Although optical transceivers operating at 100 Gb/s like 100GBASE-LR4, 100G-CWDM4, 100G-PSM4, and 100GBASE-SR4 are already available in the market. But to reduce the total cost and to obtain higher transmission efficiency, a 100G Single Lambda transceiver specification has been proposed. This article will give you an in-depth introduction to 100G single lambda from the definition, comparison with the advantages of the common 100G QSFP28, performance, and development prospects.
100G Single Lambda is an optical specification using PAM4 (four-level pulse amplitude modulation) signaling to transmit 100G data streams through a single laser/wavelength. It was first standardized by the 100G Lambda MSA (Multi-Source Agreement), an industry consortium whose common focus is to provide a new set of optical interface specifications. These specifications are developed around an optical channel data rate of 100Gb/s, aiming to use in 100G and 400G applications in a cost-effective way. Transceivers using this specification use 100G PAM4 signaling at 100G per wavelength, reducing optical complexity and cost by reducing the number of optical transmitters and receivers from four to one.
The single-λ 100G optics include the 100GBASE-DR, 100GBASE-FR (100G-FR) and 100GBASE-LR (100G-LR). These transceivers take a 4x 25G electrical signal from the host and convert the signal to PAM4 modulation using a DSP, meaning that the entire 100G data stream is transmitted by a single laser, eliminating the need for WDM or parallel fiber and reducing the number of optical components such as transmitters and receivers from four to one.
Longer Transmission Distance
The 100GBASE-DR QSFP28 was specified for 500-meter links. Later, the 100G Lambda MSA extended the reach of 100GBASE-FR to 2 km, allowing for longer links or higher loss environments. Until now, MSA has extended coverage to 10 km with 100GBASE-LR, addressing the same applications as the QSFP28 module 100GBASE-LR4.
According to IEEE, the ability to support 100G per λ (wavelength) can reduce the cost of 100GE optical signals by at least 40% with a single optical path. This means that the transition from 4 wavelengths/lambda to 1 wavelength/lambda reduces the relative cost by more than 40%.
As traffic continues to grow, the need for simpler, more cost-effective pluggable optical modules will become the key to transceiver market development, especially in high-speed and high-density applications like 200G and 400G. It makes the transition from 100G to 400G applications easier and reduces the internal complexity of 400G modules, which is more conducive to the development of 400G. At the same time, the fiber count is reduced, which is good for cost-saving.
Since PAM4 modulation has made single-lane 100G possible, upgrading from 100G to 4x 100G becomes a reality. For example, the IEEE leveraged 100GBASE-DR for the 400GBASE-DR4 optical standard. The 400GBASE-DR4 could break out into four parallel 100GBASE-DR modules and provide 400G connectivity over 500m. With 100G single lambda transceivers, 100G breakout connections from a 400G port are easy.
The 100G Lambda MSA group also helps upgrade the existing IEEE 400G standards. In the existing 400G standards, the 400G transceivers rely on 8 lanes of 50G PAM4 optical signals on the LAN-WDM wavelength grid, which has the same issues as 100GBASE-LR4 explained above. The number of wavelength channels required and the complexity of the multiplexer and demultiplexer seem costly. Realizing such shortcoming, the MSA decided to use 100G per wavelength instead of 50G and use four channels on the CWDM wavelength grid with a wider window of tolerance, which provides a lower-cost path for 400G.