Abstract: An optical amplifier includes an optical amplification medium, an excitation source to stimulate the amplification medium to output at least one wavelength gain peak, and a gain equalizer to equalize the output of the amplification medium such that gain is produced at wavelengths other than the wavelength gain peak. The gain equalizer may attenuate gain at the peak wavelength. The gain equalizer may equalize the output of the amplification medium such that gain is produced at wavelengths less than the wavelength gain peak. The optical amplifier may include both a gain equalizer and automatic level control circuitry to respectively maintain substantially uniform gain at wavelengths within an optical signal band and maintain constant output power.

Abstract: An optical amplification device which includes first and second optical amplifiers, and a controller. The first optical amplifier receives a light and amplifies the received light. The second optical amplifier receives the light amplified by the first optical amplifier, and amplifies the received light. When a level of the light received by the first optical amplifier changes by &Dgr;, the controller controls a level of the light received by the second optical amplifier to change by approximately −&Dgr;. In various embodiments, the controller causes the sum of the gains of the first and second optical amplifiers to be constant. In other embodiments, the optical amplification device includes first and second optical amplifier and a gain adjustor. The gain adjustor detects a deviation in gain of the first optical amplifier from a target gain, and adjusts the gain of the second optical amplifier to compensate for the detected deviation.

Abstract: In an optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation, there are included an optical amplifying section (2) for amplifying and outputting inputted signal light, a plurality of excitation light sources (3, 4) and an excitation light source control section (5) for controlling operations of the excitation light sources (3, 4), wherein the excitation light sources are composed of a main excitation light source (3) and an auxiliary excitation light source (4), and the excitation light source control section (5) is equipped with a control section (7) which, when the number of channels in the inputted signal light is equal to or less than a predetermined number of channels, executes control whereby the main excitation light source (3) supplies excitation

Abstract: A method and system for controlling the gain of the amplification of an optical signal is provided that includes both electrical feedforward and feedback. In a feedforward portion of an optical amplifier, the method includes receiving an optical signal and measuring an input power. Based on the measured input power and a desired gain, a feedforward pump power is determined. The pump power is adjusted based on the determined pump power. In a feedback portion of an optical amplifier, an output power is measured and gain is determined based on the output power and the measured input power. The measured gain is compared to a desired gain and the pump power is adjusted based on that comparison.

Abstract: An optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation.

Abstract: An optical amplification device which includes first and second optical amplifiers, and a controller. The first optical amplifier receives a light and amplifies the received light. The second optical amplifier receives the light amplified by the first optical amplifier, and amplifies the received light. When a level of the light received by the first optical amplifier changes by &Dgr;, the controller controls a level of the light received by the second optical amplifier to change by approximately −&Dgr;. In various embodiments, the controller causes the sum of the gains of the first and second optical amplifiers to be constant. In other embodiments, the optical amplification device includes first and second optical amplifier and a gain adjustor. The gain adjustor detects a deviation in gain of the first optical amplifier from a target gain, and adjusts the gain of the second optical amplifier to compensate for the detected deviation.

Abstract: An optical amplifier, or optical repeater, for amplifying wavelength division multiplexed (WDM) light. A first demultiplexer demultiplexes the WDM light into first and second lights corresponding to different wavelengths in the WDM light. First and second optical amplifiers amplify the first and second lights, respectively. A first multiplexer multiplexes the amplified first and second lights into a multiplexed light. A dispersion compensator compensates for dispersion in the multiplexed light. A second demultiplexer demultiplexes the disperson compensated, multiplexed light into the first and second lights. Third and fourth optical amplifiers amplify the demultiplexed first and second lights, respectively. A second multiplexer multiplexes the amplified first and second lights from the third and fourth optical amplifiers into a WDM light. The optical amplifier can be configured so that the first and second lights travel through the dispersion compensator in opposite directions.

Abstract: The present invention relates to a wavelength-multiplexed light amplifying apparatus to be used in a state of being connected to a branching portion of a multiplexing/branching unit or to be used for a m×n matrix optical switch of an optical cross-connect. The wavelength-multiplexed light amplifying apparatus is composed of a plurality of wavelength-multiplexed light amplifying units and an optical feedback loop system. A signal input port of an optical branching section in one wavelength-multiplexed light amplifying unit is connected to an output side of an optical amplifying section in the preceding wavelength-multiplexed light amplifying unit. This configuration disperses the power loss of an optical signal to perform amplification with high efficiency and further enables the expansion of the branching port in the in-service.

Abstract: A Raman amplifier providing a wideband gain for use in a wavelength division multiplexing (WDM) optical communication system. In one embodiment, a first optical amplifier Raman amplifies a wavelength division multiplexed signal light in both a first wavelength band and a second wavelength band in accordance with a plurality of excitation (pumping) lights provided to the first optical amplifier, the first and second wavelength bands being different from each other. A divider divides the amplified signal light into first and second lights in the first and second wavelength bands, respectively. A second optical amplifier amplifies the first light and has a gain band in the first wavelength band. The third optical amplifier amplifies the second light and has a gain in the second wavelength band. In various embodiments, a gain equalizer and/or an optical isolator is used in combination with the first optical amplifier providing the Raman amplification.

