Peking University photonic platform carries 81.92 Tbit/s over 1 km and reaches 4400 km in lab tests

Researchers from Peking University and their colleagues have developed a single photonic platform for links ranging from connections inside data centers to trunk lines thousands of kilometers long, ixbt.com reports. In the experiment, the system reached an aggregate rate of 81.92 Tbit/s over 1 km of optical fiber without optical amplifiers. In a separate test with amplifiers, the researchers sent data over 4400 km. ixbt.comixbt.comixbt.comOpen source ↗

Until now, equipment for short and long optical links has been built on different principles. Data centers widely use intensity modulation with direct detection, which is simpler and cheaper but limited in spectral efficiency. Trunk networks use coherent transmission, where the receiver analyzes the phase of the optical signal as well as its intensity, allowing more complex modulation formats. The difference complicates building a unified network, since moving between segments may require optical-to-electrical conversion, extra computation and regeneration.

Laser and transmitter

The system is based on a hybrid laser with an external cavity. Its gain section is made of indium phosphide, and the external optical cavity is made of silicon nitride, a very low-loss material. The laser delivers up to 70 mW of optical power, has a linewidth below 1 kHz, and a peak electrical-to-optical conversion efficiency of 13.7%. Its wavelength tuning range reaches 102 nm. It works together with a silicon photonic transmitter and receiver containing modulators and photodetectors.

Test results

On the 1 km link, 256 separate wavelength channels were used. Each carried 320 Gbit/s, giving 81.92 Tbit/s in total with dual-polarization DP-16QAM modulation at 40 GBd. The laser's output power was enough to avoid an optical amplifier along the whole link. ixbt.comixbt.comixbt.comOpen source ↗

In the second experiment, a 184 Gbit/s per channel QPSK signal traveled 4400 km over a test line with optical amplifiers. With 16QAM, the system delivered 368 Gbit/s over 1375 km.

The laser also switched its operating wavelength in less than 5 µs, and data transmission recovered in 14 µs. Optical power took about 58 µs to stabilize, but communication did not have to wait for that.

This is an experimental demonstration, not a ready replacement for existing infrastructure. The authors note that higher rates will require faster modulators, lower losses in the transmitter and better component integration. ixbt.comixbt.comixbt.comOpen source ↗