A device and method to monitor and temperature compensate change in wavelength within a WDM optical communication system is disclosed. The device includes a laser diode for generating an optical signal for temperature monitoring, a first fiber Fabry-Perot interferometer sensor unit for generating a first sensor signal according to temperature by means of the optical signal, and a processor for monitoring temperature by means of the first sensor signal and an externally provided second sensor signal and equalizing waveforms of the two sensor signals with each other. The externally provided second sensor signal is provided by a remote node that includes a second fiber Fabry-Perot interferometer sensor unit for receiving the optical signal for temperature monitoring to generate the second sensor signal according to temperature, and a waveguide grating router unit for transmitting the second sensor signal to the optical line terminal.