Scientists in Japan have developed a new type of distributed feedback (DFB) laser and have shown that it can be used to transmit data at 200 Gbps over a record distance of 10 kilometers. This research could help develop network technology that will allow Internet data centers to handle unprecedented levels of data.

Kazuki Nishimura, optical engineer in Lumentum Japan’s Datacom business unit, will present new research at the Optical Fiber Communications Conference (OFC) held March 5-9, 2023 in San Diego, California, USA.

The research contributes to the development of next-generation data centers for 800G and 1.6T Ethernet. In particular, the new technology enables electroabsorption modulators with integrated lasers with distributed feedback (EA-DFB) to operate even at 10 km transmission using conventional PAM4. It’s defined as a simple intensity modulation direct detection (IM/DD) scheme (pulse amplitude modulation),” said Nishimura.

As communication traffic continues to increase, more emphasis is placed on implementing next-generation Ethernet technologies such as 800G and 1.6T Ethernet to help data centers meet increasing demands. Although the same PAM4 technology used for 2 kilometer transmission in today’s 400G Ethernet network is considered for 800G, a new technology is needed to provide long-distance data transmission in connections between data center regions or campuses.

In the new study, the researchers designed a DFB electroabsorption (EA) modulator with a focused electrode to achieve a longer distance. They used the new laser for the first time to demonstrate 5 km 225 Gbit/s PAM4 transmission using the Coarse Wavelength Multiplexing (CWDM) wavelength range operating at 50°C. They also used the laser for 10 km 225 Gbps PAM4 transmission at 1293.5 nm. This wavelength exhibits less chromatic dispersion than the wavelength range specified for CWDM, a technology commonly used to send multiple optical signals simultaneously over optical fiber. Chromatic dispersion can cause optical signal degradation and is more problematic for longer transmission distances.

In all experiments, the new laser exhibited low emitter and closed-eye scatter quartile (TDECQ) values, indicating good transmitter performance. The researchers say their results demonstrate the potential of the focused electrode EA-DFB laser as a light source for 800G Ethernet technology, including applications within 10 kilometers. It can also be useful for 5km CWDM4 applications.

“Data center traffic is increasing significantly every year due to high-definition video streaming services such as 4k and cloud applications. “These results show that our EA-DFBs are a promising optical light source for realizing future 800GbE applications.”