New optical fibre data transmission record

Sometimes you need to have a physical reference to fully comprehend how big, fast or remarkable a certain achievement is, and that’s exactly the case with the truly astounding achievement of Japanese telco Nippon Telegraph and Telephone Corporation when it successfully demonstrated optical fibre transmission of 14 Tera bits per second over a single 160 km long optical fibre. For those who don’t know, the word Tera signifies one trillion and … you see, hard to wrap the brain cells around what that really means isn’t it. It’s why Apple talks about the iPod in terms of the number of tunes it holds. Then try this for size! That’s 140 high-definition movies per second, waaay ahead of the old record of 100 hi-def movies per second. Clearly we’re going to have enough bandwidth for high res anything a few decades from now.

The present core optical network is an optical transport network with about 1 Tbps capacity. Based on the wavelength-division-multiplexing (WDM) of signals with the channel capacity of 10 Gbps, it uses optical amplifiers with the bandwidth of about 4THz. The data traffic has been doubling every year due to the rapid spread of broadband access. We must lower the cost and raise the capacity of the core network while maintaining its reliability as the dominant communication infrastructure.

This result was reported as a post deadline paper in the European conference on optical communication (ECOC) that was held in Cannes, France from September 24 to 28.

1. Background

The present core optical network is an optical transport network with about 1 Tbps capacity. Based on the wavelength-division-multiplexing (WDM) of signals with the channel capacity of 10 Gbps, it uses optical amplifiers with the bandwidth of about 4THz. The data traffic has been doubling every year due to the rapid spread of broadband access. We must lower the cost and raise the capacity of the core network while maintaining its reliability as the dominant communication infrastructure.

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

2. Outline of experiment

Our 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. In addition, 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 (Figure 1). 160-km transmission was successfully achieved by amplifying these signals in newly developed optical amplifiers.

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