How to Migrate to 400G With 100G Single Lambda QSFPTEK Optics

Date 03/28/2025

This article introduces you to what 100G single lambda QSFP28 optics are and how to use them to seamlessly migrate from 100G to 400G.

As data volumes surge and new technologies emerge, 100G Ethernet is becoming increasingly prevalent in high-speed network deployments. Traditional 100G technologies like SR4, LR4, CWDM4, and PSM4 utilize four 25Gbps NRZ channels, leading to elevated costs that challenge operators. To address this issue, the 100G Lambda Multi-Source Agreement (MSA) group introduced a single-wavelength 100G technology aimed at reducing expenses while ensuring compatibility with forthcoming 400G standards. This advancement leverages PAM4 signaling to transmit 100G data over a single wavelength, simplifying the optical architecture and reducing component complexity. Let's explore the 100G Lambda standard to understand its role in current 100G network architectures and its potential to support the evolution toward next-generation 400G networks.

100G Single Lambda Technology Explained

Single Lambda is a 100G access technology that utilizes a single 50 GBaud PAM4 (four-level pulse amplitude modulation) wavelength signal to achieve a data rate of 100 Gbps. This method employs a DSP (Digital Signal Processor) to convert four 25G electrical signals into a single 100G channel. Previously, most 100G QSFP28 optical modules used four 25 Gbps NRZ (Non-Return to Zero) channels to achieve an aggregate 100 Gbps data rate. In contrast, PAM4 modulation doubles the data capacity compared to NRZ. Specifically, a 50 GBaud PAM4 signal transmits 100 Gbps, while a 25 GBaud NRZ signal transmits 25 Gbps.

Why Adopt Single Lambda for 100Gbps?

Reduce Optical Component Cost

Currently, the most prevalent standards for 100GbE deployment are 100GBASE-LR4 MSA, 100GBASE-CWDM4 MSA, and 100GBASE-PSM4 MSA. Network operators apply QSFP28 LR4, CWDM4, or PSM4 modules to enable 100 Gbps, which is achieved by multiplexing 4 wavelengths of 25 Gbps into a single fiber. However, the signal processing is quite complex to integrate four 25G signals into a 100G link. This complexity directly brings costly optical components.

Image Source: Cisco.com

Specifically, the design of QSFP28 LR4, CWDM4 and PSM4 are more complex than Single Lambda optics. The simplified construct components in the Single Lambda transceiver greatly reduce the cost by 40% or more.

LR4, CWDM4 and PSM4 optics: transmitter uses Clock Data Recovery (CDR) in each of the electrical interfaces, Laser Driver (LD) & Laser and even Mux; the receiver uses CDR and Trans-Impedance Amplifier (TIA) + Linear Amplifier (LA) & PIN photodiode in each of the electrical interface and even Demux.

Single Lambda optics: transmitter only uses a DSP with CDR, a single LD & laser; receiver only uses a DSP with CDR and a single TIA + LA & PIN photodiode. In contrast, 100G Single Lambda optics only use one wavelength, saving the trouble of multiplexing and demultiplexing, tight wavelength control and costly hermetic packaging.

Meet Future 400G Standard

The crowded network is pushing for a higher data rate of 400G. The 100G Lambda MSA has considered this trend, designing 100G single Lambda optics with 400G compatibility. That is, the QSFP-DD form factor is backward compatible with other QSFP form factors including QSFP28. Also, 100G single Lambda QSFP28 deploys the same 50GBaud PAM4 modulation that 400G QSFP-DD uses. For instance, the 400G-LR4 QSFP-DD uses 4 channels of 100 Gbps to achieve a total data rate of 400 Gbps, which can link to four 100G-LR4 single Lambda QSFP28 for a 400G to 100G breakout solution.

Image Source: Cisco.com

Single Lambda 100G Transceiver Introduction

According to Cisco networks, the Single Lambda 100G optics include 100G DR, 100G FR, and 100G LR. All three QSFP28 comply with 100G Lambda MSA specifications and come with duplex LC connectors. To mark the number of wavelength channels, the Single Lambda optics are also called 100G DR1 QSFP28, 100G FR1 QSFP28 and 100G LR1 QSFP28.

