Oki Electric Industry Co., Ltd.

Shusei Aoki

Katsuhiro Ishimura

Yukihiro Ozeki

Mikiya Suzuki

Shigeru Shikii

Hiroshi Takamoto

An EDFA is comprised of a pre-amp and a post-amp which are connected in series, a photocoupler a long wave pass filter (LWPF) and an LWPF controller The photocoupler is connected to an input-stage of the EDFA and enters the light signal in the LWPF controller The LWPF is located between the pre-amp and the post-amp and its cutoff wavelength is adjustable. A short-wavelength-part of the light signal which is amplified by the pre-amp is cut off by the LWPF The LWPF controller detects an input signal power of the input light signal and adjusts the cutoff wavelength of the LWPF based on the detected input signal power. Gain of light signals which are output from the post-amp are equalized ranging the extensive input signal power and covering wide signal-wavelength bands.

Optical fiber amplifier

Each optical repeater in an optical transmission system includes an optical amplifier, and a control circuit for controlling the optical transmission. Furthermore, each optical repeater transmits management information to the next optical repeater. The control circuit checks the status of the optical amplifier and obtains monitoring information. The control circuit generates management information in accordance with the monitoring information and the management information transmitted from the upstream side optical repeater. The management information is converted to an optical signal and transmitted to the next optical repeater. A receiving station receives the management information. The management information includes an ID code for an optical repeater which has failed and the status of the failure. Different categories of management information have priorities which can be changed by the receiving station, and thus the receiving station can detect the status of the optical transmission line easily and flexibly.

Method and apparatus for alarm surveillance for an optical transmission

In a variable high-voltage generating circuit for an avalanche photodiode, a pulse oscillating circuit generates pulses, a current driving circuit current-amplifies the pulses, a Cockcroft-Walton circuit boosts and rectifies the pulses from the current driving circuit, and a low-pass filter is connected at the output of the Cockcroft-Walton circuit. The avalanche photodiode is connected in series with a first resistor, and the series connection is connected to receive the output of the low-pass filter. A series connection of a transistor and a second resistor is connected in parallel with the series connection of the avalanche diode and the first resistor. A control circuit applies a variable signal to the base of the transistor, thereby to vary the voltage applied across the APD.

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Tokyo, Japan

Shusei Aoki