US Patent 7526200 Wavelength-division multiplexing optical transmitter

An optical transmission apparatus includes optical transmitters for transmitting optical signals and first monitor units for monitoring optical signals from the optical transmitters. A multiplexer is provided for multiplexing the optical signals from the optical transmitters into a multiplexed signal. A second monitor unit is provided for monitoring each optical signal which is multiplexed in the multiplexed signal from the multiplexer. A processing unit is provided for comparing a first number of optical signals detected by the first monitor units and a second number of optical signals detected by the second monitor unit.