Norio Seki

Measurement of mode partition in DFB lasers

Some DFB (distributed feedback) laser diodes have a satellite mode beside a main DFB mode even if FP modes are suppressed. In this paper, the mode partition noise is presented for several DFB lasers operating in multilongitudinal modes. The results show that under modulation at 140 Mbit/s, the mode partition coefficient k2of multimode DFB lasers is very small and at most 0.02 while that of FP lasers biased at the threshold level is 0.03 to 0.12. The numerical evaluation of the mode partition effect in two-mode DFB lasers suggests that a 20- dB suppression of the satellite mode power is enough to achieve a repeater spacing of over 100 km in the 280 Mbit/s fiber-optic transmission system with less than 0.1-dB power penalty.

Repeater spacing of 280 Mbit/s single-mode fiber-optic transmission system using 1.55 µm laser diode source

This paper describes an attainable repeater spacing for a high bit-rate single-mode fiber-optic transmission in the 1.55 μm wavelength region where laser mode partition noise comes to be significant. An expression for evaluating mode partition noise is given as the form involving the influence of laser spectral fluctuations under high bit-rate modulation, together with the intersymbol interference and the equalized pulse shape in tile optical receiver. After the validity of its numerical results is confirmed experimentally, the resulting evaluation of laser mode partition noise is connected to a systematic discussion on the attainable repeater spacing of a 280 Mbit/s fiber-optic transmission system operating at 1.55 μm, along with fiber loss versus dispersion tradeoffs. This discussion permits the attainable repeater spacing to be 60-70 km for the combination of a laser diode with 1.5-2.0 nm spectrum broadening and a fiber with the loss of 0.5 dB/km and the dispersion of 4-6 ps/km - nm.

Remote-control signal of optical loopback for supervision of long-haul fiber-optic undersea cable systems

A remote-control signal for repeater supervision to be used in a remote-controlled optical loopback method of a long-haul optical undersea cable system is proposed on out-of-service basis and the results of its transmission experiment by a field trial system are theoretically analyzed. The remote-control signal is basically composed of a pseudo-random sequence with a periodicity corresponding to a repeater selection frequency. 500 repeater selection frequencies will be available using a monolithic crystal filter (MCF) as a detection filter. By a field trial experiment, the controllability was shown to be maintained even at a bit error rate (BER) of up to 10-1with a control signal level which, being decreased by 1.9 dB, is still more than 30 dB over a filtered noise level due to random bit errors.