In recent years, optical modules with higher data rates continue to emerge, and the design complexity of optical modules is constantly increasing. With today's 100G optical networks, we are in an era that affects the cost of network hardware and the design of fiber optic infrastructure.

If the 100G optical module is simplified, because there are fewer components in the pluggable optical module, the manufacturing volume and cost can be expanded to the level of today's 10G SFP+ optical modules. Through silicon optical technology and signal processing technology, single-wave 100G optical module is available. When the new generation of 100G packages becomes available, it will be able to reuse the first generation and gradually transition, and it will also be able to upgrade directly to 400G.

Advantages of simplified 100G optical module

As 100G optical modules transition to new 100G packages, investments will be future-oriented

Reduce the total cost of 2km duplex transmission and data center leaf ridge connections with SMF (single mode fiber) links

Connect 400G switches and routers without sacrificing port bandwidth

Upgrade to 400G switches and routers one site at a time

It's time to introduce a new generation of 100G optical modules

Back in the days when 10G SFP+ pluggable optical modules were the most advanced, choices were few and simple, as their only function was to convert electrical signals into optical signals and vice versa.

In subsequent years, the demand for network bandwidth increased, which meant that the data rate of the optical link had to increase as well. It has not only increased, it has accelerated. Standards bodies such as IEEE and SFF have had to consider ways to increase data rates to outpace faster lasers and light receivers. Technologies such as WDM (wavelength division multiplexing), parallel fiber, CTLE (Continuous time linear equalization) and FEC (forward error correction) are incorporated into the standard.

This complexity affects not only the cost of the pluggable optical module itself, but also the fiber infrastructure design, which has an impact on both hardware costs and operational costs. Complexity also increases the risk of interoperability failures between optical modules and switches or routers, as well as between optical modules from different vendors. Therefore, in order to make tomorrow's 100G optical modules as low-cost and low-risk as today's 10G SFP+ optical modules, fundamental changes are needed.

What is single wavelength 100G?

The single-wave 100G optical specification was first standardized by 100G λMSA (Multi-Source Protocol). Because its vision is to create cost-effective solutions for high-density multi-TB switching, routing and transport networks. The goal is to define optical specifications that allow for future 100G and 400G optical modules that can be scaled to high-volume manufacturing, enabling low cost.

The basis of the single-wave scheme is the use of PAM4 (four-level pulse amplitude modulation). Prior to this, almost all 100G optical specifications included NRZ (non-return-to-zero), which is a two-stage binary modulation format. In contrast, PAM4 contains twice as much data without significantly increasing the speed of the optical components. Therefore, the same basic optical technology that can only carry 50G and NRZ can be used for 100G PAM4.

Forward compatibility

Eventually, when 100G SerDes (serializers) are available on switch and router ports, the ASics behind the ports can take over FEC and PAM4 functions, allowing the optical module to perform only photoelectric and electro-optical conversions. We can then increase the panel bandwidth density by using a smaller SFP package that uses a 100G channel on the electrical side to connect to the switch or router port, which might be called the SFP112.

But we haven't. At the same time, we have the QSFP28 package, which can perform FEC and PAM4 inside the module and convert the electrical 4x25G channel into a single 100G channel. The advantage of adopting this QSFP28 now is that when the SFP112 is available, traditional switches and routers using the QSFP28 module will interoperate with new hosts using the SFP112 optical module, and there is no need for 4x25G to 100G conversion because the electrical and optical interfaces are both single-channel 100G. This forward compatibility is very beneficial for network upgrade strategies, as it prevents your existing QSFP28 modules from becoming obsolete when you add new SFP112-based hardware.

The SFP112 may require a CDR (Clock and Data Recovery) circuit.

400G Outlook

Looking ahead to the latest generation of switches and routers with 400G ports, single-wave 100G is critical to upgrading networks with operational flexibility. It supports 400G QSFP-DD optical modules and is interoperable with single-wave 100G optical modules via branch cables. For example, C-light's 400G QSFP-DD DR4 can be connected to four independent 100G QSFP28 FR optical modules.

This means that if you are running your network with a device with a 100G QSFP28 port, you can upgrade just one site to a 400G device and still connect it to your existing 100G site without sacrificing port bandwidth. This minimizes your downtime, and then you can upgrade to other sites when you're ready.

C-light 100G single wave optical module

In recent years, C-light has continuously overcome difficulties, and developed a number of single-wave 100G optical modules. Up to now, a total of optical 100G QSFP28 DR1/FR1/LR1, and industrial 100G QSFP28 ZR4/ER4 have been launched, breaking the technical gap in the field of 100G single wave of C-light, is a novel choice for 100G transmission in AI era.

Figure: 100G QSFP28 DR Is ideal for data center connectivity between the backbone layer and the leaf layer