Nec Corporation

Tadayuki Chikuma

Tsutomu Tajima

A wavelength multiplexing optical transmitting apparatus includes a plurality of optical transmitters for transmitting optical signals having mutually different wavelengths, a wavelength multiplexing circuit for wavelength multiplexing optical signals, an optical amplifier for directly amplifying the wavelength multiplexed optical signal and for producing an amplified multiplexed optical signal, an optical signal counting detector for branching the amplified multiplexed optical signal into signals of the respective wavelengths and for detecting the number of optical signals presently being transmitted, and an optical amplifier control circuit for controlling an output from the optical amplifier according to the number of optical signals; the optical amplifier includes a fiber made of a material to which a rare earth element is added and an excitation light to the fiber; the optical amplifier control circuit includes an excitation light control circuit for controlling an intensity of the excitation light according to the number of light signals; wherein to obtain an intensity of amplified optical signal predetermined according to the number of light signals, the excitation light control circuit sets an injection current to the excitation light source.

Optical amplifying apparatus and linear relay optical amplifier

In an optical transmission system in which an optical main signal and a monitoring control optical signal are wavelength-multiplexed and transmitted from a transmitter and the optical signal is directly amplified by a repeater and transmitted, low frequency pulse signals which are synchronized with the respective optical main signal and monitoring control signal are multiplexed with each others, a distance of a transmission section is specified by a phase difference between the low frequency pulse signals according to a difference in propagation rate of a transmission line due to a difference of wavelength between the optical main signal and the monitoring control signal and the optimal dispersion compensation is made possible even when a required dispersion compensation is changed due to a change of the transmission line by switching the optical transmission line to a DCF having an optimal amount of dispersion compensation.

Optical transmission system

Optical signals transmitted from optical transmission panels are received by photodetectors, which detect the number of actually transmitted optical signals. A control signal depending on the number of optical signals detected is supplied to an optical amplifier. The intensity of a combined optical signal amplified by the control signal is controlled by controlling a current supplied to a pumping light source. Information representative of the number of optical signals detected is superposed onto the amplified optical signal by generating the current supplied to the pumping light source as a sine-wave signal depending on the detected number of optical signals. In a downstream optical repeater, the information representative of the number of optical signals is extracted, and the optical signal is amplified, after which the information representative of the number of optical signals is superposed again onto the amplified optical signal for transmission. Even when some of the optical transmission panels fail to operate and the optical signals transmitted therefrom are interrupted, since the combined optical signal is amplified depending on the number of optical signals detected, the optical signals are maintained at a constant gain and output level.

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Tokyo, Japan

Tadayuki Chikuma