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QSFP28 PAM4: A Solution for Extending 100G/400G Signals

November 12, 2021

With the prevalence of cloud services, AI applications and 5G, QSFP28 PAM4 was brought out and developed to satisfy the ever-growing demands for higher data rates and bandwidth. Nowadays, the core network has deployed 100G data rates and is demanding 400G, driving data centers to seek transceiver solutions with higher port densities and lower cost per bit. Due to its large data capacity and lower power consumption, PAM4 QSFP28 DWDM was developed in 2016 to support 80km transmission for 100G/400G metro network. This post is about to discuss what 100G PAM4 QSFP28 is and how it performs as a solution for 100G/400G applications.

What Is PAM4 Signaling Technology?

PAM4, also referred to as Pulse Amplitude Modulation 4-level, is one of the mainstream optical transmission technologies following non-return-to-zero (NRZ). PAM4 is a technology encoding two bits of data with four distinct signal levels. It essentially doubles the signal bandwidth of a connection with each signal level representing 2 bits of logic information. In addition, as a key role in multi-order modulation, it can minimize optical signal degradation while doubling the data rate, which makes it the most efficient and cost-effective enabler of 100G and 400G. To make it more specific, check the following figure to see how PAM4 doubles the data rate with four signal levels by comparing it with NRZ.

NRZ and PAM4 Signals Comparison

Figure 1: Comparison of Waveforms between NRZ and PAM4 Signals

The form factor in which 100G DWDM transceivers utilize PAM4 is QSFP28. Next, let's dive into how PAM4 DWDM QSFP28 supports 100G/400G applications.

How Does PAM4 QSFP28 Perform As a Solution for 100G/400G?

As a quite capable alternative for extending 100G/400G signals, QSFP28 PAM4 has recently become a trending product for network operators. Here are the benefits of adopting QSFP28 PAM4 DWDM in 100G/400G applications:

Large Data Capacity

QSFP28 PAM4 DWDM can provide up to 4.8Tb/s of data capacity over single-mode fiber (SMF) and minimize signal degradation. It can be used for 100G/400G extensions between data centers with point-to-point links and transmission distance of up to 80km.

Lower Power Consumption

It is designed to offer a lower power consumption for high-speed extended reach data center interconnects (DCI) and high-density connectivity.

Embedded DWDM

Pluggable with embedded DWDM, the PAM4 DWDM transceiver can be inserted directly into the appropriate data center routers or switches without the need of a separate DWDM converter platform, significantly reducing the cost and simplifying the deployment and maintenance. Moreover, with the right dispersion compensation modules (DCMs) and amplification system in place, QSFP28 PAM4 modules can be added to an existing DWDM network to achieve a hybrid transmission.

With all the benefits it provides, QSFP28 PAM4 DWDM modules are often adopted for 100G and 400G construction, such as point-to-point data center interconnects (DCI), 100G Ethernet metro-access over DWDM, campus and enterprise links, 5G mobile access architecture, etc.

PAM4 Applications in Data Centers and 5G Architecture

Figure 2: PAM4 Applications in Data Centers and 5G Architecture

For 100G transceiver modules, QSFP28 PAM4 can reduce the number of lasers and eliminate the need for optical multiplexing. For 400G, the largest expenditure would be optical components and related radio frequency packages. PAM4 can transmit two bits of logic information and double the bandwidth to effectively reduce the transmission costs and at the same time, meet the needs of bandwidth improvements.

FS 100G DWDM QSFP28 PAM4 Solution

Based on the bandwidth demands of global users, FS provides 100G DWDM QSFP28 PAM4 solution integrated with DWDM QSFP28 PAM4 transceiver and fiber cables to achieve high-speed signal transmission and the construction of 100G.

100G DWDM QSFP28 PAM4 Transceiver- DWDM2-Q28100G-80

FS 100G QSFP28 PAM4 Transceiver

Figure 3: FS QSFP28 PAM4 Solution- DWDM2-Q28100G-80

This 100G DWDM QSFP28 PAM4 transceiver uses PAM4 modulation to achieve 100G. It supports multiple 100G links up to 80km over single-mode fiber (SMF) via a CS connector. Equipped with a Broadcom BCM81128 chip, it can realize stable signal transmission with a power consumption of lower than 5W, which significantly cuts down the cost. It can also be added to the existing 1G/10G DWDM network to achieve hybrid data rates transmission.

Featuring low power consumption, high speed and long transmission distance, QSFP28 PAM4 would be the most cost-effective and efficient solution for data centers or campus and enterprise links to upgrade their networks into 100G/400G.

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