Abstract: In an optical transmission system, an optical terminal transmits a plurality of tone signals corresponding to a plurality of gain bands, where the frequencies of the plurality of tone signals are different from each other, and each of the plurality of tone signals has a characteristic which is varied according to detected power of optical signals in the corresponding gain band. Each optical repeater receives the plurality of tone signals, extracts the characteristics of the plurality of tone signals, and compares a signal representing each characteristic with a reference signal. The optical repeater controls the gains of optical amplification in the plurality of gain bands based on the comparison result so as to equalize the gains in the plurality of gain bands.

Abstract: An optical transmission system ensuring high-quality monitor control even if an optical fiber fault occurs. A monitor instruction sending unit sends a monitor instruction. An operating condition recognizing unit receives a response signal and recognizes the operating condition. A filtering unit filters the monitor instruction and the response signal. A monitor control unit monitors the operating condition of its own repeater in response to the monitor instruction, and generates resultant response information. A pump unit generates a pump light to cause Raman amplification within an optical fiber transmission medium. A regeneration control unit performs a regeneration control of the response signal to thereby create a regenerated signal. A modulation control unit modulates the pump light by the response information or the regenerated signal to thereby generate the response signal.

Abstract: In the method according to the present invention, an optical fiber transmission line for transmitting signal light is first provided. A Raman repeater 16 having a pumping source for supplying pump light propagating in a direction opposite to the direction of propagation of the signal light to the optical fiber transmission line is provided in the middle of the optical fiber transmission line. A terminal device having a similar pumping source is provided at one end of the optical fiber transmission line. A control signal is transmitted to the Raman repeater 16 by the pump light from the terminal device. The Raman repeater is controlled by the control signal transmitted. According to this method, the Raman repeater is controlled by the pump light from the terminal device provided at the receiving end, thereby eliminating a problem arising in the case of control by signal light as in the prior art.

Abstract: In a WDM optical communication system, at least one optical tunable filter is placed along an optical fiber provided as an optical transmission path between a transmitting station and a receiving station. The optical tunable filter has a controllable transmission factor versus wavelength characteristic. In the receiving station, the transmission characteristics (for example, optical signal to noise ratios and Q factors) for optical signals of different wavelengths propagated over the optical fiber are measured. The measurements are sent to the transmitting station. The transmitting station then properly controls both the amounts of pre-emphasis in the transmitting station and the wavelength characteristic of the optical filter on the basis of the measurements to thereby equalize the transmission characteristics for the optical signals.

Abstract: A supervisory system in a wavelength division multiplexing communications network is provided with a first and a second terminal stations and a repeater unit. The first terminal station transmits a supervisory signal to the second terminal station. The second terminal station transfers the supervisory signal to the repeater unit to be monitored. Paths to a hub station A and a hub station B can be a single path by looping back a supervisory signal output from the hub stations A and B for issuing and terminating the supervisory signal at a first and a second branch stations connected through an optical wavelength multiplexing/demultiplexing unit. If the hub station B loops back a supervisory signal, the supervisory signal output from the hub station A can be returned to the hub station A again after circulating the path.

Abstract: An optical transmission system with a mechanism to locate a fault on a transmission line effectively and efficiently to ensure the quality of communication between end stations and repeaters. Repeaters respond to a monitoring control command sent from an end station, returning a monitoring report signal that indicates their current operating status and input/output signal conditions. In the end station, a monitoring report processor identifies a faulty link section of the optical transmission line, if the monitoring report signal indicates a fiber fault. The end station sends a troubleshooting control command to cause a relevant repeater to transmit a probing light pulse signal and a complementary light pulse signal simultaneously in opposite directions. Some of the probing light pulse is reflected back as a result of Rayleigh scattering. The end station locates the fiber fault by analyzing the backscatter, using the complementary light pulse signal for synchronization.

