High spectral efficiency, wide bands allow 25.6 Tbit/s data transmission over fiber

To transmit information down an optical fiber at the highest possible rate, boosting the spectral efficiency (in bits per second per Hertz) is key. By combining a high spectral efficiency of 3.2 bit/s/Hz with optical transmission over the C (1529.55-1561.01 nm) and L (1570.83-1604.03 nm) bands, engineers at Alcatel-Lucent (Holmdel, NJ, and Nozay, France), NICT (Tokyo, Japan), and Sumitomo Osaka Cement (Funabashi, Japan) have sent data at a rate of 25.6 Tbit/s down 240 km of standard single-mode fiber in three 80 km Raman-amplified spans.

Based on differential quadrature phase-shift-keyed signaling, the system contained 80 distributed-feedback lasers (combined with external modulators) in each band operated on a 50 GHz grid, with each adjacent spectral line orthogonally polarized with respect to its neighbors. Additional modulators produced the phase-shift keying. Pseudo-random bit sequences of length (215 - 1) were transmitted through the backward-Raman-pumped fiber spans. The four simultaneous 10.7 Gbit/s end signals had bit-error rates (BERs) of lower than 2 × 10-3 (forward error correction would reduce these BERs to under 10-16 with a 7% overhead). Contact Alan Gnauck at gnauck@lucent.com.