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.

May 1st, 2007

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.

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