How to Extend 100G Metro Network to 40km with 100GBASE LR4?

Updated on Dec 11, 2021

100G qsfp28 transceiver

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 legacies 10G and 40G, seeing steady growth in long-haul networks and a boom in metro transmission. Among the commercially available 100G QSFP28 modules, 100GBASE LR4 transceiver modules, with a reach of 10km, offer a decent choice for long-reach connectivity. But is it possible to extend 100G LR4 reach to 40km while maintaining the existing network infrastructure? With the help of SOA (semiconductor optical amplifier), the answer is yes.

The Key to Extend 100GBASE LR4 to 40km-SOA

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 SOA (semiconductor optical amplifier), however, is dedicated to boosting 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.

How Does SOA Extend 100GBASE LR4 to 40km?

There are two different situations where SOA can be applied to extend 100G to 40km with 100G LR4 transceiver. Let's dive into how SOA extends 100GBASE LR4 to the distance of 40km.

Situation #1

A simple addition of the SOA, the reach of the 100G LR4 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 100GBASE 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 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

Figure 1: 100G LR4 application with SOA

Situation #2

If you already have a legacy 10G DWDM system in metro distance but need to integrate with 100G services, the SOA and 100GBASE 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/Demux 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

Figure 2: Scale to 500G with SOA and LR4 module


With 100G stretched in the long-haul networks, networks today are in the midst of massive migration to 100G in the metro and data center networks. The transition from current network architecture to 100G systems with the right interconnectivity solutions is inevitable. SOA and 100GBASE LR4 transceiver is ideal for businesses that seek a simple, reliable and cost-effective solution to extend the reach to 40km in 100G metro network.

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