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This Letter reports the first successful generation of an optical data pulse stream at bit rates as high as 640 Gbit/s – 1.28 Tbit/s, achieved by using an optical time domain multiplexing technique from a 10 Gbit/s unit. The OTDM consists of a silica planar lightwave circuit with a seven-step Mach-Zehnder interferometer. The pulse width of the original data stream is as short as 220 fs. The average output powers at 640 Gbit/s and 1.28 Tbit/s through a high power EDFA are 170 and 300 mW, respectively.

Experimental field transmissions of solitons at 10 Gbit/s over 2000 km have been successfully demonstrated using part of the Tokyo metropolitan optical loop network. The network is composed of conventional dispersion-shifted 200 core optical fibre cable which was not originally intended for soliton transmission. However, with the dispersion-allocated soliton transmission technique, an error-free 13 ps soliton data train was successfully transmitted over 2000 km. The power penalty at a BER of 10/sup -10/ was 3.1 dB.

A 170 fs transform-limited pulse train at 10 GHz has been successfully generated for the first time with a picosecond stable fibre laser and a dispersion-decreasing erbium-doped fibre amplifier which acts as a very efficient active soliton pulse compressor.

A simple and highly sensitive bias condition monitoring circuit is presented for optical quadrature phase shift keying (QPSK) modulators. The proposed asymmetric dithering technique is shown to be capable of monitoring three bias states simultaneously. The dithering penalty is shown to be less than 0.2 dB.

Spectrally efficient (2 bit/s/Hz) 1 Tbit/s DWDM transmission of 111 Gbit/s no-guard-interval PDM CO-OFDM signals with 50 GHz spacing over DSF is demonstrated. The record transmission distance of 2100 km was achieved for a 100 Gbit/s-data-rate CO-OFDM system.

The authors report a fibre/fibre-grating pulse compressor suitable for compressing high energy, high repetition rate picosecond pulses to sub-picosecond durations. Linearly chirped fibre gratings and an optical circulator are used for output chirp compensation. This scheme is not limited to wavelength regimes with anomalous dispersion in the fibre. A 10 GHz train of 7.1 ps pulses at 1548 nm was compressed to 720 fs, corresponding to a compression factor of ~10. At maximum power, the compressed pulses had 18 pJ energies and peak powers of 15 W.

Experimental field transmissions of solitons at 20 Gbit/s over 2 000 km have been successfully demonstrated using part of the Tokyo metropolitan optical network consisting of conventional dispersion-shifted fibre cables. The soliton pulse width was 10 ps and a polarisation-insensitive MQW electroabsorption modulator was used for demultiplexing. The power penalty at a BER of 10-10 was ~3.5 dB.

Polarisation- and time-domain-multiplexed 160 Gbit/s soliton signals have been successfully transmitted over 200 km for the first time. The soliton source was a 10 GHz regeneratively modelocked fibre laser and a planar lightwave circuit was used for optical multiplexing. The soliton pulse width was approximately 1.5 ps. A polariser and a nonlinear loop mirror were used for demultiplexing from 160 to 10 Gbit/s. >

A very stable 1.8 ps pulse train at 20 GHz was successfully obtained at a wavelength of 1.55 µm from a regeneratively modelocked erbium-doped fibre laser. The output pulses were compressed to as short as 172 fs by using a dispersion-decreasing erbium-doped fibre amplifier.

Single-polarisation 80 Gbit/s soliton data signals have been successfully transmitted over 500 km. The soliton source was a modelocked fibre laser and a planar lightwave circuit was used for stable optical multiplexing. A nonlinear loop mirror was used for demultiplexing, in which unequal amplitude solitons were used for clock extraction.

1.6 ps optical pulses at a wavelength of 1.3 μm have been successfully generated from a Pr3+-doped fibre laser with a nonlinear amplifying loop mirror, for the first time. The laser was a self-starting system and exhibited hysteresis with output power against pump power due to the nonlinear switching.

A single channel, time domain multiplexed 640 Gbit/s data signal has been successfully transmitted over 60 km. The width of the input pulse train was as little as 400 fs and a walk-off free, dispersion flattened nonlinear loop mirror was used to demultiplex the signal to 10 Gbit/s. The maximum transmission distance was mainly determined by the polarisation mode dispersion as well as the third order dispersion.

Pulse trains with repetition rates as high as 80~200 GHz were obtained at 1.55 µm, using rational harmonic mode-locking with an erbium doped fibre laser. A fundamental repetition frequency (fosc) of 40 GHz was first generated by applying a 40 GHz modulation frequency to an LN intensity modulator in the fibre cavity, in which the longitudinal mode spacing (Δf) was 1.5 MHz. By rationally detuning the modulation frequency by Δf/n, the authors succeeded in obtaining a repetitive oscillation of (nfosc+Δf). The maximum frequency was 200 GHz, at which n corresponds to 5.

A new type of femtosecond erbium-doped fibre laser with nonlinear polarisation rotation is presented, in which a polariser is installed at a point-symmetric position against a polarisation-sensitive optical isolator in the ring laser cavity. This technique enables us to remove the continuum (DC component) in the oscillation waveform completely and to obtain a stable pulse train as short as 136–145 fs with a 56 MHz repetition rate.