Abstract: In the method according to the present invention, an optical fiber transmission line for transmitting signal light is first provided. A Raman repeater 16 having a pumping source for supplying pump light propagating in a direction opposite to the direction of propagation of the signal light to the optical fiber transmission line is provided in the middle of the optical fiber transmission line. A terminal device having a similar pumping source is provided at one end of the optical fiber transmission line. A control signal is transmitted to the Raman repeater 16 by the pump light from the terminal device. The Raman repeater is controlled by the control signal transmitted. According to this method, the Raman repeater is controlled by the pump light from the terminal device provided at the receiving end, thereby eliminating a problem arising in the case of control by signal light as in the prior art.

Abstract: There is disclosed an optical transmission system ensuring high-quality monitor control even if an optical fiber fault occurs. A monitor instruction sending unit sends a monitor instruction. An operating condition recognizing unit receives a response signal and recognizes the operating condition. A filtering unit filters the monitor instruction and the response signal. A monitor control unit monitors the operating condition of its own repeater in response to the monitor instruction, and generates resultant response information. A pump unit generates a pump light to cause Raman amplification within an optical fiber transmission medium. A regeneration control unit performs a regeneration control of the response signal to thereby create a regenerated signal. A modulation control unit modulates the pump light by the response information or the regenerated signal to thereby generate the response signal.

Abstract: In an optical transmission system, an optical terminal transmits a plurality of tone signals corresponding to a plurality of gain bands, where the frequencies of the plurality of tone signals are different from each other, and each of the plurality of tone signals has a characteristic which is varied according to detected power of optical signals in the corresponding gain band. Each optical repeater receives the plurality of tone signals, extracts the characteristics of the plurality of tone signals, and compares a signal representing each characteristic with a reference signal. The optical repeater controls the gains of optical amplification in the plurality of gain bands based on the comparison result so as to equalize the gains in the plurality of gain bands.

Abstract: A supervisory system in a wavelength division multiplexing communications network is provided with a first and a second terminal stations and a repeater unit. The first terminal station transmits a supervisory signal to the second terminal station. The second terminal station transfers the supervisory signal to the repeater unit to be monitored. Paths to a hub station A and a hub station B can be a single path by looping back a supervisory signal output from the hub stations A and B for issuing and terminating the supervisory signal at a first and a second branch stations connected through an optical wavelength multiplexing/demultiplexing unit. If the hub station B loops back a supervisory signal, the supervisory signal output from the hub station A can be returned to the hub station A again after circulating the path.

Abstract: An optical transmission system with a mechanism to locate a fault on a transmission line effectively and efficiently to ensure the quality of communication between end stations and repeaters. Repeaters respond to a monitoring control command sent from an end station, returning a monitoring report signal that indicates their current operating status and input/output signal conditions. In the end station, a monitoring report processor identifies a faulty link section of the optical transmission line, if the monitoring report signal indicates a fiber fault. The end station sends a troubleshooting control command to cause a relevant repeater to transmit a probing light pulse signal and a complementary light pulse signal simultaneously in opposite directions. Some of the probing light pulse is reflected back as a result of Rayleigh scattering. The end station locates the fiber fault by analyzing the backscatter, using the complementary light pulse signal for synchronization.

Abstract: A supervisory system in a wavelength division multiplexing communications network is provided with a first and a second terminal stations and a repeater unit. The first terminal station transmits a supervisory signal to the second terminal station. The second terminal station transfers the supervisory signal to the repeater unit to be monitored. Paths to a hub station A and a hub station B can be a single path by looping back a supervisory signal output from the hub stations A and B for issuing and terminating the supervisory signal at a first and a second branch stations connected through an optical wavelength multiplexing/demultiplexing unit. If the hub station B loops back a supervisory signal, the supervisory signal output from the hub station A can be returned to the hub station A again after circulating the path.

Abstract: An optical amplifier including a pumping source for supplying pump light to an optical fiber transmission line is provided so that at least a part of the optical fiber transmission line produces Raman amplification to an optical signal. An optical filter unit for selectively switching between a first condition where the optical signal and the pump light are passed and a second condition where the optical signal is passed and the pump light is not passed is connected between the optical fiber transmission line and the optical amplifier. The power of the optical signal in the first condition is compared with that in the second condition, and the characteristics of the optical fiber transmission line, such as a splice loss therein, is evaluated according to the result of this comparison.

