Abstract: An optical receiver for receiving a wavelength channel signal light separated out of a wavelength division multiplexed signal light including a plurality of wavelength channel signal lights, the optical receiver includes an optical amplifier for amplifying the wavelength channel signal light, a cyclic filter having a transmission wavelength characteristic of periodically changing transmittance property for a wavelength interval between a wavelength of an adjacent wavelength channel signal light and a wavelength of the wavelength diversion multiplexed signal light, the cyclic filter passing the wavelength channel signal light amplified by the optical amplifier, and a demodulator operably connected to the cyclic filter for demodulating the wavelength channel signal light output from the cyclic filter into an electrical signal.

Abstract: The distributed Raman amplifier monitors an OSNR of each channel in a WDM light which has been propagated through a transmission path to be Raman amplified, and thereafter, is amplified by an optical amplifier in an optical repeating node; judges whether a monitor value of the OSNR is larger or smaller than a previously set target value thereof; and feedback controls a driving state of a pumping light source which supplies a Raman pumping light to the transmission path, based on the judgment result. The optical communication system comprises the above distributed Raman amplifier in each repeating span thereof, and performs a pumping light control of the distributed Raman amplifier corresponding to the repeating span selected based on the OSNR in each distributed Raman amplifier and the monitor result of span loss. As a result, it becomes possible to effectively improve the OSNR of each channel in the WDM light, and also, to reduce the power consumption.

Abstract: An optical transmission apparatus includes an optical add drop multiplexer (OADM) that adds/drops an optical signal to/from a transmission path. The optical transmission apparatus further includes a pump light multiplexer and a dispersion compensation fiber that are located downstream of the OADM on the transmission path. The optical transmission apparatus is configured to house a pump light source connectable to the pump light multiplexer to Raman amplify an optical signal in the dispersion compensation fiber.

Abstract: An optical amplifying device includes a first optical amplifier for amplifying signal light; a second optical amplifier serially connected with the first optical amplifier; an optical device for compensating deterioration of the signal light, the optical device arranged between the first optical amplifier and the second optical amplifier; a variable optical attenuator for attenuating the signal light, the variable optical attenuator arranged between the first optical amplifier and the second optical amplifier; a first automatic level controller for detecting a second amplifier output power and for controlling driving status of the second amplifier in a predetermined output power level; and a first automatic gain controller for detecting an input power of the second optical amplifier and an output power of the second optical amplifier, and for controlling an optical attenuation value of the variable optical attenuator.

Abstract: A control apparatus comprises a light monitoring unit for dividing a signal wavelength band into at least a band in which output light power of an optical amplifier tends to decrease at an decrease in the number of signal wavelengths and a band including a gain deviation band, and for monitoring inputted light power for the individual divided bands, a calculation unit for obtaining the number of signal wavelengths in the individual divided bands based on a monitor result, and a target gain correction unit for correcting a target gain based on a result of the calculation. This suppresses a transient variation of signal light level due to SHB or SRS at a high speed with a simple configuration without deteriorating noise characteristic, thus enabling optical amplifiers to be further disposed in a multi-stage fashion, which can lengthen the transmission distance of a transmission system including an optical add/drop unit.

Abstract: A control apparatus of an optical amplifier includes a monitoring section that measures power of light inputted to the optical amplifier, a power-wavelength characteristics variable section that is operable to change a wavelength characteristic of power of the light inputted, a wavelength number decrease recognition section that compares the value of the power of light measured by the monitoring section with a predetermined threshold, and a control section that controls the power-wavelength characteristics variable section when the wavelength number decrease recognition section judges that the value of the power of light falls below the threshold.

Abstract: An optical amplifier of the present invention comprises: an optical amplifying circuit which amplifies a signal light; an optical reflection medium which is disposed on an optical fiber connected to the optical amplifying circuit and is capable of reflecting a noise light which exists in a predetermined wavelength range outside a signal band, among noise lights generated in said optical amplifying circuit, to radiate the reflected noise light to the outside of a core of the optical fiber; a light receiver which receives the noise light reflected to be radiated to the outside of the core of the optical fiber by the optical reflection medium, to detect the power of the noise light; and a computation circuit which computes the total power of the noise lights generated in the optical amplifying circuit based on the detection result of the light receiver.

