By using cooled Ge-PIN photodiode to 77 K (-196) with liquid nitrogen and lock in amplification technique, automatic polarization spectral response measurement systems with measuring dynamic range of about 36 dB has been developed. From the experimental results, it is confirmed that the spectral response of polarization beam splitting ratios of fused-taper fiber couplers are slightly depending on the incident polarization angle.

2.4 Gbit/s transmission experiment over 301 km employing five semiconductor-laser optical amplifiers in cascade has been demonstrated. The results present the feasibility of the long span optical fiber transmission using semiconductor-laser optical amplifiers.

An optical amplifier repeater using two-stage semiconductor laser amplifiers with automatic power control (APC) system was inplemented for the first time. The APC system was realized by the direct monitoring of the amplified signal power. The assessment of the optical amplifier repeater confirmed the usefulness of the APC syster.

2.4 Gbit/s 4 WDM transmission experiment using a traveling-wave laser amplifier has been demonstrated. The result indicated that there exists the appropriate optical input power to the laser amplifier in order to minimize both interchannel crosstalk penalty and beat noise induced penalty.

Using an interferometric detection technique with AC modulation for searching the interference fringe signal, highly accurate polarization mode dispersion (PMD) measurement with about 0.0028 ps/m resolution has been developed, and the PMD measurement in a 60 km-long installed optical submarine cabled fiber is presented.

2.4 Gbt/s WDM and bidirectional transmission experiments has been demonstrated in the 1.55µm window. The penalties due to cross talk in the demultiplexer are investigated. The system experiments of WDM and bidirectional transmission result in the system penalties of less than 0.3 dB.

Polarization fluctuation in optical fiber submarine cable coupling under periodic variable tensile force with 4-7 tons are presented. It is found that the polarization fluctuation of the optical fiber submarine cable coupling linearly changes with periodic variable tension.

The chromatic dispersion limitation for the longspan high-speed transmission using a LiNbO3 Mach-Zehnder modulator was estimated by computer simulation techniques taking account of the chirping effect in the modulator. The simulation result shows that the allowable chromatic dispersion to satisfy the 10% eye closure is around 10,000 ps/nm at 2.5 Gbit/s.

Using an interferometric detection technique with AC modulation for searching the interference fringe signal, highly accurate polarization mode dispersion (PMD) measurement with about 0.003 ps/m resolution has been developed, and the PMD measurement in a 60 km-long installed optical submarine cabled fiber is presented. Also, fiber length dependence of PMD and comparison of the interferometric PMD measurement with other wavelength scanning PMD method are described.