Nec Corporation

Ryu Yokoyama

Takaaki Ogata

Satoshi Ishii

Yasuhiro Aoki

Shuji Yamashita

Kenichi Yoneyama

At an optical transmission system that uses plural light sources for Raman amplification, even when a failure occurred in a pumping light source in one of the light sources for Raman amplification, the signal light output level and its wavelength characteristic are not deteriorated at the final stage, and the number of components in the system is not made to be large and the cost of the system is not made to be high. This optical transmission system is provided. At an optical transmission system using 'n' light sources for Raman amplification, a first to 'n&#x2212;1'th light sources for Raman amplification do not provide spare pumping light sources, and an &#x201c;n&#x201d;th light source for Raman amplification provides the spare pumping light sources. When a pumping light source in one of the &#x201c;n&#x201d; light sources for Raman amplification had a failure, the spare pumping light source in the &#x201c;n&#x201d;th light source for Raman amplification corresponding to the failure occurred pumping light source is worked. With this, the signal light output level and its wavelength characteristic are recovered to a normal state before the failure occurred.

Optical transmission system and optical amplification method used in the system

An optical amplifying and relaying system capable of easily and highly accurately monitor troubles in optical amplifiers provided in an up and a down optical fiber transmission line opposing each other is disclosed. Monitoring light signal folding-back lines including variable optical attenuatorsandand wavelength selective reflecting meansand, respectively, are provided between optical transmission lines Land Lwhich oppose each other and on which optical amplifiersandare disposed each other.

Optical amplifying and relaying system

An optical amplifying and relaying system capable of easily and highly accurately monitor troubles in optical amplifiers provided in an up and a down optical fiber transmission line opposing each other is disclosed. Monitoring light signal folding-back lines including variable optical attenuatorsandand wavelength selective reflecting meansand, respectively, are provided between optical transmission lines Land L, which oppose each other and on which optical amplifiersandare disposed each other.

Flatness of a gain (optical output level) is maintained even when a wavelength division multiplex signal light (WDM signal light) is amplified in an optical amplification utilizing Raman amplification function. The optical amplifier comprises: two (first and second) pumping light sources for Raman amplification for outputting first and second pumping lights; the wavelength multiplexer for Raman amplification for allowing the first and second pumping lights to be incident on optical fiber transmission paths, where the WDM signal light propagates, in the direction opposite to the propagation direction of the signal light. The signal lights are Raman amplified by the both pumping lights. A wavelength of the first pumping light is set such that the gain of the Raman amplified signal light declines in the right direction, and, on the other side, the wavelength of the second pumping light is set such that the gain declines in the left direction. Gradients for showing a relation between the wavelength and the gain in Raman amplification by the first and second pumping lights are made to be in opposite directions from each other. Optical output levels and the wavelengths of the first and second pumping lights are set such that the gains for the signal lights included in the Raman amplified WDM signal light become substantially equal to each other.

Optical amplifier, optical amplifying repeater and transmission apparatus of wavelength division multiplexed signal light using the same

An optical signal repeater, in which an output level of each optical signal of WDM optical signals does not change even when the number of wavelengths of inputted WDM optical signals changes, amplifies WDM optical signals transmitted from an optical transmitter via an optical fiber transmission line. A pumping light source outputs pumping light used for amplifying the WDM optical signal. A multiplexer transmits the pumping light to an amplifier, and a splits the amplified WDM optical signals into two parts. A wavelength selection type reflector reflects only an optical signal having a specified wavelength in one part of the amplified WDM optical signals. An automatic output level controller controls the pumping light output from the pumping light source so that the power level becomes a designated level. A reflected optical signal transmitter transmits the optical signal having the specified wavelength reflected to the automatic output level controller.

Optical signal repeater and output level control method used in this repeater

An optical amplifier repeater is provided having a first optical amplifier that amplifies a main signal light and supervisory signal light transmitted on an up optical-fiber transmission line and a second optical amplifier that amplifies the main signal light and supervisory signal light transmitted on a down optical-fiber transmission line. Further, a transfer unit that is provided transfers part of the supervisory signal light transmitted on the up optical-fiber transmission line onto the down optical-fiber transmission line and transfers part of the supervisory signal light transmitted on the down optical-fiber transmission line onto the up optical-fiber transmission line. The transfer unit has an optical amplifier output side transfer unit that transfers supervisory signal light reflected by a first light-reflecting device inserted to the output side of the first optical amplifier to the output side of the second optical amplifier, and transfers the supervisory signal light reflected by a second light-reflecting device inserted to the output side of the second optical amplifier to the output side of the first optical amplifier.

Optical amplifier repeater

An optical transmission system having an optical regeneration circuit for regenerating a signal with a deteriorated signal to noise ratio. A signal light at wavelength &lgr;1 which includes a noise light is composed with a continuous light at wavelength &lgr;2 outputted from a light source to obtain a composed signal light in an optical coupler. The composed signal light is passed through a saturable absorption type optical element which transmits only the signal light having a light intensity equal to or greater than a threshold value, thereby removing the included noise light. From the signal light, only the signal at the same wavelength &lgr;2 as the wavelength of the continuous light is extracted by a wavelength divider and data signal of the incident signal light is replicated in the continuous light and outputted. Thus, a signal light having no deterioration of the signal to noise ratio at wavelength &lgr;2 can be regenerated from the signal light having the deteriorated signal to noise ratio.

Growing community of inventors

Tokyo, Japan

Ryu Yokoyama