Patent ID: 7433601

Claim:
An optical add drop apparatus comprising: a plurality of fixed wavelength drop filters connected in series to a transmission path and each demultiplexing an optical signal having a fixed wavelength from wavelength division multiplexed light flowing along the transmission path; a plurality of fixed wavelength add filters connected in series to the transmission path and to the fixed wavelength drop filters, and each adding an optical signal having a fixed wavelength to be transmitted to a transmission source of each of the demultiplexed optical signals to the wavelength division multiplexed light flowing along the transmission path; a first optical branching unit connected in series to the transmission path and to the fixed wavelength drop filter and the fixed wavelength add filters, and branching part of the wavelength division multiplexed light flowing along the transmission path; a variable wavelength drop filter demultiplexing an optical signal having a wavelength corresponding to a specified value from the wavelength division multiplexed light branched by the first optical branching unit; a second optical branching unit connected in series to the transmission path, the fixed wavelength drop filters, the fixed wavelength add filters and the first optical branching unit, and branching a part of the wavelength division multiplexed light flowing along the transmission path in a direction different from the wavelength division multiplexed light branched by the first branching unit; and an optical multiplexing unit multiplexing the wavelength division multiplexed light branched by the first optical branching unit and by the second optical branching unit, wherein the variable wavelength drop filter demultiplexes an optical signal having a wavelength corresponding to a second specified value from the wavelength division multiplexed light multiplexed by the optical multiplexing unit.