100G 80KM DCI Solutions Comparison: Coherent, PAM4 or QSFP28 ZR4

With the rapid advancements in artificial intelligence, virtual reality, and the Internet of Things, data traffic is experiencing unprecedented growth, leading to the widespread deployment of data centers. Ensuring data center resource sharing, business continuity, and disaster recovery necessitates robust data center interconnect (DCI) solutions. This article will introduce three key solutions for 100G 80km DCI: 100G coherent DWDM technology, 100G PAM4 DWDM transmission, and 100G QSFP28 ZR4 optics, aiming to identify the most effective option for long-haul DCI needs.

Introducing Three 100G 80km DCI Solution Options

100G Coherent

100G coherent DWDM technology enables the transport of 100G capacity over a single wavelength across long distances. Coherent optical devices can transmit signals even over distances of up to 1000km. Coherent optics use advanced modulation techniques, such as QPSK, 8QAM, or 16QAM, to transmit multiple symbols per bit, condensing signals for speed benefits. However, this kind of modulation leads to demanding technical requirements. Coherent detection and DSP technology are needed to compensate for various transmission impairments in the electrical domain and simplify the transmission link. Coherent 100G optics are typically available in CFP and CFP2 form factors, which means they cannot be directly inserted into most data center switch ports. As a result, additional DWDM (Dense Wavelength Division Multiplexing) equipment for networking and technical support is required to manage and simplify transmission links.

FS coherent solutions, featuring the M Series CFP2-DCO coherent transceivers, provide full tunability across the 50GHz ITU-T grid and support flex-grid DWDM tuning. These transceivers, compatible with the M6500 Series OTN platforms, can select among three-phase modulation schemes for varied applications. The M6500 Series supports plug-and-play modules, visual management, and flexible service configuration. It includes an Optical Supervisory Channel (OSC) and an Electrical Supervisory Channel (ESC), offering flexibility and scalability for hybrid networks. It supports 10G/40G/100G OTN/SDH/Ethernet services, enabling 200G over a single wavelength, ideal for high-capacity, low-power data center interconnects.

Figure1. 100G Coherent DWDM Solution for Long-Haul Transmission

100G PAM4 DWDM

PAM4 is the key technology of this solution which transmits two bits in one symbol slot, halving the signal bandwidth. Also, PAM4 can minimize signal degradation and double the data rate. In addition, PAM4 optical modules can be used directly in the switches of embedded DWDM networks, which is a cost-effective and simple solution for customers willing to build embedded DWDM data networks.

FS PAM4 solutions, featuring transceivers with built-in Inphi Chips, offer high-speed performance and low power consumption. These transceivers are optimized for use with the DCP910 Series. The DCP910 Series is a complete, high-reliability Dynamic Connectivity Platform designed for long-distance, high-bandwidth applications. It supports the transmission of up to 40 channels at multiple data rates, maintaining simplicity through automated zero-touch provisioning. This series is highly integrated with a 40-channel DWDM mux/demux, optical amplifiers, dispersion compensation modules, and an optical supervisory channel, providing significant space savings and improved operational and maintenance efficiency.

Figure2. 100G PAM4 DWDM Solution for Long-Haul Transmission

Currently, FS has released the latest DCP920 series products, which embeds a 4x 100G PAM4 module, allowing the seamless use of 100GBase-SR4/LR4/IR4 modules, which ensures switch compatibility while greatly reducing costs. DCP920 series is a true open line DWDM platform designed specifically for modern DCI and long-distance applications. The DCP 920 series allows users to remotely manage them through a web interface. Combined with the OSC function, users can monitor network status in real time, simplifying installation, configuration, and fault diagnosis. It provides 4x channels of 100G services for 0-80km point-to-point transmission over a single fiber, with zero-touch provisioning and no need for a relay station.

100G QSFP28 ZR4

The 100G QSFP28 ZR4 supports 100G Ethernet for extended reach up to 80km transmission that provides point-to-point network connectivity solutions between data centers without the need to deploy either complicated and costly open-line systems or legacy CFP/CFP2 interfaces. The module supports the standard KR4 FEC (Forward Error Correction) baud rates, which will help receive-side detect and correct bit errors and improve the overall quality of the link. Therefore, the 100G ZR4 QSFP28 transceiver can operate on a point-to-point link up to 80km without optical amplification and dispersion compensation.

Figure3. 100G QSFP28 ZR4 Solution for Long-Haul Transmission

Coherent vs PAM4 vs QSFP28 ZR4: Choose the Best One for Your Network

In the realm of optical transmission, comparing 100G Data Center Interconnect (DCI) solutions—Coherent, PAM4, and QSFP28 ZR4—each offers distinct advantages. Coherent technology excels in long-distance applications with its high spectral efficiency and robust error correction capabilities. PAM4 simplifies optical systems, offering higher bandwidth efficiency suitable for 100G services for 0-80km point-to-point transmission, and high-speed connections within data centers. QSFP28 ZR4, a standardized module, supports up to 80km transmission, which is ideal for standardized optical networks requiring medium to long distances. FS provides tailored solutions encompassing all three options, ensuring optimal performance and cost-effectiveness based on specific customer requirements and application scenarios.