| 摘要 |
Equipped between a transmitter 20 and an optical multiplexer module 25 of a division/multiplexer unit 24 are band-pass filters 23 - 1 through 23 -m letting only a light of right wavelength pass while reflecting other wavelengths light. The transmitter 20 is equipped with a reflection light monitor 26 for monitoring a reflection light from the band-pass filters 23 - 1 through 23 -m for examining an intensity of a reflection light. A wavelength of a light oscillated by a tunable laser diode (LD) unit 21 is controlled so as to make the intensity of the light smaller than a threshold value.
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