Abstract: An optical amplifier includes a light source that generates excitation light in a wavelength band for Raman-amplifying signal light, an input unit that inputs the signal light and the excitation light to an optical fiber, and a processor connected to the light source. The processor executes a process including: acquiring a gain reduction amount of Raman amplification according to power of the signal light input to the optical fiber; determining a target gain based on the gain reduction amount acquired; judging whether a Raman gain corresponding to power of spontaneous emission light generated when the signal light is Raman-amplified in the optical fiber achieves the target gain determined; and setting power of the excitation light according to a judging result at the judging.

Abstract: An optical amplifier is disclosed that includes an input monitoring part configured to monitor an input wavelength division multiplexed light; an amplification part configured to amplify and output the input wavelength division multiplexed light; an output monitoring part configured to monitor the wavelength division multiplexed light output from the amplification part; a gain control part configured to perform gain control so that the ratio of output light intensity monitored by the output monitoring part to input light intensity monitored by the input monitoring part is constant; and a response speed switching part configured to switch the response speed of the gain control.

Abstract: A wavelength division multiplexed optical amplifier, enabling elimination of the problems of oscillation and fluctuation in output due to ASE at the time of a rapid change in the number of input wavelengths, provided with a first-stage optical amplifying unit, second-stage optical amplifying unit, a common AGC circuit for common AGC of the first and second optical amplifying units, and a pumping light distribution means for applying pumping light to the first and second-stage optical amplifying units with a predetermined distribution ratio.

Abstract: An optical amplifier is disclosed that includes an input monitoring part configured to monitor an input wavelength division multiplexed light; an amplification part configured to amplify and output the input wavelength division multiplexed light; an output monitoring part configured to monitor the wavelength division multiplexed light output from the amplification part; a gain control part configured to perform gain control so that the ratio of output light intensity monitored by the output monitoring part to input light intensity monitored by the input monitoring part is constant; and a response speed switching part configured to switch the response speed of the gain control.

Abstract: A wavelength division multiplexed optical amplifier, enabling elimination of the problems of oscillation and fluctuation in output due to ASE at the time of a rapid change in the number of input wavelengths, provided with a first-stage optical amplifying unit, second-stage optical amplifying unit, a common AGC circuit for common AGC of the first and second optical amplifying units, and a pumping light distribution means for applying pumping light to the first and second-stage optical amplifying units with a predetermined distribution ratio.

Abstract: Locating a fault of a transmission line in a system which performs bidirectional optical communication between a station-side device and plural subscriber devices and in which a transmission line 1 extending from the station-side device is branched by a branching/coupling device into plural transmission lines 2 each connected to the subscriber devices. The present invention provides a supervisory unit to the transmission line 1 and attenuators to respective transmission lines 2. The supervisory unit emits an optical test signal, observes a reflected signal of the test signal while changing the attenuation of the attenuators and locates the fault based on a return time and a return loss when the test signal returns as a reflected signal.

Abstract: The low voltage current mirror circuit of the present invention including multiple circuit elements each forming a current mirror, and concatenating the multiple circuit elements to form a cascode current mirror circuit, comprises voltage dropping means for mutually connecting inter-control-electrode nodes of each of the multiple circuit elements, to cause the predetermined voltage drop between the inter-control-electrode nodes. According to such a simplified constitution, it is realized to lower the input voltage and output voltage of the current mirror circuit.

Abstract: A drain terminal of a first N-channel MOS transistor is connected to an output side of a first current mirror input current via a voltage drop device, a first current mirror input current is supplied to the gate terminals of first, third, and fifth N-channel MOS transistors, and a second current mirror input current is supplied to the gate terminals of second and fourth N-channel MOS transistors.