In the field of optical communications, technological innovations are changing rapidly as data transmission rates continue to increase. In recent years, higher data rate pluggable optical modules have evolved rapidly, and the complexity of their design and interaction with switch and router hosts has increased. Today's 100G optical modules have become a key factor in the cost of network hardware and the design of fibre optic infrastructures, and Single-Lambda 100G, the next-generation standard for optical communications technology, is becoming the mainstream of the market.

What is Single-Lambda 100G?

The 100G Lambda MSA (Multi-Source Agreement), which uses a single-wavelength 100Gbps PAM4 (Pulse Amplitude Modulation 4) modulation technique, standardises the specifications for Single-Lambda 100G optical modules.

Previously, most 100G optical module specifications used NRZ, a two-level binary modulation format. PAM4 contains twice as much data as NRZ and does not require a significant increase in the speed of the optics. As a result, the same basic optics that can only transmit 50G using NRZ can also be used for 100G PAM4.

Designed to create cost-effective solutions for high-density switches, routers and transport networks, the goal of the MSA is to define an optical module specification that will enable future 100G and 400G pluggable optical modules to be produced in high volume and thus at low cost.

ETU-LINK's 100G DR1/FR1/LR1/ER1 Optical Modules

What is PAM4?

PAM4 (Pulse Amplitude Modulation) is a four-level pulse amplitude modulation. PAM4 signalling technology is a modulation technique that uses four different signal levels to transmit signals, and in optical module applications it is the intensity of the light that is modulated.

NRZ (non-return-to-zero) is a conventional modulation scheme used by almost all low-speed optical modules and most other 100G optical modules, which modulates the intensity of light in two levels and is therefore binary.

The PAM4 uses four levels of encoding and can therefore encode two bits per optical pulse cycle instead of one as in NRZ. As a result, PAM4 has roughly the same signal bandwidth as NRZ, but transmits twice as much data as NRZ. However, the application of PAM4 technology also poses some challenges, such as the increased effect of amplitude noise. To address these challenges, Single-Lambda 100G technology employs a variety of advanced techniques such as de-emphasis, detailed characterisation of optical transmitters, advanced digital filter equalisation, clock recovery circuits and strong FEC (Forward Error Correction).

PAM4 transmits two bits per pulse, so twice as much information can be transmitted in the NRZ.

In summary, the combination of PAM4 technology and Single-Lambda 100G has revolutionised the field of optical communications. They not only enhance the data transmission rate and efficiency, but also ensure the stability and reliability of data transmission through a series of advanced technical means. With the continuous progress of technology and the deep expansion of application, it is believed that PAM4 and Single-Lambda 100G will play an even more important role in the field of optical communication in the future.