QSFP28 LR4 Application: The Enabler of 100G Metro Transmission Over 40KM

Posted on October 25, 2019
September 18, 2020

The amount of data traffic today is staggering and has more stringent demands on bandwidth and data transmission performance. At present, 100G optical transceiver has replaced both legacy 10G and 40G, seeing steadily growth in long-haul networks and a boom in metro transmission. Among the commercially available 100G QSFP28 modules, QSFP28 LR4 transceiver modules, with a reach of 10km, offer a decent choice for long-reach connectivity. But is it possible to extend 100G QSFP28 LR4 reach to 40km while maintaining the existing network infrastructure? With the help of SOA (semiconductor optical amplifier), the answer is yes.

Trends in Metro Networks: Steady Shift to 100G

The metro optical market is highly competitive in the past few years, consisting of widely varying applications such as data center interconnect (DCI), mobile transport (backbone, backhaul, and fronthaul), wholesale services, and enterprise wavelength and packet connectivity services. Which all calls for scalable and agile optical solution to match service requirements in an efficient manner. With the advent of 5G, the speed upgrade for access network in mobile transport architectures will provide additional drivers for metro network investment.

Although the vast majority of metro networks is based on 10G or 40G today, 100G is widely viewed as the best option to address the explosive growth occurring in the metro since it is easier to expand to allow for the dramatic changes lie ahead. The estimated share of metro WDM ports of each speed in 2020 is illustrated below, indicating the 100G metro deployment will outperform the legacy 10G and 40G.

100g metro network trend.jpg

Why Use 100G QSFP28 LR4 With SOA in Metro?

The persistent demand for higher bandwidth necessitates the deployment of even higher optical transmission capacity, both in long-haul networks but also in metro access networks. QSFP 100G LR4 transceivers have been around for some time and are in mainstream adoption now. They are hot-swappable, low-voltage optical transceivers using four x 25Gbps (up to 28Gbps ) WDM signals in the 1310nm region with 800GHz spacing. However, the reach of standard 100G QSFP28 LR4 transceivers is specified up to 10km, so the issue of reach extension still persists.

It' s commonly known that the attenuation of QSFP 100GBASE LR4 is in 1310nm wavelength, typically higher than in the 1550nm band, making amplification an important requirement. A normal EDFA (erbium doped fiber amplifier) would not work as it amplifies 1550nm range of signals but blocks the 1310nm signal. The semiconductor optical amplifier (SOA), however, is dedicated to boost signals in 1310nm wavelength optical transmission systems. FS SOA is a compact amplifier module delivered in a simple plug-and-play design, which is independent of transceiver form-factor – it can be fully integrated into FMT advanced 1U/2U/4U chassis for space-saving.

Extending the Reach of 100G QSFP28 LR4 Optics to 40km

A simple addition of the SOA, the reach of the 100G LR4 QSFP28 can be easily extended to approximately 40km. When deploying SOA in 100G LR4 connectivity, it acts as an optical pre-amplifier - meaning it is used in front of the QSFP28 LR4 receiver end to boost the incoming weak signal. In this case, SOA enables an optimal solution for external amplification of the LR4 100G signal when it needs to reach further than 10km. This solution takes advantage of current network infrastructure with minimal disruption to existing services, moreover, it is more flexible to further accommodate new equipment as need occurs. Deploying SOA with 100G QSFP28 LR4 presents an economically viable choice, together with greater space, power and bandwidth efficiency. The solution is also suitable to the form factor CFP, CFP2 or CFP4.

QSFP28 LR4 application with SOA.jpg

If you already have a legacy 10G DWDM system in metro distance but need to integrate with 100G services, the SOA and QSFP28 100G LR4 module amplification solution can also justify your need. The SOA-powered LR4 transceiver signal can be multiplexed together with 10G DWDM signals using a WDM Mux/Denux with an dedicated 1310nm port. For example, when deploying a 40CH DWDM Mux/Demux with 1310nm ports, we will get 40×10G signal and an additional 100G signal together. This could help scale the network to 500G at maximum. However, in this scenario, the transmission distance would be over 10km but not as far as 40km. Depending on the multiplexer loss, fiber loss and transceiver form-factor, the maximum transmission distance can be evaluated.

500g QSFP28 LR4 application.jpg


With 100G stretched in the long-haul networks, networks today are in the midst of a massive migration to 100G in the metro and data center networks. The transition from current network architecture to 100G systems with right interconnectivity solutions is inevitable. SOA and 100G QSFP28 LR4 transceiver is ideal for businesses that seek a simple, reliable and cost-effective solution to extend the reach of their networks. FS 100 Gbps LR4 QSFP28 module supports highly reliable operations in metro and data center networks. All of FS optical transceivers undergo rigorous qualification and certification testing to provide an end-to-end solution supporting mission-critical applications.