| 摘要 |
PROBLEM TO BE SOLVED: To prevent receivers from operating under an adverse condition beyond a peculiar optimum power band even if power changes in accordance with the number of use channels by providing respective second filtering means of the upstream of amplifier means. SOLUTION: Optical amplifiers 3 operating as preamplifiers for the receivers 2 are installed on the upstream of the respective optical receivers 2. First light selection filters 4 are inserted between the respective optical receivers 2 and the optical amplifiers 3. Second optical selection filter 5 having the same filtering characteristics, namely, almost central wavelengths and the same pass bands as the first positioned on a down stream side are provided in front of the respective optical amplifier 3 like the filters 5 against the filters 4. The respective second optical filters 5 receive multiplex signals transmitted by optical waves supplied by a link L, execute first filtering and receive signals transmitted by the channel with the wavelength of the optical amplifies 3 positioned at the rear of the second filters 5 as a center in a subsequent processing. |
