Progress Toward Ultrahigh-bit-rate All-optical TDM Transmission Systems

A b s t ra c t -The re('cn I progress t owu i d ltlr ru/(i SI opl'icu 1 ,fihi> r t ru nsni ission systems employing a I 1 opticul lime-domnin n7idtiple.xiti~ (7DM) frclriiiqrre.z is reviewed. 0utlinc.s of (he latest I00Ghitl.s transnzission experiments und lhci ri~lutecl Icc.hno1ogie.r are de.vc,rihed including state-of-the-art performuni'es arulBiture prospects. All-optical time-domain signal processing technologies are now being developed for realizing ultrahigh-bit-rate optical time-division-multiplexing (TDM) transmission systems [ 1-51. The major technologies include high-speed picosecond optical pulse generation [6-81, all-optical multi/demultiplexing (MUX/DEMUX) [9171, linear or soliton pulse transmission, and optical timing extraction techniques [4,18-24]. Here, recent progress on very high-speed optical TDM transmission up to 100Gbit/s is introduced together with the essentiial technologies. Figure 1 depicts the experimental setup of the latest lOO-Gbit/s transmission experiment over 200 km that uses newly developed optical TDM technologies [4]. A wavelength-tunable mode-locked Er fiber laser (ML-EDFL) [8] provides stable 6.3-GHz, :3.5 ps transform-limited (TL) pulses for external modulation (2"-1, PRBS) by a LiNb03 modulator. A 16:l planar lightwave circuit (PLC) multiplexer stably multiplexes the baseline 6.3 Gbit/s signal into 100 Gbit/s. The TDM IOO-Gbit/s signal is then transmitted through five fibers connected via four in-line Ed-doped fiber amplifiers. The center wavelength of the ML-EDFL is set to the zero dispersion wavelength of the 200 km fiber. At the receiver side, a novel timing extraction phase-locked loop (PLL) [4] using a traveling-wave laser-diode amplifier (TW-LDA), used a$ a phase detector, extracts the prescaled clock of 6.3-GHz from the received 100-Gbit/s signal. Using the four-wave-mixing (FWM) process instead of gainmodulation as adopted in the previous PLL [ 221, very stable polarization-independent (PI) timing extraction is achieved with the lowered jitter of 0 . 3 ~ ~ . The extracted 6.3-GHz clock is used to drive both the all-optical DEMUX and the optical receiver. Finally, the novel PI-FWM demultiplexer (DEMUX) [ 171 using a polarization-maintaining 3 k.m fiber demultiplexes the 100Gbitls signal into the 6.3GbiUs original. With this configuration, a 100 Gbitls optical signal, 16 x 6.3-Gbit/s, has been successfully transmitted through a 200-km fiber without any polarization controllers. 6.3 G bivs 100 Gbit/s