Achieve 1.6Tb/s transmission on 1600km G.654.E optical fiber?

 Current commercial coherent modems use the most advanced coherent technology and have higher-order modulation formats, such as 64QAM under Probabilistic Constellation Shaping (PCS), soft-decision SD-FEC and digital subcarrier modulation (DSCM) to improve spectrum efficiency.

In addition to improving spectrum efficiency, operators also want to achieve higher symbol rates to reduce network costs and simplify network management. At last year’s OFC conference, Infinera and Corning jointly demonstrated “ Real-time 100.4 GBd PCS-64QAM transmission of 1.6Tb/s Super-Channel over 1600 kilometers of G.654.E fiber .” The topology is as follows:

According to Infinera, it was the first real-time 1.6TB/s (2×800G) DCO ( Digital Coherent Modem) using PCS-64QAM and DSCM. Its symbol rate reaches 100.4Gbd, which can achieve 800 Gb/s rate and transmit a record of 1600 kilometers with 2 dB OSNR margin . This 2*λ 1.6 Tb/s DCO module is shown in the figure below and consists of 2×800G DSP ASIC and hybrid integrated electro-optical module.

Among them, the DSP ASIC is manufactured using a 7nm process and supports two optical channels with net data rates of 100Gb/s to 800Gb/s per wavelength. Symbol rates are tunable from 32GBd baud to 100GBd, and multiple modulation formats are supported, from 8D hybrid to PCS-64QAM.

The electro-optical module consists of a two-channel photonic integrated circuit (PIC), matched with the corresponding 2-λ high-speed analog driver and transimpedance amplifier ASIC. When the DCO is configured for the PCS-64QAM modulation format, the symbol rate is 100.4 GBd and the information rate is 10 b/sym, providing a net data rate of 800 Gb/s per wavelength (after all overhead is removed). The roll-off coefficient of the digital pulse shaping filter in the transmitter DSP is set to 6.25%, and the single-channel optical bandwidth (BW) is 106.675 GHz.

The above figure (a) shows the spectrum of the DCO optical module output port CH1. It can be seen that the 8 digital subcarriers used in the DSP achieve power uniformity of ±0.3 dB across the entire signal spectrum, thus proving the large bandwidth of the DCO transmitter (3 dB BW>50 GHz). The picture above ( b ) is the corresponding receiving spectrum read directly from the DSP ASIC in B2B mode .

Figure (a) below records the Q factor as a function of transmit power per channel at 800 Gb/s wavelength after transmitting over 1600 km of G.654E fiber. At the optimal transmit power of 2.5 dBm, the OSNR margin under the FEC threshold is about 2 dB.

Figure (b) above shows the OSNR margin for FEC thresholds in 50 Gb/s increments as a function of per-channel data rate after transmitting over 1600 km of G.654E fiber. It can be seen that when the net data rate per channel decreases by 50 Gb/s, the OSNR margin can increase by approximately 1 dB, and the OSNR margin in the 400 Gb/s rate mode reaches 9.2 dB.