Abstract: A computer for controlling a pre-emphasis process is provided at end terminal stations which are the terminal stations of a trunk. When a pre-emphasis process is performed to an optical signal directing from a terminal station to another terminal station, the computer of the terminal station controls the process. First, the terminal station causes another terminal station to transmit the spectrum information of the thus-received optical signal, and receives the information. The terminal station obtains the spectrum information of its own received optical signal. The terminal station arranges data for each transmission source of the received optical signal, and calculates the amount of a pre-emphasis process to be performed at a transmission side. The terminal station transmits pre-emphasis execution instructions to the other terminal stations according to the thus-calculated results.

Abstract: A supervisory system in a wavelength division multiplexing communications network is provided with a first and a second terminal stations and a repeater unit. The first terminal station transmits a supervisory signal to the second terminal station. The second terminal station transfers the supervisory signal to the repeater unit to be monitored. Paths to a hub station A and a hub station B can be a single path by looping back a supervisory signal output from the hub stations A and B for issuing and terminating the supervisory signal at a first and a second branch stations connected through an optical wavelength multiplexing/demultiplexing unit. If the hub station B loops back a supervisory signal, the supervisory signal output from the hub station A can be returned to the hub station A again after circulating the path.

Abstract: An optical amplifier including a pumping source for supplying pump light to an optical fiber transmission line is provided so that at least a part of the optical fiber transmission line produces Raman amplification to an optical signal. An optical filter unit for selectively switching between a first condition where the optical signal and the pump light are passed and a second condition where the optical signal is passed and the pump light is not passed is connected between the optical fiber transmission line and the optical amplifier. The power of the optical signal in the first condition is compared with that in the second condition, and the characteristics of the optical fiber transmission line, such as a splice loss therein, is evaluated according to the result of this comparison.

Abstract: A circulator guides wavelength multiplexed light that is received from a main transmission path to a 1st fiber grating. The 1st fiber grating reflects light of wavelength &lgr;1. Wavelength multiplexed light that has passed through the 1st fiber grating is guided to a 2nd fiber grating. The 2nd fiber grating reflects light of wavelength &lgr;n. The circulator guides the signal light that has been reflected from the 1st and 2nd fiber gratings to a branch transmission path. The length of the transmission path between the 1st and 2nd fiber gratings is determined based on the transmission rate or frequency of the signal that is transmitted using light of wavelength &lgr;n.

Abstract: In a WDM optical communication system, at least one optical tunable filter is placed along an optical fiber provided as an optical transmission path between a transmitting station and a receiving station. The optical tunable filter has a controllable transmission factor versus wavelength characteristic. In the receiving station, the transmission characteristics (for example, optical signal to noise ratios and Q factors) for optical signals of different wavelengths propagated over the optical fiber are measured. The measurements are sent to the transmitting station. The transmitting station then properly controls both the amounts of pre-emphasis in the transmitting station and the wavelength characteristic of the optical filter on the basis of the measurements to thereby equalize the transmission characteristics for the optical signals.

Abstract: To improve the OSNR on a receiving side it is necessary to control pre-emphasis, and further to automatically control the pre-emphasis. Furthermore, when carrying out wavelength-division multiplexing, it is also necessary to control wavelength. The optical spectrum of signal lights is detected in both a transmitting terminal station and a receiving terminal station, a transmitting side spectrum detection result and a receiving side spectrum detection result are compared, and the levels and wavelengths of signal lights to be transmitted are controlled.

Abstract: In a light transmission system, each terminal equipment amplitude-modulates an optical main signal with a supervisory control signal of a proper frequency allocated to respective repeating installations. The repeating installations which have received the optical main signal demodulate the supervisory control signal from the optical main signal. The repeating installations detect that the supervisory control contains the own frequency component to judge it as a supervisory control signal addressed to the own installation from the terminal equipment. Alternatively, a branching installation is provided to extract the supervisory control signal before being coupled by an optical coupler in the branching installation, and amplitude-modulates the optical main signal at the output of the optical coupler with the supervisory control signal.