Wavelength division multiplexing optical transmission apparatus

Abstract

Light signals having different oscillation wavelengths issued from a plurality of light sources are optically modulated and combined into a combined light signal to be later transmitted. The combined light signal is partly passed through an optical band pass filter and then sent to an optical detector so that the optical detector detects input timing of the light signals of the respective wavelengths in the combined light signal. A driving voltage detection circuit detects a voltage value of a driving electric signal corresponding to an output detection pulse of the optical detector to associate the respective wavelengths of the light signals with the corresponding voltage values. When a comparator finds a difference between the voltage values of the adjacent wavelengths and judges that the difference is smaller than a set value, an alarm generator issues an alarm indicating that the wavelengths are close. A control circuit holds as a reference the voltage value of the first period corresponding to the wavelength of specific reference one of the light sources, and controls the oscillation wavelength of the light signal of the reference light source to be always constant by feeding the voltage value of the subsequent period corresponding to the wavelength of the reference light source back to the control circuit for monitoring.