 kilometers and 20 kilometers. The coherent technology will be applied starting from 1.6T.

Rack-level interconnection: Coherent light technology can be used for high-density connections within data centers, especially in high-performance computing scenarios such as AI clusters.

The advantages of coherent light technology

High-speed connection

Coherent optical transmission technology offers high-speed data transmission rates, meeting the demand for large-scale data exchange between data centers. By adopting high-speed modulation formats and advanced digital signal processing technologies, coherent optical transmission systems can achieve data transmission rates of hundreds of gigabits per second or even higher.

Long-distance transmission

Coherent optical transmission technology has excellent long-distance transmission performance and can achieve high-speed data transmission over distances ranging from tens to hundreds of kilometers, meeting the demand for long-distance interconnection between data centers.

Large-capacity transmission

With the continuous expansion of data center scale and the growth of data volume, the demand for network bandwidth and capacity is also increasing. Coherent optical transmission technology utilizes the high bandwidth characteristics of optical fibers to achieve large-capacity data transmission, supporting large-scale data exchange and sharing among data centers.

Flexibility and reliability

Coherent optical transmission systems have high flexibility and reliability, and can adapt to different network environments and application scenarios. By adopting digital signal processing technology, the transmission parameters can be dynamically adjusted to adapt to various network conditions, and it has a strong anti-interference ability, ensuring the stability and reliability of data transmission.

The market development and challenges of coherent light technology

Market development

The coherent optical module market has witnessed remarkable development over the past decade and is expected to maintain rapid growth in the coming years. According to Lightcounting's forecast, the market sales of DWDM optical modules adopting coherent technology were 1 billion US dollars in 2020 and are expected to reach 2.5 billion US dollars by 2025, with a compound annual growth rate of 20.1%.

Technical challenges

Although coherent light technology has many advantages, its application in data centers still faces some challenges. The cost and power consumption of coherent optical modules are relatively high, which limits their application in short-distance transmission. In addition, the complexity of coherent light technology also poses higher requirements for the maintenance and management of equipment.

Future development trend

"Sinking of application scenarios"

Coherent optical technology is expanding from backbone networks (>1000 kilometers) to metropolitan area networks (100-1000 kilometers) and even edge access networks (<100 kilometers), and is gradually becoming the mainstream solution for data center interconnection (DCI). In the future, as the speed of optical modules continues to increase, coherent technology is expected to further penetrate into application scenarios with shorter transmission distances.

Miniaturization and integration

The development trend of coherent optical modules is miniaturization and integration to meet the demand for high-density connections within data centers. For instance, 400G coherent optical modules have adopted miniaturized pluggable packages (such as QSFP-DD) and support multiple modulation formats and transmission distances.

Integrate with new technologies

Coherent optical technology will be integrated with new technologies such as optical circuit switches (OCS), wavelength division multiplexing (WDM), and Software Defined Networking (SDN), further enhancing the flexibility and efficiency of data center networks.

Summary

Coherent light technology, with its characteristics of high speed, long distance, large capacity and high reliability, is becoming an important solution for interconnection and internal connection in data centers. Although it still faces some challenges in terms of cost and power consumption, with the continuous advancement of technology and the continuous expansion of application scenarios, the application prospects of coherent light technology in future data centers are broad. It will provide strong support for the future development of data center networks and help data centers cope with the increasing demand for data traffic.