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.

We show the general formula of the signal to noise ratio in chains with amplifiers and attenuators using nonclassical properties of light. From the results, we show that quantum noise can be effectively controlled. For the application we show that the optical fiber transmission system with conventional optical amplifiers can be designed as if the noiseless optical amplifiers are used.

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.

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.