Izumi Yokota

Evaluation of 4-Gbit/s optical fiber transmission distance with direct and external modulation

Transmission characteristics for a recently modulated measured distributed-feedbacked (DFB) laser and an externally modulated DFB laser using a Ti:LiNbO/sub 3/, Mach-Zehnder modulator at 4 Gb/s are discussed. The transmission characteristics are estimated by an advanced eye-pattern analysis method. The maximum measured fiber dispersion with a directly modulated laser is 100 to 140 ps/nm when the chirp power penalty is 1 dB. However, for external modulation, there is no power penalty after transmission over a 2220-ps/nm dispersive fiber. This confirms that external modulation has superior transmission characteristics. The modulation scheme for 4-Gb/s systems in terms of these results is discussed. >

1.05 Tbit/s WDM transmission over 8,186 km using distributed Raman amplifier repeaters

We have achieved a 1.05 Tera bit/s WDM transmission over 8186 km using distributed Raman amplifier repeaters. Signal bandwidth was 31.2 nm and the optical SNR improvement was about 1.5 dB in contrast to using an EDFA repeater.

Optical coherent broad-band transmission for long-haul and distribution systems using subcarrier multiplexing

The system configuration and future possibility of a coherent optical transmission system using subcarrier multiplex- ing (SCM) techniques are described. First, signal multiplexing techniques for coherent optical trans- mission are compared, and appropriate application for coherent SCM system is discussed. By comparing optical modulation meth- ods, optical frequency modulation (FM) using direct modulation of a DFB-LD and a heterodyne detection is shown to be feasible. lkansmission system using a configuration with a local laser in the transmitter is unaffected by polarization and is cost-effective. Phase noise can be suppressed by a phase-noise-canceling circuit (PNC) in a heterodyne receiver. This circuit is also effective for compensating for the frequency instability of light sources. A theoretical simulation of a coherent SCM system showed that a 100 channel of 30-MHz FM signal or a 15 channel of 155-Mb/s signal can be distributed to 10 000 subscribers using single stage or double stage optical amplifiers. To confirm the feasibility of coherent SCM transmission, pre- liminary experiments have been performed with optical FM by 2-channels 560-Mb/s ASK-SCM signal and a heterodyne detection using 3-electrode DFB-LDs. With a local LD setting at the transmitter, a span-loss margin of 40.7 dB was obtained using single stage Er3+-doped fiber amplifier (EDFA), and the system was insensitive to the state of polarization in the transmission fiber. In a subcarrier transmission of 560 Mb/s DPSK signal, the PNC effectively suppressed phase noise and the influence of IF frequency deviation. Finally, application of coherent SCM combined with optical frequency division multiplexing (OFDM) is discussed. A model allocation of optical carriers is proposed and possible receiving channel number is estimated.

Modulation schemes for multi-gigabit optical transmission systems

Compares four intensity modulation schemes in terms of their spectrum broadening and transmission characteristics. The schemes examined are direct modulation, Mach-Zehnder interferometer type modulation, electroabsorption type modulation, and a direct phase-shift and self-homodyne intensity modulation (DPSH-IM) method proposed here. The dispersion-limited transmission distance of these schemes has been estimated by computer simulation. It is shown that direct modulation of currently available distributed feedback lasers suffers large waveform distortions due to chirping and chromatic dispersion in the fibre. It is concluded that unless chirping characteristics of lasers are greatly improved, low-chirp modulation schemes such as the Mach-Zehnder interferometer type modulation, electroabsorption type modulation, and the DPSH-IM will be adopted for multigigabit long-distance optical transmission systems.<<ETX>>

Impact of stimulated Raman scattering between WDM signals over an ultra-wide bandwidth

We investigated quantitatively the gain deviation caused by stimulated Raman scattering between WDM signals over a 200-nm-wide band. The results of calculations and experiments indicated that the gain deviation saturated as a WDM signal bandwidth became wider.

1.22 Tbit/s WDM transmission over 7,221 km with 38 nm bandwidth expanded by distributed Raman amplifier and EDFA

By using a signal bandwidth expansion combined with a distributed Raman amplifier and an EDFA, we have achieved WDM transmission over 7,221 km at 1.22 Tbit/s in the L-band alone. The scheme seems to be more practical because it has relatively low loss gain equalization, the shorter wavelength OSNR improvement, and effective gain tilt compensation.