OPTICAL TRANSMISSION DEVICE, OPTICAL COMMUNICATION SYSTEM, AND OPTICAL SIGNAL TRANSMISSION METHOD

An object is to perform wavelength filtering of an optical signal while preventing filter narrowing in an optical transmission apparatus. A branching unit (11) branches a wavelength-multiplexed optical signal (SIN) including an optical signal of a first wavelength into an optical signal (S1) and an optical signal (S2). A wavelength selection unit (12) blocks an optical signal of a first wavelength band including the first wavelength in the optical signal S(1). A filter unit (13) allows passage of an optical signal (ST) of a second wavelength band including the first wavelength in the optical signal (S2). A multiplexing unit (14) multiplexes and the optical signal (ST) and an optical signal of a second wavelength. The second wavelength band is wider than the first wavelength band.