An Introduction to Single-Lambda 100G optics

100G single lambda is a popular PAM4 signaling based optical specification. 100G single lambda is widely used for the transmission of 100G data stream over a single wavelength or laser. 100G Lambda MSA governs the development of this specification and it is developed to be used in 400G and 100G applications. 

The appearance of 100G single lambda is not uncommon as various optical transceivers such as 100GBASE-SR4, 100GBASE-LR4, 100G-CWDM4, and 100G-PSM4 come with four sets of receivers and transceivers to operate within 25Gb/s parallel lanes. These four optical signals are either optically multiplexed or coupled through parallel fibers to a single fiber for the transmission of data. This arrangement cannot be achieved without the involvement of expensive optical components. On the other hand, 100G lambda is a cost-effective solution that can help you in higher transmission efficiency at a reduced cost. Transceivers designed to comply with this specification utilizes 100G PAM4 signaling technology for 100G transmission per wavelength – an arrangement that decreases overall cost and optical complexity by reducing optical receivers and transmitters count from four to one.

According to an estimate, around 60% of the total cost of a pluggable 100GE optical module can be attributed to its optical components. Common 100G QSFP28 modules available in the market (such as 100GBASE-SR4) come with discreet optical components to achieve 25Gbps per lane. It’s the number of discreet components that determines the final price of an optical transceiver. A transceiver with fewer discreet components will cost lesser than one with a larger number of discreet components. 

100GBASE-LR4 is proposed for up to 10km stretched links consisting of 4 multiplexed wavelengths carried by a single fiber. However, tightly spaced wavelengths with LAN-WDM wavelength spacing cannot be considered without expensive hermetic packaging for optimum laser temperature controlling. 

Now, let us proceed with the second option I.e. 100GBASE-CWDM4. This option is better in terms of wavelength spacing however, in this configuration, links beyond 2km are not possible. Here come the third options i.e. 100GBASE-PSM4. This option uses 4 pairs of fibers and one wide wavelength for data transmission; thus, it can resolve the complexity that comes with multiple wavelength lasers. The 100GBASE-PSM4 is a good option but it can be considered for up to 500m links only. 

Let us bring 100G single lambda into the discussion now. The three transceivers included in the lineup of 100G single lambda are; 100GBASE-LR (100G-LR)., 100GBASE-FR (100G-FR), and 100GBASE-DR. these transceivers are designed to receive an electrical signal from the host (in 4 x 25G configuration) and come with a DSP to translate the received signals using PAM4 modulation unlike PSM4, LR4, or CWDM4 where NRZ signals are used. The application of PAM4 signals on one wavelength means that a single laser can be utilized for the transmission of the full 100G data stream. This networking infrastructure enables you to eliminate the requirement of parallel fibers or WDM resulting in the reduction of required optical components like receivers and transmitters. The 100GBASE-DR supports up to 500m links whereas the 100GBASE-FR and 100GBASE-LR are available for 2km and 10km links respectively. 

In light of the above-mentioned facts, it could be established that the latest version of 100G single lambda does not only offers cheaper 100G links but also reduces the complications of the optical components. According to IEEE experts, carrying 100GE optical signals through a single optical lane can help you achieve up to 40% savings in terms of deployment cost. That means, shifting from four wavelengths to one wavelength can result in over 40% cost reduction.

As internet traffic is growing, the need for cost-effective and simple pluggable optical modules will become the necessity of transceiver development, especially for high-density and high-speed applications like 200 and 400G. 100G Lambda can make the 100 to 400G transition easier by reducing the structural complexity of 400G modules. At the same time, it will also bring great savings by reducing the fiber count. 

Upgradation from 100G to 4 x 100G has now become a possibility – thanks to PAM4 modulation technology. Consider 100GBASE-DR as an example here which has been leveraged by the IEEE for the 400GBASE-DR4 standard. The 400GBASE-DR4 can be resolved as 4 x 100GBASE-DR modules to provide 400G connectivity for up to 500m distance. A 400G port can easily be resolved into 100G breakout connections with the help of 100G single lambda transceivers.

The 100G Lambda MSA group has also contributed to the up-gradation of the existing 400G IEEE standards. In the existing standards, the 400G optical transceivers rely on 8 x 50G PAM4 lanes. That high number of wavelengths and the complexity of demultiplexer and multiplexer seems impractical and costly in various networking environments. To cater to these challenges the 100G Lambda MSA group came ahead with the idea of using 100G per wavelength in 400G links – the arrangement in which four channels instead of eight channels are required on the CWDM wavelength grid. As a result, a lower-cost path to 400G up-gradation emerged. 

• 100G single lambda is a cost-effective solution available for the deployment of 100G links 
• The three transceivers utilized in the construction of 100G single lambda links are 100GBASE-FR, 100GBASE-DR, and 100GBASE-LR
• Using a single wavelength for 100G transmission saves up to 40% in terms of costs