Abstract: An optical transmission apparatus includes a demultiplexer for separating wavelength-division multiplexing light received from a first optical transmission line into signals of different wavelengths to transmit the signals to an outside and a multiplexer for multiplexing signals of different wavelengths received from the outside to transmit multiplexed signals to a second optical transmission line. An input check unit is provided for monitoring a power level of a signal separated by the demultiplexer and for providing an output indicative thereof. An output adjuster is provided for intercepting a signal from the outside so as to inhibit receipt of the signal from the outside by the multiplexer depending on the output of the input check unit.

Abstract: It was difficult to detect a wavelength error. Further, a wavelength error of an optical add signal is accompanied by a calculation error of the number of wavelengths of a wavelength division multiplexing signal, which causes a set value of an optical signal level to become abnormal, resulting in the degradation of the optical signal. According to the present invention, part of an inputted optical add signal 118 is reflected by a mirror 117, and is thereby inputted into an optical wavelength multiplexer 105 in the reverse direction so that the optical add signal is returned to paths 115-1 through 115-16 corresponding to wavelengths ?1 through ?16. If the returned optical add signal is an optical add signal having a correct wavelength (in FIG. 1, ?16), the optical signal enters its corresponding backward direction optical detector 113-16. Accordingly, it is possible to check whether or not a wavelength of the optical add signal is correct.

Abstract: A problem to be solved in an optical communication system for carrying out bidirectional transmission between communication nodes by wavelength-division-multiplexed optical signals is that a plurality of optical add-drop multiplexers installed in the communication nodes are required for each transmission direction, and therefore, the communication cost is increased. An optical circulator or an optical coupler is arranged at an input/output port of the optical add-drop multiplexer and the wavelength-division-multiplexed optical signals are assembled for each transmission direction, whereby optical signals transmitted bidirectionally can be handled by one optical add-drop multiplexer.

Abstract: In the variable gain compensating apparatus, input power of optical amplifiers employed in respective optical repeaters is monitored, and the monitored input power is transferred to a down-stream side by using supervisor (SV) light. In a repeater equipped with a variable gain tilt compensator, input power monitor information of the optical amplifiers employed in the respective repeaters provided on the upper stream side is acquired from a supervisor signal. While utilizing a linear relationship established between a gain tilt of an optical amplifier and input power of the optical amplifier, the acquired input power monitor information is compared with a reference power value so as to calculate gain tilt amounts of the respective optical amplifiers. Then, the optimum gain tilt compensation amount of the variable gain tilt compensator is determined based upon the calculated gain tilt amounts.