Abstract: Disclosed herein is a signal transmission method in a wavelength-division-multiplex (WDM) transmission system. The WDM transmission system comprises a first WDM terminal for transmitting a WDM signal, a second WDM terminal for receiving the WDM signal, and an optical add-drop multiplexer (OADM) node for transmitting to a network element an optical signal of a specific wavelength of the WDM signal which is transmitted between the first and second WDM terminals. The WDM signal is transmitted from the first WDM terminal to the second WDM terminal regardless of whether an optical signal is added or dropped at the OADM node. The network element employs an optical signal of an idle wavelength of the WDM signal that has no transmission data, to transmit another transmission data that is transmitted by the network element.

Abstract: A parallel signal automatic phase adjusting circuit includes a signal generator for generating a signal having a predetermined frequency, an oscillating circuit for generating a clock signal having a frequency smaller than an inputted clock signal by the predetermined frequency, and adjusting circuits, respectively corresponding data signal channels, each adjusting the generated clock signal so as to be synchronized with the corresponding data signal, based on an arithmetic operation of trigonometric functions using both phase comparing information, derived from comparison between the corresponding data signal and the generated clock signal, and frequency information regarding the corresponding data signal, the generated clock signal and the signal from the signal generator. The circuit is useful, for example, when digital data transmitted through a large number of parallel data signal lines between data terminals, because the size of and the cost for the circuit are reduced.

Abstract: In an optical communication system, a pre-compensation is conducted for an influence of a polarization dispersion and a polarization dependent loss, which an optical signal transmitted from a transmitter station to a receiver station receives from a communication channel, at a transmitter station. The influence of the polarization dispersion and the polarization dependent loss from the transmission channel is cancelled when the receiver station receives the optical signal.

Abstract: In an optical transmission device, when wavelength division multiplexed light formed from signals of a plurality of wavelengths are received, an optical signal of one wavelength comprised in this wavelength division multiplexed light is planarized and non-signal light of the same wavelength is reproduced. The reproduced light is modulated with a transmission data string, an optical signal is generated, and a wavelength division multiplexed light comprising the generated optical signal is transmitted.

Abstract: One of two optical fibers connecting communication stations is used for transmitting multiple wavelength light supplied from a multiple wavelength light source supply apparatus, and the other for a bidirectional communication using optical signals of respective wavelengths generated from the multiple wavelength light. Alternatively, a transmission of multiple wavelength light and a bidirectional communication using the optical signals are enabled by only one optical fiber.

Abstract: A dispersion compensating method for carrying out automatic level control with the use of target output power and an ASE correction value corresponding to the number of wavelengths to multiplex and making output power of a wavelength multiplexed signal constant, comprising the steps of: switching into automatic gain control in which the output power of the wavelength multiplexed signal is made constant, to carry out increase/decrease of the wavelengths to multiplex; varying a dispersion compensating amount based on the increase/decrease of the wavelengths by the automatic gain control; calculating an ASE variation amount due to the change in the dispersion compensating amount; and reflecting the ASE variation amount on the ASE correction value and switching into the automatic level control.

Abstract: A frame transmitting apparatus that transmits a frame including data to be transmitted or a frame including control data for a data-transmission control via a network includes a frame generating unit that generates a frame including identification-information-added data to which 1-bit identification information indicating whether a block obtained by dividing data into every n bits includes the control data is added, where n is a positive integer, and an error control code for a data-transmission error control; and a frame transmitting unit that transmits the frame generated.

Abstract: A dispersion compensating method for compensating wavelength dispersion occurring in an optical transmission line, includes the steps of: a) performing dispersion compensation by causing an optical signal, supplied from the transmission line, to pass through a variable dispersion compensator; and b) controlling a dispersion compensating amount in the variable dispersion compensator according to code error information corresponding to a type of code in a received data signal obtained from receiving the optical signal having undergone the dispersion compensation.

Abstract: A power-down delay unit 15 for delaying cutoff of a voltage is provided in the power supply line for supplying power to an optical module 14 of a transponder unit 16 of each wavelength. The power-down delay unit 15 assigns a different delay in power disconnection each wavelength. The length of the delay is a time required by an AMP unit or longer to change from an ALC mode to an AGC mode. With the configuration, when the power supply for supplying power to the plurality of transponder units 16 becomes faulty and output of a number of wavelengths simultaneously stops, the actual optical signal gradually stops output wavelength by one wavelength. Thereby a nonlinear effect because of going up of a power of an optical signal too much is not occurred, therefore it is able to prevent an undesired influence for a wavelength not to be stopped.

Abstract: The object of the present invention is to provide a WDM optical communication system and a WDM communication method wherein deviation of transmission characteristics of optical signals of respective wavelengths is reliably controlled, based on reception information such as the OSNR, BER and the like measured at the receiving end, thereby enabling optimal transmission conditions to be realized. For this purpose, the present WDM optical communication system transmits WDM signal light of wavelengths ?1˜?n, which has been generated by the transmitting end of one terminal station, to the receiving end of the other terminal station through an optical transmission path. At the receiving end, the OSNR and BER of the optical signals of wavelengths ?1˜?n are measured, and the result is superimposed on overhead information transmitted along the opposing line of the optical transmission path as reception information.

