Fiber-optic “hero” experiments are alive and well: researchers at NTT (Tokyo, Japan) have transmitted data at a 14 Tbit/s rate over a single 160-km-long optical fiber. The rate bested the previous record of about 10 Tbit/s. Rather than using existing linear amplifiers that covered two or three narrower amplification bands, requiring remultiplexing of the resulting separate signals, the researchers extended the bandwidth of an L-band amplifier so that it was 1.75 times (7 THz) larger than that of conventional amplifiers.
The experiment used carrier-suppressed return-to-zero differential-quadrature phase-shift keying. Seventy wavelengths with 100 GHz spacing were modulated at 111 Gbit/s and then multiplexed and amplified; in addition, each signal was polarization-division-multiplexed, doubling the number of channels to 140. To up the modulation speed beyond that of conventional Mach-Zehnder lithium niobate modulators, NTT developed a hybrid integration technology that combines silica-based planar-lightwave circuits with lithium niobate lightwave circuits. The company aims to construct a practical 10 Tbit/s-class large-capacity-core optical network. For contact information, see www.ntt.co.jp/sclab/contact_e.