| 摘要 |
PROBLEM TO BE SOLVED: To make the wavelength selected for a variable wavelength filter coincident with the wavelength of desired light signals by controlling the filter. SOLUTION: A wavelength control circuit 6 roughly adjusts the pass wavelength of a variable wavelength filter 1 in advance based on a preset control signal 13 in accordance with a wavelength channel select signal 12 outputted from a selector 4. The light signal passed through the roughly adjusted filter 1 is received by means of a light receiving element 5 and the element 5 outputs a first electric signal 15 having the magnitude corresponding to the light intensity of the optical signal and a second electric signal 11 which is a modulation signal component. The signal 15 is inputted to the wavelength control circuit 6 and the circuit 6 outputs such a wavelength control signal that finely changes the pass wavelength of the filter 1 to the longer wavelength (or shorter wavelength) side. When the pass wavelength of the filter 1 is changed, the first electric signal 15 changes in accordance with the wavelength the signal 15 and pass characteristic of the filter 1 so that the pass wavelength of the filter 1 can become coincident with the wavelength of the signal 15. |
