Output port switching device in N-WDM system

An output port switching device in an N-WDM (N-channel Wavelength Division Multiplexing) system with a switching backup output port having a laser generator serving a backup light source, comprising:

• a change-over switch (18) for switching plural ports having plural electric signal converted from plural optical signal by a optical/electrical converter;
• a backup light source path (19) having a wavelength-variable light source which is linked to the change-over switch;
• a first multiplexer (14) for wavelength-multiplexing plural optical signals output from said plural ports;
• a trouble-occurring port monitoring mechanism portion (17) comprising a wavelength-variable filter (20) for monitoring whether an occurrence of a trouble on the basis of an optical signal branched from the output optical signal of said first multiplexer and a light amount detector (21);
• and
• a second multiplexer (15) for wavelength-multiplexing the output optical signal of said backup light source path (19) with the output optical signals of the other normal ports,
• wherein said change-over switch (18) selects and switches an optical signal to which some trouble is monitored by said trouble-occurring port monitoring mechanism portion (17), said backup light source path (19) is controlled so that the wavelength thereof is substantially coincident with the wavelength of the optical signal to which the trouble is detected, and
• wherein the controlled optical signal and the output optical signal of said first multiplexer (14) are multiplexed by the second multiplexer (15).