To make possible ideally making a station side loss zero and transferring only with a subscriber side loss increase by connecting a transmitting element to a receiving element with a specified branch coupler.
A transmitting unit 21 having the transmitting element LD as an optical module and a receiving unit 22 having the receiving element PD are respectively connected to one side two output ends among four output ends of a 2×2 branch coupler 24. Further, the other two output ends of the 2×2 branch coupler 24 are connected respectively to optical star couplers through optical fibers. Further, the 2×2 branch coupler 24 is formed on a planer light wave circuit(PLC). By connecting with this X branch coupler, a branch loss 3dB in the station side is made zero ideally compared with being connected with a Y branch coupler, and the transmission becomes possible only with the subscriber side loss of 3dB. Thus, the matter that a transmission distance of a subscriber line is prolonged becomes possible.
MIKI NORIMOTO
HASHIMOTO HITOSHI
HAGA KAZUO
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