Abstract: An optical amplifier and an optical multiplexing transmission system using the same are disclosed. Automatic restoration of the operation becomes possible and malfunctioning of an APSD function is prevented. The optical amplifier using Raman amplification includes; a Raman excitation light source for generating Raman light; and a detection circuit for detecting a signal error in an OSC (optical supervisory channel) signal transmitted in addition to optical transmission signal. When the detection circuit detects a bit error in the OSC signal, an output power from Raman excitation light source is controlled so as not to injure the human body.

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: 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: A trunk apparatus prevents a signal error due to a fluctuation in an optical power in a WDM communication system. A monitoring and controlling signal transmitting and receiving circuit sends transmission power information regarding a transmission power monitored by a transmission power monitor to an immediately proceeding trunk apparatus located on a downstream side of the local trunk apparatus. The monitoring and controlling signal transmitting and receiving circuit receives the transmission power information sent from an immediately preceding trunk apparatus located on an upstream side, and sends the received transmission power information to an automatic gain control circuit. The automatic gain control circuit controls the optical amplifier based on the transmission power information received from the immediately preceding trunk apparatus so as to equalize the transmission power of the local trunk apparatus to the transmission power of the immediately preceding trunk apparatus.

Abstract: An optical transmission device that can be applied to a wavelength-multiplexed optical transmission system includes a first part creating a supervisory control signal to be transmitted in optical formation together with an optical main signal, the supervisory control signal comprising a vector of elements respectively corresponding to wavelengths. The device further includes a second part converting a vector included in a supervisory control signal received from a remote optical transmission device into another vector by a process using a path matrix in the vector received forms diagonal elements of the path matrix, the above another vector being transmitted to a next stage in the wavelength-multiplexed optical transmission system.

Abstract: An optical amplifier and an optical multiplexing transmission system using the same are disclosed. Automatic restoration of the operation becomes possible and malfunctioning of an APSD function is prevented. The optical amplifier using Raman amplification includes; a Raman excitation light source for generating Raman light; and a detection circuit for detecting a signal error in an OSC (optical supervisory channel) signal transmitted in addition to optical transmission signal. When the detection circuit detects a bit error in the OSC signal, an output power from Raman excitation light source is controlled so as not to injure the human body.

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 &lgr;1˜&lgr;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 &lgr;1˜&lgr;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 an wavelength-multiplex optical amplifier control apparatus and method which executes an automatic level control on an optical amplifier to maintain an output optical power of the amplifier at a constant level, first and second power levels are photoelectrically detected from an input optical signal carrying wavelength-division multiplexed data, by using first and second quantization characteristics. Based on the detected first and second power levels, it is detected whether an optical power of at least one channel in the multiplexed data is partly turned off or partly changes. The execution of the automatic level control is inhibited when it is detected that the optical power of at least one channel in the multiplexed data is partly turned off or partly changes.