In recognition of the ever-growing demand for information transmission and the rapid expansion of critical global infrastructures such as the internet, data centers, and cloud computing, the optimization and advancement of data communication interconnect technologies have become pivotal issues requiring urgent attention. In this context, we acknowledge the significant evolution of data communication interconnect technologies, which are now on the verge of an even greater technological leap. By analyzing the core advancements of 800G and 1.6T optical transmission systems and envisioning the future technological paths toward 3.2T bandwidth, we will lead the industry into a new era.

Technological Evolution and Core Drivers

From search engines and interactive maps to social networks and public cloud services, nearly all popular internet applications rely on large-scale data center (DC) infrastructures. These data centers typically consist of tens of thousands of computation, storage, and acceleration nodes, interconnected via pure electrical packet switching (EPS) networks or hybrid networks based on EPS and optical circuit switching (OCS). The evolution of optical interconnect technologies within these networks has been driven by the need to balance cost, energy efficiency, bandwidth, and node density.

For example, Google, to meet the ever-growing bandwidth demands of its data center networks, has developed five generations of optical interconnects. From the first generation of 10G SFP+ to the latest 800G OSFP, the bandwidth has increased by 80 times, energy efficiency has risen by 6 times, and linear density has improved by 24 times. Throughout this evolution, the technology path for data centers (<1km) and campus interconnects (<10km) has largely followed a similar trajectory.

The expansion of bandwidth in this process has primarily been achieved through three key technical paths:

1. Increasing Baud Rate: From 10G to 800G, baud rates have risen from 10Gbaud to 50Gbaud, and even 100Gbaud.
2. Optimizing Modulation Formats: From RZ/NRZ to PAM4, increasing spectral efficiency.
3. Increasing Parallel Channels: Using wavelength division multiplexing (WDM) or spatial multiplexing technologies to scale transmission capacity.

On this basis, future advancements are expected to achieve a total bandwidth of 3.2T by increasing the single-channel rate from 200G to 400G (IM-DD) or adopting coherent technologies.

200G/lane IM-DD Technology: Advantages and Challenges

IM-DD (Intensity Modulation – Direct Detection) has become the preferred technology for short-range transmission within data centers due to its low cost and low complexity. Its core advantage lies in combining high baud rates (such as 50Gbaud) with PAM4 modulation to achieve a 200G single-channel rate. However, as the baud rate increases, the system faces certain physical limitations, such as reduced receiver sensitivity, four-wave mixing (FWM), chromatic dispersion (CD), and polarization mode dispersion (PMD).

Solutions to these challenges include:

1. High-order FEC (Forward Error Correction) and equalization techniques, such as KP4 FEC and linear equalization, to compensate for link budget loss.
2. Wavelength management technologies, such as LAN-WDM4 (800GHz spacing) or polarization interleaving (XYYX), to suppress FWM.
3. Component optimization: Using 5nm CMOS DAC/ADC and InP EML/PD with bandwidths exceeding 55GHz.

800G-LR1 Coherent Lite Technology — Breaking Through Campus Network Bottlenecks

For 10km campus networks, IM-DD technology is limited by CD and FWM, making Coherent Lite technology a more optimal solution. Its main advantages include:

1. Bipolar Modulation: QPSK modulation improves the Euclidean distance of the constellation map to the coordinate origin, effectively doubling the link budget.
2. Local Oscillator (LO) Gain: The LO enhances the received signal, reduces the laser power requirements, and allows the use of low-cost DFB lasers.
3. High Dispersion Tolerance: By migrating from the C-band to the O-band, dispersion can be reduced from 200ps/nm to 13ps/nm, simplifying DSP (Digital Signal Processing) design.

However, for Coherent Lite technology to be widely used in Data Center Interconnect (DCI) applications, several practical challenges, such as DSP power optimization, still need to be addressed.

Towards 3.2T: Technological Paths and Key Innovations

Achieving 3.2T bandwidth expansion requires finding a balance between performance, cost, and energy efficiency. Potential technological paths include:

1. Photonics Integration: Using silicon photonics to integrate 16×200G channels while enhancing the efficiency of modulators and wavelength division multiplexing (WDM) performance.
2. 400G/lane IM-DD: Overcoming component bandwidth limitations by using PAM6 modulation to reduce bandwidth requirements, supplemented by advanced FEC and interference suppression technologies (such as multipath interference management).
3. 6T/wavelength Coherent Lite: This technology offers the advantage of relatively low component bandwidth requirements (similar to 200G channel IM-DD) while having high tolerance to optical channel impairments such as chromatic dispersion, polarization mode dispersion, four-wave mixing, and in-band optical interference.

Throughout this process, innovation in photonic integration, high baud rates, and low-power coherent optical technologies will be critical to achieving the goal of expanding bandwidth to 3.2T.

HTF’s Industry Contribution

HTF, as a professional supplier of optical fiber products and WDM system solutions, plays a vital role in the development of transmission technologies within the industry. With a dedicated team of experts possessing over ten years of experience in optical communication product development, optical fiber solutions, device development, and manufacturing, HTF is at the forefront of providing high-performance transmission solutions.

HTF’s mission is not only to provide customized products and services but also to assist its partners in optimizing fiber infrastructure and enhancing transmission performance. Whether through design, product supply, or after-sales support, HTF remains committed to driving continuous innovation and progress in the field of global data communication technologies.