Abstract: In an optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation, there are included an optical amplifying section (2) for amplifying and outputting inputted signal light, a plurality of excitation light sources (3, 4) and an excitation light source control section (5) for controlling operations of the excitation light sources (3, 4), wherein the excitation light sources are composed of a main excitation light source (3) and an auxiliary excitation light source (4), and the excitation light source control section (5) is equipped with a control section (7) which, when the number of channels in the inputted signal light is equal to or less than a predetermined number of channels, executes control whereby the main excitation light source (3) supplies excitation

Abstract: Method and apparatus using four wave mixing (FWM) for wavelength conversion. An optical waveguide doped with a rare earth element is pumped so that an input optical signal is amplified as the input optical signal travels through the optical waveguide. The optical waveguide is provided with at least one light which, together with the input optical signal, causes four wave mixing (FWM) to occur in the optical waveguide. The FWM causes a converted optical signal to be produced in the optical waveguide and having a wavelength different from the input optical signal. If the input optical signal is modulated by a transmission signal, then the converted optical signal will also be modulated by the transmission signal. The optical waveguide can be, for example, an erbium doped optical fiber operating as an erbium doped fiber amplifier (EDFA). Therefore, an EDFA can be used for both amplification and wavelength conversion.

Abstract: A Raman amplifier providing a wideband gain for use in a wavelength division multiplexing (WDM) optical communication system. In one embodiment, a first optical amplifier Raman amplifies a wavelength division multiplexed signal light in both a first wavelength band and a second wavelength band in accordance with a plurality of excitation (pumping) lights provided to the first optical amplifier, the first and second wavelength bands being different from each other. A divider divides the amplified signal light into first and second lights in the first and second wavelength bands, respectively. A second optical amplifier amplifies the first light and has a gain band in the first wavelength band. The third optical amplifier amplifies the second light and has a gain in the second wavelength band. In various embodiments, a gain equalizer and/or an optical isolator is used in combination with the first optical amplifier providing the Raman amplification.

Abstract: In an optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation, there are included an optical amplifying section (2) for amplifying and outputting inputted signal light, a plurality of excitation light sources (3, 4) and an excitation light source control section (5) for controlling operations of the excitation light sources (3, 4), wherein the excitation light sources are composed of a main excitation light source (3) and an auxiliary excitation light source (4), and the excitation light source control section (5) is equipped with a control section (7) which, when the number of channels in the inputted signal light is equal to or less than a predetermined number of channels, executes control whereby the main excitation light source (3) supplies excitation

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first-light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: An optical amplifier, or optical repeater, for amplifying wavelength division multiplexed (WDM) light. A first demultiplexer demultiplexes the WDM light into first and second lights corresponding to different wavelengths in the WDM light. First and second optical amplifiers amplify the first and second lights, respectively. A first multiplexer multiplexes the amplified first and second lights into a multiplexed light. A dispersion compensator compensates for dispersion in the multiplexed light. A second demultiplexer demultiplexes the dispersion compensated, multiplexed light into the first and second lights. Third and fourth optical amplifiers amplify the demultiplexed first and second lights, respectively. A second multiplexer multiplexes the amplified first and second lights from the third and fourth optical amplifiers into a WDM light. The optical amplifier can be configured so that the first and second lights travel through the dispersion compensator in opposite directions.

Abstract: An optical amplifier of a wavelength-division multiplexing transmission system that includes a pre-stage optical amplifying unit and a post stage optical amplifying unit. The pre-stage optical amplifying unit has a rare-earth element doped optical fiber and a pump light source for inputting a pump light to the rare-earth element doped optical fiber. The post-stage optical amplifying unit has a second rare-earth element doped optical fiber and a pump light source for inputting a pump light to the second rare-earth element doped optical fiber. The pre-stage optical amplifying unit and the post-stage optical amplifying unit are optically connected by a detachable optical coupling device. In addition, a gain equalizing unit, positioned on an output side of the optical fibers, compensates for wavelength-dependency of a gain characteristic of the optical fibers.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: The invention provides an optical fiber amplifier which assures stable operation of a pump light source and efficiently makes use of residual pump power to achieve improvement in conversion efficiency. The optical fiber amplifier includes a rare earth doped fiber. Pump light from a pump light source is introduced into one end of the rare earth doped fiber by way of a first optical coupler, and residual pump light originating from the pump light and arriving at the other end of the rare earth doped fiber is applied to the other rare earth doped fiber amplifier or the loss compensation of a dispersion compensating fiber by Raman amplification.

Abstract: An optical communication system having a transmitting station for outputting WDM (wavelength-division multiplexing) signal light, an optical fiber transmission line, a receiving station, and an optical repeater including an optical amplifier. The transmitting station includes a supervisory circuit for detecting the number of channels of the WDM signal light and transmitting supervisory information including the number of channels to the optical repeater. The optical repeater further includes a circuit for controlling the optical amplifier so that the output level of the optical amplifier becomes a target level. The target level is set according to the supervisory information. According to the structure, it can be possible to provide a system which can easily respond to a change in the number of WDM channels.

Abstract: The invention provides an optical fiber amplifier which assures stable operation of a pump light source and efficiently makes use of residual pump power to achieve improvement in conversion efficiency. The optical fiber amplifier includes a rare earth doped fiber. Pump light from a pump light source is introduced into one end of the rare earth doped fiber by way of a first optical coupler, and residual pump light originating from the pump light and arriving at the other end of the rare earth doped fiber is applied to the other rare earth doped fiber amplifier or the loss compensation of a dispersion compensating fiber by Raman amplification.