Abstract: A Raman amplifier, at the time of start up or the like, drives a predetermined number of pump light sources among a plurality of pump light sources, in a stable region, and judges a Raman gain in the transmission line, and based on the judgment result, specifies a pump light source to switch on and a pump light source to switch off, among the plurality of pump light sources, and controls the drive state of the pump light sources that are switched on. As a result, the plurality of pump light sources are appropriately driven corresponding to the system requirements so that stable behavior is possible, and constant control of Raman gain can be realized at a high accuracy.

Abstract: An optical node apparatus according to the present invention amplifies a WDM signal light input to an input port, and thereafter, branches the amplified WDM signal light by an optical branching coupler to send the branched lights to first and second optical paths, and selects the light propagated through the first optical path by an optical switch to amplify the selected light by a post-amplifier, thereby outputting the amplified light from an output port, when the optical node apparatus is operated as an optical amplification repeating node. When the operational state is upgraded to an optical add/drop multiplexing node, an OADM section is connected between a set of connecting ports on the second optical path, and the adjustment of the OADM section is performed utilizing the WDM signal light branched by the optical branching coupler, and thereafter, the switching of the optical switch is performed to select the light on the second optical path side.

Abstract: The present invention aims at providing a method for controlling wavelength characteristics of optical transmission powers by Raman amplification, in which the wavelength characteristics of optical transmission powers are automatically compensated without giving any losses to channel lights to thereby improve transmission characteristics, and an apparatus adopting the same. To this end, the method for controlling wavelength characteristics of optical transmission powers by Raman amplification according to the present invention supplies Raman pump light to an optical transmission path (Raman amplifying medium); compensates the wavelength characteristics of optical transmission powers caused by transmission of WDM signal light through the optical transmission path, by gain wavelength characteristics of generated Raman amplification; and monitors the wavelength characteristics of optical transmission powers after Raman amplification to thereby control the gain wavelength characteristics of Raman amplification.

Abstract: A monitoring apparatus, based on an optical power monitored in photodetectors arranged at input and output ends of a transmission line, in a condition where pump light is supplied to the transmission line at a time of initial startup of an optical communication system, obtains a relationship for the noise light generated due to Raman amplification, between forward direction noise light power and backward direction noise light power, and while in service, converts the backward direction noise light power monitored by the photodetectors at the input ends of the transmission line into the forward direction noise light power in an arithmetic processing section, in accordance with the relationship obtained at the time of the initial startup. As a result the power of noise light generated due to Raman amplification, can be monitored in real time at high speed.

Abstract: An optical transmission apparatus is provided with an optical filter on a transmission line between a reception end of a transmission line and an OSC receiver. The optical filter has transmission characteristics such as to pass main signal light and optical supervisory channel light (OSC light), and to cut off noise light contained in at least one end portion band on a short wavelength side and a long wavelength side of an OSC transmission band used for reception of OSC light. By such a configuration, even in a case where the OSC light is Raman amplified and transmitted, the influence of noise light due to Raman amplification can be reduced, and OSC light can be received reliably, enabling high dependability to be realized.

Abstract: An optical node apparatus according to the present invention amplifies a WDM signal light input to an input port, and thereafter, branches the amplified WDM signal light by an optical branching coupler to send the branched lights to first and second optical paths, and selects the light propagated through the first optical path by an optical switch to amplify the selected light by a post-amplifier, thereby outputting the amplified light from an output port, when the optical node apparatus is operated as an optical amplification repeating node. When the operational state is upgraded to an optical add/drop multiplexing node, an OADM section is connected between a set of connecting ports on the second optical path, and the adjustment of the OADM section is performed utilizing the WDM signal light branched by the optical branching coupler, and thereafter, the switching of the optical switch is performed to select the light on the second optical path side.

