NTT Sets Optical Record: 14 Tbps over a Single Fiber

Nippon Telegraph and Telephone Corporation (NTT) set a new optical transmission record — 14 terabits per second (Tbps) over a single 160 km long optical fiber. Significantly, the demonstration ran optical signals at 111 Gbps over a DWDM system supporting 140 channels. This greatly exceeded the current record of about 10 Tbps over a single fiber.

NTT said its reach is driven to increase the core capacity of its optical transport network, which currently stands at about 1 Tbps. Current networks use wavelength-division-multiplexing (WDM) of 10 Gbps signals.

While 10 Tbps transmission over a single optical fiber has been achieved in the laboratory, NTT said it was necessary to use linear amplifiers that covered two or three amplification bands because of the limited range of existing amplifiers. However, this multi-band configuration is not cost-effective. To increase the transmission capacity, NTT set out to achieve two goals simultaneously: WDM transmission with high spectral efficiency and optical amplifiers with greatly enlarged bandwidth.

Some key points of NTT’s optical transmission breakthrough:

The experiment used the carrier suppressed return-to-zero differential quadrature phase shift keying (CSRZ-DQPSK)*1 format and ultra-wide-bandwidth amplifiers.
70 wavelengths with 100-GHz spacing were modulated at 111 Gbps using the CSRZ-DQPSK format and then multiplexed and amplified in the bandwidth of 7 THz.
Each 111 Gbps signal was polarization-division-multiplexed so the number of channels was doubled to 140. This yielded the total capacity of 14 Tbps. The 160 km distance was achieved by amplifying these signals using newly developed optical amplifiers.
The experiment also demonstrated that it is possible to transmit 100 Gbps signal with forward error correction bytes and management overhead bytes of the OTN frame over long distances allowing the construction of large capacity optical networks that offer 10 Tbps or more.
NTT said CSRZ-DQPSK modulation and its new high-speed optoelectronic device technologies make it possible to generate dense WDM signals with bit rates of 100 Gbps and beyond per channel and transmit them over long distances.