Abstract: A Raman amplifier can easily reduce the gain variation in Raman amplification even when the power of an input signal varies. The Raman amplifier is provided with (a) an optical fiber that Amplifies an input lightwave to produce an output lightwave, (b) a pump-lightwave-supplying means that supplies pump lightwaves having a plurality of wavelengths to the optical fiber, and (c) a control unit that controls only the power of the pump lightwave having the shortest wavelength among the pump lightwaves so that the average value of the gain of the Raman amplification by the optical fiber in an intended wavelength range can be maintained constant.

Abstract: The present invention relates to an optical amplifier that can operate with low electric power consumption and can sufficiently compensate for the variation of gain spectrum induced by temperature fluctuation. The optical amplifier comprises an amplification optical fiber, a pumping light supplier, and a gain equalizer. The light inputted to the optical amplifier is amplified in the amplification optical fiber, and thereafter the amplified light passes through the gain equalizer. By passing the amplified light through the gain equalizer, the gain spectrum of the amplification optical fiber is equalized and the temperature dependence of the gain spectrum is compensated. At this time, the wavelength of the pumping light supplied from the pumping light supplier to the amplification optical fiber is set such that the gain variation spectrum of the amplification optical fiber depending on temperature becomes smooth.

Abstract: The invention relates to an optical amplifier capable of achieving high-speed gain control in a wide dynamic range with a simpler constitution. A gain control circuit of the optical amplifier includes a first photodetector for outputting a voltage having a linear relation with power of part of signal light to be inputted to the optical amplifier medium, a second photodetector for outputting a voltage having a linear relation with power of part of the signal light amplified in the optical amplifier medium, a comparator for outputting a difference between the voltages respectively outputted from the first and second photodetectors, and a drive circuit for supplying a desired drive current to a pumping light source in response to the voltage outputted from the comparator.

Abstract: The invention relates to an optical amplifier capable of achieving high-speed gain control in a wide dynamic range with a simpler constitution. A gain control circuit of the optical amplifier includes a first photodetector for outputting a voltage having a linear relation with power of part of signal light to be inputted to the optical amplifier medium, a second photodetector for outputting a voltage having a linear relation with power of part of the signal light amplified in the optical amplifier medium, a comparator for outputting a difference between the voltages respectively outputted from the first and second photodetectors, and a drive circuit for supplying a desired drive current to a pumping light source in response to the voltage outputted from the comparator.

Abstract: The present invention relates to an optical amplifier and the like comprising a structure for effectively suppressing transient output signal power fluctuations caused by delays in control. The optical amplifier including an amplification optical fiber comprises a control system (17) for monitoring, through a light-receiving device, power fluctuations in part of light tapped by a branching device and regulating the power of pumping light outputted from a pumping light source. A delay medium is disposed between the branching device and the amplification optical fiber, so as to reduce the difference between the time required for signals transmitted through the branching device to reach the input end of the amplification optical fiber and the response time of the control system, thereby suppressing fluctuations in the output signal level.

Abstract: The present invention relates to an optical amplifier comprising a structure which prevents transmission quality from lowering and enables constant gain control with a higher speed and higher accuracy. In a typical embodiment of the present invention, amplified light from an EDF is once guided to an optical filter by way of an optical circulator. Of thus guided amplified light, noise light passes through the optical filter, whereas each of signal components is reflected thereby, so as to separate the noise light and signal components from each other. The noise light having passed through the optical filter is detected by a photodetector, and gain control is carried out by a gain control circuit so as to suppress fluctuations in the detected noise light power.

Abstract: The present invention relates to an optical amplifier and the like comprising a structure for effectively suppressing transient output signal power fluctuations caused by delays in control. The optical amplifier including an amplification optical fiber comprises a control system (17) for monitoring, through a light-receiving device, power fluctuations in part of light tapped by a branching device and regulating the power of pumping light outputted from a pumping light source. A delay medium is disposed between the branching device and the amplification optical fiber, so as to reduce the difference between the time required for signals transmitted through the branching device to reach the input end of the amplification optical fiber and the response time of the control system, thereby suppressing fluctuations in the output signal level.

Abstract: The present invention relates to an optical amplifier and the like comprising a structure for effectively suppressing transient output signal power fluctuations caused by delays in control. The optical amplifier including an amplification optical fiber comprises a control system for monitoring, through a light-receiving device, power fluctuations in part of light tapped by a branching device and regulating the power of pumping light outputted from a pumping light source. A delay medium is disposed between the branching device and the amplification optical fiber, so as to reduce the difference between the time required for signals transmitted through the branching device to reach the input end of the amplification optical fiber and the response time of the control system, thereby suppressing fluctuations in the output signal level.