Abstract: A Raman amplification apparatus includes a pumping light supplying section, a main signal wavelength light level acquisition section, a monitoring signal wavelength light level acquisition section, a function information storage section for storing, as function information, information regarding functions for deriving a noise amount and a gain by Raman amplification with regard to a monitoring signal wavelength light with respect to pumping light power supplied from the pumping light supplying section, and a transmission characteristic derivation section for deriving a transmission characteristic on an optical transmission line based on information acquired by the main signal wavelength light level acquisition section and the monitoring signal wavelength light level acquisition section and the function information stored in the function information storage section, and Raman gain is derived with high accuracy in comparison with the conventional technique.

Abstract: To obtain automatic gain control with high accuracy by including first and second light monitors, a reference light supplying unit supplying reference light of which wavelength is set within a gain band of a distributed Raman amplification and out of a wavelength band of main signal light to the optical transmission path, a first reference light monitor monitoring a power of the reference light input to the optical transmission path from one end side thereof, a second reference light monitor monitoring the power of the reference light output from the other end side of the optical transmission path, and a controlling unit controlling supply of pump light in a pump light supplying unit as well as supervising a state of the optical transmission path, based on monitor results from the first and second light monitor and the monitor results in the first and second reference light monitors.

Abstract: A Raman amplifier inputs pump light into an optical fiber (transmission path) through which an optical signal passes, to amplify the optical signal. An optical receiving unit is provided downstream of the Raman amplifier and monitors the power of the optical signal amplified by the Raman amplifier. A calculating unit determines Raman amplification gain based on the power of the optical signal monitored by the optical receiving unit, and calculates the power of a noise component included in the optical signal based on the gain. The calculating unit, in real-time, calculates the power, which varies in complicated manners depending on conditions, and outputs information concerning to the power to another apparatus at a frequency on the order of milliseconds.

Abstract: A light amplifying device including a Raman amplifier to Raman-amplify a signal light by inputting excitation lights of a plurality of wavelengths to a transmission path through which the signal light propagates, a plurality of measuring units measuring powers of light output from the Raman amplifier in a plurality of wavelength bands included in an amplification band of the Raman amplifier, a calculating unit calculating a ratio of the respective powers measured by at least two of the plurality of measuring units, and a control unit controlling a power ratio of the respective excitation lights input to the transmission path by the Raman amplifier based on the ratio calculated by the calculating unit.

Abstract: The WDM optical transmission system using distributed Raman amplification, before starting operation of main signal light, transfers a plurality of lights having different wavelengths to that of the main signal light (for example Raman amplification pump lights or the like) between first and second optical transmission devices connected to opposite ends of a transmission line, monitors transmission line input and output power for each light, calculates a transmission line loss in each wavelength using the monitor results, and specifies a type of the transmission line based on a loss wavelength characteristic that can be estimated from the calculation result. Then the power of pump light provided to the transmission light is optimized in accordance with the type of transmission line.

Abstract: A light amplifying device including a Raman amplifier to Raman-amplify a signal light by inputting excitation lights of a plurality of wavelengths to a transmission path through which the signal light propagates, a plurality of measuring units measuring powers of light output from the Raman amplifier in a plurality of wavelength bands included in an amplification band of the Raman amplifier, a calculating unit calculating a ratio of the respective powers measured by at least two of the plurality of measuring units, and a control unit controlling a power ratio of the respective excitation lights input to the transmission path by the Raman amplifier based on the ratio calculated by the calculating unit.

Abstract: An optical communication system, where in an optical transmission apparatus arranged on a transmission side of respective repeating sections, an OSC optical amplifier is provided on an OSC light optical path between from an OSC transmitter to a multiplexer, and the OSC optical amplifier is controlled so that the power of OSC light transmitted on the transmission path becomes a previously set target value. As a result the OSC light is amplified by a different amplifying device to that for the main signal lights at the time of transmission. Therefore even in the case where the span losses are large, OSC light can be reliably received by the optical transmission apparatus on the reception side.