100GBASE-DR Single Lambda QSFP28

QSFP-100G-DR-S Single lambda transceiver complies with IEEE 100BASE-DR specification. It supports up to 500m link over duplex OS2 single-mode fiber (SMF) at a wavelength of 1310nm. The 100GBASE-DR QSFP28 is mainly used for short-reach spine-leaf data center interconnect (DCI), where most optical links are within 100m. Another restriction is less tolerance for the insertion loss of a limited number of patch panels.

100GBASE-FR Single Lambda QSFP28

100G Single Lambda MSA then introduces the QSFP-100G-FR-S to extend the fiber link to a 2km reach. The 100G-FR complies with the IEEE 100BASE-FR specification, supporting up to 2km link over duplex OS2 SMF at a wavelength of 1310nm. The 100GBASE-FR QSFP28 enables longer DCI links and leaves more room for higher link loss applications.

100GBASE-LR Single Lambda QSFP28

The third bro is QSFP-100G-LR-S. Through duplex OS2 SMF at 1310nm, 100G LR reaches up to 10km link. The LR QSFP28 brings a long-haul 10km reach to the Single Lambda series 100G optics, extending the interconnect capability beyond two buildings even in nearby cities. It is ideal for new network deployment for the core switch to core/aggregation switch interconnect in the campus network.

	QSFP-100G-DR	QSFP-100G-FR	QSFP-100G-LR
Wavelength	1310 nm	1310 nm	1310 nm
Distance	500m	2km	10km
Connector	Duplex LC	Duplex LC	Duplex LC
Cable Type	OS2 SMF	OS2 SMF	OS2 SMF
Transmitter	EML	EML	EML
Receiver	PIN	PIN	PIN
DDM	Support	Support	Support
Modulation	PAM4	PAM4	PAM4
Receiver Sensitivity	<-5.9dBm	<-6.4dBm	<-7.7dBm
TX Power	-2.9~4dBm	-2.4~4dBm	-1.4~4.5dBm
Power Consumption	≤4.5W	≤4.5W	≤4.5W
Protocols	IEEE 100BASE-DR, 100G Lambda MSA, IEEE 802.3bm	100G Lambda MSA 100G-FR Spec QSFP28 MSA	100G Lambda MSA 100G-LR Spec QSFP28 MSA

Seamlessly Migrate to 400G with 100G Single Lambda Optics

Given that single lambda 100G DR, 100G FR and 100G LR are QSFP28 form factor designs. It is compatible with the QSFP-DD form factor that applies to 400G Ethernet. Correspondingly, it is recommended to adopt 100G Single Lambda optics in 400G networking design. The benefit is that it allows connecting a new 400G site to a legacy 100G site with 4 links. So you only need to bring 400G hosts to one site but don’t need to upgrade the existing 100G architecture while getting 400G link access.

For instance, using QSFPTEK 100G DR QSFP28, you can achieve a 400G to 4x 100G breakout solution. Connect a new 400G ToR switch to a legacy 100G switch with four separate links.

Left side: Insert a 400G QSFP-DD DR4 module into the ToR switch 400G port

Right site: Plug four 100G QSFP28 DR modules into four 100G switch ports

Link: use an MTP to 4 LC duplex OS2 breakout SMF to connect the two sites

Conclusion

To drive down 100G deployment costs, the 100G Lambda MSA specified a standard to enable 100 Gbps on a single wavelength, greatly reducing optical complexity. Besides, it looks forward to future high-speed networks, integrating the 400G compatibility to Single Lambda 100G optics. 100G Single Lambda QSFP28 is a future-proofing solution for seamless 100G to 400G migration.

QSFPTEK offers 100G Single Lambda optics, including QSFP-100G-DR-S, QSFP-100G-FR-S and QSFP-100G-LR-S; and 400G QSFP-DD transceivers. A full 400G to 4x 100G breakout solution is also provided. If you have any questions, feel free to contact [email protected].