Abstruct-A supervisory (SV) signal transmission scheme for long haul optical amplifier systems is described. The scheme is based on subcarrier overmodulation of the line signal and features simple configuration; due to the use of EDFA gain modulation, no additive optical components are required in a submarine repeater to transmit a response signal. This paper discusses the subcarrier modulation index and frequency used for the SV signaling, the most significant design parameters. The dependence of the signal-to-noise ratio (SNR) on the modulation index in SV signal transmission is analyzed to clarify the modulation index value required for reliable SV signaling. In addition, the line signal impairment caused by subcarrier overmodulation is also analyzed to show the system's in-service feasibility. The subcarrier frequencies used for command and response signal transmission are discussed from the experimental results on the frequency response of an optical amplifier system and EDFA gain modulation efficiency.

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The FSA submarine optical amplifier system (submarine fiber using optical amplifiers) has been developed. It can transmit signals up to 10 Gbit/s with a repeater spacing of 100 km. The submarine repeaters contain optical amplifiers for six line pairs to yield a maximum capacity of 60 Gbit/s. This paper describes its system configuration, the repeater configuration, and the fiber dispersion management scheme used to realize bit-rate flexible transmission and in-service monitoring.In long-haul optical amplifier systems, since the amplified spontaneous emission noise from the optical amplifier is the main impairment limiting the transmission distance, an S N R design technique that takes this noise into account is developed. Finally, the results obtained after the commercial installation of this system in the Kagoshima-Okinawa route (total length 905 km) are reported, including chromatic dispersion characteristics and S N R values at both 2.5 Gbit/s and 10 Cbit/s transmission. The effectiveness of the system design is verified through the demonstration of good transmission performance and the feasibility of in-service monitoring.

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