Optical Fiber Interconnection Solutions for Co-packaged Optics (CPO)

The co-packaged optics (CPO) market is experiencing rapid growth, driven by the increasing demand for high-speed data transmission and the exponential expansion of data centers and cloud services. According to data from LightCounting, the demand for network speeds driven by artificial intelligence is more than ten times higher than current levels. LightCounting expects that shipments of CPO technology will begin with 800G and 1.6T ports, with commercialization starting between 2024 and 2025 and large-scale deployment occurring between 2026 and 2027. This technology will be primarily applied in short-distance data communication scenarios for hyperscale cloud service providers.

CPO Development Roadmap

Co-Packaged Optics (CPO) is a photoelectric co-packaging technology that packages the optical engine and the switching chip together, achieving high integration, reducing costs and power consumption. The optical engine (OE) refers to the part of the optical transceiver module that is responsible for processing optical signals. CPO assembles the optical engine and the switching chip on the same socket to form a co-packaging of the chip and the module. The closer the optical engine is to the switching chip, the shorter the optical signal distance is, which leads to lower SerDes power consumption.

NVIDIA's latest product roadmap highlights plan to launch a CPO version of the Quantum 3400 X800 InfiniBand switch in Q3 2025, followed by the Spectrum4 Ultra X800 Ethernet switch in 2026. The InfiniBand switch will feature 144 MPO optical interfaces, supporting 36 3.2T CPO modules, with four 28.8T switching chips inside, providing a total switching capacity of 115.2T.

The architecture of these switches leverages a multi-plane design, enabling efficient distribution of optical signals. After entering through MPO optical ports, fibers are split by a shuffle box into four separate paths, each connecting to a different switch chip. This approach effectively segments the signal source into smaller units, which are then aggregated at the CX8 network card. The multi-plane setup allows independent planes to operate concurrently, optimizing throughput and reducing signal congestion. The shuffle box plays a pivotal role in this architecture, performing critical signal routing and processing functions.

Shuffle Box - Between front panel and Optical Engines (OE)

High-speed CPO switches are projected to require thousands of internal fiber connections. Managing the routing of these fibers within the switch's compact structure poses multiple challenges, including maintaining uniform fiber lengths despite varying distances between optical engines and the front panel, as well as preventing excessive bending that could lead to signal degradation. To overcome these obstacles, advanced solutions such as flexible optical backplane shuffle technology are employed. When paired with high-density connectors and adapters, this approach effectively minimizes length variations and ensures robust, high-performance signal transmission.

Fiber flexible circuit products enable higher-density optical routing solutions. Conventional 1U optical patch panels typically support up to 24 fiber connections for splicing and distribution. In a 40U cabinet (with a height of 2 meters), this results in a total fiber capacity of just 960 fibers. By integrating optical fiber flex circuits with high-density MT connectors, a 1U optical panel can accommodate up to 600 fibers (12*50). When scaled to a 40U cabinet, the total fiber capacity increases dramatically to 24,000 fibers-representing a 20-fold increase in density compared to conventional solutions. This significant improvement in density is a key advantage for high-speed, high-capacity data centers and networking systems.

High-density Optical Fiber Connectors - on Front Panels

The shuffle box utilizes high-density connectors, such as MPO and MMC connectors, to enable high-speed, high-density signal connections and transmissions, meeting the demands for network performance and equipment integration in data center applications. CPO switches require extensive fiber deployment internally, and using high-fiber-count MPO connectors can significantly reduce the number of ports needed on the front panel.
For example, a 51.2T CPO switch may require 1,152 optical fibers, including 1,024 standard single-mode fibers and 128 polarization-maintaining fibers. By utilizing 16-fiber MPO connectors, 64 MPO adapter ports (16 × 64 = 1,024) are needed, streamlining deployment and improving integration efficiency.

But if LC connectors are used instead of MPO connectors, 1,024 fibers would require 512 connectors (512 × 2 = 1,024), which would result in 512 adapter ports on the CPO front panel. A standard 1U chassis would be unable to accommodate such a large number of ports. This comparison highlights the critical need for high-density connectors.

PM Fiber Assemblies Between External Laser Source (ELS) and OE

There are two types of laser sources for CPO: Integrated Laser Source (ILS) and External Laser Source (ELS).

Integrated Laser Source (ILS): This refers to integrating the laser source with the Photonic Integrated Circuit (PIC) within the same package, forming a single-package solution.

External Laser Source (ELS): In this configuration, the laser source and PIC are separated into distinct modules. Although this setup occupies more space, its advantages include simpler manufacturing processes, lower costs, and reduced impact of ASIC chip heat dissipation on the laser's stability.

Due to its ease of maintenance and broad accessibility, the External Laser Source (ELS) is currently one of the most widely adopted solutions for CPO light sources. The performance of CPO optical engines is highly sensitive to the polarization state of the incident light from the ELS, requiring the laser polarization state to remain stable during signal transmission. To achieve this, Polarization Maintaining Fiber (PMF) is employed to connect the light source to the switching chip. PMF ensures that light propagates along a single polarization direction within the fiber, ensuring signal stability and transmission reliability.

Photonics Integrated Circuit (PIC) Connections

Optical interconnection between silicon-based optoelectronic chips and external optical fibers is a critical packaging technology that requires low-loss signal transmission and high-precision alignment at the micrometer scale. Due to the high refractive index of silicon-based materials, the waveguide mode field diameter is typically much smaller than that of single-mode optical fibers, leading to high insertion losses during mode conversion.

3D optical waveguides overcome the limitations of traditional planar waveguide technologies by enabling flexible light guidance and coupling in three-dimensional space, meeting the demands of more complex packaging configurations. Fabricated using advanced techniques such as photolithography and laser direct writing, 3D optical waveguides offer precise geometric control and superior optical performance, providing a reliable solution for the efficient interconnection of next-generation silicon-based optoelectronic chips.

With over 20 years of expertise in the field of passive optical device manufacturing, HYC can provide customized optical interconnect solutions for future CPO connectivity:

Fiber Flex Circuit: Supports automated fiber routing design and cabling, capable of meeting high-volume production requirements.
MPO/MTP Assemblies: Utilizing high-precision mold design and advanced injection molding technology, HYC offers high-density, high-reliability fiber connectivity solutions for AI data centers.
Polarization-Maintaining (PM) Assemblies: With mature process technologies and automated production capabilities for key processes, HYC ensures large-scale supply and consistency of PM products.
Optics Design Platform: Equipped with capabilities in space optics design and coupling, sub-micron alignment, precision optical back-end processing, and optical analysis capabilities, HYC provides design-in and joint development support for Photonic Integrated Circuit (PIC) connections.

HYC's optical interconnect solutions not only meet the high-performance requirements of CPO modules but also support the future trends of optical module integration and high-speed interconnect development.

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For more information, https://www.hyc-system.com

This release was published on openPR.