Abstract: In a WDM optical communication network composed of a transmitter, an optical switching device (an optical cross-connect, an optical router, etc.) and a receiver, when transmitting switching information to the optical switching device, the transmitter suspends the transmission of a main signal by a wavelength for switching of a WDM optical signal and transmits switching information instead. Upon receipt of this switching information, the optical switching device switches a route, re-starts the transmission of a main signal after the switching is completed and transfers the main signal through the switched route. The signal speed of switching information is sufficiently lower than the modulation speed of the main signals with other wavelengths.

Abstract: A Raman excitation control method enabling to reduce the number of couplers and photodetectors (PD) for providing an optical transmission unit with reduced cost The method is provided for use in optical amplification to amplify an optical signal using Raman excitation light fed into an optical transmission line. A backward light of a laser diode producing the Raman excitation light is monitored by an optical back power monitor. The monitored power value is compared with an initial set value stored in a memory for the laser diode. Based on this comparison result, a feedback control is performed against the light emission power of the laser diode.

Abstract: Measuring a wavelength dispersion amount of an optical transmission line without disconnecting the optical transmission line. A measuring signal is transmitted together with a main signal from a first node while the optical transmission line is in operation. The measuring signal is extracted and returned at an opposing node. A delay time required for the measuring signal to return is measured. A length of optical transmission line between the nodes is calculated from the measured delay time. A wavelength dispersion amount of the optical transmission line is calculated based on the calculated length.

Abstract: An optical transmission equipment in an optical communication system interconnecting two optical transmission equipment sets by a main transmission line and a backup transmission line. An optical amplifier amplifies and outputs optical signals from one transmission line in use, interconnecting the optical transmission equipment concerned with neighboring upstream optical transmission equipment, and outputs the optical signals including a signal component and a noise component. A controller controls an optical signal level so that a signal component in the optical signal reaches a predetermined level.

Abstract: In the WDM communication system, in the absence of data to be transmitted on an optical channel, a pilot signal transmitting means transmits the channel-unique pilot signal data on the channel. A WDM communication apparatus on a receiving end detects the pilot signal data in the received WDM signals, and on the basis of the detection result, it evaluates whether each channel is used or not. It is thus easy to recognize which channel is unused (idle) of the WDM signals, so that channel resources can be used effectively according to the traffic.

Abstract: An optical wavelength multiplexing apparatus is capable of controlling an attenuation amount of a variable optical attenuator at high speed, thereby preventing an optical level change generated by an upstream WDM section from flowing into a downstream WDM section.

Abstract: A Raman excitation control method enabling to reduce the number of couplers and photodetectors (PD) for providing an optical transmission unit with reduced cost. The method is provided for use in optical amplification to amplify an optical signal using Raman excitation light fed into an optical transmission line. A backward light of a laser diode producing the Raman excitation light is monitored by an optical back power monitor. The monitored power value is compared with an initial set value stored in a memory for the laser diode. Based on this comparison result, a feedback control is performed against the light emission power of the laser diode.

Abstract: Disclosed herein is a signal transmission method in a wavelength-division-multiplex (WDM) transmission system. The WDM transmission system comprises a first WDM terminal for transmitting a WDM signal, a second WDM terminal for receiving the WDM signal, and an optical add-drop multiplexer (OADM) node for transmitting to a network element an optical signal of a specific wavelength of the WDM signal which is transmitted between the first and second WDM terminals. The WDM signal is transmitted from the first WDM terminal to the second WDM terminal regardless of whether an optical signal is added or dropped at the OADM node. The network element employs an optical signal of an idle wavelength of the WDM signal that has no transmission data, to transmit another transmission data that is transmitted by the network element.

Abstract: An optical transmitter is provided with: an optical signal generator for generating a main signal to be transmitted and its inversion signal as optical signals of different wavelengths; and a wavelength division multiplexer for wavelength division multiplexing the optical signals of different wavelengths generated by the optical signal generator and transmitting the multiplexed optical signal. By transmitting the main signal to be transmitted and its inversion signal as the wavelength division multiplexed optical signal (containing optical signals of different wavelengths corresponding to the main signal and the inversion signal), “inter-channel crosstalk” which occurs during multi-wavelength batch amplification by an optical amplifier (Raman amplifier, semiconductor optical amplifier, etc.) can be suppressed effectively, independently of the performance/characteristics of optical devices.

Abstract: In a method of measuring a wavelength dispersion amount of an optical transmission line without disconnecting the line and an optical transmission system using this measuring method, a measuring signal is transmitted together with a main signal from a first node while a line is in operation, the measuring signal is extracted and returned at an opposing node, a delay time required for the measuring signal to return is measured, a length of an optical transmission line between the nodes is calculated, and the wavelength dispersion amount of the optical transmission line is calculated based on the length at the first node.